STRUCTURES OF MATTER
Every bit of matter - wether solid, liquid of gas - is a SUBSTANCE or a mixture of substances.
After modules 01 - 04 you know atoms, elements, chemical bonds and nomenclature,
zo you can look at the matter and substances in a more chemical manner, and less in the fysical manner.
Now you are going to apply your knowledge on the microworld of atoms, ions and molecules.
You will understand more of matter.
We consider matter als everything that has mass and volume.
1. The particle character of matter
What do you think: is air a substance?
Explain your answer.
Almost all matter that we know around us, is built up of mixtures.
can be separated in components, up to pure substances.
in turn are built up of one kind of equal particles: molecules or atoms or ions.
Pure substances (if not already elements) can be decomposed into elements.
is built up of only one kind of atoms.
Will air be a pure substance of a mixture? explain
Every substance is built up of 'particles': molecules, macromolecules or (complex / simple) ions.
In special cases, a substance may be built up of atoms.
All those particles can differ in size, molecular mass, charge or in (a)polar character and in cinetic energy (movement, vibration).
Imagine a substance built up of very movable particles: they are small, light and with little attraction forces.
Will this substance be solid, liquid or gas? Explain your answer.
Goto answer 05-03
Heating up a substance (= adding energy) means that every particle receives cinetic energy (movement energy). This particle will increase its movement. This can be done in a dislocation of the particle, but also in more vibration.
To that phenomena is not really a limit; the particle always can increase movement, that is: get hotter, up to millions of grades Celcius.
The movement becomes every time heavier.
Attention: very likely something will happen to that substance.
Cooling a substance has a limit. During cooling the movement decreases.
Eventually the particle has no movement anymore; it is still.
Less movement than no movement is impossible. Even the lightest particles, with hardly any mutual attraction forces, will become still at sufficient low temperature.
If in a gas, the particles first become a liquid (there is still movement), and finally a solid is made with a (molecular) lattice.
Less movement than no movement is impossible
and a lower temperature than the minimum temperature does not exist = 0 K(elvin) (= -273ºC)
You may say that temperature is a measure for movement of the particles.
Explain if the following statement is true or not:
"Not using units, the molar mass equals the molecular mass."
The mass of matter (weight) is concentrated for the very biggest part in the nucleons (the protons and neutrons).
The electrons weight as good as nothing; you may neglect their mass on the whole.
This also means that the mass of a particle directly depends on the number of nucleons in that particle.
A Hydrogen molecule contains two Hydrogen atoms and one Oxygen atom
This way, a new unit was introduces for mass:
- every Hydrogen atom contains one proton in the nucleus
- every Oxygen atom contains eight protons and eight neutrons in the nucleus
- a water molecule contains 2 + 16 = 18 nucleons (nuclear particles)
the atomic mass unit = the average weight of one nuclear particle
So if a particle contains, for example, hundred nucleons, then the (molecular) mass of this particle will be 100 a.m.u.
One atomic mass unit (a.m.u.) is such an incredible small bit of mass that no balance on earth can really weight it. Balances work with grammes, milligrammes, but not much less than that.
- a water molecule contains 2 + 16 = 18 nucleons
so the mass of one water molecule will be 18 a.m.u.
To have one gram of matter (measurable on a balance thus), you need all toghether 6 x 1023 nucleons.
This number is also called: the number of Avogadro), but mostly we talk about: 1 MOL
One MOL in chemistry is a unit of numbers, just like a pair (2), or a dozen (12).
So you can have 1 MOL of molecules, 1 MOL of ions, 1 MOL of electrons, 1 MOL of protons, etcetera.
Don't confuse MOL with the mole in biology!
Do you think that the total number of humans on earth will be more of less than 1 MOL?
Make an estimation to find the answer.
Goto answer 05-05
Check the following:
One water molecule has 18 neucleons; so one water molecule weights 18 a.m.u.
1 MOL of water contains 6 x 1023 water molecules;
1 MOL of water contains 6 x 1023 x 18 nucleons;
6 x 1023 nucleons have a mass of 1 gram → 1 MOL of water weights 18 gram.
Molecular mass and molar mass are equal, if you ignore the units.
- the mass of 1 water molecule = 18 a.m.u. = molecular mass (micro level)
- the mass of 1 MOL of water molecules = 18 grams = molar mass (macro level)
Mass number & atomic mass
There is something that can difficult the calculations with those concepts, and that is the existance of isotopes.
for example: Of the element Chlorine do exist two types of isotopes in nature: Chlorine atoms with 18 neutrons and Chlorine atoms with 20 neutrons.
Of course every atom of Chlorine has also 17 protons.
1 MOL of the isotope 35Cl has a mass of 35 g [atomic mass = 35]
1 MOL of the isotope 37Cl has a mass of 37 g [atomic mass = 37]
In nature exists a mixture of two isotopes in the proportion of (±)3 : 1
which means that the element Chlorine, as it occurs in our world, has an average atomic mass of about 35,5
Something like that is the case with many elements. That's why in practice most atomic masses of the elements are not exactly the same as the mass number of one isotope of that element. In tables you find always the averages.
Calculate the molecular mass of kitchen salt NaCl.
Molecules can differ in size. Water has very small molecules and proteins are enormous macromolecules.
Amilos also is very big; it is a polyglucose, built up of many connected molecules of glucose.
Suppose that one molecule amylose has 800 monomers and the formula is C6H10O5)n,
then calculate the molecular mass of this polymer.
It is not easy to imagine the size of one particle of a substance; it is incredible small.
Yet there are (relative) big differences between those particles: like starch, having macromolecules, so big that the water in which the starch was dissolved, turns cloudy/trouble. The smaller sugar molecules will never cause this outlook. A sugar solution always will be a transparant mixture, like most solutions in water.
And about solids and liquids, in practice you can observe them, even knowing that the particles are so tiny. They are so close toghether that we can see the collection.
But you need an enormous number of particles before they are visible as a substance.
Gases can only be seen if the molecules are colored.
One cristal of sugar can contain 100.000.000.000.000.000 molecules C12H22O11."
Is this statement true of false?
The diagramme below shows the relation between the units on micro level (atoms etc) and on macro level (grammes etc.). The unit MOL is found in the centre of the scheme:
4 grams of the substance CuSO4.5H2O is weighted.
How many MOLs of hydrated Copper sulphate (light blue cristals) is that?
Use tabel V of the table book.
From grammes to MOL you must use the molecular mass. In this case: Cu + S + 9O + 10H = 63.5 + 32.1 + 144 + 10 = 249.6
249.6 gram of the substance (hydrated Copper(II)sulphate) = 1 MOL.
1 gram = 1/249.6 MOL
4 grammes = 4 x 1/249.6 MOL = 0.016 MOL
4 grammes of CuSO4.5H2O equals 0.016 MOL CuSO4.5H2O
0.016 MOL CuSO4.5H2O weights four grammes.
Suppose that a glass of beer (say: 100 ml) contains 5 ml of alcohol (C2H5OH, density of alcohol = 0,8g/ml)
How many grammes of alcohol are found in one liter of beer?
We already know the number of ml, but the question is to find grammes of a liquid (alcohol)
so you understand that we will need the density. d = 0,8 e.g.: 1 ml of alcohol has a mass of 0,8 gram.
5 ml weights 5 x 0,8 gram (= 4 grammes).
One glass (=100 ml beer) contains 5 ml = 4 gr alcohol
1 liter (=1000 ml) must contain 10 times more = 40 gr of alcohol [that is enough to slow down the growth of brain cells!!]
Explain to anyone the significance of every arrow in the scheme about MOL calculations.
True or False? Explain!
Goto answer 05-10
- 12 g of Carbon contain 1 mol of atoms
- 28 g Nitrogen contain 1 mol of molecules
In particular we look at the volume of 1 MOL of gas. Because that is special in the case of gases. (and not with (s) or (l))
Any gas at the temperature of 0oC and a pressure of 1 atm. has the volume of 22,4 liter per MOL (= molar volume of gases).
Att.: Every gas has the same molar volume, but mind: not the same molar mass!!
It does not matter with what gas you are dealing, the volume that it occupies is always determined by the temperature and the pressure of that gas,
wether the molecules are big or small.
We apply that with the following formula:
The temperature T is given in Kelvin!! The pressure in Nm2. The volume in m3
The constant c is: n x R, where:
n = the number of MOL and R = 0,0821 J x mol-1 x K-1
Calculate the volume of 10 grammes of Hydrogen gas, 10 grammes of Heliumgas and 10 grammes of butane gas;
all measured at a temperature of 0oC and 1 atm.
In question 11 is a problem: at 0ºC and 1 atm., the butane gas is no longer a gas, but a liquid.
- then what is your conclusion about the boiling point of butane?
- what can you say about the calculated volume?
Calculate the gas volume at 25ºC and 76cm Hg.
Name some substances that exist in pure form (so: not mixed with anything):
- at home, in the street or in shops
- in nature
The pure substance is built up of only one kind of particles. If the pure substance is built up o molecules, then all molecules in that substance are equal. The substance can be represented with one molecular formula.
As soon as other molecules do mix, then the whole in impure. Then you have got a mixture of substances.
The pure substance could be built up of ions. In that case different ions are present in the pure substance (positive and negative ones).
Are we then talking about a pure substance?
Take for example kitchen salt. It is built up of two kinds of ions, nicely arranged in an ionic lattice (Na+ and Cl-).
The substance had one clear formual: NaCl (the ions are close toghether in the proportion 1:1.
If the substance is built up like that, and can be indicated with one formula, then we say: this substance is pure.
As soon as strange ions come in, or molecules, then you've got a mixture.
The substance has become impure.
Have a look: film.
Talking about phases, officially (aq) is not a phase.
Below a scheme that shows models of each phase on the level of particles. You can find that also in the tables.
In solid state, the particles are positioned on a fixed place; they cannot dislocate. They cannot move around. But yes, they can (and often will) be in some vibration, but are not mobile. The vibrations depend on the temperature. At very low temperatures, the vibration can even stop.
Normally al those particles toghether make a regular pattern, a lattice. You can observe that outside: a cristal structure. But there are solid substances without cristal structure: amorphic. Examples are: glass, plastic and gel.
In the liquid phase the particles have a certain movability; they can deslocate, turn around each other. Just like all particles, they also have a certain vibration movement. The whole movement depends on the character of those particles (for example: being big or small) and on the temperature (cinetic energy).
The particles in a liquid do not form stiff structures, no cristals, but do remain close, as close as possible like in a solid, thanks to the mutual attraction. It is wrong to think that a liquid is something in between solid and gas. Liquids and solids have a comparable density. The fact that the particles can move, around each other, causes the liquid character.
In the gasphase the particles are completely separated from each other; they move separately; they have all freedom for that, but dependent of the character of the particles and the temperature.
Regularly the gas particles collide mutually (or they collide against the walls of the gas holder) and thus change there movement direction. If they have no longer enough energy, for example at cooling, than a collision could end with the staying toghether of the particles → liquid or solid.
N.B. About liquids there is this misconception:
In a liquid, just as in a solid, the particles stay close toghether.
The difference with a solid is that the particles in a liquid are not in e fixed position, a lattice, but can move around each other; they have enough cinetic energy for that.
You could also say: the mutual attraction is not enough to make a lattice. Taking away energy, cooling for example, could cause a lattice anyway. Heating, so when particles aquire more energy, than it can happen that they start to remove from each other (go to gas phase).
In a liquid the particles are that close toghether that there is no option (as in gases) to put them more togheter and getting smaller volume.
(aq) we use many times in chemistry, but is no phase. Het means a mixture where a solute is dissolved in water.
NaCl(aq) means: a solution of salt in water.
What can we observe during the following processes, and explain you answer:
- H2O(l) → H2O(g)
- CuSO4(aq) → CuSO4(s)
- Na2CO3.10H2O → Na2CO3(l)
Pure theoretically calculating we could distinguish 18 kinds of mixtures of two components, if we apply:
- having three different phases,
- the mixture is composed of two components, and
- every mixture can be homogeneous as well as heterogeneous.
|(s) + (s)
||(s) + (l)
||(s) + (g)
|(l) + (s)
||(l) + (l)
||(l) + (g)
|(g) + (s)
||(g) + (l)
||(g) + (g)
The scheme shows nine theoretical mixtures that all can be (also theoretically) homo and heterogeneous.
Note that the reality is different.
- (l) + (s) and (s) + (l) are equal.
- (g) + (g) is always homogeneous; there is no heterogeneous form of it.
- (g) + (s) only exist as heterogeneous mixtures.
Try to fill in the open lines of the schemes.
A couple of examples:
- A mixture of salt and sugar cristals: (s) + (s) heterogeneous
- a mixture of CO2 in water (soda water) is homogeneous, but becomes heterogeneous as soon as you open the bottle.
- air is a mixture of gases (always homogeneous)
What mixture is indicated with (aq)?
How many different real mixture types can you recall?
Explain your choice
If beer is considered as a mixture of water and alcohol, what kind of mixture is that?
Goto answer 05-20
What kind of mixture is bronze?
A very common mixture in chemistry is: (s)+(l)-homogeneous
(s) is some solid, dissolved in (l), may be water (there are many solvents!).
An aqueous solution is of course a mixture with water as the solvent.
The dissolved substance, the solute can be (s), (l) or (g).
1 liter 1,0 M NaCl (you say: 1 molar NaCl) contains 1 mol NaCl-particles.
How many mol of chloride ions and Sodium ions are present in 0,2 mol NaCl?
Suppose that you have a bottle of 1 liter and you drop that by accident. The beer has a Vol% of 6 (heavy beer).
The density of the alcohol is 0,8 g/ml (or kg/l).
How many molecules of alcohol did you drop?
Goto answer 05-23
How atoms may have a tendency to attract negative particles (mostly electrons), is called ELECTRONEGATIVITY (see module 3).
The Electronegativigy is abbreviated with the letter E.
Wether or not electrons (negative particles) are attracted easy or difficultly by neutral atoms (and possibly been 'eaten', depends much on the nuclear (postive) charge and the atomic ray (distance) of that atom.
The bigger the nuclear charge, the stronger the attraction forces on the negative particles.
The bigger the distance of the negative charges to the nucleus, the weaker the attraction forces.
Explain that an atom of Chlorine will attract electrons stronger that an atom of Iodine.
In the Periodic Table, the nuclear charge increases from left to right, while the number of main levels remains te same. The outmost level, the outer shell will be attracted stronger, and the atom becomes smaller from left to right.
The consequence of this is that the attractin force of the atom to the negative particles outside the atom will increase, so the E(lectronegativity) in one Period will increase from left to right.
In table 5, find the third period and the value of E of every element;
Note also the atomic ray of every element and explain why this atomic ray every time decreases.
dGoto answer 05-28
The atomic ray increases in the Periodic Table from top to down, because every time there is an extra main shell.
Negartive particles (like electrons) will be attracted every time weaker from top to down, because every time the distance is bigger.
In the table, find the seventh main shell and note from top to down the atomic rays as well as the value of E (put the data in a small table).
Draw a little graph: atomic ray on the x-axis and E on the y-axis
You must explain the graph.
If a molecule has an non symmetrical distribution of charges, then that molecule does have a so called 'dipole moment":
dipole moment = charge x distance
With that distance we mean the distance between the centre points of the charges.
Find in the tables the bonding distances, the bonding angles and the dipole moments of the molecules: Carbon dioxyde, sulphur dioxyde and sulphur trioxyde.
Explain the dipole moment of the last one (= 0)
The dipole moments of the four Hydrogen Halogenes are as follows:
Explain these data with the theory.
If the dipole moment of a molecule equals 0, then this substance is non polar; if not, then the substance is polar.
Polar substances have dipole moments.
Polar substances, so substances with ions or substances with dipole molecules, mix well with other polar substances; for example: water with alcohol.
Non polar substances mix well with non polar substances; for example: fat with oil.
Polar substances do not mix well with non polar substances (and v.v.): water and oil.
"ALIKES DO LIKE EACH OTHER".
Mix 'Iodine water (polar) with tetra(l) or petrolether (non polar solvents) and explain your observations.
Explain why oil and fat are non polar.
From the above text must be clear that the presence of charges in a molecule has enormous influence on the molecule.
If in one molecule or in a complex ion two equal charges are close toghether, they will influence each other: repulsion;
that's how a substance gets special properties.
an example is ethane diacid, or: oxalic acid:
The C - C bond in the middle is under great tension (because of the repelling action of the positive charges).
That will weaken that C - C bond.
The consequence is that oxalic acid (different from the normal carbon acids) breaks easily (is easily to oxydise).
Normally a C-C bond is difficult to break.
Check in a table book if oxalic acid indeed is a reductor.
Another example is: cationic acids (see module 9)
If you dissolve an Iron(III)salt in water, you get in the centre of a complex a small and strong positive Iron ion with close around it an number of water molecules.
The δ--side of the Oxygen atoms is attracted by that positive Iron ion.
The δ+-atoms of Hydrogen in the water molecules will become under the influence of that same Iron ion with a certain repulsion as a consequence.
Some complex ions can, because of this effect, even donate some H+ ionsand thus act as a weak acid (cation acid).
Find in the table with acids and bases the three chloro ethane acids, and explain their difference in acid strength.
Most solids are built up with a lattice, with one of a couple of different particles in it.
The forces that bind the particles (attraction) can be very different, and determine some properties of that substance.
Most metals have strong attraction between the positive metal ions and the negative free electrons in the lattice (see module 3)
Those free electrons can be considered as a kind of glue that holds the ions in there positions in the lattice.
The lattice is in fact the regular arrangement of the metal atoms. In it strong charge forces do rule the result.
Some properties of metals are: metal shine, conductibility for electricity, they are solid (exept Mercury) and often have rather high melting points (not always).
In salts are strong attraction forces between positive and negative ions (see module 3).
Those inter ionic forces determine the strength of the lattice and so the melting point. Most important here are the charges of the ions and the distances between them (i.e., they are determined by ionic rays).
A strong lattice has small ions with high charges.
Thus, for example MgO has a stronger ionic lattice than NaCl, because the Magnesium and the Oxygen ions are smaller and have more charge than the Sodium and Chloride ions.
Un such an ionic lattice, the positive and the negarive ions are nicely arranged. Inside always the dominat charge forces.
Properties: cristals, high melting points, in molten state they do conduct. the cristals do not conduct electricity!
In most liquids and solids the particles are hold toghether by inter molecular attraction forces:
In solids, the particles will stay in a molecular lattice. Molecular lattices are stonger when the molecules have more dipole character (a bigger dipole moment), and if they have more mass (are bigger).
- the not very strong vanderwaals forces, or: mass forces.
- polar forces in the case of dipole molecules
- Hydrogen bridges
Find a table with solids. Chose two substances(s) for every type of lattice. And controle their melting points.
Are they in accordance with the theory?
In general the attraction forces in molecular lattices are not as strong as in metalic or ionic lattices.
So molecular lattices will have lower melting points.
In the case of real low attraction forces, they have no lattice at all at normal temperatures, but will be liquid or gas.
Substances with molecular lattice will have covalent bondings between the particles, so mostly built up of non metals.
Exceptions are solids without any lattice structure (amorph) and substances with an atomic lattice, like diamant.
Apart from amorph Carbon, there are two well known lattice structures:
Technically it is possible to change graphite into diamant under high pressure. The density can become higher this way.
- diamant with cubic cristals and a density of 3,5
- graphite with hexagonal cristals and a density of 2.2
You can get artificial diamant from graphite.
The molecular lattices are no good conductors; may half conductors.
A change of phase is not really a chemical change, not a chemical reaction (although the difference is not always that clear).
When internally something happens with the particles of a substance (they really change), than you have got a chemicalreaction.
But when those particles only change in position, vibration, energy etc, and inside they do not really change, than we prefer to talk about a physical change.
Physical changes can be changes of phase.
Thus, particles in a lattice (a solid) can change structure in different ways:
When a substance with an ionic lattice melts, ((s) → (l)) or dissolves ((s) → (aq)),
than the consequence is that the ions start to move freely.
- When melting (when heating a dry substance).
- When dissolving (always in a solvent like water)
Well known phase changes are:
| (s) (l)
||melting, solidification, freezing
| (l) (g)
||boiling or condensation
| (l) (g)
or (s) (g)
| (g) (s)
It can be fun to look at some Youtube films about this topic. For example: the following
Phase changes are not always real chemical reactions; they belong to the physical phenomena.
Mind that something like boiling is really something different from decomposition!!!
People sometimes confuse these concepts.
There are also substances that, at heating, do nog melt of boil, but decompose, like sugar.
Describe schematically the following two processes:
- "boiling" of sugar (theoretically)
- decomposition of sugar (what really happens when you heat sugar)
A couple of examples of phase changes:
- melting of ice: H2O(s) H2O(l)
- evaporation of gasoline: C8H18(l) C8H18(g)
- melting of Lead: Pb(s) Pb(l)
Melting point & Boiling point
|1. The LATTICE is the most important factor in determining a melting point.
How strong is a lattice? How easily can it be molten?
Melting means that the lattice is destroyed, and it costs a lot of energy to destroy a strong lattice.
The strength of an ionic lattice depends on the charges of the ions and of their mutual distances.
In the lattice of CaO (with charges 2+ and 2-) wil melt more difficultly than the lattice of NaCl (with charges 1+ and 1-).
Apart from that, also the ions of CaO are smaller (so: closer toghether)
Small ions cause stronger lattices. They are closer toghether
Salts, in general, will have high melting points.
Also metalic lattices depend on charges and distances.
Between the metals exist rather some differences: in general a metalic lattice will be strong (high melting point), but ther are exeptions:
Mercury(l) is at normal temperatures a liquid. Lead, Tin, Lithium, Sodium, Potassium have no strong lattice. They melt easily.
Extremely strong are the lattices of: Chromium, Wolfframium and Vanadium. Also see table V)
2. VANDERWAALS-FORCES are the second factor in determining the melting points.
They exist in particular in molecular lattices, of which the strength depends on:
Substances with molecular lattices do not have high melting points.
- the participation of Hydrogen bridges
- the participation of polar atoms (with δ- and δ+)
- the molecular masses. Big molecules cause higher melting points than smaller ones.
So: melting points depend on the strength of the lattice:
- First check the presence of charge related forces; how big are the charges and the ionic rays?
- Check then the vanderwaals forces, they depend on the molecular masses.
- Place the follwing substances in order of increasing melting points:
- Kitchen salt, Potassium chloride, Bromium, water, water free chalk (CaO), graphite.
Boiling points depend (in order of importance) on:
- Charge related forces between the mutual particles (are they ions or dipole molecules?)
- VanderWaals forces; so compare the M(olecular masses).
- The threedimensional shape of the particles:
The more spherical a molecule is, the smaller is its surface, the smaller are the mutual attraction forces, and the lower the boiling point.
Spherical particles escape more easily (this will boil more easily).
Goto answer 05-39
- Place the following substances in order of increasing boiling points:
- water, Nitrogen, hexane, 2.3-dimethylbutane, glycerol.
Gaseous substances at room temperature, in general, have no or little attraction forces between the particles.
They are not polar and have no Hydrogen bridges.
Explain the characteristics in the graph:
Phase changes are not considered as chemical reactions. But mind: it is not always that easy to distinguish between chemical and physical processes.
There are substances that never reach a melting or boiling point. Long before the come to melting or boiling, the decompose (and that certainly is a chemical process).
Watch carefully the filmon Youtube about heating of sugar, and try to explain your observations.
statement: During evaporation of solid I2 Iodine atoms are formed.
Is this statement true of false? Explain
Also watch again this
Goto answer 05-42
When the particles of a liquid receive more energy, or even when lattice particles receive energy, (for example because the substance is heated), than you increase the movement and the vibrations of those particles.
At a certain moment this movement will become so heavily, that the particles cannot longer stay toghether:
The internal attraction forces are no longer sufficient to keep them toghether.
When they become completely loose from each other, so a gas is formed, those particles still can collide.
But even so, they will not stay toghether after the meeting because of the energy.
Of course, they will stay toghether again at cooling down. Then the substances can become liquid or solid again.
Chose the right answer and explain your choice:
Aspirine does not dissolve in water because:
- aspirine is a solid and water is a liquid
- aspirine molecules do not have a polar character
- that water does not contain stomach acids
- the melting point of aspirine is too high.
ionic substance that dissolves in water: Sodium chloride
The ions Na+ and Cl- escaping from a lattice (this happens at the surface of the cristal) immediately are surrounded by water molecules (because of polar attraction forces).
The ions still attract each other, but not enough to come back in a lattice. Those water molecules make that impossible.
In this case, we have a soluble salt.
Other ions, smaller ones or more charged, also surrounded by water molecules (=hydrated), often can come toghether again and form a lattice. Their mutual attraction is big enough to succeed in that.
heterogeneous mixture: (example) oil + water
The polar molecules of water attract each other, while the non polar oil molecules stay and stick toghether. Mixing water and oil molecules has no success.
- polar substances attract polar substances (like sugar that dissolves well in water)
- non polar substances attract non polar substances (like fat in petrol)
- polar substances do not mix with non polar substances (like water and oil)
ANY KIND LOOKS FOR ITS OWN KIND
Compare the two graphs, and draw your conclusions (S = solubility)
Matter, wether a pure substance or a mixture, can conduct electrical current when in that Matter there are present: charged particles that can move freely with sufficient movability.
So if ions can move freely in a substance or in a mixture (like molten or dissolved salt), then that substance conducts electricity.
Explain that the substances below will conduct electricity, yes or no.
One conducting substance will conduct better than the other; not all conductors are equal, have the same quality.
The conductability depends on:
Applications of the conducting substances can be found, for example: in current wiring, electrodes, salt bridges, electrolysis.
- The concentration of the charged particles, their number; the more charged particles, the better the conductibility. A high concentration conducts better than a low concentration.
- The movability of the charged particles. Small ions mostly conduct better than big ones. Note that here the phenomena hydratation (surrounding water molecules) can have big influence.
Sometimes small ions can be hindered in its movability by those surrounding water molecules.
- A hydratated ion moves slower, but mind: hydratated Hydrogen ions have a special mechanism to move extremely fast. They can conduct very well. The H+ of the H3O+-ions are superquickly transported from one ion to the other.
The substances below do conduct electricity. Explain why:
- All metals
- Solutions with ions
- Molten kitchen salt
Will the following substances conduct electricity? Explain.
- Calcium chloride(s); Lead(l); water(l); ice(s); kitchensalt(aq); diamant; oil(l); acetic acid(aq); acetic acid(l).
The hardness of solids can vary considerably, dependent on the threedimensional structure and on the forces that hold this structure toghether.
The more ionic the substance, the harder it will be.
In ionic and in metalic lattices ions cannot move or displace internally.
The hardest substance seems to be diamond that has an 'atomic lattice' of Carbon atoms.
Every C-atom is connected with four other C-atoms, so is you look well, the diamond actually is one big molecule.
It has the perfect structure; every particle is connected through atomic bonds / covalent bonds.
Polymers are built up of macromolecules; they can have a more or less spherical shape, but not always.
The molecules can be long, without interconnections and then we deal with soft plactic.
On the other hand, if there are intermolecular connections between these macromolecules, we could have hard plastic.
soft plastic, at heating, can more or less melt; hard plastic cannot melt.
In chemistry we speak about thermoplast and thermohard.
Hygroscopic substances like to absorb water(vapor) from the atmosphere.
That's why they are applied as drying substance, for example in packages with electronic apparatus.
When they absorb water, the water molecules are built in in the salt cristals. In the meantime, these cristals remain solid and dry for a long time.
The water molecules are built in in the ionic lattices.
Only after absorbing very much water(vapor), the substance may become wet.
Examples: Copper)II)sulfate (light blue); Calcium Chloride; Sodium carbonate; and many other salts.
But also phorphorpentoxyde (P2O5) is extremely hygroscopic; only: this substance does not only absorb the water, but also reacti with it.
Dehydrated (dry) Copper(II)sulfate can be used to prove the presence of small amounts of water in a mixture.
Explain what you can observe, or which observations should be done?
Plaster, Cement, Bricks
Plaster has a formula: (CaSO4)2.H2O and is able to absorb (slowly) lots of water.
When mixing water free (dry) plaster with water, at the beginning the mixture will be a misture of (l) + (s),
but after building in the water(l) into the solid, you stay with a solid: hydrated plaster (hard matter).
(CaSO4)2.H2O(s) + 3H2O(l)
the raw material for cement is a mixture of Calcium carbonate + Alluminiumoxydes + SiliciumOxydes.
You must heat the mixture very intensly, then first the carbonate will change into CaO.
At temperatures above 1500ºC reactions occur between those oxydes of Calcium, Aluminium and Silicium, ans salts are made like silicates and aluminates of Calcium, often still in the presence of Iron.
The final mixture is very well grinded and sold als Portland Cement.
this cement is extremely hygroscopic. With water it forms a mixture that within minutes becomes extremely hard.
On our planet we have enormous amounts of water. The following substance in abundance after water is sand, with the main component SiO2.
The other components are, for example, compounds of Iron (gives sand the brownish color) and compounds with aluminium.
Apart from Silicium oxyde, also silicates are present in earth.
Clay also contains silicates of Aluminium: silicate compounds where part of the Si-atoms are substituted by Al-atoms.
Clay has a kind of folded structure, caused by macromolecules.
They have a two-dimensional structure and can - in the presence of water - easily move over each other. That's why clay feels slippery.
But, if you heat clay very strongly (bake) the water molecules disappear, the folded layers come very close toghether and will create threedimensional connections. A very hard structure is the consequence: brick and ceramics in various qualities.
to be done in the school lab.
|The purpose is that you investigate a number of substances according to the six items below.
||You receive a sample, not knowing what it is.
After every observation you must try to draw a conclusion.
|The substances to investigate can be:
||The six items of attention for every substance are:
- phosphor pent(a)oxyde
- ethanol (alcohol)
- magnesium hydroxyde
- carbon disulfide
- ammonium chloride
- sulfuric acid(aq)
- tetra (nail polish remover)
- calcium oxyde
- Describe the visual properties of the substance.
- If the substance is (s), then investigate:
- the solubility in (non) polar liquids
- wether the melting point is high or low
- the conductability for electric current
- If (l), then investigate:
- the mixability of the substance with (non) polar liquids
- wether the boiling point is high or low
- the conductability for electric current
- Find out if the substance in aqueous solutions react acid or basic.
- Use the data from tables if you have an idea about the investigated substance; and note from what tables you got the data.
- What could be the substance? Why do you think so?
The proper method to separate a mixture of substances in its components depend on the character of that mixture and of the components.
For example, its of no use to filtrate a homogeneous mixture.
To chose the best method, you must know the properties of the substances.
Extraction of a solid mixture means: adding a solvent in which one of the components will dissolve and the other not.
Then you can separate the solution form the remaining solid, by starting the filtration.
Finally you can - if desired - evaporate the solvent and stay with the solid component.
This way hot water can extract certain substances from thea leaves. You separate components from each other and the soluble components are consumed.
The remaining substances (what's left from the leaves) is thrown away.
A mixture of Iodine and Potassium permanganate kan be separated by adding alcohol. The Iodine dissolves, but the salt does not.
And what about making coffee?
Draw a visualizes work scheme of how to separate certain colorants in flowers.
Imagine that here these colored substances dissolve in alcolhol; those not soluble remain as a 'residue'.
Some special extractions are:
- when heating the same mixture as above (Iodine + permanganate (= (s) + (s)) the Iodine will evaporate.
But immediately at some cooling, the Iodine will sublimate at the walls of the device (use a glass funnel and you will observe the Iodine cristals coming back, and separated from the salt cristals.
- From a mixture of Iron and Sulphur powder, you can 'extract' the Iron with a magnet.
Chromatography often is applied in chemical labs:
a mixture (meaning with different particles) passes a fixed, solid layer (paper, Aluminium oxyde gel, of other porous substances)
The different particles of the dissolved mixture are more or less strongly absorbed by that fixed layer (dependent on, for example, polarity)
touch a piece of filter paper in black ink (that for sure is a mixture of various colorants). That piece of paper shows a small black spot or tiny black horizontal line.
Chose a 'solute' and put the paper with its lower side into that solute. By capillarity, that solute will go up in the paper and also pass the ink spot. At that very moment the solute will take the components up, with the solute and with different rates.
That's how the most bad solubel component will remain at its original place, will not move up.
But another component that dissolves reasonably in the solute, will go up with that upmoving solid.
That's how you separate the components. At the end you can observe different spots with different colors at different places.
Do you think that is is possible to separate a (g) + (g) mixture with paper chromatography into the components? Explain.
Goto answer 05-50
Electrophoresis and Chromatography
A special filter paper is wetted with an aquaous solution, maybe acid, basic or neutral.
In the middle you put a spot of a protein mixture.
The proteins move under influence of an electric field, and according to their charge, in a certain direction:
The result that can be seen in the image indicates that probably an acid liquid was used to wet the filter paper.
- proteins in basic environment (OH- is present) mostly have a negative charge
- proteins in acid invironment (H+ is present) mostly have a postive charge
- the proteins in their iso electric point (more about that later!) are neutral
Explain in details how this apparatus works.
there are different chromatographic methods like:
- paper chromatography
- column chromatography
- gas chromatography
About the special type of chromatography, the column chromatography.
The column (a glass tube) is full of a special solid (sand, Aluminium oxyde, a certain gel, and others)
On top of the column content is placed a mixture that just will be absorbed by the content (gel) and immediately after that, you open a tap and drops of a solute are provided to the column. This solute goes through the column and will take the mixture with it, every component at its own rate. That rate depends on factors like:
how big are the particles of a component? how soluble is the component in the solute? how well is the component absorbed at the solid content of the tube? etc.
Every five or ten seconds a new test tube is places under the column to receive the outcoming drops. At the end of this process, every test tuybe contains a bit of the solute, and some tubes will contain certain amount of a component.
There are very good detection methods to find out what component is in every tube.
Explain in details how the apparatus works.
Gas chromatography also is a method that applies absorbtion.
Substances will be absorbed by a 'carrier'.
A long, thin, spiral shaped tube is full of a porous solid, the carrier.
Continuously an (inert) gas is passing that tube, or better: the carrier.
That gas could be, for example, He, coming from a cylinder where the gas pressure can be controlled very well. Helium is one, but there are other inert gases.
At the beginning of the tube there is an injection room where a gas mixture can be injected. That unknown gas mixture is to be investigated.
The injected small amount of gas mixture immediately is taken with the carrier gas He all through the tube and the solid carrier.
One component will move faster that the other, dependent on its absorbtion by the carrier. So one gas will leave the tube earlier than the other.
At the end of the tube, for example with a micro flame that react with color change, the outcoming component will change that color.
A detector can analyse that color as well as the intensity of the color, and give a signal that can be printed out.
Thus you cannot only determine which component was present in the mixture, but also its percentage.
Explain in details how the apparatus works.
One of the separation mechanisms of particles, in columns, is based on the size difference of the particles.
Which particles will leave the column first: the biggest or the smallest?
This is a separation method based upon the difference in boiling points of liquids.
If you heat a mixture of liquids, the liquid with the lowest boiling point will boil first, escape first (evaporate) from the mixture.
The vapor enters the condensation tube with cooling. There this component will condens and collected.
The other components, with higher boiling points, remain behind until reaching higher temperatures.
Good controll of the temperature is needed during the whole process.
example: you can distill wine, where alcohol with the lower boiling point (78ºC) will escape. the water will remain behind
At what temperature wine can be distilled to get the alcohol?
Filtration is only possible with heterogeneous mixtures, and with particles whos size is big enough for the filter. They cannot pass, but the (smaller) liquid particles can.
Filters exist in all kinds, from very fine to very rude.
You clearly have a solid in a liquid, a heterogeneousmixture, and the precipitate(s) has reasonable heavy cristals.
Then you can start to 'decantate' = let the liquid go while the solid remains behind.
Normally we deal here with homogeneous mixtures. Otherwise you would filter or decantate.
You heat such a mixture carefully. The liquid evaporates and the solid remains.
Of course only when the liquid and the solid can stand heating without decomposing.
Centrifugation can only be done with heterogeneous mixtures. Often it is chosen as a faster method than filtration.
The particles with the biggest mass (that must be the solid) will precipitate at the bottom of the tube under influence of centripetal forces.
It deals with a homogeneous mixture of (l) + (s)
The image shows a method to evaporate carefully (on boiling water in a water bath).
Such a water bath can only serve as such if a temperature of 100ºC is enough to evaporate the liquid.
The dissolved substance will remain behind.
Explain why the production of seasalt needs evaporation.
You apply this method for example when you have a suspension: a trouble mixture of (s) + (l) that could not be separated with a filter.
The solid could be built up os very tiny cristals or even macromolecules.
There are methods for centrifuging (g) + (g). Gas centrifuges are applied to separate, for example, heavy Hydrogen from normal Hydrogen.
Every substance contains energy; it can be a lot or little, but always there is chemical energy in matter, in a latent or potential way.
This internal energy becomes manifest under certain circumstances: if the substance participates in a reaction, so: if the substance changes.
To remember: there are many forms of energy: radiation energy, cinetic energy, electrical energy, potential energy, chemical energy.
Explain that explosives must have lots of energy.
Make an estimation of the internal (chemica) energy of the following substances, and put them in order of increasing energy content:
Petrol, water, TNT, Hydrogen, carbon dioxyde, Sodium chloride Sulphur, wood, sugar.
Humans (and animals) must eat. The human body cannot without food, receives the energy from nutricion. Proteins are primarily for growth and maintanance, but sugars and fats are for the energy.
Which nutricians we use dayly in Europe to have energy for our activities?
In our body energy rich substances are converted into products. Are we here dealing with exothermic or endothermic reactions?
When adding energy to a substance, that substance normally wil get hotter. The particles receime more movement!
Only if that increase of energy is accompanied with phase change, then (temporarily) something extra is happening:
during this change engery is used to remove particles further from eacht other, or the lattice of the substance is destroyed.
The temperature does not change during this change of phase as long as the two phases are still there.
What are the extreme values in this graph?
or: which minimum and maximum values of temperature are there?
Which conclusions do you draw?
The important elements in combustion of fuel are: Hydrogen and Carbon, with the final products: water and carbon dioxyde (CO2).
Coal contains lots of Carbon and natural gas relatively more Hydrogen.
What is better for the environment: burning of coal or burning of natural gas?
When carbohydrates are burned, in fact two elements H and C react with Oxygen. att.: Hydrogen is the most reactive one, so that one will be the first to consume the Oxygen.
If enough Oxygen is present, Carbons turn is there. Shortage of Oxygen creates carbon monoxyde (CO) or even you can see the black clouds of soot.
The formation of CO2 takes place all over the world and is considered a cause of the heating up of earth, including raise of see level.
This could create big problems in the future. Last fifty years the amount of carbon dioxyde has an increase of about 15%.
In what ways does Europe contribute to the increase of CO2 in the atmosphere?
Ethanol (alcohol) can be made in large amounts, for example from fermenting sugar cane.
biogas is a mixture of gases (with relative lots of methane) that is formed in the bacterial fermentation of shitty products.
Hydrogen can be made in a process of electrolysis. Unfortunately this costs rather some energy, so what's the nett effect? If you must first make energy out of natural gas to make Hydrogen for energy, why is that?
But nevertheless, lots of research is needed to resolve the problems and to find the best ways for Hydrogen production.
there are ideas. We could learn something from plants and their photosynthesis. In this process, under influence of sun light, water is split into Hydrogen and Oxygen. Wouldn't that be a beautiful mixture to create energy without any production of carbon dioxyde?
Hydrogen would be a very good fuel. Why?
Alternative, non chemical sources for energy: nuclear energy, water plant energy, wind energy, solar energy.
Batteries and penlites have the function to deliver electrical energy. So they must contain energy: chemical energy.
The substances in batteries and penlites must be rich in energy. Otherwise they are useless.
Petrol is an energy-rich substance, but you never meet petrol in penlites. Other substances are used, staying quietly in their position, being not so dangerous (explosive).
In module 7 we will talk about those substancies full of energy and how they deliver that energy during chemical reactions.
You must know that batteries and penlites suffer chemical reactions and that chemical energy is transformed in to electrical energy.
An "empty" penlite is not really empty. The energy rich substances are used, transformed into energy-poor substances. Recharging a battery is a process wherein energy-rich substances are reproduced.