Kinetic Particle theory

Kinetic Particle theory

Matter
- all matter is made up of tiny particles
- the particles of matter move or vibrate about randomly in all directions
- the three states of matter, solid, liquid and gas, result from the different arrangements and motion of these particles

Matter
-> No fixed volume (can be compressed)
Gases have...

• no fixed volume
• no fixed shape
• a low density

Arrangement of particles: The particles are very far apart and are are not held together.
Motion: The particles are free to move in any direction within a container and at very high speeds.

-> Fixed volume
No fixed shape- Liquids have...

• a fixed volume
• no fixed shape
• a medium density

Arrangement of particles: The particles are closely packed. They are held together but not rigidly.
Motion: The particles are able to slip and roll over one another.

Fixed shape- Solids have...

• a fixed volume
• a fixed shape
• a high density

Arrangement of particles: The particles are packed very closely together. They are held tightly in a rigid structure.
Motion: The particles can only vibrate about a fixed position.

Start->                                                            Process                                             -> End

Solid:

-Packed 

-Vibrate in fixed positions
-Forces of attraction-> very strong

Process:
- gain heat
- KE increases
- Forces of attraction weakens

Liquid:
-vibrates more vigorously

Relative density

Solid-> high

Liquid-> moderate

Gas-> Low

test- e.g. place in water

solid+ sublimation= gas

solid+ melting= liquid

Liquid+freezing= solid

liquid+boiling=gas

gas+deposition= solid

gas+ condensation= liquid

e.g. Melting of ice- physical change

photosynthesis in plant leaves- chemical change

dissolving sugar in water- physical change

burning a piece of wood- chemical change

Water in 3 states: 

Solid- e.g. iceberg

Liquid- e.g. sea

Gas- e.g. water vapor in surrounding air

Melting

- water spreads out and fills the container

- gases spread out even more, filling any space available

Arrangement of particles

Particles of a solid are in a fixed framework, held close together and vibrate.

Particles of a liquid are still in contact but free to move around

Particles in a gas are far apart. They move quickly and randomly in any direction.

- random movement of smoke particles caused by collisions with invisible air particles.

Diffusion in gases: e.g.

At first

In the process

In the end

It takes time because the air and bromine molecules are colliding with themselves and each other.

Rate of which different gases diffuse into the air

Lighter molecules-> diffuse more quickly

experiments:

 Diffusion in liquids:

Diffusion rate higher in higher temperatures.

                                          

Melting

solid-> liquid

increase in temp.

1. Heat energy is absorbed by particles in the solid. The heat energy is converted into kinetic energy. The particles start to vibrate faster about their fixed positions.
2. When the temp. is high enough, the vibrations of the particles become sufficient to overcome the attractive forces between them. The particles begin to break away from their fixed positions.
3. The particles are  no longer in their fixed positions. The particles slide over one another. The substance is now a liquid.

The temp. at which a solid becomes a liquid is called its melting point.

Freezing

liquid-> solid

decrease in temp.

1. Energy is given out by the particles of the liquid. The particles lose kinetic energy and begin to move more slowly.
2. When the temp. is low enough, the particles no longer have enough energy to move about freely. Some particles start to settle into fixed positions.
3. All the particles settle into fixed positions. Particles can only vibrate about their fixed positions. The substance is now a solid.

The temp. of which a liquid becomes a solid is called its freezing point. Heat energy is given out during the cooling process.

Boiling

liquid-> gas at the boiling temp. (boiling)

1. Energy is absorbed by particles in the liquid. The particles gain kinetic energy and start to move faster as the temp. rises.
2. Eventually the particles throughout the liquid have enough energy to overcome the forces holding them together. The particles can now spread far apart and move rapidly in all directions.
3. The substance is now gas.

The temp. at which a liquid boils to become a gas is called its boiling point. Different substances have different boiling points.

When a liquid boils, bubbles of gas are seen. These bubbles are formed when the liquid changes to vapor. The bubbles also consist of other gases dissolved in the liquid. The bubbles rise to the surface and escape into the air.

Evaporation

Sometimes a liquid can turn into a gas at temperatures lower than the boiling point. This process is called evaporation. Evaporation occurs because some particles have enough energy to escape as a gas from the surface of the liquid.

Liquids that evaporate quickly at room temp. are called volatile liquids. They usually have boiling points just above room temperature. e.g. petrol and perfume.

Both boiling and evaporation involve a liquid changing into a gas, but boiling is different from evaporation in these ways....

Condensation

gas is cooled sufficiently-> liquid

When water vapor touches a cold surface, condensation occurs and liquid water is obtained.

Heat energy is given out during condensation. As the temp. drops, the gas particles lose energy and move more slowly. Eventually, the movement of the particles becomes slow enough for the gas to change into a liquid.

Sublimation

e.g. when dry ice (solid carbon dioxide) is exposed to temperatures higher than -78 degree celsius, it turns directly into carbon dioxide gas without melting. like dry ice, some solids change into gas without going through the liquid state. This is called sublimation.

It occurs because particles at the surface of the solid have enough energy to break away from the solid and escape as a gas. e.g. Iodine and ammonium chloride. Substances that sublime may also change directly from a gas into a solid without going through the liquid state. This process is called condensation.

Dry ice :D

Diffusion in Gases

The process by which move freely to fill up any available space is called diffusion.

Gas particles of different masses diffuse at different rates. Besides being smaller,e.g. hydrogen particles are lighter than other air particles. Gases of different masses diffuse at different rates.

The mass of a gas particles is called its molecular mass. The smaller the molecular mass of the gas, the lighter it is. Hydrogen is the lightest of all gases and is about 20 times higher than air.

Experiment for rate of diffusion:

 
The fumes are formed when the two react. This end that the compound is formed nearer to means that the particles from  the other end moves faster than the particles from this end. Gases with lower molecular masses diffuse faster than those with higher molecular masses.

Diffusion in Liquids

Diffusion also takes place in liquids. 

e.g. a small crystal of potassium manganate(VII) is introduced into a beaker of distilled water. It dissolves to form a deep purple solution, which settles at the bottom of the beaker. Diffusion slowly takes place until the solution becomes uniformly purple.

Diffusion is the movement of particles from a region of higher concentration to a region of lower concentration. This applies to gases as well.

Effect of temperature on the rate of diffusion:

The rate of diffusion increases as the temperature of the solution increases. (The higher the temperature, the faster the rate of diffusion)

Particles gain more energy as the temperature increases. They can move faster and this increases the rate of diffusion.

Purification and Separation

A pure substance
-made up of only one substance.
-not mixed with any other substance.
e.g. white diamond is only made of carbon.
Air is not a pure substance-mixture of gases such as carbon dioxide, oxygen, nitrogen and water vapor.


Purity is important in food and beverages. Chemicals are added to make them last longer, look more attractive or taste better (preservatives and dyes).
Tests for purity:

1. check the substances' melting points and boiling points.(solid that has exact and constant melting point is pure- a pure solid will melt completely at one temperature)

-> impurities affects the melting point of a substance by lowering its melting point or cause melting to take place over a wider range of temperatures.
constant boiling point: if liquid is impure, its boiling point will increase and also boil over a range of temperatures.(greater amount of impurities, the higher the boiling point of liquid)
(If the pressure on liquid is increased, the boiling point is also raised/ If pressure is decreased, boiling point is also lowered.)

























       

        2. use Chromatography.(also used to test for safe food dyes/coloring)

Chromatography is the technique of using a solvent to separate a mixture into its components.(can be used to separate dyes in ink, pigments in plants, amino acids obtained from proteins, to identify poisons or drugs and to detect banned substances in food)

-> Paper chromatography(small drop of ink placed in the middle of filter paper
-> addition of ethanol causes the spot of ink in the middle to spread out into different colored rings. Each ring represents a different dye that made up the ink.








Another method:
The solvent ascends or travels up the chromatography paper.

-> the solvent continues to travel up the paper and dissolves the dyes.
-a dye not very soluble will not be carried far along the paper while a dye very soluble will be carried far along the paper(depending on solvent)

Colored spots are left in different places on the chromatography paper at the end of the experiment.


















Special points:
1) Mixture must be above solvent level-> prevents mixture from dissolving directly into solvent.
2) Mixture dot needs to be small-> too much ink will smudge the chromatogram.
3) Starting line has to be drawn in pencil-> graphite(pencil lead) will not dissolve in solvent and will not spoil/interfere in results of chromatography.
4) Solvent should keep traveling upwards-> ensure good separation of ink components.








Separating a Solid from a Liquid


Decanting: simplest way to separate water from pebbles is to pour the water away.
-> used to separate a dense, insoluble solid from a liquid.

-> Decanting to separate a dense, insoluble solid from a liquid.
















Filtration: used to separate small solid particles from a liquid. 
e.g. to separate sand and water
e.g. of small solid particles: sand, clay, dust, particles and precipitates

A solid can be separated from a liquid by filtration because the filter paper acts as a sieve. A liquid can pass through the pores of the filter paper but a solid could not.
Solid that remains on filter paper-> residue
liquid or solution that passed through filter paper-> filtrate






Evaporation to Dryness and Crystallization:
Many substances such as salt, dissolves in water to form solutions. To separate such substances, filtration is not used, instead we evaporate water from the solution.
e.g. When salt solution is evaporated to dryness, solid salt is recovered.(used to recover salt from seawater)
However, many substances decompose when they are heated strongly. For example, sugar will decompose when it is heated strongly. Most crystals give off water to become powder when heated. Evaporation to dryness is bot a good method of purification(after water removed, any soluble impurities present will be left on the crystals)
- the best method  of obtaining a pure solid sample from the solution is crystallization.
How?- water is removed by heating the solution and heating is stopped when hot saturated solution is formed. The resulting solution is allowed to cool to room temperature and the dissolved solid will be formed as pure crystals. 
To test for saturated solution- a clean glass rod is dipped into the solution and removed. A small amount of solution on the rod will cause crystals to form on the rod as it cools.
(saturation point/ crystallization point)


Example of obtaining copper(II) sulphate crystals from copper(II) sulpphate solution:
copper(II) sulphate solution-------(heat until mixture is saturated)-----------> saturated copper(II) sulphate solution---------(allow solution to cool)-----------> copper(II) sulphate crystals+ solution(contains soluble impurities)-------(filter the mixture)-------> copper(II) sulphate crystals

Separating Solids

Filtration: A mixture of for example, sand and salt(both solids), can be separated by filtration using water as the solvent.- Salt is soluble in water but sand is not.

Procedure

1. Pour distilled water into mixture of salt and sand. Stir and warm the mixture.

2. Pour warm mixture into a filter funnel lined with filter paper. Collect filtrate.

3. Wash residue with a little distilled water to remove all of the salt solution from it. The residue is sand.

4. Pour filtrate into  evaporating dish and evaporate filtrate to dryness. Salt is left in the evaporating dish.

Magnets can be used to separate solids.

- some metals are magnetic(common: iron, nickel, cobalt) 

- steel is also magnetic

- In recycling, magnets are used to recover magnetic materials from domestic waste

Sublimation: a substance sublimes from one that does not.

Separating a Liquid from a Solution

When a solid dissolves in a solvent, a solution is formed. E.g. salt solution, sugar solution.

To collect solute from the solution- evaporate the solvent. 

Obtaining the solvent....

- A pure solvent can be separated from a solution by simple distillation.(boiling a liquid and condensing the vapor) 

Diagram of simple distillation:

1. The solution boils in the distillation flask, water vapor rises to enter the condenser.

2. In the condenser, water vapor is cooled and condenses to change back into pure water.

3. Pure water is collected as distillate in a beaker.

4. The salt solution remaining in the distillation flask becomes more concentrated as the distillation proceeds. If the distillation proceeds, a solid residue of salt will be left in the flask.

As the salt solution is heated, its temperature increases. When the solution finally boils, the thermometer records a temperature 100 degrees Celsius( temperature of the water vapor) The temperature remains unchanged until all the water has boiled off.

Separating Liquids

Liquids that do not dissolve in each other are described as immiscible. Oil and water are immiscible in each other.

To separate immiscible liquids, we use a separating funnel.

E.g. oil and water

Separating miscible liquids...

e.g. ethanol and water- mixed together to form a solution.

-separated by a technique called fractional distillation

(a column called the fractionating column is attached to the flask and condenser. Many glass beads in the fractionating column provide a large surface area for vapor to condense on. A fractionating column may be filled with plates or a spiral, instead of glass beads)

During fractional distillation, the liquid with the lowest boiling point will distill over to the condenser first. Vapors of liquids with higher boiling points condense along the inner wall of the fractionating column and re-enter the flask.

-> diagram of fractional distillation

-> water vapor condenses in fractionating column and drops back into the flask. Ethanol which has a lower boiling point than water, reaches the upper part of the column and is distilled over. (At this stage the thermometer would show a constant temperature of 78 degrees celsius- boiling point of ethanol)

-> ethanol is collected as the distillate in the receiver.

• fractional distillation is used in industries to obtain nitrogen, argon and oxygen from air.
• it can also be used to separate mixtures of liquids such as crude oil.
• ethanol is formed when glucose solution undergoes fermentation in the presence of yeast. Ethanol and glucose solution can be separated by fractional distillation.

Summary

Crystallization(main features):

1) Makes the substance pure.

2) Solution should be saturated.

3) Change in state of substance from aqueous(a.q.)-> substance that has dissolved in water  to solid.

Chromatography(main features):

1) To separate a mixture.

2) To find out the number of components.

3) Depends on solubility of compounds or substances in a solvent.

E.g. TRAVELS...

FAST (Higher solubility)

SLOW

Filtration:

1) Differentiate between differently-sized substances.

Compounds and Mixtures

Compounds:

A compound is a substance which contains 2 or more elements chemically combined.
e.g. magnesium+oxygen= magnesium oxide(compound). It has very different properties from the elements that form it. 
Mixtures and Compounds

(element)+(element)-> compound
e.g. sodium+chlorine-> sodium chloride
(element)+(compound)-> compound
e.g. oxygen+ carbonmonoxide-> carbon dioxide
(compound)+(compound)-> compound
e.g. Carbon dioxide+water-> carbonic acid


Properties of a compound:

• properties of a compound are different from the properties of its constituent elements.
• compounds can be broken down into simpler substances by chemical methods
• the different elements in a compound are joined together in a fixed proportion by mass. e.g. water is a compound made only by joining together 2 atoms of hydrogen to one atom of oxygen. The ration of hydrogen atoms to oxygen atoms is always 2:1.

Chemical formula of a Compound

- a compound can be represented by a chemical formula. It is written by putting together the chemical symbols of the elements that make up the compound.

Chemical formula has the types of atoms present in the compound and ratio of different atoms present in the compound.

Decomposition of Compounds 

-Heat can be used to form compounds. Heat can also be used to break down compounds into elements/ simpler compounds.(Thermal decomposition)

-Besides heat, compounds can also be broken down by electricity into simpler substances.

Mixtures


- A mixture is formed when 2 or more substances are added together without chemical bonds being formed. Examples of mixtures include muddy water and air. Air is made up of of gases such as nitrogen and oxygen, etc.
-Constituents of a mixture may be all elements, all compounds or combination of elements and compounds. Substances in mixture can be solids, liquids or gases.

• components of a mixture can be separated by physical methods. e.g. filtration, distillation or chromatography.
• chemical properties of a mixture are the same as those of its components.
• no chemical reaction takes place when a mixture is formed.-little or no energy change
• components of mixture can be mixed in any proportion. (proportion of constituents in a mixture are not fixed)

Example: Alloys

-> example of a mixture.(mixture of metals with other elements)-usually metals but sometimes non-metals like carbon.

-> widely-used- tend to be stronger than pure metals