Notes on IGCSE Chemistry Part 1A - States of Matter

1.1 understand the three states of matter in terms of the arrangement, movement and energy of the particles

1.2 understand the interconversions between the three states of matter in terms of:

• the names of the interconversions

• how they are achieved

• the changes in arrangement, movement and energy of the particles.

1.3 understand how the results of experiments involving the dilution of coloured solutions and diffusion of gases can be explained

1.4 know what is meant by the terms:

• solvent

• solute

• solution

• saturated solution

1.5C know what is meant by the term solubility in the units g per 100 g of solvent

1.6C understand how to plot and interpret solubility curves

1.7C practical: investigate the solubility of a solid in water at a specific temperature

 

Features of the 3 states of matter

Feature	Solid	Liquid	Gas
Particle arrangement	Close together in regular pattern	Able to move over each other, close together in random arrangement	Far apart, random arrangement
Volume	Fixed, cannot be compressed	Fixed, cannot be compressed	Can be compressed
Shape	Fixed shape, cannot flow	Able to flow	Able to flow
Particle movement	Vibrate in fixed positions	Able to move over and around each other	Random movement in all directions

 

Interconversions

• Interconversions, or changes of state, are physical changes not chemical changes.

 

 

Heating

• When a substance is heated, its particles take in thermal energy

• Thermal energy is converted to kinetic energy and increases their movements

• When the substance reaches a certain point in temperature, the thermal energy is used to overcome the effect of the forces of attraction, rather than raising temperature

  • Forms a straight line on a time-temperature graph

• Melting = solid -> liquid

  • Some of the bonds between particles are broken

• Evaporating = liquid -> gas

  • All remaining bonds are broken

  • Boiling is when evaporation is at maximum (evaporation can occur below the boiling point)

 

Cooling

• When a substance is cooled, the particles lose thermal energy to the surroundings and move slower (less kinetic energy)

• When the substance reaches a certain point, bonds form between particles.

• Freezing = liquid -> solid

• Condensing = gas -> liquid

 

• Certain substances don’t have a liquid form and change from solid to gas or gas to solid.

• Sublimation = solid -> gas

• Deposition = gas -> solid

 

Diffusion and solubility

• Solvent = liquid in which a solute is dissolved to form a solution (common solvents include water and ethanol)

• Solute = solid that dissolves into a solvent

• Solution = liquid mixture where the solute is uniformly distributed within the solvent

• Saturated solution = point where the solvent cannot dissolve any more solute at that temperature

 

Diffusion

• Diffusion = movement of particles from high concentration to low concentration

• Factors affecting diffusion:

  • Temperature

  • Concentration gradient (difference in concentration)

  • Diffusion distance

 

Solubility

• Solubility = maximum amount of solute which can dissolve in a solvent at a given temperature

• Find solubility:

  1. Divide mass of solute by mass of solvent

  2. Multiply by 100g

  3. Use units g/100g in answer

• Solubility curve = graph that shows solubility against an independent variable (e.g. solvent quantity, temperature)

  • As it is a curve, it allows you to predict solubilities you have not tested

You may be asked to plot a solubility curve in the test and use the x- and y-axes to make predictions. These are some easy marks, just keep in mind SLAPUK when you plot the graph and use a ruler to make predictions!!

 

Potassium Manganate experiment: explained

 

• When potassium manganate crystals are dissolved in water, a purple solution forms.

• This occurs because water and potassium manganate particles move freely

  • They can mix and form a solution

• The final solution is a weaker colour because the potassium manganate particles are less concentrated