Determining purity

Pure substance
-only one substance
- determine by checking melting point of a solid
- determine by checking the boiling point of a liquid
- determine using chromatography

Pure solid
- exact and constant melting point

Pure liquid
- exact and constant boiling point

Effect of impurities on melting point
- greater the amount of impurities, the lower the melting point, and cause melting to take place over a range of temperature

Effect of impurities on boiling point
-if liquid is impure, the boildin point will increase and it will also boil over a range of temperatures, the greater the amount of impurities, the the higher the boiling point of liquid

Effect of pressure on boiling point
-if pressure surrounding a liquid increase, it's boiling point will increase.

Measuring Experimental Technique

Time
SI unit : Second(s)
equip: stopwatch, stopclock

Temperature
SI unit : Kelvin (K) ; Degree celcius
equip: thermometer, datalogger

Masses
SI unit : kilogram (kg)
equip: electronice balance

Volume
SI unit : m3 (3 is suppose to be small)
Equip : depends on the volume and accuracy needed

Collecting gas
-depends on the solubility
(whether gas is soluble in water)
-density
(how dense gas is compared to air)

Collecting gas - method 1
-Displacement of water, used to collect insoluble gases (hydrogen, oxygen, carbon dioxide)

Collecting gas - method 2
-Downward delivery, used to collect gases that are denser than air and soluble in water

Collecting gas - method 3
-Upward delivery, used to collect gases that are less dense than air and soluble in water

Measuring volume of gas
-using a gas syringe

Chemistry ; what i have learnt

1) kinetic particle theory

Solid - particles of solid are held together by very strong forces of attraction and do not move freely, and they only have enought kinetic energy to vibrate and rotate abour their fixed positions. therfore their fixed shape, the particles of solid are very close together so solid is unable to be compressed

Liquid - particles of liquid are helf together by a weaker forces compared to solid, they move freely and slide over one another thus they don't have a fixed shape, the particles are also quite closely packed together so they cannot be compressed

Gas - particles of liquid are held together by a very weak force and gas has a lot of kinetic energy held in fixed position therefore their fixed shape. The large space in between gases are also the result gas can be compressed easily so it does no has a fixed volume

Changes of state

-Melting
as heat energy is being supplies the particles vibrate faster until the vibrations overcome the attractive forces between particles and it starts to break away from it's fixed position, it slide over one another and become a liquid

-Freezing
particles lose kinetci energy and begin to move more sloqly, when the temperature is low enough the particle start to settle into fixed positions, after it is settled in their respective fixed postition, it is now a solid.

-Boiling
as the particle gain kinetic energy it move faster and eventually having enought energy to overcome the forces holdining them together, they spread far apart and move rapidly in random directions, now it is a gas.



Heating curve of a solid ; melting process (not so curvy though)

Cooling curve of liquid (Freezing process)

Heating curve of liquid (boiling process)