chem topic 1

what is electrolysis?

decomposition by electricity (a chemical method)

test for chloride ions

1. dissolve solid sample in water

2. add excess dilute nitric acid

3. followed by silver nitrate solution

4. white ppt (AgCl) formed

• 1. add acidified silver nitrate solution

  2. white ppt (AgCl) formed

test for water

turns dry blue cobalt (II) chloride paper pink

flame test steps

1. cleaned platinum wire is put into conc. HCl (aq)

2. dipped into solid sample

3. heated in non-luminous (blue) flame

4. flame colour is recorded

explain the principle of the distillation process

1. when sea water is heated, water vapor escapes and passes through the condenser

2. vapour is cooled by cold water flowing around the condenser

3. water vapour condenses to form liquid water

saturated solution

a solution containing the maximum amount of solute at a certain temperature

crystallisation

• a method used to separate a dissolved solid (solute) from a solution

• saturated solution is obtained by heating the solution to evaporate some of the solvent

• large crystals form upon slow cooling of saturated solution (the solubility of the solid in the solvent decreases with decreasing temperature)

what is fractional distillation?

a method used to separate a mixture of miscible liquids which have different boiling points

steps of fractional distillation of liquid air

1. air is filtered and purified (removes CO2, dust, water vapour, etc.)

2. purified air is cooled and compressed (repeatedly) to -200 °C

3. liquid air at -200 °C is introduced at the lower part of the fractionating tower /column

4. liquid air is slowly warmed and gases are collected one by one

uses of oxygen gas

1. respiration

2. supports combustion of fuels

uses of carbon dioxide gas

1. raw material for photosynthesis

2. dry ice (solid CO2) is used to provide a low temperature for different purposes (storing ice cream)

3. make fire extinguishers as it does NOT support combustion and is DENSER than air

4. used in soft drinks

use of helium gas

to fill balloons and airships as it is chemically inert and lighter than air

• hydrogen gas is not used as it is explosive / flammable

use of neon gas

make neon light signs as it emits red light at a high temperature

use of argon gas

to fill up space in a light bulb to prevent oxidation of the metal (tungsten)

uses of nitrogen gas

• to make ammonia (NH3) which is then used to make fertilisers

• provides a chemically inert environment (food is packaged in gaseous nitrogen to increase shelf life)

• liquid nitrogen provides a low temperature to store biological samples (cells) and freeze food

physical properties

• appearance

• colour

• odour

• solubility

• density

• melting point

• boiling point

• viscosity

• electrical conductivity

• thermal conductivity

uses of NaOH (aq) from electrolysis of brine

• soap

• bleaching solution

• waste water treatment

uses of Cl2 (g) from electrolysis of brine

• bleaching solution

• sterilisation of drinking water

• HCl (g)

• HCl (aq)

uses of H2 (g) from electrolysis of brine

• fuel

• NH3 (g)

• HCl (g)

• HCl (aq)

chalk — formation, hardness, uses

1. sea animals with dried shells, shells fall to sea bed and built up a deposit, under high temperature and pressure deposit is converted to chalk after millions of years

2. hardness: soft

3. uses: white pigment in paper, plastics, paints

limestone — formation, hardness, uses

1. under high temperature and pressure, CHALK is converted to LIMESTONE

2. hard

3. cement, concrete

marble — formation, hardness, uses

1. under much higher temperature and pressure, chalk OR limestone is converted to marble

2. hardest

3. monuments, floors, materials for construction

action of water on calcium carbonate // CaCO3 (s)

no reaction / insoluble

action of acids on calcium carbonate // CaCO3 (s)

• HCl (aq)

  CaCO3 (s) + 2HCl (aq) —> CaCl2 (aq) + H2O (l) + CO2 (g)

• HNO3 (aq)

CaCO3 (s) + 2HNO3 (aq) —> Ca(NO3)2 (aq) + H2O (l) + CO2 (g)

action of heat on calcium carbonate // CaCO3 (s)

decomposes upon heating to give white calcium oxide // CaO (s) and carbon dioxide

tests for calcium and carbonate in calcium carbonate

1. calcium ion

   • flame test which gives a brick red flame

2. carbonate ion

   • addition of dilute HCl, after which effervescence occurs and turns limewater milky due to formation of insoluble calcium carbonate

• if excess CO2 is bubbled into the milky suspension, mixture turns clear again

  • also, can heat the solid in a test tube and put a burning splint into the tube. flame extinguishes as CO2 which is decomposed on heating does NOT support combustion

the lime cycle

weathering

the process by which rocks are broken down into smaller particles by physical and chemical processes

(natural processes such as wind, water, and temperature changes)

erosion

when rocks are broken down and the particles are carried away by water, wind and gravity

examples of physical processes causing weathering

1. change in temp

• causes repeated cooling and expansion of rocks

• cracks are formed on rocks

2. water gets into those cracks

• and freezes into ice at low temperature, causing further expansion and cracking of the rocks

examples of chemical processes causing weathering

1. normal rain water is acidic (pH 5.6)

• carbonic acid formed when CO2 dissolves in rain water

• carbonic acid reacts with calcium carbonate to form water soluble calcium hydrogencarbonate which is broken down

2. acid rain

• also causes breaking down of calcium carbonate

3. calcium carbonate decomposes slowly at elevated temperature

• forming calcium oxide + carbon dioxide

carbonate + acid

CO2 ; effervescence

calcium carbonate + dilute HCl reaction

CaCO3 + HCl —> calcium chloride + H2O + CO2

how to separate insoluble from soluble in a mixture?

1. shake a mixture of X and Y with water

2. filter the mixture using a funnel with filter paper and the residue is X

3. evaporate the filtrate and the solid formed is Y