Chapter 7/11 - Oxygen/Oxides/Seperation/Analysis

Question 1

Oxygen + oxides

Air is a mixture of gases: 21% O2, 78% N2, 0.9% argon, 0.04% CO2 and other gases like water vapour

Metal oxides are bases - Alkali when dissolved
non-metal oxides are bases when dissolved
Non-metal tend to be gases > combustion of fossil fuels produces harmful non-metal oxides:CO2 reflects infrared (causes green house effect, nitrogen/sulphur make acid rain

Answer 1

See Diagrams for this aswell:
We can prove experimentally about 1/5 of air is O2 using:
- Gas syringe: 1) One syringe filled with 50cm³ of air other 0 2)Plunger of syringe pushed so thats the air passes over hot copper 3) Oxygen in the air reacts with copper(II) Oxide. Cu goes to Brown > Black 4)Repeated until all oxygen reacts - Will decrease 1/5 to leave 40cm³
IRON WOOL + WATER: As oxygen in air reacts with the Iron wool, water takes its place in space tube reducing volume of tube about 1/5

Question 2

CO2

Making CO2 - See Diagram also

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

Test for CO2 - Turns Limewater (CaCO3) milky

Answer 2

Properties of CO2

• Denser than Air
• Slightly soluble in water - will dissolve more underwater

Uses of CO2

• Carbonate drinks - Dissolves under pressure but comes out when pressure is released
• Fire extinguishers(Black ones) for electrical fires - CO2 is denser than Air (O2) so sits over flames excluding O2 preventing Combustion

Question 3

Chromatography - See Diagram

• A separation + Analytical technique in which a mixture can be separated into its basic component parts on the basis of solubility
• Solvent below mixture so dots dont dissolve into mixture at bottom of beaker
• Rf value = Distance travelled by pigment from pencil line to pigment front/Distance travelled by solvent from pencil line to solvent front

Answer 3

Method

• Bottom of paper is dipped into solvent, it works its way up between the fibre by capillary action
• When solvent reaches mixtures, the soluble parts dissolve and go up solvent with paper
• Most soluble parts move quickest
• Remove paper when solvent travelled as far up the paper as it can

Question 4

Other separation techniques 
See DIAGRAMS ALSO
1) Solid from liquid(Suspension)
 - Filtration: Filter to collect residue, wash through with distilled water, Dry with paper towels
2) Solute from Solvent
 - Crystallisation: Heat to remove 2/3 volume of solution, cool to allow crystal to form, filter off water or leave to evaporate 
3) Two immiscible liquids
 -Decant: Pour off top less dense layer

Answer 4

4)Solvent from a Solution
Distillation: Heat solution until solvent is boiling, solvent enters the Liebig condenser, touches sides and transfers heat into flowing water within, pure solvent collected in beaker
5) Two miscible liquids - Fractional Distillation
- Solution is heated at temp of substance with L.B.P, Vapour of L.B.P enter column with glass beads inside, Then rest is the same as distillation. 96% pure other solvent left in flask

Question 5

Methods of collecting Gases
SEE DIAGRAMS ALSO

Gas syringe: - Collects any gas/measures accurate volumes, can measure rates, pure sample of gas

Over water: - Collects insoluble gases
- Pure sample of Gas

Answer 5

Upward delivery:

• Collects Gas less dense than air so gas rises and displaces air downwards
• Impure sample

Downward Delivery:

• Collects Gases Which are denser than air which drops down and displaces air upwards
• Impure sample

Question 6

Analysis of molecules

Water: Turns Anhydrous copper(II) sulphate from white to Blue
Turns cobalt Chloride paper blue to pink

Oxygen: Relights a glowing splint

Hydrogen: Burns with a squeaky pop

Chlorine: Cl(g) bleaches damp litmus paper

Answer 6

Carbon Dioxide: Turns lime water milky white. Lime water = white precipitate

Ammonia: Turns damp litmus blue because it forms an alkali an alkali when dissolved water so producing OH Ions

Question 7

Testing for positive Ions

Flame tests:
1) Eye protection - Put little HCl in beaker
2)Heat a flame test wire in blue flame of bunsen until the only colour produced is 🍊
3)Dip wire into the concentrated clean HCl
4) Dip wire into powder/sample to be tested. Placed into bunsen flame and record flame produced. Repeat the procedure for each sample - clean wire each time in HCl
Wire = Nichrome

Answer 7

Results

K > Lilac/Purple 
Na > Yellow
Si > Deep red (crimson)
Ca > Brick red (Bright orange)
Cu > Green
 Li > Red
Ba > Apple Green

Question 8

Testing for Negative Ions

Carbonates (CO3): Add dilute acid (Soluble nitric). Observe: Bubble and fizzing

Sulphates: - Make solution of suspected sulphate in pure water, Add dilute HCl (Kills any other white solid producing compound), Add BaCl2
Observe: White precipitate BaSO4 will form
Ammonia test - turns damp litmus paper from red to blue

Answer 8

Halides

1) Make solution of suspected Halide
2) Add nitric acid
3) Add silver nitrate

Observe: i) AgCl - White solid

            ii) AgBr - Cream solid
            iii) AgI - Yellow solid