Practicals

Question 1

reflux equipment (3)

Answer 1

• condenser (water out/in) vertical
• round bottom / pear shaped flask
• under heat

Question 2

distillation equipment (5)

Answer 2

• thermometer (bulb of thermometer would be where gas product would be collected)
• condenser (out/in) horizonal
• round bottom flask
• beaker to collect product
• under heat

Question 3

purifying an organic liquid (5)

Answer 3

• place solution in separating funnel
• add Na2CO3 to remove any acid impurities (if needed)
• remove organic layer (if less dense than water 1gcm-3 then would be the top layer)
• add drying agent e.g. CaCl2 / MgSO4 (wont react with extract)
• redistill collecting at the boiling point of desired product

Question 4

purifying an organic solid (6)

Answer 4

• recrystallise by dissolving solid in minimum amount of hot solvent
• cool
• scratch with glass rod
• filter under reduced pressure (using Buchner funnel)
• wash with cold solvent
• dry solid

Question 5

methods of checking purity of product (3)

Answer 5

• melting / boiling point - measure and compare to known values from data (or narrow range)
• TLC - run TLC and calculate Rf value + compare to known data
• NMR / IR - run NMR / IR and compare spectra of a known sample, should contain similar peaks

Question 6

test for alkenes (2)

Answer 6

• Br2
• orange to colourless

Question 7

test for COOH (2)

Answer 7

• Na2CO3
• bubbles + fizzing

Question 8

test for phenol (4)

Answer 8

• Br2
• decolourises
• pH / indicator test
• pH lower than 7 / paper turns orange

Question 9

test for haloalkane (3)

Answer 9

• AgNO3 in ethanol
• AgX ppt forms
• rate of hydrolysis can be compared to data

Question 10

test for 1° / 2° alcohols (2)

Answer 10

• Cr2O7- / H+
• orange to green

Question 11

monitoring rate of hydrolysis of haloalkanes (6)

Answer 11

• add ethanoic acid and aqueous AgNO3
• warm
• monitor first appearance of ppt
• AgCl - slow white ppt
• AgBr - moderate cream ppt
• AgI - fast yellow ppt

Question 12

making a standard a standard solution (6)

Answer 12

• weigh known mass of solid by difference using balance
• dissolve in 100cm3 water in a beaker
• add to 250cm3 volumetric flask
• rinse beaker and pour into flask
• make up to 250cm3 mark with distilled water using pipette
• invert to mix

Question 13

methods to decrease % uncertainty (1)

Answer 13

• use more accurate equipment

Question 14

causes of errors in enthaply calculations (5)

Answer 14

• loss of heat into surroundings - use lid / insulator
• not carried under standard conditions
• not taking specific heat capacity of apparatus into account
• incomplete reaction
• evaporation after weighing

Question 15

MnO4- / Fe2+ titration and colour change (2)

Answer 15

MnO4-(aq) + 8H+(aq) + 5Fe2+ (aq) -> Mn2+ (aq) + 4H2O (l) + 5Fe3+ (aq)

purple to colourless

Question 16

I2 / S2O3 2- titration and colour change (2)

Answer 16

2S2O3 2-(aq) + I2
(aq) -> 2I- (aq) + S4O6 2-(aq)

brown to colourless

Question 17

Cu2+ / I2 titration

Answer 17

2Cu2+ (aq) + 4I- (aq) -> 2CuI (s) + I2 (aq)

Question 18

colour of organic layer of halogens (3)

Answer 18

• chlorine - colourless
• bromine - yellow
• iodine - purple

Question 19

test for carbonate CO3 2- + equation

Answer 19

• Add any dilute acid and observe effervescence.
• Bubble gas through limewater to test for CO2 – will turn limewater cloudy (also fizzing of CO2)
• 2HCl + Na2CO3 = 2NaCl + H2O + CO2

Question 20

test for sulphates + equations

Answer 20

• acidified barium chloride is added to a solution that contains sulphate ions + a white precipitate form
• Ba2+ (aq) + SO42-(aq) = BaSO4(s)

Question 21

test for positive ions (cations)

Answer 21

• reacting NH4+ with warm
  NaOH(aq) forming NH3 gas
• NH3 gas indentified by pungent smell or turns red litmus paper blue