RP

Question 1

Making volumetric solutions

Answer 1

1. Weigh out precise amount of solid
2. Add to small volume of water, rinse weighing boat and stir until it’s all dissolved
3. Transfer to volumetric flask using funnel and rinse beaker with distilled water
4. Rinse sides of volumetric flask until it’s at bottom of meniscus
5. Invert volumetric flask to mix contents and check meniscus again

Errors:

Question 2

Titration

Answer 2

1. Add the standard solution to burette and make sure there’s no bubbles
2. Use pipette filler and pipette to transfer Unknown solution into conical flask, rinse conical flask with distilled water
3. Add a few drops of phenolphthalein indicator to solution in conical flask
4. Record initial reading on burette
5. Place conical flask on white tile to see colour change
6. Add solution form burette slowly while swirling conical flask
7. Add solution drop by drop near end point until solution changes colour
8. Record final burette reading in table and calculate titre volume / change in volume
9. Repeat until two concordant (within 0.1) results obtained and calculate average

• Alkali in conical flaks and acid in burette

• Reduce uncertainty in burette by decreasing concentration in burette and increasing concentration in conical flask

Question 3

Measuring enthalpy change using calorimetry

Answer 3

1. Weigh anhydrous copper sulfate
2. Using measuring cylinder, place 25cm3 of distilled water into polystyrene cup and record initial temp then start timer
3. Stir liquid continuously and place cup in beaker for extra insulation
4. Start timer and record temp every half minute for three mins
5. At fourth minute add powdered anhydrous copper sulfate to water and DONT record temp
6. At fifth min continue recording temp until 15 mins while stirring
7. Plot graph of temp against time
8. Line of best fit b4 addition and one after then extrapolate both lines to fourth minute
9. Determine temp change at fourth min

Errors:
• Heat transfer to surroundings
• Assumes heat capacity of water

Improve accuracy:
• Lid
• Electronic sensor

Question 4

Measuring enthalpy change using combustion

Answer 4

1. Fill copper can with water and record initial temp with thermometer
2. Measure and record mass of empty spirit burner then add fuel and redord mass
3. Light wick to heat water and stir constantly until fuel completely burnt
4. Record temp of water
5. Burner with all fuel - burner with remaining fuel = mass of fuel burnt

• Not all heat transferred to water but lost to surroundings

Question 5

Rate of reaction

Answer 5

1. Add HCl to ‘acid’ tube and put into plastic container
2. Use measuring cylinder to measure sodium thiosulfate into another test tube and place in plastic container with cross under it
3. Place thermometer in tube
4. Record start temp add 1cm of acid to thiosulfate then start timing
5. Look through tube form above and record time for cross to disappear
6. Record final temp and calculate average with initial temp
7. Pour cloudy contents into sodium carbonate solution
8. Add hot water to plastic container 55’C max
9. Measure more sodium thiosulfate into new tube and insert into plastic container
10. Warm tube up for 3 mins to neutralise acid
11. Repeat to obtain results for atleast 5 temps

• Time taken to produce sulfur at different temps is rate of reaction

• Graph of amount of sulfur against time
• Initial rate of reaction proportional to 1/time

Question 6

Testing for Group 2 metals

Answer 6

1. Add 10 drops barium chloride to first test tube
2. Add 10 drops NaOH to test tube
3. Swirl
4. Continue to add drops until it’s in excess
5. Record observations
6. Repeat for calcium bromide, magnesium chloride & strontium chloride
7. Repeat for ammonia solution and sulfuric acid

Ammonium: All NVC except Mg2+ has white ppt Mg(OH)2

NaOH: All white ppt X(OH)2 except Ba2+ NVC

H2S04: All white ppt XS04 except Mg2+ coluorless solution

Question 7

Test ammonium ions

Answer 7

1. Add 10 drops NaOH with pipette to test tube with 10 drops ammonium chloride
2. Swirl test tube
3. Place in water bath
4. Hold damp litmus paper near mouth of test tube to test fumes
5. Red litmus paper becomes blue in presence of ammonia gas

Question 8

Test for halide ions

Answer 8

1. Small amount of nitric acid should be added to sample with pipette
2. Then small amount of silver nitrate
3. If white ppt forms Cl- present
   • If cream ppt forms Br- present
   • If yellow ppt forms I- present
4. Add ammonia
   • AgCl colourless in dilute ammonia
   • AgBr colourless in concentrated ammonia
   • AgI not soluble in ammonia

Question 9

Test for Hydroxide ions

Answer 9

1. 5 drops of ammonia on Petri dish with lid
2. Dampen red litmus paper and place on other side of petty dish
3. If hydroxide ions form when in contact with water
4. Ammonia vapours turn litmus paper blue

Question 10

Test for carbonate ions

Answer 10

1. Add dilute HCl to test tube with pipette
2. Add equal amount of sodium carbonate
3. Quick attach bung with delivery tube to another test tube with limewater(Ca(OH)2, Swirl
4. Gas transferred to other test tube
5. Carbonate ions react with hydroxide ions to form CO2 gas which turns lime water milky

• Na2CO3 + 2HCl -> 2NaCl + H2O +
CO2

• Ca(OH)2 + CO2 -> CaCO3 + H2O

Question 11

Test for Sulfate ions

Answer 11

1. Add equal volume of HCl and BaCl
2. White precipitate of Barium sulfate is formed:

Ba^2+(aq) + SO4^2-(aq) —>
BaSO4

Question 12

Methyl orange indicator and phenolphthalein colour change

Answer 12

• Methyl: Red to orange
• Phenolphthalein: Colourless to pink

Acid to alkaline