4️⃣ PAG 8: Measuring rates of reaction

Question 1

Safety

Answer 1

• 2.0 mol/dm3 aqueous hydrochloric acid: IRRITANT
• the sulfur dioxide made in this reaction is TOXIC and CORROSIVE. Take extra care if you are asthmatic.
• chemical splash proof eye protection

Question 2

Equipment

Answer 2

Equipment
• a range of conical flasks (100 cm3, 250 cm3)
• rubber bung and delivery tube to fit conical flask
• water trough
• clamp stand, boss and clamp
• a range of measuring cylinders (25 cm3, 100 cm3, 250 cm3)
• stopwatch
• marble chips
• dilute hydrochloric acid at different concentrations (between 0.25 and 2.0 mol/dm3)
• 2 dp balance
• weighing boat
• paper with a cross on
• 0.1 mol/dm3 sodium thiosulfate

Question 3

• The reaction between calcium carbonate (marble chips) and hydrochloric acid can be monitored by ??
• The reaction between sodium thiosulfate and hydrochloric acid can be monitored by ??

Answer 3

• The reaction between calcium carbonate (marble chips) and hydrochloric acid can be monitored by measuring the volume of gas produced at regular intervals over a period of time.
• The reaction between sodium thiosulfate and hydrochloric acid can be monitored by measuring the amount of time taken until you cannot see a cross under the conical flask.

Question 4

Method 1 – calcium carbonate and hydrochloric acid (6)

• investigating change of concentration

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Answer 4

Method 1 – calcium carbonate and hydrochloric acid

1 Fill the water trough with water, fill the measuring cylinder with water, and clamp the cylinder upside down in the water trough.
2 Set up the conical flask, bung and delivery tube so that the exit of the delivery tube is under the measuring cylinder.
3 Add 50 cm3 of 2 mol/dm3 hydrochloric acid into the conical flask.
4 Add 1 g of marble chips into the conical flask, put the bung back into the flask as quickly as you can, and start the stopwatch.
5 Record the volume of gas collected every 30 seconds for 10 minutes.
6 Repeat steps 1 to 5, but in step 3 use different concentrations of acid:
• 1 mol/dm3 hydrochloric acid
• 0.5 mol/dm3 hydrochloric acid
• 0.25 mol/dm3 hydrochloric acid.
Try to make sure that similar sizes of marble chips are used in each case.

Question 5

Calcium carbonate and hydrochloric acid - analysis

- including line of best fit

Answer 5

Analysis

For each concentration of hydrochloric acid, plot a graph to show:
volume of gas (cm3) on the vertical axis
time (s) on the horizontal axis
draw a curve of best fit

For each concentration of acid, calculate the mean rate of reaction until the reaction stopped:

Mean ROR (g/s) = total mass of gas produced / reaction time

Describe the effect of increasing the concentration of acid on the mean rate of reaction. Use your graphs and calculations in step 2 to help you.

Question 6

Calcium carbonate and hydrochloric acid - to investigate changing temp.

Answer 6

Part 2 - Changing the temperature

Carry out the experiment described above, but:

• keep the concentration of acid the same
• warm the acid to different temperatures using a hot water bath or a Bunsen burner, tripod and gauze
  measure and record the temperature of the acid
• describe the effect of increasing the temperature on the mean rate of reaction

Question 7

Calcium carbonate and hydrochloric acid - to investigate changing SA:V.

Answer 7

Part 3 - Changing the surface area to volume ratio

Carry out the experiment described above, but:

• keep the temperature and concentration of acid the same
• use different sized pieces of calcium carbonate, including a powder
• describe the effect of increasing the surface area to volume ratio on the mean rate of reaction

Question 8

Safety - of fizzing in reaction mixture

Answer 8

Fizzing in the reaction mixture Spray or foam escaping, which may damage skin and eyes. Use a large conical flask so there is plenty of space inside. Do not look over the top when adding the calcium carbonate.

Question 9

Method 2 – sodium thiosulfate and hydrochloric acid

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Answer 9

1 - Using a measuring cylinder, add 50 cm3 of dilute sodium thiosulfate solution to a conical flask.
2 - Place the conical flask on a piece of paper with a black cross drawn on it.
3 - Using a different measuring cylinder, add 10 cm3 of dilute hydrochloric acid to the conical flask. Immediately swirl the flask to mix its contents, and start a stop clock.
4 - Look down through the reaction mixture. When you can no longer see the cross, record the time on the stop clock.
5 - Measure and record the temperature of the reaction mixture, and clean the apparatus as directed by your teacher.
6 - Repeat steps 1 to 5 with different starting temperatures of sodium thiosulfate solution // or different conc. of acid: • 1 mol/dm3 hydrochloric acid
• 0.5 mol/dm3 hydrochloric acid
• 0.25 mol/dm3 hydrochloric acid.

7 - Repeat the whole investigation (steps 1–5) twice more and record the results in the second and third blank columns of the table.
8 - Calculate the mean time for each of the acid concentrations, leaving out any anomalous values from your calculations. Record it in the fourth blank column, giving your answer to the nearest second.

Question 10

Analysis - sodium thiosulphate, hcl

Answer 10

Analysis

• Calculate 1,000 / time for each temperature. This value is proportional to the rate of reaction.
• Plot a graph to show:
  reaction rate (/s) on the vertical axis
  temperature (°C) on the horizontal axis
  draw a curve of best fit

Question 11

Sodium thio..

Describe the effect of increasing the temperature of the reaction mixture on the rate of reaction. Use your graph to help you.

(2)

Answer 11

The rate of reaction increases as the temperature increases. The rate increases by a greater amount at higher temperatures.

Question 12

Suggest a reason why the same person should look at the black cross each time.

Answer 12

Different people may decide that they cannot see the cross at different amounts of cloudiness, leading to errors in deciding when to take the reaction time.

Question 13

Sulfur dioxide - harm and precaution

Answer 13

Sulfur dioxide Can cause irritation to the eyes and lungs, particularly to people with asthma. Make sure the room is well ventilated. Avoid breathing directly over the top of the flask.

Question 14

Hot hcl?

Answer 14

Hot hydrochloric acid Causes skin and eye irritation. Burns to the skin. Wear gloves and eye protection. Do not heat above 60°C.

Question 15

Hot sodium thiosulfate solution ?

Answer 15

Burns to the skin. Do not heat above 60°C.