6.1 Chemical Change & Rate of Reaction

Hydrochloric acid reacts with aqueous sodium thiosulfate to form a precipitate, which makes the solution turn cloudy.
The formation of the precipitate can be used to show how fast the reaction proceeds, using the apparatus shown below.

A student used this method to investigate the effect of changing the concentration of the sodium thiosulfate solution on the speed of the reaction.
The student used different concentrations of sodium thiosulfate solution.
All other variables were kept the same.

Give two variables which were kept the same in the investigation.

The results of the experiments are shown plotted on the grid below

Draw a line of best fit on the grid.

Suggest two reasons why not all of the points lie on the line of best fit.

From your graph, deduce the speed of reaction when the concentration of sodium thiosulfate is 0.075 mol/dm³. Show clearly on the graph how you worked out your answer.

Explain why the speed of reaction increases when the concentration of sodium thiosulfate is increased.

Sketch on the grid the line you would expect if the experiments were repeated at a higher temperature

A student investigated the rate of reaction between magnesium ribbon and four different solutions of dilute sulfuric acid, A, B, C and D. The sulfuric acid was in excess in all experiments.

Four experiments were carried out.

Experiment 1

Using a measuring cylinder, 30 cm³ of aqueous sulfuric acid A was poured into a beaker.

The stop clock was started and a 4 cm length of magnesium was added to the sulfuric acid in the beaker. The mixture was stirred constantly.

The time taken for all of the magnesium to react and disappear was measured. The beaker was rinsed out with distilled water.

Experiment 2

Experiment 1 was repeated using solution B of sulfuric acid.

Experiments 3 and 4

Experiment 1 was repeated, using solutions C and D of sulfuric acid.

Use the stop clock diagrams to record the times in the table. 

Plot the results for Experiments 1, 2, 3 and 4 on the grid and draw a smooth line graph.

   .......................... mol/dm³

[2]

Why was the same amount of magnesium used in Experiments 1, 2, 3 and 4? 

Another experiment was carried out.

A 4 cm length of magnesium ribbon was added to dilute sulfuric acid. The temperature of the solution was measured before and after the reaction. The observations were recorded and the gas given off tested.

Observations: Rapid effervescence and the tube felt hot. A lighted splint popped.

Use the thermometer diagrams to record the temperatures.

Suggest a different method which could be used to investigate the rate of the reaction between magnesium and sulfuric acid.

State the difference in the apparatus used and measurements to be taken.

Apparatus: ...................................................................................................................................

Measurements: ..........................................................................................................................

A teacher investigated the rate of a reaction between two solutions, J and K, and sulfuric acid at different temperatures.

 Four experiments were carried out.

Experiment 1

A large measuring cylinder was used to pour 50 cm³ of distilled water and 40 cm³  of sulfuric acid into a 250 cm³ conical flask.
A small measuring cylinder was used to add 2 cm³  of methyl orange and 5 cm³  of solution J to the mixture in the conical flask. The temperature of the mixture was measured.
The reaction was started by adding 5 cm³ of solution K to the conical flask, immediately starting the timer and swirling the mixture.
The time taken for the mixture to turn pale yellow was measured. The final temperature of the mixture was measured.

Experiment 2

Experiment 1 was repeated but the mixture in the conical flask was heated to about 30 °C before adding the  solution K. The temperature of the mixture was measured.
5 cm³ of solution K was added to the conical flask. The timer was started and the mixture swirled.
The time taken for the mixture to turn pale yellow was measured. The final temperature of the mixture was measured.

Experiment 3

Experiment 1 was repeated but the mixture in the conical flask was heated to about 40 °C before adding the  solution K to the flask. The same measurements were taken.

Experiment 4

Experiment 1 was repeated but the mixture in the conical flask was heated to about 50 °C before adding the solution K to the flask. The same measurements were taken. 

Use the stop-clock diagrams to record the times in the table.

Work out the average temperatures to complete the table.

Plot the results on the grid and draw a smooth line graph.

From your graph deduce the time taken for the mixture to turn pale yellow if Experiment 1 was repeated at an average temperature of 60 °C.
Show clearly on the grid how you worked out your answer

[1]

[2]

[2]

[2]

Two experiments were carried out to show what factors affect the rate of decomposition of hydrogen peroxide, H₂O₂.
In each experiment the volume of gas produced was measured every minute for ten minutes.

Experiment 1

The student used a mixture of 50 cm³ of hydrogen peroxide, 50 cm³ of water and 1 g of manganese(IV) oxide at a room temperature of 20 °C. The results were plotted to obtain the graph shown.

Experiment 2

The student repeated Experiment 1 but did not record how much of each substance was used. The points were plotted on the grid.

Complete the graph for Experiment 2. 

Suggest the composition of the mixture used in Experiment 2. Explain your suggestion.

Composition: ...................................................................

Explanation: ....................................................................

What is the function of the manganese(IV) oxide?

Sketch on the grid the curve that you would expect if Experiment 1 was repeated at 10 °C.

Two experiments using catalysts were carried out. Catalysts R and S were used to break down 50 cm³ of aqueous hydrogen peroxide at a temperature of 20 °C. The volume of oxygen given off was measured using the apparatus shown.

Complete the table to show the volumes of gas measured in each experiment at the times shown in the table below.

Plot a graph to show each set of results. Clearly label the graphs R and S.

Which result using catalyst R was inaccurate?

Which is the better catalyst in this reaction? Explain your answer.

Sketch a line on the grid to show the graph you would expect if the reaction with catalyst R was repeated at 50°C.

Identical pieces of steel were placed in two different boiling liquids for 12 hours.
The graphs show how the mass of each piece of steel changed.

Give one similarity in the change in mass of the steel in both liquids.

Describe two ways in which the mass loss shown in graph A is different from that shown in graph B.

 
1. .......................................................................................................................................
...........................................................................................................................................
2. .......................................................................................................................................
.....................................................................................................................................

State two different safety precautions that would need to be taken when carrying out this investigation.

1. .......................................................................................................................................
2. .......................................................................................................................................

A student investigated the speed of reaction when iodine was produced by the reaction of solution L with potassium iodide at different temperatures. Five experiments were carried out.

Experiment 1

A burette was filled with the aqueous solution L to the 0.0 cm³ mark.

10.0 cm³ of solution L was added from the burette into a boiling tube and the initial temperature of the solution was measured. Using a measuring cylinder, 5 cm³ of aqueous potassium iodide and 3 cm³ of aqueous sodium thiosulfate were poured into a second boiling tube. Starch solution was added to this boiling tube and the mixture shaken.

The mixture in the second boiling tube was added to the solution L, shaken and the clock started. These chemicals reacted to form iodine which reacted with the starch. When a blue colour appeared, the clock was stopped and the time measured and recorded in the table. The final temperature of the mixture was measured.

Experiment 2

Experiment 1 was repeated but solution L was heated to about 40 °C. The temperature of the solution was measured before adding the mixture in the second boiling tube. When a blue colour appeared, the clock was stopped and the time measured and recorded in the table. The final temperature of the mixture was measured.

Experiment 3

Experiment 2 was repeated, heating solution L to about 50 °C.

Experiment 4

Experiment 2 was repeated, heating solution L to about 60 °C.

Experiment 5

Experiment 2 was repeated, heating solution L to about 70 °C.

Use the thermometer diagrams in the table to record the temperatures and complete the table.

Plot the results on the grid below and draw a smooth line graph.

From your graph, work out the time taken for the blue colour to appear if solution L was heated to 80 °C. The final temperature of the reaction mixture was 64 °C. Show clearly on the grid how you obtained your answer.

Suggest the purpose of the starch solution in the experiments.

[1]

Predict the effect on the time and speed of the reaction in Experiment 5 if it was repeated using a less concentrated solution of L.

Time: ..............................................................

Speed: .............................................................. 

Why was a burette used to measure solution L instead of a measuring cylinder? 

Dilute hydrochloric acid was added to excess calcium carbonate in a beaker as shown.

The beaker was placed on a balance and the mass of the beaker and contents recorded every minute.

The results are shown in the table.

Plot the results on the grid and draw a smooth line graph.

Use your graph to determine the mass of the beaker and contents after 30 seconds.

Show clearly on your graph how you worked out your answer.

Why does the mass of the beaker and contents decrease?

Suggest the purpose of the cotton wool.

After how long did the reaction finish?

A second experiment was carried out using hydrochloric acid at a lower temperature.

On the grid sketch a curve to show the expected results for this experiment.

Label this curve C.

The speed of reaction between excess copper carbonate and dilute nitric acid was investigated using the apparatus below.

The temperature of the nitric acid was 20 °C.

The volume of carbon dioxide produced was measured every minute for six minutes.

Use the gas syringe diagrams to complete the table of results.

Plot the results on the grid below and draw a smooth line graph.

Which point appears to be inaccurate? Explain why.

Sketch on the grid, the graph you would expect if the experiment was repeated using nitric acid at a temperature of 60°C.

A student carried out an experiment to investigate the speed of reaction between sodium thiosulfate solution and dilute nitric acid. Sulfur is formed during this reaction and the mixture turns cloudy.

Experiment 1 method

Using a measuring cylinder, 100 cm³ of sodium thiosulfate solution was poured into a 250 cm³ beaker. The beaker was placed on a cross drawn on a piece of paper.

20 cm³ of dilute nitric acid was added to the beaker and the timer started.

The time until the cross could not be seen was taken. The time was recorded in the table. 

Experiment 1 was repeated using different volumes of sodium thiosulfate as shown in the table. All experiments were carried out at 20 °C.

Table of results

Why was the total volume of solution kept constant? 

In Experiment 2, which is the last liquid to be added to the beaker? 

[4] 

The experiments were repeated at 40 °C. Suggest how the results would differ. Explain your answer.

A student investigated the effect of temperature on the speed of reaction between hydrochloric acid and aqueous sodium thiosulfate. When these chemicals react they form a precipitate, which makes the solution go cloudy. The formation of this precipitate can be used to show how fast the reaction proceeds, using the set up shown below.

Five experiments were carried out.

Experiment 1

By using a measuring cylinder 50 cm³ of aqueous sodium thiosulfate was poured into a flask. The temperature of the solution was measured. The conical flask was placed on the printed text. 10 cm³ of hydrochloric acid was added to the flask and the timer started. The time taken for the printed text to disappear from view was recorded in the table. The final temperature of the mixture was measured.

Experiment 2

50 cm³ of aqueous sodium thiosulfate was poured into a conical flask. The solution was heated until the temperature was about 30 °C. The temperature of the solution was measured. 10 cm³ of hydrochloric acid was added to the flask and Experiment 1 was repeated.

The final temperature of the liquid was measured.

Experiment 3

Experiment 2 was repeated but the sodium thiosulfate solution was heated to about 40 °C before adding the hydrochloric acid.

The initial and final temperatures were measured.

Experiment 4

Experiment 2 was repeated but the sodium thiosulfate solution was heated to about 50 °C before adding the hydrochloric acid.

The initial and final temperatures were measured.

Experiment 5

Experiment 2 was repeated but the sodium thiosulfate solution was heated to about 60 °C before adding the hydrochloric acid.

The initial and final temperatures were measured. Use the thermometer diagrams to record all of the initial and final temperatures in the table.

Complete the table of results to show the average temperatures.

Table 1

Plot the results obtained on the grid and draw a smooth line graph.

Why was the same volume of sodium thiosulfate solution and the same volume of hydrochloric acid used in each experiment? 

[3]

[1]

Explain one change that could be made to the experimental method to obtain more accurate results.

Change: ................................................................

Explanation: .......................................................

A catalyst is a substance that speeds up the rate of a chemical reaction and remains unchanged at the end of the reaction.

Hydrogen peroxide solution, H₂O₂, breaks down to form oxygen. This decomposition is very slow if a catalyst is not used.

The speed of reaction between excess magnesium and dilute hydrochloric acid was investigated using the apparatus below.

The volume of hydrogen produced was measured every minute for six minutes.

Use the gas syringe diagrams to complete the table.

Plot the results on the grid below. Draw a smooth line graph.

Why is the volume of gas given off the same at 5 minutes and 6 minutes? 

Which point appears to be inaccurate? Explain why. 

Sketch on the grid the graph you would expect if the experiment were repeated using the same volume of acid which was half as concentrated. 

Hydrogen peroxide breaks down to form oxygen. The volume of oxygen given off can be measured using the apparatus below.

Solids W and X both catalyse the breakdown of hydrogen peroxide. The syringe diagrams show the volume of oxygen formed every 20 seconds using these catalysts at 25 °C.

Use the gas syringe diagrams to complete the table.

Plot a graph to show each set of results. Clearly label the curves.

Which solid is the better catalyst in this reaction? Give a reason for your choice.

Solid: .......................................................

Reason: ................................................. 

Why is the final volume of oxygen the same in each experiment?

Sketch a line on the grid to show the shape of the graph you would expect if the reaction with catalyst X was repeated at 40 °C. 

Magnesium reacts with dilute sulphuric acid to form hydrogen gas. The speed of the reaction was investigated using the apparatus below.

In an experiment 50 cm³ of dilute sulphuric acid was added to a large piece of magnesium. A student measured the total volume of gas produced at 2 minute intervals. Use the measuring cylinder diagrams to complete the table.

Plot the student’s results on the grid. Use the points to draw a smooth line graph.

A student investigates the speed of reaction when aqueous hydrogen peroxide breaks down using a catalyst, manganese(IV) oxide. The catalyst remains unchanged at the end of the reaction. The apparatus was set up as shown in the diagram.

Experiment 1
By using a measuring cylinder, 20 cm³ of hydrogen peroxide solution was poured into a conical flask. One spatula measure of manganese(IV) oxide was added to the flask, the bung was quickly put in the flask and the timer started.

The volume of gas collected in the measuring cylinder at 10 seconds, 20 seconds and 30 seconds was measured. The results are shown in the table below.

Experiment 2

By using a measuring cylinder, 15 cm³ of hydrogen peroxide was poured into the conical flask. The instructions were repeated exactly as given for Experiment 1, but 5 cm³ of distilled water was also added to the flask.

Use the diagrams to record your results in the table below.

Experiment 3

Experiment 1 was repeated using 10 cm³ of hydrogen peroxide and 10 cm³ of distilled water. Record your results in the table.

Experiment 4

Experiment 1 was repeated using 5 cm³ of hydrogen peroxide and 15 cm³ of distilled water. Record your results in the table.

Plot your results on the grid for each Experiment. Draw 4 graphs and label each clearly with the number of the Experiment.

[1] 

[2]

State a practical method you could use to prove that manganese(IV) oxide was a catalyst in Experiment 1.

An investigation into the reaction of calcium with water was carried out using the apparatus below. The temperature of the water increased during the experiment.

The volume of hydrogen collected at one minute intervals was measured.

Use the diagrams to record the volumes in the table.

Plot the results on the grid. Join all of the results with a smooth curve.

What type of chemical reaction occurs when calcium reacts with cold water? 

An aqueous solution of hydrogen peroxide decomposes very slowly to form oxygen. The speed of decomposition can be increased by using a catalyst. Two possible catalysts are the solids copper(II) oxide and chromium(III) oxide.
Plan an investigation to find out which of these two oxides is the better catalyst for this decomposition. The space below can be used for a diagram. 

A student investigated the speed of reaction between aqueous hydrochloric acid and marble chips (calcium carbonate). The apparatus below was used.

5 test-tubes were put in a rack. To each test-tube was added 10 cm³ of different solutions of aqueous hydrochloric acid and a marble chip. The marble chips were the same size.

Experiment 1

By using a measuring cylinder 10 cm³ of the solution P of aqueous hydrochloric acid was placed in the first test-tube.

A marble chip was added and the volume of gas collected after two minutes was measured. Use the gas syringe diagram to record the volume.

Experiment 2

Experiment 1 was repeated using solution Q of aqueous hydrochloric acid. Use the diagram to record the volume of gas collected in the table.

Experiments 3, 4 and 5

Experiment 1 was repeated using the solutions R, S and T of aqueous hydrochloric acid in the third, fourth and fifth test-tubes.

Use the diagrams to record the volumes in the table.

Experiment 3

Experiment 4

Experiment 5

Table of results

Plot your results on the grid. Draw a straight line graph.

Which result appears inaccurate? Give a reason for your choice.

Experiment: ..................................................................................

Reason: .......................................................................................... 

How would the student know which of the reactants in the experiment was in excess? 

Is manganese(IV) oxide a catalyst?

A catalyst is a substance that speeds up a chemical reaction and remains unchanged.

Hydrogen peroxide, H₂O₂ breaks down to form oxygen. This reaction is very slow without a catalyst. Describe an experiment to show that manganese(IV) oxide is a catalyst for this reaction.

You are provided with the following items.

Hydrogen peroxide solution

Manganese(IV) oxide

Measuring cylinder

Balance

Beaker

Filtration apparatus

Splints / Bunsen burner

Distilled water

The addition of calcium carbonate to excess dilute nitric acid produces carbon dioxide. The volume of carbon dioxide given off at 20 second intervals was recorded and plotted on the grid.

Draw a smooth line graph on the grid.

Circle the result which appears to be incorrect? Why have you selected this result? 

Why does the reaction slow down? 

A student carried out an experiment to investigate the speed of a reaction between sodium thiosulfate and dilute hydrochloric acid.

Na₂S₂O₃ + 2HCl → 2NaCl + H₂O + S + SO₂

Experiment 1

By using a measuring cylinder, 50 cm³ of sodium thiosulfate solution was poured into a 100 cm³ beaker. The was placed on a cross drawn on a piece of paper. 10 cm³ of hydrochloric acid was added to the beaker and the timer started. 

The time was taken until the cross could not be seen. The time was recorded in the table.

Experiments 2, 3, 4 and 5

Experiment 1 was repeated using different volumes of sodium thiosulfate as shown in the table. All experiments were carried out at 25 °C

Table of results 

Why does the cross on the paper disappear? 

Why was the total volume kept constant? 

In which order should the water, hydrochloric acid and sodium thiosulfate solution be added to the beaker 

First: ................................................

Second: ................................................

Last: ................................................ 

The experiments were repeated using a 250 cm³ beaker instead of a 100 cm³ beaker. Suggest how the results would differ. Explain your answer. 

An experiment was carried out using the apparatus below

By using a measuring cylinder, 20 cm³ of hydrogen peroxide was placed was placed in the flask and 0.8 g of the catalyst, managnese(IV) oxide was added. The bung was replaced and the gas collected was measured at 1 minute intervals. The results were placed on the grid.

What mass of manganese(IV) oxide would remain at the end of the experiment? 

What would be the effect of using a rubber connector with a hole in it. 

A student investigated the speed of reaction between aqueous potassium bromate and
potassium iodide solution. A burette was filled up to the 0.00 cm³ mark with aqueous potassium iodide. To each of 5 test-tubes was added 6 cm³ of aqueous potassium iodide to be used in the 5 following experiments.

Experiment 1

By using a measuring cylinder 12 cm³ of aqueous potassium bromate was poured into a small beaker. To this solution was added 4 cm³ of water, 2 cm³ of hydrochloric acid, 5 cm³ of starch solution and 1 cm³ of sodium thiosulphate solution.

The beaker was placed on a cross drawn on a piece of paper. From one of the test-tubes 6 cm³ of aqueous potassium iodide was added to the mixture in the beaker and the timer started. A dark blue colour formed. The timer was stopped when the cross on the paper could not be seen. Use the stop clock diagram to record the time in the table.

Experiment 2

By using a measuring cylinder 10 cm³ of potassium bromate solution was poured into a beaker. The instructions were repeated exactly as given for Experiment 1, but 6 cm³ of water was added to the beaker. Use the diagram to record the time in the table.

Experiments 3, 4 and 5

Experiment 1 was repeated using the volumes of aqueous potassium bromate and water specified in the table of results.

Record the times in the table.

Table of results 

Plot the results on the grid. Draw a smooth line graph.

From your graph estimate the time of the reaction if Experiment 1 was repeated using 5 cm³ of potassium bromate and 11 cm³ of water.

Show clearly on your graph how you worked out your answers.