Catalysts

When solutions P and Q are mixed together, a purple mixture forms. This mixture slowly becomes colourless.

A student pours 25 cm³ of solution P into a conical flask and then adds 25 cm³ of solution Q.

The student uses a beaker to measure out these volumes.

Name a piece of apparatus that could be used to measure these volumes more accurately.

The student investigates this reaction using the apparatus shown in Figure 7. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 8 shows the results.

The concentrations of the solutions are kept constant in each experiment.

State one other variable that should be kept constant.

State, and explain in terms of particles, how the time taken for the cross to become visible would change if a temperature of 80 °C was used.

The concentration of solution Q is 26.8 g dm^–3.

Calculate the mass of solid Q present in 25 cm³ of solution Q.

The student repeats the experiment at 20 °C, with the addition of a catalyst.

Explain how the addition of a catalyst will affect the rate of reaction.

Hydrogen peroxide, H₂O₂, decomposes into oxygen and water.

A catalyst can be used to increase the rate of this reaction.

Use a word or phrase from the box to complete the sentence about the mass of the catalyst in a reaction.

During a reaction, the mass of a catalyst_........ .

Complete the balanced equation for this reaction and add the missing state symbol.

When solutions P and Q are mixed together, a purple mixture forms. This mixture slowly becomes colourless.

A student pours 25 cm³ of solution P into a conical flask and then adds 25 cm³ of solution Q.

The student uses a beaker to measure out these volumes.

Name a piece of apparatus that could be used to measure these volumes more accurately.

The student investigates this reaction using the apparatus shown in Figure 1. The student measures the time taken for the cross to become visible. The experiment is repeated at different temperatures.

Figure 2 shows the results.

The concentrations of the solutions are kept constant in each experiment.

State one other variable that should be kept constant.

State, and explain in terms of particles, how the time taken for the cross to become visible would change if a temperature of 80 °C was used.

The concentration of solution Q is 26.8 g dm^–3.

Calculate the mass of solid Q present in 25 cm³ of solution Q.

mass of solid Q =_........ g

The student repeats the experiment at 20 °C, with the addition of a catalyst.

Explain how the addition of a catalyst will affect the rate of reaction.

This question is about elements in group 7, the halogens.

Which halogen is a green gas at room temperature and pressure?

Bromine, chlorine and iodine all react with heated iron wool.

Figure 6 shows the speed of these reactions.

When iron wool is heated with chlorine, iron chloride is formed.

Write the word equation for this reaction.

Give the name of the halogen in Figure 6 that is the most reactive with iron.

34.4 % of the mass of iron chloride is iron.

Calculate the mass of iron and the mass of chlorine in 125 g of iron chloride.

mass of iron =_........ g mass of chlorine =_........ g

Alkenes react with halogens.

When iron chloride is added to the reaction mixture, the reaction is much faster but the products are the same.

Use words from the box to complete the sentences.

The iron chloride speeds up the reaction because it is_........

After the reaction, the mass of iron chloride is_........

In some chemical reactions, bonds are broken in the reactant molecules and new bonds are formed to make the product molecules.

Which row is correct about the energy changes for these processes?

Hydrogen reacts with fluorine.

Figure 7 shows the bond energies for the bonds in the three molecules in the equation.

Calculate the energy change for this reaction.

energy change =_........ kJ mol

*(b) The reaction profile for an uncatalysed exothermic reaction is shown in Figure 8.

Using some examples of catalysts you have met in chemistry, discuss what catalysts do and their effect on the activation energy of a reaction.

You can use Figure 8 to illustrate your answer.

Figure 5 shows a sample of hydrogen peroxide solution decomposing to form water and oxygen gas.

Write the word equation for hydrogen peroxide solution decomposing.

In this reaction hydrogen peroxide is a solution, water is a liquid and oxygen is a gas.

Draw one straight line from each substance to its correct state symbol.

Describe the test to show the gas produced is oxygen.

Figure 6 shows the electron arrangement for an atom of hydrogen and an atom of oxygen.

Complete the dot and cross diagram in Figure 7 for a molecule of water, H₂O.

Draw outer shell electrons only.

Liver contains the enzyme catalase.

A piece of liver was added to another sample of hydrogen peroxide solution.

Figure 8 shows the results.

Figure 9 shows a graph of the volume of oxygen produced from the hydrogen peroxide with and without liver.

Figure 9

Complete the missing label on the axis of the graph.

Describe what the graph shows about the difference in decomposition of hydrogen peroxide with and without liver.

Describe how the apparatus in Figure 8 could be modified to find the volume of gas produced when the liver is added to the hydrogen peroxide.

The word equation for the reaction between magnesium and dilute hydrochloric acid is

magnesium + hydrochloric acid magnesium chloride + hydrogen

The reaction was carried out using the apparatus shown in Figure 6.

A strip of magnesium ribbon was placed in the conical flask. 100 cm³ of dilute hydrochloric acid was added to the conical flask.

The mass of the flask and contents was measured at regular intervals. The loss in mass was calculated. Figure 7 shows a graph of the results.

Name the apparatus that could be used to measure out 100 cm³ of dilute hydrochloric acid.

Explain why there is a loss in mass of the flask and contents.

The graph shows that the rate of reaction slows as the reaction takes place.

Explain, in terms of particles, why the rate of reaction between magnesium ribbon and dilute hydrochloric acid slows as the reaction takes place.

The experiment was repeated using the acid at a higher temperature. All other conditions were kept the same.

State the effect of the higher temperature on the mass loss after two minutes.

The original experiment was repeated using the same mass of magnesium powder instead of the magnesium ribbon. All other conditions were kept the same.

Sketch, on the graph in Figure 7, the line you would expect for this experiment.

Some reactions are affected by the presence of a catalyst.

State the effect of a catalyst on a reaction.

Devise a simple experiment to find out what happens to the mass of a solid catalyst during a reaction.

Hydrogen peroxide decomposes to form water and oxygen.

The rate of this reaction can be found by measuring the volume of oxygen formed after different time intervals.

Hydrogen peroxide solution is placed in a conical flask. The apparatus is set up as shown in Figure 3.

State the name of the piece of apparatus labelled Z in Figure 3.

At the end of the reaction the bung is removed from the conical flask. A glowing splint is put into the gas in the flask.

State what you would see.

A solid catalyst can be used for this reaction.

A given mass of catalyst is more effective if it has a large surface area.

State how you could increase the surface area of some lumps of solid catalyst.

The experiment is repeated three times once using a more dilute solution of hydrogen peroxide once using a lower temperature once using a larger flask

In each case, all other conditions are kept the same.

Circle the word that shows the change in the rate of decomposition in each case.

Complete the balanced equation for the reaction and fill in the two missing state symbols.

_........ H₂O₂(aq) 2H₂O(_........ ) + O₂(_........ )