Five ways to speed it up — questions

1. describe

Match each change to its effect on the rate of a reaction.

Write the number of the matching option.

1. Slower
2. Faster

• 1. Using more concentrated acid: ______
• 2. Cooling the mixture: ______
• 3. Using larger pieces of the solid: ______
• 4. Adding a catalyst: ______
• 5. Raising the pressure of two reacting gases: ______

Nudge (only if you are stuck): Three of the changes speed a reaction up.

2. state

Which statement about a catalyst is correct?

Circle one answer.

• It increases the amount of product made
• It increases the rate of a reaction and is used up
• It increases the rate of a reaction and is unchanged at the end
• It slows down a reaction that is too fast

Nudge (only if you are stuck): What is left at the end of the reaction?

3. identify

You want to find out how temperature affects the rate of the reaction between sodium thiosulfate solution and dilute hydrochloric acid. The mixture slowly turns cloudy, and you time how long it takes. Which things must you keep the same? Select all that are correct.

Tick every correct statement.

• The time for the mixture to turn cloudy
• The volume of sodium thiosulfate solution
• The concentration of hydrochloric acid
• The concentration of sodium thiosulfate solution
• The volume of hydrochloric acid
• The temperature of the mixture

Nudge (only if you are stuck): In a fair test only one thing is changed on purpose, and one thing is measured.

4. explain

In a pressure cooker, water boils at about 120 °C instead of 100 °C. Vegetables cook faster in a pressure cooker than in an open pan of boiling water. Which statement explains why?

Circle one answer.

• The high pressure squeezes the food, so its reactions are faster
• The boiling breaks the food up, giving a larger surface
• The food is hotter, so the cooking reactions are faster
• The steam acts as a catalyst for the cooking reactions

Nudge (only if you are stuck): Cooking is a set of chemical reactions in the food.

5. state / explain / predict

Hydrogen peroxide solution breaks down very slowly into water and oxygen. A pupil adds five cubes of raw potato, and the solution froths. Potato contains catalase, an enzyme. (a) State the job of the catalase in this reaction. (b) When the froth stops, she lifts the cubes out and drops them into fresh hydrogen peroxide. It froths again. Explain what this shows about the catalase. (c) She repeats the first experiment with five cubes of boiled potato. Predict what she sees, and explain your prediction.

(a) The job of the catalase

(b) What the second froth shows

(c) Boiled potato

Nudge (only if you are stuck): For (c), think about what high temperatures do to enzymes.

6. identify

For which reaction would raising the pressure increase the rate?

Circle one answer.

• Magnesium ribbon with hydrochloric acid
• Copper(II) carbonate with nitric acid
• Two solutions mixed to form a solid
• Nitrogen gas with hydrogen gas

Nudge (only if you are stuck): Pressure pushes gas particles closer together.

7. state / explain / predict

Biological washing powder contains enzymes that break down food stains. The label says: "Best at 40 °C. Do not use above 60 °C." (a) State what is meant by an enzyme. (b) Explain why the powder should not be used above 60 °C. (c) Supplement. Explain, using activation energy, how the enzymes make the stains break down faster. (d) A non-biological powder is the same, but it has no enzymes. Predict how fast it removes the same stain at 40 °C, compared with the biological powder. Explain your prediction.

(a) An enzyme

(b) Above 60 °C

(c) Supplement: activation energy

(d) No enzymes

Nudge (only if you are stuck): Treat the enzyme as a catalyst for (a), (c) and (d).