6. Rates of reaction (required practical 5 - effect of concentration on the rate of reaction)

Question 1

What is the practical investigating?

Answer 1

the effect of concentration on the rate of reaction

Question 2

What is a hypothesis?

Answer 2

• a proposal that could explain a fact or an observation
• it must be testable

Question 3

What are the steps for investigating the effect of concentration on the rate of reaction with the disappearing cross reaction?

Answer 3

1. Use a measuring cylinder to put 10cm3 of sodium thiosulfate solution into a conical flask
2. Place the conical flask onto a printed black cross
3. Add 10cm3 of hydrochloric acid into the conical flask
4. Swirl the solution and start the stopwatch
5. Look down through the top of the flask, after a certain time the solution will turn cloudy
6. Stop the clock when we can no longer see the cross
7. Carry out the experiment again using lower concentrations of sodium thiosulfate solution
8. Repeat the whole experiment and calculate mean values for each concentration of sodium thiosulfate solution

Question 4

What do you not include when calculating a mean?

Answer 4

ANY anomalous results

Question 5

When is a measurement reproduceable?

Answer 5

if it can be repeated by another person or using a different technique or equipment and still get the same result

Question 6

What is the problem with the disappearing cross experiment?

Answer 6

• different people have different eye sights
• so some people can see the cross for longer than others

Question 7

What are the steps for investigating the effect of concentration on the rate of reaction with the experiment producing hydrogen gas?

Answer 7

1. Use a measuring cylinder to place 50cm3 of hydrochloric acid into a conical flask
2. Attach the conical flask to a bung and a delivery tube
3. Now place the delivery tube into a container filled with water
4. Place an upturned measuring cylinder also filled with water over the delivery tube
5. Add a 3cm strip of magnesium to the hydrochloric acid and start a stopwatch
6. The reaction produces hydrogen gas which is trapped in the measuring cylinder
7. Every 10 seconds, measure the volume of hydrogen gas in the measuring cylinder and continue until no more hydrogen is given off
8. Repeat the experiment using different concentrations of hydrochloric acid

Question 8

What do both of these experiments show us?

Answer 8

the greater the concentration of a chemical in a reaction, the faster the reaction takes place