rates of reaction

The rate of a chemical reaction depends on several factors, including temperature, reactant concentrations (or pressures), surface area of solid reactants, and the presence or absence of a catalyst. One method to measure the rate of a reaction is by determining the rate at which a product, such as a gas, is formed. In this practical, you will investigate how the concentration of hydrochloric acid affects the rate of reaction when added to magnesium. You will measure the rate of reaction by observing the rate at which hydrogen gas is produced.

aim

investigate the relationship between concentration, temperature, surface area and rate of reaction

equipment

• hydrochloric acid

• measuring cylinder

• conical flask

• pipette

• delivery tube

• delivery tube and bung

• trough of water

• clamp and stand

• magnesium

• stop clock

• thermometer

• ice/water bath/bunsen burner

steps (concentration)

1. comparing 2 and 1mol/dm³ of hydrochloric acid

2. measure 50cm³ of one in a measuring cylinder using a pipette

3. pour hydrochloric acid into a conical flask with a bung and delivery tube

4. push the measuring cylinder into the trough and slowly lower the top of it into the water to eliminate the risk of air bubbles

5. clamp the measuring cylinder in place

6. place the delivery tube underneath the cylinder

7. add the magnesium to the conical flask, start the stop clock, put the bung immediately on the top of the conical flask

8. water is forced out of the measuring cylinder as gas is produced

9. record change in water every time

10. repeat for other concentration of hydrochloric acid

alternative (concentration/surface area)

use a gas syringe connected to delivery tube and measure volume of gas collected every 10 seconds

steps (temperature)

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. swirl the flask to mix its contents, and start a stop clock

4. look down through the reaction mixture. when the cross can no longer be seen, record the time on the stop clock

5. measure and record the temperature of the reaction mixture, and clean the apparatus as directed by a teacher

6. repeat steps 1 to 5 with different starting temperatures of sodium thiosulfate solution.

steps (surface area)

1. prepare 3 sets of marble chips, one for each size. adjust the numbers so each set has the same mass

2. add a measures volume of dilute acid to the conical flask. plug flask with cotton wool

3. place flask and marble chips on balance and record mass

4. remove cotton wool and add the chips to the acid, start the stop clock

5. record the mass each 30s