Rates of reaction core practicals

Rates of reaction core practicals

Changing the concentration of acid

methods for changing the concentration of acids

1. Support a gas syringe with a stand, boss and clamp.

2. Using a measuring cylinder, add 50 cm³ of dilute hydrochloric acid to a conical flask.

3. Add 0.4 g of calcium carbonate to the flask. Immediately connect the gas syringe and start a stop clock.

4. Record the time for every 10 cm³ of gas produced.

5. When the reaction is complete, clean the apparatus as directed by the teacher.

6. Repeat steps 1 to 5 with different concentrations of hydrochloric acid.

changing the temp

Carry out the experiment described above but:

• keep the concentration of acid the same

• warm the acid to different temperatures using a hot water bath, or a Bunsen burner, tripod and gauze

• measure and record the temperature of the acid

• describe the effect of increasing the temperature on the mean rate of reaction

Changing the surface area to volume ratio

Carry out the experiment described above but:

• keep the temperature and concentration of acid the same

• use different sized pieces of calcium carbonate, including a powder

• describe the effect of increasing the surface area to volume ratio (decreasing the particle size) on the mean rate of reaction

Hazards, risks and precautions

It is important in this practical activity to use appropriate apparatus and methods. This includes the safe use and careful handling of substances.

Evaluate the hazards and the precautions needed to reduce the risk of harm. For example:

observing colour changes

There are a number of ways to investigate the rate of a reaction in Chemistry. This is an outline of the required steps to undertake one of these methods. It is important in this core practical to use appropriate apparatus to make and record a range of measurements accurately, including mass, time, temperature and volume.

Aims for observing colour changes

To investigate the effect of changing the temperature on the rate of a reaction.

Sodium thiosulfate solution reacts with dilute hydrochloric acid:

Sodium thiosulfate + hydrochloric acid → sodium chloride + water + sulfur dioxide + sulfur

Na₂S₂O₃(s) + 2HCl(aq) → 2NaCl(aq) + H₂O(l) + SO₂(g) + S(s)

The sulfur forms a cloudy yellow-white precipitate during the reaction. The time taken for this to achieve a given cloudiness provides a way to measure the reaction time.

Method of observing colour changes

method of observing colour changes (this is the method non image)

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

4. Measure and record the temperature of the reaction mixture.

5. Look down through the reaction mixture. When the cross is no longer visible, record the time on the stop clock.

6. Measure and record the temperature of the reaction mixture, and clean the apparatus as directed by the teacher.

7. Repeat steps 1 to 6 with different starting temperatures of sodium thiosulfate solution.

Hazards, risks and precautions for observing colour changes