Everything Science Grade 12

CHAPTER 3. REACTION RATES 3.2

• Which reaction proceeds the fastest?


• Can you explain this?
  Conclusions:

The reaction with powdered marble is the fastest. The smaller the pieces

of marble are, the greater the surface area for the reaction to take place. The

greater the surface areaof the reactants, the faster the reaction rate willbe.

Activity: Reactant concentrationand reaction rate.

Aim:

To determine the effectof reactant concentration on reaction rate.

Apparatus:

Concentrated hydrochloric acid (HCl), magnesium ribbon, two beakers, two

test tubes, measuring cylinder.

Method:

1. Prepare a solution of dilute hydrochloric acid in one of the beakers by
   diluting 1 part concentrated acid with 10 parts water. For example, if you
   measure 1 cm^3 of concentrated acid ina measuring cylinder and pour it
   into a beaker, you will need to add 10 cm^3 of water to the beaker aswell.
   In the same way, if you pour 2 cm^3 of concentrated acid intoa beaker, you
   will need to add 20 cm^3 of water. Both of theseare 1:10 solutions. Pour
   10 cm^3 of the 1:10 solution intoa test tube and mark it ’A’. Remember to
   add the acid to the water, and not the other wayaround.


2. Prepare a second solution of dilute hydrochloric acid by diluting 1part
   concentrated acid with20 parts water. Pour 10cm^3 of this 1:20 solution
   into a second test tube and mark it ’B’.


3. Take two pieces of magnesium ribbon of the same length. At the same
   time, put one piece of magnesium ribbon into test tube A and the other
   into test tube B, and observe closely what happens.

Test tube A

1:10 HCl solution

Test tube B

1:20 HCl solution

Mg ribbon Mg ribbon

The equation for the reaction is:

2 HCl + Mg→ MgCl 2 + H 2