Investigating the factors that affect the rates of reaction between magnesium and hydrochloric acid

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GCSE Chemistry investigation

Rates of reaction

Investigating the factors that affect the rates of reaction between magnesium and hydrochloric acid

Key variables

Temperature

Concentration of acid

Surface area of magnesium

Use of a suitable catalyst

Strength of acid

Mass of magnesium

Stirring solutions

Volume of acid

I have chosen to investigate the concentration of acid

Prediction

I predict that there will be more hydrogen produced in the same amount of time when the concentration of the acid is greater.

I predict that the concentration of the hydrochloric acid will be directly proportional to the rate of reaction. Therefore, as the concentration doubles the rate of reaction will double. So twice the hydrochloric acid used, twice hydrogen will be produced in the same amount of time as using less hydrochloric acid. The gas produced will be hydrogen.

Justification of prediction

 The rate of reaction will double because as the concentration increases there will be more mols per litre. Using the collision theory, as the concentration increases there are more reactant particles in the water to collide with the magnesium. This increases the chance of collisions so there will be more collisions, and hence greater chance of successful collisions. This means that the reaction will be faster if there are more collisions. If there is twice the amount of particles to collide then number of collisions will double, thus doubling the chance of successful collisions. There will be twice as many particles to collide with the Mg particles.

Metal + acid                  salt + hydrogen

HCL + Mg                 MgCL + H+ions

2HC L+ Mg                 2MgCL + 2H

Therefore, in the same amount of time twice the amount of hydrogen is produced.

Acids produce hydrogen + ions in solution

The collision theory

Chemical reactions can only occur when reacting particles collide with each other and with sufficient energy. The minimum amount of energy particles need to react is the activation energy.

The rate of a reaction depends on:

Temperature

When the temperature is increased the particles have more kinetic energy, so some move faster and so collide more often with more energy. The particle energy may then be greater than the activation energy, which is the energy needed to start a reaction so more particles will have more energy. Therefore, collisions must occur with enough energy to react. If the temperature is increased by 10 o C then the reaction rate will double.

Concentration of acid

This increases the concentration of reactants in solutions and the frequency of collisions.

There are more particles, mols per litre, so more collisions and therefore a greater chance of collisions and so a faster rate of reaction.

Surface area

When a substance’s area is increased, e.g. when you have a powder, the area of reactant is exposed so there are more collisions. There is more chance of successful collisions.

Use of a suitable catalyst

These increase the rate of reaction and don’t get used up. They give the particles an active site surface) to react. It lowers the activation energy so that particles don’t need as much energy for successful collisions. The energy required for collisions is lower.

I expect the graphs for my experiment to look like this.

                                                                        1.Original concentration

                                                                        2.Greater concentration

                                                                        3.Greatest concentration

V

O

L

U

M

E


Outline procedure

Apparatus

Retort stand

Conical flask

Bung with delivery tube

Gas syringe

2 clamps

Stopwatch

Measuring cylinder

Ruler

Glass Beaker

Method

First, Set up a retort stand with clamp and clamp a gas syringe to it. The syringe should only be so far off the ground so that you can attach it to a conical flask through a delivery tube. The syringe should be horizontal. Pour 50ml of HCL into the conical flask. You should have a bung like the one shown in the diagram. Measure 10cm of Mg and put it into the flask and quickly put the bung into the flask. Start the stopwatch immediately and then take the reading on the syringe every 30 seconds. Do this until the reaction stops.

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Then, repeat the experiment using more and more concentrated HCL.

I will be measuring the amount of Hydrogen produced in this experiment. As more Hydrogen is produced the further the syringe will move outwards.

Variables

Controlled: My controlled variables are the temperature of the acid, the size of the surface area of the magnesium, the volume of the acid/water solution and the length of the magnesium strip. I will not stir the HCL, partly so the rate is not affected and also because if I did the hydrogen would escape anyway.

Fair test

I will ...

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