The Rate of Reaction Of Metals with Acids

The Rate of Reaction Of Metals with Acids

Introduction

In this investigation I will be looking at the rate of reaction between a metal, which will be magnesium ribbon, and an acid. The acids will either be hydrochloric, ethanoic, sulphuric or phosphoric acid. I will be finding out if the activation energy changes depending on whether a strong or weak acid is used. I will also be investigating whether or not there is a change in the order of reaction if a dibasic acid is used instead of a monobasic acid.

Planning

This investigation is therefore split up into separate experiments.

Experiment 1 is to find the activation energy for the reactions between hydrochloric acid and magnesium ribbon, then ethanoic acid and magnesium ribbon. The only way to find the activation energy is to time how long it takes for the reaction to complete at different temperatures. Experiment 2 is to find the order of reaction between magnesium ribbon and hydrochloric acid, then sulphuric acid. There are several methods that can be used to find the order of reaction:

· I could use an excess of magnesium ribbon and note down how much gas has evolved every 10 seconds until the reaction has finished.

· I could repeat the same procedure as above, but with an excess of acid instead of magnesium ribbon.

· I could use an excess of acid and change the concentration, this would not require the reaction to be completed so I would have to time how long it takes for a set amount of hydrogen gas to form.

There are several chemical equations that are relevant to this investigation:- Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g)

Mg(s) + H2SO4(aq) MgSO4 + H2(g)

Mg(s) + 2CH3CO2H(aq) Mg(CH3CO2)2(aq) + H2(g)

3Mg(s) + 2H3PO4(aq) Mg3(PO4)2(aq) + 3H2(g)

In my experiments I will not be using phosphoric acid due to time restrictions and it is not relevant to the problems I am discussing, because it is a tribasic acid and I am comparing monobasic and dibasic acids. The equation needed to find the activation energy in a reaction is called the Arrhenius equation.

In k = constant – EA/R (1/T)

Where k = rate constant

EA = activation energy (J mol¹)

R = gas constant, 8.31 J K¹ mol¹

T = temperature in Kelvin

Initial Problems

- The time restriction makes it extremely hard to find the order of reaction by timing how long it takes for all the magnesium to disappear. - I do not want to directly heat acid as this is dangerous when only