Investigating Rates Of Reaction

Rate of Reaction - Sodium Thiosulphate and Hydrochloric Acid

Aim

Investigation, to find out how the rate of reaction between Sodium

Thiosulphate and Hydrochloric acid is affected by changing the

concentration.

Introduction

I must produce a piece of coursework investigating the rate of

reaction, and the effect different changes have on them. The rate of

reaction is the rate of loss of a reactant or the rate of development

of a product during a chemical reaction. It is measured by dividing 1

by the time taken for the reaction to take place. There is five

factors which affect the rate of a reaction, according to the

collision theory of reacting particles: temperature, concentration (of

solution), pressure (in gases), surface area (of solid reactants), and

catalysts. I have chosen to investigate the effect of concentration on

the rate reaction. This is because it is the most practical to

investigate. Dealing with temperatures is a difficult task especially

when we have to keep constant high temperatures. Secondly the rate

equation and the constant k changes when the temperature of the

reaction changes. We have no gases and solids involved therefore it is

easy to deal with solutions. Similarly the use of a catalyst

complicates things, and if used incorrectly could alter the outcome of

the experiment.

The theory behind this experiment is that 'Increasing the

concentration can increase the rate of the reaction by increasing the

rate of molecular collisions.'

GRAPH

I will place the reaction mixture on a paper with a black cross-drawn

on it. When the cross is completely obscured, the reaction will have

finished. The time taken for this to happen is the measure of the rate

of reaction. We must do this several times, and change the

concentration of Sodium Thiosulphate.

The rate of reaction is a measure of the change, which happens during

a reaction in a single unit of time. The things that affect the rate

of reaction are as follows:

* Surface area of the reactants

* Concentration of the reactants

* The temperature at which the reaction is carried out

* Use of a catalyst

Reaction equation is mentioned above but rate equation could only be

decided by doing experiments. So the following procedure can be used

to carry out the experiment.

Plan

Equipment

* 2 Measuring cylinders

* Beaker

* Stopwatch

* Paper with black cross on it

* Sodium Thiosulphate (different concentrations)

* Hydrochloric acid (same concentration each time)

* Water (different concentrations)

* Pipette

Prediction

I predict that the greater the concentration of Sodium Thiosulphate

solution the faster the chemical reaction will take place. Therefore,

the cross will disappear more quickly due to the cloudiness of the

solution. I predict that as concentration is doubled the amount of

time taken for the reaction is halved. This means that both graphs

drawn up in my analysis will have positive correlation, and will

probably be curved as the increase in rate of reaction will not be

exactly the same as the concentration is increased. This can be

justified by relating to the collision theory.

If solutions of reacting particles are made more concentrated there

are more particles per unit volume. Collisions between reacting

particles are therefore more likely to occur. All this can be

understood better with full understanding of the collision theory

itself: For a reaction to occur particles have to collide with each

other. Only a small percent result in a reaction. This is due to the

energy barrier to overcome. Only particles with enough energy to

overcome the barrier will react after colliding. The minimum energy

that a particle must have to overcome the barrier is called the

activation energy, or Ea. The size of this activation energy is

different for different reactions.

I think that the concentration of a solution effects the rate of

reaction because 'the rate of reaction depends on how frequently the

molecules of the reacting substances collide. A more concentrated

substance