Investigation a Chemical Reaction between Sodium Thiosulphate and Hydrochloric Acid

Authors Avatar

Investigation a Chemical Reaction between Sodium Thiosulphate and Hydrochloric Acid 

Introduction

The purpose of this investigation is to find what effects the changing of two easily changeable variables have on the rate of this reaction. cg.

The reaction is between the two chemicals: sodium thiosulphate solution and dilute hydrochloric acid. They react as in the equations below:

sodium thiosulphate + hydrochloric acid  sodium chloride + sulphur + sulphur dioxide + water

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

Background Knowledge

The rate of a reaction depends on four factors:

  • Temperature
  • Concentration
  • Catalyst
  • Size of Particles/ Surface Area

A catalyst is a separate substance, which speeds up a reaction. Once the reaction has occurred the catalyst is left behind. This makes it unsuitable for the type of experiment I am going to do. A catalyst is also discontinuous variable. Foucault

Particles can only collide when the two sorts can meet, therefore a reaction can only occur on the surface of the material. By increasing the area of the material, which is available to collide, the speed of the reaction will increase. This variable is very hard to control the exact surface area of the two reactants as they both come in an aqueous solution.

In this particular investigation the two variables, which are going to change, are temperature and concentration.

The Collision Theory explains these reaction rates, as they are based on how often and how hard the reacting particles collide with each other. Reactions only happen if the particles collide with enough energy. The initial energy is known as the activation energy, it is needed to break the initial bonds.

· By increasing the temperature, more energy is given to the particles causing them to move faster. As they move faster they cover more area and therefore are therefore collide more often, from this you can predict that raising the temperature will increase the rate of reaction.

I predict with this variable that temperature is proportional to rate of reaction

· By increasing the concentration the number of particles will increase. This increases the likeliness of the particles colliding and so the rate increases. I predict that doubling the concentration of the acid, the rate of reaction will double.

Both of these are independent, continuous variables. As the temperature reaction is exothermic, I predict that this will have the biggest affect. Heat is given out by the reaction, which will give more energy to the particles, which will cause them to react quicker.

For both temperature and concentration I think the reactions are proportional because:

· Doubling the speed at which the particles travel, will double the distance they can travel in a set time and so double the probability of them colliding. 

· Doubling the number of particles doubles the probability that they will collide. 

Preliminary Investigation

I am going to obtain a number of preliminary results to find out the best concentration of Sodium Thiosulphate, Hydrochloric Acid and Water.

Firstly I performed several experiments to do with the concentration variable. Firstly I investigated how a change in the Sodium Thiosulphate would affect the time taken for the water to go cloudy. The method, which I used, was to firstly collect all the apparatus. This included; a beaker, paper marked with a cross, stopwatch, 50cm3 measuring cylinder, 10cm3 measuring cylinder, water, Sodium Thiosulphate and Hydrochloric Acid. I used 10cm3 of Hydrochloric Acid as a constant value, the value of Sodium Thiosulphate ranged from 10cm3 to 50cm3. The Sodium Thiosulphate was firstly added into the beaker, which was placed over the ‘X’ marked paper. When the Hydrochloric acid was added the stopwatch was started. Once the ‘X’ was no longer visible the stopwatch was stopped.

Join now!

This was followed out for all 5 different values. Once the results were collected the same procedure was followed out for each value, along with 10cm3 of water.

Results Table: idea.

Secondly a similar experiment was followed out testing the result of a varied hydrochloric acid value and keeping a constant value of 50cm3 of Sodium Thiosulphate. This reveals what difference it would make if you change the hydrochloric acid.

Results Table:

I am happy with these two tables as they provide adequate results. I will be using water in both of the experiments, as it seems to slow down the reaction ...

This is a preview of the whole essay