Production of Epsom salts

Introduction

In this coursework, I am going to be making Epsom salts, Magnesium sulphate crystals is another name for Epsom salts. It is commonly being called Epsom salts because the salt is found in spa water from Epsom. They can be used for different things including manufacture of mordants for the dyeing industry, in the tanning of leather and manufacture of some lawn treatments. Epsom salts can be made in the laboratory by adding magnesium ribbon to dilute sulphuric acid. The chemical formula for the crystals is MgS047H2O. It is called the water of crystallisation as it is part of the crystal structure and if it is removed the solid changes from crystals to powder. If an excess of magnesium ribbon is added to dilute sulphuric acid all of the acid will react and the hydrogen will be liberated leaving a solution of magnesium sulphate in water and if the water is evaporated off slowly crystals of MgS047H2O will form. There are a number of factors that can influence the rate of a chemical reaction. These include:

The temperature
The concentration of reactants in the solution
Catalysts
The pressure of gases

The temperature: When two chemicals react, their molecules have to collide with each other with sufficient energy for the reaction to take place. Heating the mixture will raise the energy levels of the molecules involved in the reaction. Increasing temperature means the molecules move faster.

The concentration of reactants in the solution: Increasing the concentration of the reactants will increase the frequency of collisions between the two reactants

Catalysts: Catalysts speed up chemical reactions. Only very minute quantities of the catalyst are required to produce a dramatic change in the rate of the reaction

: If one of the reactants is a solid, the surface area of the solid will affect how fast the reaction goes. This is because the two types of molecule can only bump into each other at the liquid solid interface

The pressure of gases: By increasing the pressure, you squeeze the molecules together so you will increase the frequency of collisions between them

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Catalysts: Catalysts speed up chemical reactions. Only very minute quantities of the catalyst are required to produce a dramatic change in the rate of the reaction

The pressure of gases: By increasing the pressure, you squeeze the molecules together so you will increase the frequency of collisions between them

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Complete Method

This practical is in two parts: the first part I will look at what happens to the rate of reaction when the concentration of the acid is changed. The second part I will be making magnesium sulphate crystals (Epsom salts).

Equipment I used for the practical:

A measuring cylinder

A small beaker

A stop-watch

Three pieces of magnesium ribbon which is of equal length

Three sulphuric acid solutions of three concentrations 1.00 mol dm-3 ,0.50 mol dm-3 and 25.0cm3

First part:

I first cut three approximately 2cm in length sized pieces of magnesium ribbon
I used a measuring cylinder to measure out 25.0cm3 of 1.00 mol dm-3 sulphuric acid and then placed it in a clean beaker.
I added a piece of magnesium ribbon to the acid and used a stop watch to time how long it took for all of the magnesium to react.
I rinsed out the beaker then repeated the steps but this time using 25.0cm3 of 0.50 mol dm-3 sulphuric acid
Repeated the steps a third time and using 25.0cm3 of 0.25 mol dm-3 sulphuric acid

Second part:

I measured out 10cm3 of 1.00 mol dm-3 sulphuric acid.
I then cut a 50cm strip of magnesium ribbon and weighed it. It weighed 0.539g.
I added the magnesium to the acid and waited for it to react. There was some magnesium left at the end of the experiment.
I poured the liquid into an evaporating basin
I then heated the evaporating basin containing the solution to remove half of the water and allowed it to start so the crystals form slowly.
I then weighed the crystals.

The reaction between magnesium and sulphuric acid can be represented by the following equation:

Mg(s) + H2S04(ag) → MgS04(ag) + H2(g)

Results

When a piece of magnesium with mass more than 0.24g is added to 10cm3 of 1.00 mol dm-3 sulphuric acid 0.24g of magnesium will react with the sulphuric acid in the solution. The rest of the magnesium will not react because there is not enough sulphuric acid in the solution. The 0.24g of magnesium which doesn’t react should produce 1.2g of Epsom salts so the theoretical yield of Epsom salts is 1.2g

The theoretical yield of a reaction is the amount of product that would be formed if the reaction went to completion. Theoretical yield is determined by stoichiometric calculations.

The mass of the Epsom salts I produced was 0.9g

Therefore my actual yield obtained was 0.9g

A measured amount is called the actual yield. It is the amount of product I actually produced in the reaction.

To get the percentage yield I need to do:

Percentage yield = (Actual yield/Theoretical yield) x 100%

= (0.9/1.2) x 100%

= 75%

Percentage yield is a ratio of the actual to the theoretical yield expressed as a percentage. It is a way of measuring how successful a reaction has been.

I think the reaction was efficient since I made 75% of the maximum possible 100%. Thus, the practical was also successful since I obtained an efficient actual yield and I was able to get my actual yield properly and accurately. I would not recommend this procedure for large scale production since I obtained a 75% yield which means you will lose 25% in every production.

Cost of Making Epsom salts

I am going to calculate the cost of making Epsom salts.

I used the following reagents:

1.00 mol dm-3 sulphuric acid £3.41 per litre I used 25 cm3

Magnesium ribbon £3.70 per 100 g I used 0.539g

The mass of Epsom salts I produced was 0.9g

1.00 mol dm-3 sulphuric acid costs £3.41 per litre and I used 25 cm3 so the cost is:

3.41/1000 =0.00341 which is the same as 0.341p per cm3 so 25 cm3 costs 0.341 x 25 = 8.53p

Magnesium ribbon costs £3.70 per 100g and I used 0.539g so the cost per gram is:

3.70/100 = £0.037 which is the same as 3.70p so 0.539g costs 3.70 x 0.539 = 1.9943p

So the total cost of making 0.9g of Epsom salts is 8.53 + 1.9943 = 10.5243p

The cost per gram is 10.5243/0.9 = 11.69p (rounded of to nearest penny)