Chemistry Coursework - Sodium Thiosulphate

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Chemistry Coursework
Planning

Aim: To find the effect of concentration of thiosulphate on the rate of reaction between sodium thiosulphate and hydrochloric acid.

Introduction:

Word Equation for the reaction:

Balanced Symbol Equation for the reaction:

Observations during the reaction:
• A yellow precipitate of Sulphur starts to form and the reaction mixture goes cloudy. • A colourless, poisonous gas of sulphur dioxide is given off. • Sodium Chloride (salt) and Water also form. The salt dissolves in the solution, and the water mixes in.

Rate of Reaction
The rate of a chemical reaction is a measure of change of given quantity with time. There are two ways to measure the rate of a reaction:
1. measure the rate at which a reactant is used up
2. measure the rate at which a product is formed

Collision theory is used to explain how different factors affect the rate of chemical reaction. The collision theory states that for a reaction to take place between reacting particles (ions, molecules or atoms) it is necessary that they collide. Particles must also have a sufficient amount of energy to react. This minimum amount of energy which reacting particles must possess to reaction is called the activation energy. This energy is used to break bonds in the reacting particles in order that products can form. Without this activation energy, particles simply bounce off each other without reacting.

Chemical reactions can only happen if reactant particles collide with enough energy. The more frequently particles collide, and the greater the proportion of collisions with enough energy, the greater the rate of reaction.

Different reactions can happen at different rates. Reactions that happen slowly have a low rate of reaction. Reactions that happen quickly have a high rate of reaction.

The temperature, concentration, light, surface area of reacting solids, and the use of catalysts, are all factors which affect the rate of a reaction.

Temperature:
An increase in temperature will increase the rate of a chemical reaction.

• Increasing the temperature causes the particles (H+ ions from HCl and Sodium Thiosulphate particles) to gain energy • They start to move faster
• They collide more often and with greater force
• There are more successful collisions per unit time (thus increasing the rate of reaction)

Since we are measuring the effect of concentration in our reaction, temperature must be kept constant (at room temperature).

Concentration:
An increase in the concentration of a reactant will increase the rate of a chemical reaction.

• There are more reactant particles (Sodium Thiosulphate particles) per unit volume • There is a greater chance of the particles colliding (with H+ ions from HCl) • There are more successful collisions per unit time (thus increasing the rate of reaction

The reaction between sodium thiosulphate and dilute hydrochloric acid can be used to demonstrate how the concentration of a reactant can affect the rate of a chemical reaction. In his reaction the concentration of sodium thiosulphate is varied and the time for a given mass of sulphur to form recorded. The diagrams below help to explain the affect of concentration on rate of reaction:

Light:
Light is a form of energy and it causes many chemical reactions to take place. Some photochemical reactions need the continual presence of light while others only require light to initiate them. Examples of these reactions include photosynthesis and in photographic film.

Since we are measuring the effect of concentration in our reaction, we must keep the light levels the same while performing the experiment.

Surface Area:
If a solid reactant is broken into small pieces or ground into a powder:

• Its surface area is increased
• More particles are exposed to the other reactant and are available to react • There are more frequent collisions between the...
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