Science Coursework

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Science

Coursework

Sumaiya Vora

10z

Title

Investigation on how the rate of reaction

between sodium Thiosulphate and hydrochloric

acid is affected when the concentrations of

sodium Thiosulphate are changed.

Aim:

?        I am going to investigate how the rate of reaction is affected when

the concentration of sodium Thiosulphate is changed. The

experiment will be done by mixing the various concentrations of

sodium Thiosulphate with hydrochloric acid and by timing how long

it takes for a cross to disappear. This will be able to be done

because one of the products of the reaction is sulphur, which is an

insoluble substance. As it forms the mixture becomes cloudy and

the cross will eventually won’t be seen.

Word and Symbol Equation

Sodium              + Hydrochloric                  Sodium+ Sulphur+ water + sulphur

Thiosulphate           Acid                        Chloride    dioxide  

        (Aq)         (g)        (L)       (s)

Na2S202  + 2HCL                2NaCl+S+H2O+SO2

Background Information

?        Sodium Thiosulphate

Sodium Thiosulphate is a chemical used in photography. If a clear solution

of sodium Thiosulphate was mixed with hydrochloric acid a reaction

occurs and a creamy yellow precipitate is produced which is sulphur. Along

with sulphur, sulphur dioxide, water and sodium chloride are formed. This

precipitate does not form immediately, but it begins to appear after a

short while, this therefore turns the mixture cloudy

Rates of Reaction

Rates of reactions can go at all different sort of rates. One of the

slowest reactions is iron rusting. Other slow reactions are chemical

weathering like acid rain damage to limestone buildings and statues. A

metal like magnesium reacting with acids to produce bubbles is a normal

speed reaction. A really fast reaction is an explosion such as firework.

The rate of reaction depends on four main aspects. They are

1.        Temperature

The temperature affects the rate of reaction because it makes the

rate of reaction time slow down or get quicker. If the temperature

has been increased then the reaction is quicker and the solution

becomes cloudy quicker. If the temperature has been decreased then

the reaction is slower. When the temperature increases the particles

have more kinetic energy and therefore there will be more successful

collisions betweens the reactions. As a result the rate of reaction

increased.

2.        Concentration

If the concentration is higher then the reaction is quicker. Therefore if

the concentration of sodium Thiosulphate was higher then the reaction is

quicker. This is because when the concentration is higher there are more

particles of solute and the greater the chances of successful collisions.

The more change of collisions between reactants the faster the rate of

reaction will be.

3.        Catalysts

If a catalyst was added to the experiment then the reaction would be

faster and also less energy will be needed for the reaction to occur. As

the activate energy of reactions is reduced. Catalysts speed up the rate

of chemical reactions without themselves being used up. In my

investigation I do not propose to use a catalyst but if I did I would use

the same mass.

4.        Size of particle (surface area)

The surface area and the particle size also have an effect on the rate of

reaction. If the surface area is larger then the reaction will be quicker.

If the particle size is larger the reaction will be slower. So therefore if

the surface area is smaller the reaction is slower and if the particle size

is smaller the reaction is faster.

As well as these main aspects other minor things affect the rate of

reaction.

Firstly if the solute and the solvent were stirred then the reaction would

be faster. In this case if the sodium Thiosulphate and hydrochloric acid

were stirred then the rate of formation would be quicker. Furthermore

more collisions of particles will increase the rate of reaction

?        Measuring rates of reactions

The rates of reactions can be observed by looking at how quickly the

reactants are used up or how quickly the products are formed. These are

three different ways that the rates of reactions can be measured. These

are

1.        Precipitation

This is when the product of a reaction has become cloudy. (In this

experiment this method is going to be sued to measure the rate of

reaction). I will time how quickly a cross-placed of the bottom of the

reaction vessel to disappear. The faster the cross disappears the faster

the rate of reaction as the faster the production of sulphur.

2.        Change in mass (usually an gas is given off as a

product)

Any reaction that produces a gas can be carried out on a mass balance

and as the gas is released then the mass goes down.

3.        Volume of gas given off

This involves the use of a gas syringe to measure the volume of gas given

off.

The rate of reaction can be measured by the 1 divided by the

time=(1/time) or by the average time. (1/average time)

?        Collision theory.

The collision theory basically is that the rate of reaction depends on how

often and how hard the reacting particles collide with each other. The

basic theory is that the particles have to collide in order to react and

they have to collide hard as well. The faster the collisions the faster will

be the rate of reaction. Any factor that increases the number of

successful collisions between reactants e.g. temperature will increase the

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rate of reaction.

1.The temperature increases the number of collisions. When the

temperature is increased the particles all move quicker therefore there

will be more collisions

 

2. Concentration or pressure increases the number of collisions. If the

solution is made more concentrated it means there are more particles of

reactants knocking about the water molecules, which makes collisions

between particles more likely. In a gas increasing the pressure means the

molecules are more squashed up together so these are going to be

collisions.

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