Rates Of Reaction Sodium Chloride

Rates Of Reaction : Sodium Chloride + Sulphur + Sulphur Dioxide + Essay, Research Paper

Planning

This investigation is about rates of reaction and what affects them. In this

case I am going to look at hydrochloric acid and sodium thiosulphate which is a

precipitation reaction. 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) A reaction will only occur where the particles of the

reactants meet and combine. This is called the collision theory. Therefore it

stands to reason that to increase the rate of reaction it is necessary to cause

more particles to collide harder and make it happen more often. There are

several ways to do this and these make up the variables for this experiment.

They are listed below along with predictions as to their affect on the

reaction. Increasing the pressure. By reducing the volume in

which the same amount of particles exist the pressure is increased. Once

the same number of particles are in a smaller area there is less space in

which to move and so the particles are more likely to hit each other. It

is therefore possible to predict that increasing the pressure will result

in an increase in the rate of reaction. I will not test this variable

because the school doesn’t have the facilities to test it. However

pressure is a continuous variable. Using a catalyst is another method I could use. A

catalyst is a separate substance which speeds up a reaction. After the

reaction has happened it gets left behind. This makes this variable

unsuitable for the type of experiment I am going to do. A catalyst is also

a discontinuous variable with only one likely useful catalyst emerging. Energy. By giving the particles extra energy they

will move faster. This means that they cover more ground and are therefore

more likely to hit each other which in turn makes the reaction faster. The

best way to give energy to a particle is as heat and so I can predict that

raising temperature will increase the rate of reaction. This is a

continuous, independent variable. I shall test this variable – see below. I predict that temperature is

proportional to rate of reaction. Concentration. Just as increasing the pressure will

increase the number of particles colliding, so will the concentration. By

putting more particles into the reaction, the chance of them colliding

increases and so the rate increases. This variable is continuous and

independent. I shall test this variable. I predict that by doubling the concentration of the acid, the rate

of reaction will double. Surface area. Particles can only collide when the

two sorts can meet. Therefore a reaction can only occur on the surface of

the material. Therefore by increasing the area of the material which is

available to collide the speed of the reaction will increase. I predict

that doubling the surface area will double the speed of the reaction. This

variable is continuous but I shall not test it because it is hard to

control the exact surface area of the two reactants as they both come in

an aqueous solution. I am going to test the two variables concentration and temperature.

Both of these are independent, continuous variables. I think that concentration

will have the biggest affect because the reaction is exothermic. Therefore even

while I am testing concentration, heat will be given out by the reaction which

will give more energy to the particles and so cause them to reach their

activation energy sooner. In addition to this, looking at the original

equation, it becomes clear that for every one mole of sodium thiosulphate, you

need two moles of hydrochloric acid. Therefore increasing the number of

hydrochloric acid particles will have a greater effect than if one were to

increase levels of sodium thiosulphate. I think that both concentration and energy are proportional

because: ·

doubling the number of particles doubles the

probability that they will collide

and ·

doubling the speed at which these particles travel will

double the distance they can travel in a set time and so double the probability

of them colliding. This proportionality can be expressed using algebra thus: X’

= XY’ / Y To carry out this experiment, I will need the following

equipment:

A3020 computer, light sensor, beaker, distilled water, sodium thiosulphate,

hydrochloric acid (stock bottle), electronic scales, thermometer, burette,

light, black paper, bunsen burner, tripod, mat. Firstly I shall test the variable "concentration of

HCl", testing five different strengths. I shall set up the equipment as in

the diagram below completely surrounding the light sensor with paper to ensure

that the only light which reaches it passes through the beaker containing the