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

reactants. As the reaction progresses, the sulphur will collect in the water

and form a cloudy solution. As more sulphur is formed, less light can get

through the solution and reach the sensor. I will put the hydrochloric acid

into the beaker and prepare the computer. I shall then put the sodium

thiosulphate into the beaker and start the computer reading. The computer

records light levels as a percentage of original levels against time and is

much more accurate than using a stop watch. I shall allow the reaction to take

place for 60 seconds. I shall then use the computer’s accurate analysis

facility to record how long it took for light levels to fall to 60% of the

original. Often one of the possible weaknesses in an experiment such

as this is that the different concentrations of acid are often made up

inaccurately. To solve this problem I shall use one large bottle of 0.5 molar

hydrochloric acid and use distilled water to dilute it to different

concentrations: 20, 40, 60, 80, and 100% acid. Because I need 20ml of acid and

20ml of sodium thiosulphate I shall use varying quantities of water. For

example, when making 20% concentration, I shall mix the water and acid

16ml/0.25ml respectively. After the experiment, I shall be able to draw a graph

comparing concentration and reaction time. If my prediction is correct, the

graph will be proportional. I shall back up my results for this section by using

results generated by another group using the optical method outlined in the

plan for the second variable below. I conducted the experiment as per my plan, although I had to

disregard the first few computer results as the system took a while to

configure. However I did several things to ensure the accuracy of my project.

These included: ·

Washing out the glassware with distilled water before

use and between measurements. This was designed to prevent any foreign ions

getting into the solution as this could damage the results. ·

Using an analogue thermometer when heating the

hydrochloric acid as this enables me to be more accurate than with a digital

thermometer. ·

Using a small measuring cylinder and funnel when

measuring out hydrochloric acid, water, and sodium thiosulphate rather than

using beakers. The results for the first variable are displayed in Table 1

below. There was only time to take measurements once for each concentration as

other groups needed to use the computer. However because the computer is very

accurate and because I also took results from another group, this will not pose

too great a problemConclusions

Before I can represent my data in graph form and then test my prediction, I

have to look at the way the data is laid out. I predicted that both variables

would be proportional. This implies that as temperature goes up, time taken

goes down. However because reaction time goes down, reaction rate is actually

increasing. The best way therefore to represent the results in graph form is to

draw a graph of concentration/temperature against the reciprocal of the time

taken. Graph 1 shows concentration against the reciprocal of the

time. However it is clear that it is not a straight line graph but rather a

curve, gradually getting steeper as molarity increases. It is clear that my

prediction was wrong and that the graph is not proportional. I can further test

this by running my results through the formula for proportionality. X’ = XY’ / Y so X’ = (0.056 x 60) /

20 = 0.168 If my prediction was correct the reciprocal of time taken

for 60% concentration should be 0.168. In fact it is 0.09. The slow growth of

the graph followed by a massive increase can be explained by looking at

activation energy. All of the reactions happened at room temperature (about

210C). Clearly this energy was only enough to push some of the particles beyond

their activation energy. However because the reaction is exothermic it gives

out energy and this energy pushes more particles to activation energy and these

in turn release more heat. More particles of HCI available to reaction with the

sodium thiosulphate means more heat given out and more particles being pushed

to activation energy. The investigation could have been improved by testing the

temperature variable on the computer as the stop watch I used could not cope

with the speed of the reaction. It would also have helped to test each

concentration more than once to ensure that the results were true. When using

the light sensor I should have covered the underside of the sensor with black

material rather than sticking on paper as this could have let in some light. In

addition I should have used an artificial source of light as the natural light

in the room was constantly changing as clouds pass in front of the sun. I could

also have used a burette to measure out the reactants although the measuring

cylinder was quite accurate. Squash Ball experiment"Squash Ball Experiment Input Variables: Pressure Of Air in Ball Type Of Surface Height Of Drop Temperature of Ball Material of Ball Acceleration Due To Gravity Mass Angle Of Surface Air Resistance Diameter of BallOutcome: Height Of BouncePrediction??????????????? The

squash ball will bounce higher as the temperature gets warmer. This is because

as it gets warmer the atoms in the ball vibrate more. This means that when it

hits the ground the atoms push each other way forcing the ball to bounce

higher. When the temperature is lowered the opposite occurs because the atoms

have less energy and therefor push each other further away. The graph would

look like this:The graph begins to level out because parts of the ball

begin to melt at certain temperatures as the atoms get more energy and break

their bonds turning the ball into a liquid. A theory, which links into this

experiment, is the kinetic theory. This is because the kinetic theory deals

with atoms vibrating as they receive more energy and they then break their

bonds. This is linked to this experiment as the squash ball’s atoms get more

energy and vibrate more before breaking their bonds to become a liquid when the

ball hits a critical temperature. I don’t think the graph will go through 0,0,

as even when the ball is at 0 degrees it will still bounce. I am using a large

range of results as well. DiagramMethod??????????????? We set up

the apparatus as shown in diagram and then heated the ball to a set

temperature. We then dropped it from 70 cm high and measured the bounce. We

then repeated that temperature another 4 times to gain an average. We had to be

careful with the Bunsen burner and so we wore goggles. To keep the experiment

fair the only thing, which we changed each time, was the temperature. We used

the same ball through out the experiment and checked the ball was at the same

temperature each time. We dropped it onto the same table from the same height

as well. The range of temperature we used was from 5 degrees Celsius to 70

degrees Celsius. Some of the results needed to be repeated to make sure that

they were accurate.ResultsTemperature (c)??? Measurements

(Cm) ??????????????? Result ???? 1???????? Result ??? 2????????? Result ??? 3 ???????? Result ???? 4???????? Result ???? 5???????? Average 5????????????? 10??????????? 11??????????? 13??????????? 12??????????? 11??????????? 11.9 10??????????? 15??????????? 21??????????? 20??????????? 19??????????? 13??????????? 17.6 20??????????? 20??????????? 23??????????? 21??????????? 26??????????? 24??????????? 22.8 30??????????? 25??????????? 29??????????? 26??????????? 26??????????? 23??????????? 25.8 40??????????? 21??????????? 21??????????? 22??????????? 26??????????? 28??????????? 23.6 50??????????? 30??????????? 30??????????? 29??????????? 28??????????? 25??????????? 28.4 60??????????? 31??????????? 33??????????? 32??????????? 35??????????? 36??????????? 33.4 70??????????? 37??????????? 31??????????? 33??????????? 35??????????? 37??????????? 34.6 ?Conclusion??????????????? From my

results I can conclude that as the temperature of the ball rises the height of

the bounce gets higher. This is in line with the kinetic theory, which defines

that as the ball gets hotter the atoms get more energy and vibrate more. When

the ball hits the surface then the atoms are pushed together and because they

are vibrating more they push each other further away causing the ball to bounce

higher. In this experiment the kinetic theory only lasts for a specific set of

temperatures. This is because when the ball hits a certain temperature it

starts to melt. At 0 degrees Celsius the ball will still bounce as the atoms

are still vibrating. The graph proves that the theory works for this

experiment, as it is a straight line to start with. However as the ball gets

nearer the critical temperature the extra height it bounces becomes less and

less. This is shown as the graph levels off. The sketch graph I drew in my

prediction matched the real graph showing that the science I used to explain my

prediction was correct.Evaluation??????????????? Looking

at my results I can say that they were quite reliable and accurate. I had one

anomalous result even after an average over five measurements. I can say that

looking at my results when I repeated results they were quite close together. I

think that I did the experiment quite well although I found it hard to spot

where the ball bounced too. This is why I did an average over 5 measurements.

To improve the experiment I would need to use specialist equipment like lasers

so I could be sure where the ball bounced too. Ways in which I could extend

this experiment are to use a different kind of rubber in the ball so that it

doesn’t melt at such a low temperature this way I could carry on to see whether

the kinetic theory is still right at higher temperatures. Also I would like to

see what happened when the ball was at 0 degrees Celsius. I would like to do

this to see whether the atoms still vibrated causing the ball to bounce. If it

did I would like to carry on getting lower and lower to see whether there was a

temperature where the atoms no longer vibrated (Absolute Zero)