Find out the effect of concentration on the reaction between Sodium Thiosulphate and Hydrochloric Acid.

Rate of Reaction

Introduction:

The RATE of a reaction is the SPEED at which a reaction happens. If a reaction has a low rate that means the molecules combine at a slower speed than a reaction with a high rate. Some reactions take hundreds, maybe even thousands of years while other can happen in less than one second. The rate of reaction depends on the type of molecules, which are combining.

There is another big idea with rates of reaction... COLLISION THEORY. The collision theory says that the more collisions in a system, the more likely combinations of molecules will happen. So if there are a higher number of collisions in a system... More combinations of molecules will occur, the reaction will go faster, and the rate of that reaction will be higher.

Forces that change the speed of reactions:
Reactions happen, no matter what. Chemicals are always combining or breaking down. Over and over again but not always at the same speed. There are a few things, which really affect the speed of the reaction and the number of collisions that can occur.

Temperature

Increasing the temperature increases the speed of the reacting particles and faster particles collide more often than slow ones. The increase in the number of collisions leads to an increase in the collision frequency and rate of reaction. Increasing the temperature also gives the particles more energy so that they collide with more violence. Energetic particles have a better chance of their collisions leading to a reaction.

Concentration

In a higher concentration solution there are more particles to react therefore there are more collisions and a higher collision frequency. As a reaction depends on collisions happening, a higher collision frequency leads to a faster reaction rate. If we were doing a reaction with acid and we double the number of acid particles, we double the number of collisions and therefore are likely to double the reaction rate.

Pressure

Pressure affects the rate of reaction especially when you look at gases. When you increase the pressure the molecules have less space to move around. That greater concentration makes them collide with each other more often. When you decrease the pressure molecules don't hit each other as much and there are fewer collisions. That lower pressure lowers the rate of reaction.

Surface area

Surface area is controlled by the particle size of a solid. A powder has a higher surface area than lumps and therefore a powder has more atoms or ions exposed on its surface in a position to react. More collisions take place between the ions or molecules in the surrounding liquid. The collision frequency in increased and so is the rate of reaction.

Catalyst

This is a preview of the whole essay

Surface area

Catalyst

A catalyst is substance that alters the rate of reaction without being used up. Usually the reaction is speeded up. Catalysts are usually transition metals or transition metal compounds. An example of a catalyst is iron which catalyses the reaction of nitrogen and hydrogen to produce ammonia. A catalyst usually works either by providing a surface for the reaction to take place or by forming intermediate compounds.

Aim:

The aim of this experiment is to find out the effect of concentration on the reaction between Sodium Thiosulphate and Hydrochloric Acid.

Planning:

I have chosen to investigate the effect of concentration on a reaction, between hydrochloric acid and sodium thiosluphate.

Both the sodium thiosluphate and the hydrochloric acid are soluble in water, that’s why I will change the concentration sodium thiosluphate. I will keep the volume of hydrochloric acid constant through out the experiment while volume of sodium thiosluphate. the total volume used in each experiment will be 50cm³.

As soon as I done that I will then stat the stopwatch. When the reactants are mixed, a fine precipitate of sulphur starts to form. The solution turns cloudy and more yellow. As the precipitate forms, the ink cross on white paper slowly disappears. The stopwatch will be stopped. The time will be recorded. The equation for this is as follow:

Sodium + Hydrochloric Sodium + Water + Sulphur + Sulphur

thiosulphate acid chloride dioxide

Na2S2O3 (aq) + 2HCl (aq) 2NaCl (aq) + H2O (I) +SO2 (g) + S (s)

Prediction:

I predict that the greater the concentration of Sodium Thiosluphate in the solution the faster the chemical reaction will take place. Therefore, the cross will disappear more quickly due to the cloudiness of the solution. But only up to a point after this the solution will not react within a reasonable time.

I think the concentration of a solution affects the rate of reaction because the rate of reaction depends on how frequently the molecules of the reacting substances collide. A more concentrated substance has more molecules for a given volume than a more dilute substance. Because there are more molecules about, the frequency of successful collisions is greater, and the reactions happen faster.

Apparatus:

Conical flask
Stopwatch
Paper with black cross on it
3 measuring cylinders
2 beakers
Lab coat
Sodium thiosulphate
Hydrochloric acid
Distilled water

Fair test:

In this experiment I am trying to find the rate of reaction using concentration as a factor, so there is a number of things I need to make sure that test is fair.

Firstly, I need to keep a chemical at a constant concentration. So, in this experiment I have chose to keep hydrochloric acid at a constant concentration. I could have, however, used sodium thiosulphate as a constant, but I had chosen to use hydrochloric acid.

I must make sure that the solution is kept at a constant volume throughout the experiment. If the volume is different, then it could give different results to if it was at a constant volume.

I must also make sure that I add both the water and the sodium thiosulphate at exactly the same time (into the conical flask with the hydrochloric acid in it), or it could affect the results of the experiment.

I must start the stopwatch at the exact time as hydrochloric acid into the Sodiumthiosulphate and distilled water.

Lastly I must ensure that the conical flask is completely clean and free of any water or any other substance before I attempt to start the next experiment.

Method:

I wore lab coat

I collected the apparatus and set up as shown in diagram.

On a clean white paper I marked cross (x)

Then I put conical flask on the white paper, marked x on it.

I wrote Na2S2O3 on one conical flask, HCl on other one to avoid the mix up.

I measured 5cm³ of hydrochloric Acid (same concentration each time) with measuring cylinder and poured into a conical flask.

I measured 40cm³ of sodium thiosluphate with large measuring cylinder and poured it into a conical flask.

I measured 5cm³ of distilled water with measuring cylinder and poured into conical flask.

I poured sodium thiosluphate into the conical flask, which was placed on top of piece of paper cross on it.

I poured distilled water into sodium thiosluphate.

Then I poured hydrochloric acid into sodium thiosluphate and distilled water.

As hydrochloric acid touched sodium thiosluphate and water, I started the stopwatch.

A yellow precipitate of Sulphur started to produce and the cross-started to disappear.

As the cross disappear completely, I stopped the stopwatch and checked the time, and record into my result table.

Then I repeated the experiment twice.

Diagram:

Safety:

To make sure my experiment is safe, I will follow laboratory rules, which include:

The wearing of safety goggles to protect my eyes from chemical splashes.
Standing up to conduct the experiment, therefore reducing the risk of tripping and spilling chemicals.
Taking care when handling chemicals, particularly Hydrochloric acid and Sodium Thiosulphate because they are irritants. I will not touch my eyes or mouth until I have thoroughly washed my hands.
Taking care when using glassware to prevent injury.

Results:

Table 1:

Table 2:

Table 3:

Average time = T1+T2+T3

Conclusion:

On these tables of results I have used 4 tables to make the data understandable. To work out the average, I added up the both results and divided by 2. I have worked out the average that then the results will be more accurate.

I have found that my prediction was correct. The rate of reaction was quicker when there was a higher concentration of sodium thiosulphate. This can easily be seen when I look at the results table.

My results support the prediction I made because I said ‘the greater the concentration of Sodium Thiosulphate the faster the rate of reaction time.’ I believe I was correct ‘the reaction time will be faster with a more concentrated solution because, the more particles there are, the frequency of successful collisions is greater and therefore the reaction rate is speeded up’.

My graph is a smooth curve. I am confident with my results because my line is on nearly all of the points. My graph shows that the more concentrated the thiosulphate solution the quicker the cross disappears. I know this because when there is 45cm³ of sodium thiosulphate and no water it only took 15 seconds for the cross to disappear whereas when there is 5cm³ of sodium thiosulphate and 40cm³ of distilled water it took 224 seconds to disappear.

Evaluation:

I feel that my experiment was fairly successful, and relatively easy to perform. I had two anomalous results shown in my graph after an average over three measurements. I can say that looking at my results when I repeated results they were quite close together.

To improve my results I would do more preliminary work to make sure my method was as accurate as possible and that I was more familiar with doing the experiment.

I think it would be a good idea to repeat the experiment more than two times to improve my results. I think it would be better to work with another person so one person will put substances together while the other will start timing.