Investigation a Chemical Reaction between Sodium Thiosulphate and Hydrochloric Acid

Introduction

The purpose of this investigation is to find what effects the changing of two easily changeable variables have on the rate of this reaction. cg.

The reaction is between the two chemicals: sodium thiosulphate solution and dilute hydrochloric acid. 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)

Background Knowledge

The rate of a reaction depends on four factors:

Temperature
Concentration
Catalyst
Size of Particles/ Surface Area

A catalyst is a separate substance, which speeds up a reaction. Once the reaction has occurred the catalyst is left behind. This makes it unsuitable for the type of experiment I am going to do. A catalyst is also discontinuous variable. Foucault

Particles can only collide when the two sorts can meet, therefore a reaction can only occur on the surface of the material. By increasing the area of the material, which is available to collide, the speed of the reaction will increase. This variable is very hard to control the exact surface area of the two reactants as they both come in an aqueous solution.

In this particular investigation the two variables, which are going to change, are temperature and concentration.

The Collision Theory explains these reaction rates, as they are based on how often and how hard the reacting particles collide with each other. Reactions only happen if the particles collide with enough energy. The initial energy is known as the activation energy, it is needed to break the initial bonds.

· By increasing the temperature, more energy is given to the particles causing them to move faster. As they move faster they cover more area and therefore are therefore collide more often, from this you can predict that raising the temperature will increase the rate of reaction.

I predict with this variable that temperature is proportional to rate of reaction

· By increasing the concentration the number of particles will increase. This increases the likeliness of the particles colliding and so the rate increases. I predict that doubling the concentration of the acid, the rate of reaction will double.

Both of these are independent, continuous variables. As the temperature reaction is exothermic, I predict that this will have the biggest affect. Heat is given out by the reaction, which will give more energy to the particles, which will cause them to react quicker.

For both temperature and concentration I think the reactions are proportional because:

· Doubling the speed at which the particles travel, will double the distance they can travel in a set time and so double the probability of them colliding.

· Doubling the number of particles doubles the probability that they will collide.

Preliminary Investigation

I am going to obtain a number of preliminary results to find out the best concentration of Sodium Thiosulphate, Hydrochloric Acid and Water.

Firstly I performed several experiments to do with the concentration variable. Firstly I investigated how a change in the Sodium Thiosulphate would affect the time taken for the water to go cloudy. The method, which I used, was to firstly collect all the apparatus. This included; a beaker, paper marked with a cross, stopwatch, 50cm3 measuring cylinder, 10cm3 measuring cylinder, water, Sodium Thiosulphate and Hydrochloric Acid. I used 10cm3 of Hydrochloric Acid as a constant value, the value of Sodium Thiosulphate ranged from 10cm3 to 50cm3. The Sodium Thiosulphate was firstly added into the beaker, which was placed over the ‘X’ marked paper. When the Hydrochloric acid was added the stopwatch was started. Once the ‘X’ was no longer visible the stopwatch was stopped.

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This was followed out for all 5 different values. Once the results were collected the same procedure was followed out for each value, along with 10cm3 of water.

Results Table: idea.

Secondly a similar experiment was followed out testing the result of a varied hydrochloric acid value and keeping a constant value of 50cm3 of Sodium Thiosulphate. This reveals what difference it would make if you change the hydrochloric acid.

Results Table:

I am happy with these two tables as they provide adequate results. I will be using water in both of the experiments, as it seems to slow down the reaction ...

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This was followed out for all 5 different values. Once the results were collected the same procedure was followed out for each value, along with 10cm3 of water.

Results Table: idea.

Results Table:

I am happy with these two tables as they provide adequate results. I will be using water in both of the experiments, as it seems to slow down the reaction rates, which allows for more accurate results.

The third preliminary experiment I performed involved heat. In this investigation I tested how the effect of heat changes the reaction rate. I used 10cm3 Sodium Thiosulphate and 5m3 of Hydrochloric Acid. As the experiments reaction rate is so fast, 40cm3 of water was added along with the two chemicals to slow it down. The mixture of water and Sodium Thiosulphate is added to the beaker along with a thermometer. It is put on a tripod over the Bunsen burner. It is heated until it is reached the desired heat. It is quickly removed from the tripod and placed on the 'X’ marked paper. The Hydrochloric acid is added and the stopwatch is started. Once the cross is no longer visible the stopwatch was stopped. This was repeated for different heats until all the required results were obtained..

Results Table:

In these investigations to improve my results I could have continued to test more variables. Luckily from my results I have been able to decide which variables I am going to test in my final investigation. These experiments were not performed at their best and could easily have been contaminated. The measuring cylinders could have been swapped around and the volumes weren’t measured completely accurately.

From these preliminary investigations I have discovered:

· Water will slow down the experiment, as it dilutes it, allowing for more accurate results.

· Increasing the amount of Sodium Thiosulphate speeds up the reaction rate as the water goes cloudy much quicker.

· Increasing the Hydrochloric Acid slows down the reaction rate and it takes longer for the cross to disappear.

· All of the values of the individual chemicals for the above experiments provide good results and therefore will be used in the investigation.

From this preliminary investigation I have decided to use water in all of my experiments. I will keep a constant volume of 55cm3, which is made up of; 5cm3 HCl, and 50cm3 of water and Sodium Thiosulphate, which will vary in volumes between each other. I am going to perform 2 main experiments repeating the method varying the concentration of water and Sodium Thiosulphate, but keeping the concentration of Hydrochloric Acid constant.

Apparatus

· 2 * 100cm3 beaker

· 10cm3 small measuring cylinder

· 2 * 50cm3 large measuring cylinder

· Test-tube

· Stopwatch

· ‘X’ marked paper

· Thermometer

· Tripod

· Gauze

· Heat proof mat

· Bunsen Burner

· Tongs

· 3 * boiling tubes

· Boiler tube holder

· Water

· Hydrochloric Acid

· Sodium Thiosulphate

Plan

Method

· For the first experiment: The apparatus needed is collected, which is found in the apparatus list.10cm3 of Sodium Thiosulphate solution is measured using a large measuring cylinder, which is then put it into the conical flask. The second large measuring cylinder is used to measure out 40cm3 of water and is added to the beaker. The small measuring cylinder is used to measure out 5cm3 of hydrochloric acid into the test-tube. This will make the total volume of liquids up to 50cm3.

The ‘X’ marked paper is placed underneath the beaker. The Hydrochloric Acid is added and the stop clock is started. Thee time taken for the ‘X’ to disappear is recorded. The apparatus should be rinsed out well to be used again. The method is repeated for the varied concentrations of water and sodium thiosulphate solution, keeping the concentration of Hydrochloric Acid constant.

· For the second experiment:

The identical concentrations of water, Hydrochloric Acid and Sodium Thiosulphate as in the first experiment were used for the second. Each chemical is measured out in separate measuring cylinders and placed in separate boiling tubes. 80cm3 of water is measured out into the beaker. The beaker is placed over the gauze on top of the tripod, which is placed on a heatproof mat. The thermometer is placed inside the water bath. A stopwatch, ‘X’ marked paper, which is underneath a separate beaker are all ready to be used at this point. The three boiling tubes are placed in the water bath along with the thermometer. The Bunsen burner is lit with a constant blue flame underneath the water bath. Once the thermometer has reached the desired heat, it is recorded and the three boiling tubes are removed as quickly as possible to allow for the least amount of heat loss possible. The three chemicals are quickly poured into the separate beaker and the stopwatch is started. At this point the temperature is recorded for the second time. Once the ‘X’ is no longer visible the stopwatch is stopped and the time is recorded. An average of the two temperatures is made for accuracy. The apparatus is washed thoroughly. This method is repeated until all the required results are recorded for the varied concentrations.

The following diagrams may be used for a visual method:

Diagrams

Fair Test

To make sure the experiment is fair I will perform the following procedures:

· There was a constant volume in all of liquid in all of the experiments.

· Completely rinse all of my apparatus. I will do this so I remove all the particles from previous experiments allowing for the right concentration.

· I will make sure that all the chemicals are measured correctly for accurate results.

· I will not stir the chemicals at all, and try to move them around as little as possible, this is to prevent any unwanted collisions which may speed up the rate of reaction.

· I will make sure that the measuring cylinders are not mixed up for the Hydrochloric Acid and Sodium Thiosulphate.

· The same Bunsen burner and gas tap will be used to maintain continuity; a blue flame will also be used throughout the experiment.

All of these precautions will make my final results more reliable.

Safety

In my experiment I will try carry out everything as safely as possible. This will include:

· Cleaning up all spills- this must be done quickly and appropriately, or many accidents could occur.

· Not running- due to the heated liquids and glassware, you could easily fall and hurt yourself or others.

· Acids are corrosive- the chemicals should be handled carefully as they may cause harm.

· Wear goggles- goggles should be worn at all times, as heating chemicals is often dangerous due to the spitting of splashing of the liquids.

· Use tongs when carrying hot glassware- when dealing with hot substances tongs should always be used.

· A heatproof mat and a gauze should be used- this will avoid damage to the equipment.

· Wear an apron- this should be worn to protect skin and clothing.

Analysis

Results Table

The above results have been put into the following graphs to give a further understanding of the reaction rate.

Prediction

I predict that as the temperature is increased the rate of reaction will increase. I also predict that as the concentration of the sodium Thiosulphate increases the rate of reaction will increase.

These can be justified by relating to the collision theory (diagram found in the background knowledge).

When the temperature is increased the particles will have more energy and therefore move faster. They will collide more often and with more energy. Particles with more energy are more likely to overcome the activation energy barrier to a reaction and therefore react successfully.

If solutions of reacting particles are made more concentrated there are more particles per unit volume. Collisions between reacting particles are therefore more likely to occur. All this can be understood better with full understanding of the collision theory itself; for a reaction to happen particles have to collide with each other. Only particles with enough energy to overcome the energy barrier will react after colliding. So if the concentration of a solution is increased there are more reactant particles per unit volume. This increases the chance of reactant particles colliding with each other and therefore increases the reaction rate.

With these predictions I have a fair idea of how my graphs will eventually look. Both graphs drawn up in my analysis will have positive correlation. The experiment involving temperature will have a faster reaction rate due to its high-energy particles.

Further Analysis

From my graphs and results it is possible to see that my prediction was correct. The experiment involving temperature had a faster reaction rate than the experiment involving concentration.

From the graph and the results you are able to see that the higher the concentration of Sodium Thiosulphate, the faster the reaction rate. The water is therefore only dilutes the solution thus making the rate slower. Due to the increased amount of concentration, the numbers of particles also increase and therefore the particles are closer together. They have a greater possibility of colliding, therefore a faster reaction rate. On the graph revealing the rate of reaction, you can see how close the concentration and rate are that it provides a reasonable accurate line of best fit. These are very constant results.

From the graph revealing how temperature affects the time taken for the reaction to finish, it is obvious to see that temperature makes a difference. The higher the temperature is, the faster the rate of reaction occurs. A good example to prove this theory is; food can be kept longer in a refrigerator before going off due to the cold temperature as the reaction has been slowed down. This can also be proved by the collision theory that when the temperature is higher, the particles move faster therefore there are more collisions. The collisions are also more energetic, and this energy is higher than the activation energy so the reaction is faster. The experiment was also an exothermic reaction, due to the fact that heat was given out, thus the experiment has a fast reaction rate. Most of the reaction takes place in the first 100 seconds, leaving the second half of the experiment with a very slow reaction. From the graph revealing the reaction rates, show that this reaction rate is faster than the experiment using the concentration variable.

These results and graphs both prove my predictions.

Evaluation

I thought the experiment was a success. The results proved my predictions as well as the theories I have used to back up my investigation.

The graphs reveal that my results were not completely accurate as they weren’t completely constant. This could have easily been caused by the fair test list not being followed identically. It is most likely caused by the experiments not being timed properly. The results should have been repeated a few times and an average taken to make sure of their accuracy.

The second experiment was found to be the most complicated due to the three separate boiling tubes and the need for speed. From the graphs it reveals that these are the most varied results. An average temperature was taken for accuracy, although the entire experiment should have been repeated for a second time to have acquired a set of 2 results.

I am happy with the variety of results given within the time limit and feel they are adequate for the graphs to be drawn up well.

If I could I would have spent more time getting my temperature closer to the designated temperature.

The thermometer reading was not completely accurate as it was not digital. A water bath could have been used to programme the liquids to the desired temperature. These inaccuracies could be the cause for many of the failed results.

The equipment was rinsed with tap water, which contains many impurities, which may have contaminated the liquids. Distilled water should have been used as it is pure and has no impurities.

To make this investigation completely flawless, the fair test would have to be followed very carefully. Higher tech equipment should be used for more accurate results as well as one person performing the experiment to understand the experiment completely.

Although there are these inaccuracies the overall results proved to be adequate.

To further my investigation on rates of reaction I could have performed experiments with different variables. I could investigate the two variables; using a catalyst and surface area. Although these two variables are predicted to be more complicated due to their individual characteristics other chemicals and methods could be used. Performing more investigations will provide a wider understanding for the theme, rates of reaction.