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# Effect of Concentration on Rate of Reaction

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Last updated date: 17th Sep 2024
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## Introduction

In a reaction, many elements or compounds react together to form one or more new products based on the basic elements of the compounds involved in the chemical reaction. The reaction may occur between solids, liquids, and gases, and the rate of each reaction is different from another which depends on a number of factors. Some chemical compounds called catalysts or enzymes help in accelerating the rate of reaction. This rate of reaction is also dependent on the amount or concentration of substances involved in the reaction.

In this article, the effect of concentration on the rate of the reaction between sodium thiosulphate and hydrochloric acid has been discussed in the form of an experiment.

### About the Rate of Reaction

In any chemical reaction, several reactants react to form one or more new products. These reactants can be gases, solids or even liquids. The rate of reaction depends on many determinants or factors. The presence of catalysts can also accelerate the speed of any reaction. One of the essential components that determine the rate of reaction is the concentration of the reactants taking part in the chemical reaction. In this article, we are going to study the effect of concentration on reaction rate by observing a chemical reaction. The results obtained from the reaction between Na2S2O3 and HCl helps you to understand the topic more clearly.

### Aim

To understand the effect of concentration on the rate of reaction between sodium thiosulphate (Na2S2O3) and hydrochloric acid (HCl).

### Theory

The rate of the reaction directly depends on the products of the molar concentration of reactants. In this experiment, we will study the reaction between Sodium thiosulphate (Na2S2O3) with hydrochloric acid (HCl).

Na2S2O3 (aq) + 2HCL (aq) → H2O (l) + SO2 (g)+ 2 NaCl (aq) + S (s)

We can also write the above reaction in ionic form as:

S2O3-2 (aq) + 2H+ (aq) → H2O (l) + S (s) + SO2 (g)

The solution obtained after the reaction is opaque and has a milky appearance due to the presence of sulphur. If we increase the temperature or concentration of the reactants, then the rate of precipitation of sulphur also increases. It happens because when concentration increases, molecular collisions also increase per unit time, which results in a fast rate of product formation.

The reaction is between the aqueous solutions of Na2S2O3 and HCl, the rate of which directly depends on the product of the molar concentration of each component of the reaction.

The chemical reaction formula between HCl and Na2S2O3 is as follows:

Na2S2O3 (aq) + 2HCL (aq) → H2O (l) + SO2 (g)+ 2 NaCl (aq) + S (s)

Here, we can see the products of the reaction are water, sulphur dioxide (SO2 ), sodium chloride (NaCl) and a sulphur atom. Where SO2  is formed in the gaseous state, NaCl is formed in the aqueous state and sulphur collects in the solid-state.

With the increase in the temperature of the system, the precipitation of sulphur increases. With the increase in concentration, a collision between molecules also increases which increases the chances of getting the products of the reaction, and an increase in temperature provides more kinetic energy to the reaction which in turn increases the rate of reaction, thereby, resulting in faster production of products.

### Materials Required

The materials and apparatus required for conducting the reaction are as follows:

• Five flasks of 100ml each

•  Two burettes of volume 50 ml each

• Pipette

• Burette stand

• Stopwatch

• Sodium thiosulphate

• 1M Hydrochloric acid

• Five conical flasks (100 ml)

• Two burettes

• Burette Stand

• Pipette

• Stopwatch

• Sodium Thiosulphate

• 1M Hydrochloric Acid Solution

### Procedure

1. First of all, take five conical flasks and rinse them with water to clean any residue. Now, label them as 1, 2, 3, 4 and 5 respectively.

2. Draw the cross mark on any white tile.

3. Take a burette and add 10 ml of Na2S2O3 solution in flask 1 using it. Similarly, add 20 ml of Na2S2O3 solution in flask 2, 30 ml in flask 3, 40 ml in flask 4 and 50 ml solution in flask 5.

4. Now, add distilled water in every flask such that the combined volume of water and Na2S2O3 solution becomes 50 ml. It means we need to add 40ml, 30ml, 20 ml and 10 ml distilled water in flasks 1, 2, 3 and 4 respectively.

5. Take 10 ml of 1M HCl solution in a test tube using the burette. Add it in flask 1, which contains 40 ml water and 10 ml Na2S2O3. Shake it thoroughly and then start the stopwatch immediately.

6. Place the flask on the white tile having a cross mark. Observe the cross mark from the top and stop the stopwatch as the cross mark becomes invisible. Note the time taken for the whole process.

7. Repeat the same procedure with flask 2, 3, 4 and 5. Note the time when the cross mark becomes invisible in every container.

9. Add 40ml of distilled water in the first flask, 30ml in the second, 20ml in the third, 10ml in the fourth and none in the fifth flask.

10. 10ml HCl is to be added to the first flask with the help of a burette and the stopwatch should be started immediately.

11. Take a white tile and put a cross mark on it distinctly. Put the first flask on the time and observe.

12. Observe till the solution is milky and the mark on the tile is visible and note the time right there.

### Observations and Results

 Flask Number The volume of Sodium Thiosulphate present in the flask The volume of Distilled water present in the flask The volume of HCl added in the solution Time 1 10 ml 40 ml 10 ml ……….s 2 20 ml 30 ml 10 ml ……….s 3 30 ml 20 ml 10 ml ……….s 4 40 ml 10 ml 10 ml ……….s 5 50 ml 0 ml 10 ml ……….s

The above image shows the graph between 1/t (on the y-axis) and the concentration of Na2S2O3 (on the x-axis). We will obtain a straight sloping line, as shown in the figure.

From the above graph, it is clear that 1/t is directly proportional to the concentration of Na2S2O3 solution taken during the experiment. We know that 1/t is the direct measure of the rate of reaction. Hence, the pace of chemical reaction in this case directly depends on the concentration of Na2S2O3. However, it doesn't mean that the speed of any chemical reaction doesn't depend on conc. of HCl. We will see a similar result if we keep the concentration of sodium thiosulphate constant and raise the concentration of hydrochloric acid. This experiment clearly shows the effect of concentration on Rate of Reaction.

The product formed from the reaction is milky in appearance due to the presence of sulphur. Increasing the temperature increases the rate of precipitation.

Noting the time and plotting a graph with 1/t on the y-axis and the concentration of Na2S2O3  on the x-axis where t is the time taken to form products at different concentrations. It was observed that the graph shows a straight sloping line which means that 1/t is directly proportional to the concentration of Na2S2O3 which means increasing the concentration increased the rate of reaction as well.

If the concentration of sodium thiosulphate was kept constant and the concentration of hydrochloric acid was increased, the same trend would be observed.

## FAQs on Effect of Concentration on Rate of Reaction

1. What are the determining factors which affect the rate of reaction?

From the above experiment conducted, it is observed that the concentration of reactants has a direct effect on the rate of reaction. Other factors include temperature conditions given to the reaction, state of existence of the reactants, presence of catalysts and changes in the surface area affecting the rate of reaction.

To know more about the theory, materials required, observation, results, and conclusion of the experiment on the effect of concentration on the rate of reaction between sodium thiosulphate and hydrochloric acid, visit Vedantu's website or download the app. Vedantu gives you solutions to your queries as well as free resources to study from which you can download in PDF format and access anytime, anywhere!

3. What was the result of the reaction?

The result of the reaction can be summed up as follows:

Na2S2O3 (aq) + 2HCL (aq) → H2O (l) + SO2 (g)+ 2 NaCl (aq) + S (s)

It was observed that in a reaction, with an increase in the concentration of sodium thiosulphate gradually while keeping the concentration of hydrochloric acid constant, the rate of reaction has increased slowly. If “t” is the amount of time taken for the products to form then 1/t is directly proportional to the concentration of sodium thiosulphate.

The same result will be obtained if the concentration of hydrochloric acid was increased gradually while the concentration of sodium thiosulphate was kept constant.

4. What are the precautions to be taken during the experiment to study the effect of concentration on reaction rate?

First of all, one must ensure that the apparatus must be thoroughly clean before starting the process. Any impurities can lead to inaccuracy during the experiment. Moreover, it is essential to measure the volumes of the distilled water, sodium thiosulphate and hydrochloric acid accurately. You must use the same tile with the same cross mark for all the observations. The temperature variation can also affect the rate of reaction. Hence, it is essential to complete to prevent any temperature variation. Start the stopwatch immediately as you add the HCl in the solution. Finally, view the cross mark on the tile from the top from the same height during the observations.

5. What are the determinants that can affect the rate of reaction?

There is a direct effect of concentration on Rate of Reaction, as shown in the above experiment. The physical state of the reactants' surface area can also affect the pace of any reaction. For instance, if any metal reacts with gas, then only the molecules present at the surface of the metal can react with gas molecules. Hence, we can increase the surface area of reactants by cutting them in pieces to increase its rate of reaction. An increase in temperature can also enhance the rate of reaction because it will boost the kinetic energy of reactant particles. A presence of a catalyst can also accelerate the chemical reaction.