Investigate the Rate of Reaction of Sodium Thiosulphate and Hydrochloric Acid

Investigate the Rate of Reaction of Sodium Thiosulphate and Hydrochloric Acid


Sodium thiosulphate reacts with Hydrochloric acid reacts to form a yellow precipitate of sulphur. The equation is:

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

The time taken for the same amount of yellow precipitate to be produced provides a method of measuring the rate of reaction at different concentrations

It is simple to investigate the impact of concentration on the rate of reaction in the reaction between sodium thiosulphate and hydrochloric acid. Sodium thiosulphate is a white crystal, and hydrochloric acid is colourless. Sulfur, water, sodium chloride salt, and sulphur dioxide gas are the products of their reaction. Sulfur is a solid that has a bright yellow colour. The development of this product signifies the end of the reaction. As the goods are being created, this can be seen by the colour shift and disappearance of the red mark. In order to lower the concentration and study the reaction at various reactant concentrations, water is added to sodium thiosulfate.

Aim: to investigate the rate of reaction of sodium thiosulphate and hydrochloric acid.

The experiment uses a reaction between sodium thiosulphate and hydrochloric acid to examine how concentration affects reaction pace.

Prediction: (what you expect you will find out from the experiment) (what you think you will find out from the experiment)

When both concentrations are high, the reaction will proceed quickly and end in the shortest amount of time possible. As the hydrochloric acid is titrated into the reaction, more water reduces the concentration of sodium thiosulphate in comparison to a constant concentration, lengthening the time until the reaction is complete.

1. Put on reading glasses to keep chemical splashes out of your eyes. When dangerous hydrochloric acid pours into the eyes, it can irritate or harm the eyes.

Put on a gas mask.

to avoid breathing in the gaseous sulphur dioxide. The reaction produces sulphur dioxide gas, a colourless gas with a potent, suffocating odor, as one of its byproducts. When inhaled, it is toxic, especially for people with asthma. It quickly disintegrates in water to produce sulfuric acid. Therefore, it’s important to avoid breathing in the gas.

3. Put on a lab coat, a protective suit, and closed-toed shoes to shield your legs. Long hair should be tied up securely and likely be covered by a cap. This will stop the chemicals from coming into contact with your skin. When they come into contact with your skin, the chemicals utilised can be harmful and coercive and result in burns.

4. After the experiment, properly dispose of the substances. and clean any used glassware or equipment. to reduce the potential dangers of the chemicals. Incorrect disposal of the chemicals can also result in their improper use.

If split carelessly, corrosive HCL can react with work surfaces and other points of contact.

Materials and Method:

Variables: (independent, dependent, and controlled)

The concentration of the reactant affects how long it takes for the reaction to complete. Since the time it takes for a reaction to end reduces as concentration rises, time is indirectly proportional to concentration. Reactant concentration can be regulated. The concentration of hydrochloric acid is constant, but when distilled water is added to the conical flask together with sodium thiosulfate, it can be controlled to be reduced. The burette is employed because it is accurate in measuring the addition of sodium thiosulfate and distilled water amounts. A conical flask’s transparency and glass construction make it simple to see how the reaction is progressing. Since it is made of glass, the chemicals that react with it cannot easily corrode it. The white tile makes observation easier as the reaction becomes obscure enough to obscure the making. The reaction comes to an end at this point. The reaction’s duration is determined by the stopwatch.

Processing results

Draw a graph showing the sodium thiosulphate solution concentration versus time.

After linking the point of best fit, the graph takes the shape of a straight line. The graph shows that as concentration levels rise, the 1/ time it takes for the red mark to vanish also rises proportionally. As concentration rises, reaction rate accelerates and reaction time shortens; conversely, as concentration falls, reaction rate slows and reaction time lengthens. The solution turns yellow when equilibrium is reached.


Include responses to the following query along with coverage of the mark scheme’s stated subjects.

Why did water become introduced to the sodium thiosulfate in the conical flask before the hydrochloric acid was injected during the reaction?

A universal solvent is water. It aids in forming the solution by aiding in the dissolution of the sodium thiosulphate, which facilitates the reaction. Additionally, distilled water plays a part in modifying the solution’s concentration to the desired molar concentration so that it can be included in the final solution.

Values that don’t match the rest of the data are anomalies. This is because the reactant was measured precisely. There could be measurement errors that cause the reactants to be added or removed. This alters the rate of the response, which corrupts the final results and causes anomalies. In addition to concentration, there may be other factors that influence the reaction’s rate. These include natural elements like temperature, which has an impact on the reaction’s rate and causes anomalies. Other impurities may also contaminate the device. 

Since the experiment produces reasonably accurate data to look into the experiment’s purpose, it can be trusted.

Since the rate of reaction is dependent on one concentration component, specifically the concentration of sodium thiosulphate, the reaction can be a first-order reaction. Acid hydrochloric in concentration is constant. The concentration of the material being reacted with determines the rate of reaction in a direct proportion.


Despite a few oddities, the practical was flawless and accurate enough for us to observe and research the impact of concentration on reaction pace. The practical was successful since it contributed to the kinetic analysis of concentration and its impact on the reaction’s pace. There are other factors, such as temperature, that affect the rate of the reaction in a recommendation to a feature practical. To prevent tampering with the observation, the experiment can be conducted under temperature-controlled conditions. The factor can also be taken into account when studying and practising how heat will affect the reaction’s behavior.


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