Variables:
Independent
- The concentrations of hydrochloric acid.
- Volume of water
- Volume of Hydrochloric acid
Dependent
- Time taken for the cross to disappear.
- Colour change of the sodium Thiosulphate and hydrochloric acid.
- Change in temperature after the reaction is over.
Constant
- Volume of hydrochloric acid used.
- Volume of sodium Thiosulphate used.
- Concentration of sodium Thiosulphate
- Surroundings
- Room temperature
Molar calculations to calculate the concentration of HCl after diluting it with water:
The molar value of HCl in a solution can be calculated for each dilution. This is given by the formula:
Volume of HCl X RMM
Total volume of HCl
RMM
RMM of hydrochloric acid is 36.5.
Fair testing:
- Make sure that the concentration and volume of the independent variable is always kept constant for each trial.
- Take all readings at eye- level to get the most accurate measurements.
- Make sure that the temperature in the lab is kept constant. It should be maintained throughout the experiment.
- Take more than 1 trial with each concentration so that an accurate average reading can be taken
- If there are anomalies in the results, repeat the experiment again for the anomalous reading.
- Start the stopwatch as soon as you pour the hydrochloric acid into the sodium thiosulphate. Stop the watch as soon as the cross on the paper disappears completely.
Safety hazards and precautions:
- Hydrochloric acid and sodium thiosulphate are corrosive in nature. Make sure that you wash your hands immediately if you come in contact with the two chemicals.
- All chemicals cause irritation in the eye if they come in contact with it. To prevent any eye injury, make sure that you wear safety goggles to protect your eye.
DATA COLLECTION AND RESULTS
ANALYSIS AND CONCLUSION:
From the graph we can clearly see that as the concentration of sodium Thiosulphate increases the rate of reaction takes place faster as more collisions take place. The time taken for the reaction decreases due to the concentration increasing and also collision rate increasing..
Considering, the table results and the graph we can say that as the concentration of hydrochloric acid increases the time taken for the cross to disappear will decrease. The reaction is more exothermic, which means gives off more heat if the concentration of hydrochloric acid increases.
This is because of the simple concept of the collision theory, which says as the concentration increases there is lesser space created and more molecules produced. So therefore there will be more collisions taking place, therefore the reactants have a greater chance of reacting.
There could be minimal errors on the experiment as the concentrations could possibly not be accurate.
But to conclude we can say that as the concentration increases, time taken for the reaction to finish will be lesser.
Sources of errors:
- The readings may not have been completely accurate because they could not be taken exactly at the eye level.
- The apparatus was not totally dry when we started using it causing an unexpected dilution to occur.
- There may be a little inaccuracy in the graph readings since the smooth curves are drawn by hand.
- When the HCl is poured into the conical flask, the stopwatch is started only after a minor delay. It is also stopped after a small time interval when we see that the cross has disappeared completely.
- The apparatus might not be in the best use.
Improvements:
- It should be made sure that the apparatus is in best use.
- No parallax errors should occur and all readings should be taken accurately.
- The stopwatch should be started accurately and therefore anomalies would be avoided.
