Question

In an experiment, hydrochloric acid reacted with different volumes of sodium thiosulfate in water. A yellow precipitate was formed during the reaction. A cross drawn at the base of each flask became gradually invisible due the formation of this yellow precipitate. The time taken for the cross to become invisible was recorded. A partial record of the experiment is shown.
Experimental Record
Flask Volume of
HCl Volume of
Sodium Thiosulfate Volume of
Water Time
1 10 mL 10 mL 40 mL 14 seconds
2 10 mL 20 mL 30 mL
3 10 mL 30 mL 20 mL
4 10 mL 40 mL 10 mL
Based on your knowledge of factors that affect the rates of chemical reactions, predict the trend in the last column of the experimental record. Use complete sentences to explain the trend you predicted. You do not have to determine exact values for time; just describe the trend you would expect (increase or decrease) and why it occurs. The last trend in the last column should be?

Answer 1

Answer:

The time decreases steadily

Explanation:

We know that the rate of chemical reaction is defined as how fast or slow a chemical reaction proceeds. Hence a chemical reaction is said to proceed at a faster rate if it takes a lesser time for the reaction to get to completion.

There are certain factors that affects the rate of reaction, prominent among them is the concentration of reactants. Concentration simply means the amount of substance in a system.

Taking a look at the table given in the question, we will realize that the volume of HCl remained constant, the volume of thiosulphate increased steadily while the volume of water decreased steadily. Remember that concentration increases when less water is added to the system. This implies that the reactant concentration increases steadily. Hence, according to the collision theory, particles collide more frequently and the rate of reaction increases.

As the rate of reaction increases, it now takes a lesser time for the reaction to get to completion (indicated by the disappearance of the cross). Hence as we move down the table, it takes lesser and lesser time for the cross to disappear. This means that the column for time will decrease steadily.