9 (a) Calcium carbonate reacts with dilute hydrochloric acid to produce carbon dioxide gas - Edexcel - GCSE Chemistry - Question 9 - 2020 - Paper 1

To calculate the average rate of reaction, we can use the formula:

$ext{rate} = \frac{\text{volume of gas produced}}{\text{time taken}}$

We know that 90 cm³ of carbon dioxide was produced in 5 minutes. First, we convert 5 minutes to seconds:

$5 \text{ minutes} = 5 \times 60 = 300 \text{ seconds}$

Now applying the values into the rate formula:

$\text{rate} = \frac{90 \text{ cm}^3}{300 \text{ s}} = 0.3 \text{ cm}^3s^{-1}$

When the temperature increases, the particles gain more energy. This results in:

1. Higher Energy: Particles have more kinetic energy which causes them to move faster.
2. More Frequent Collisions: The increased speed leads to more collisions between the acid and calcium carbonate particles.
3. Successful Collisions: A higher proportion of these collisions have enough energy to overcome the activation energy barrier, increasing the overall rate of reaction.

To test the student's prediction about the effect of increasing the concentration of hydrochloric acid on the rate of reaction with zinc, follow this plan:

1. Apparatus Required:

   • Balance
   • Measuring cylinder or pipette
   • Suitable reaction vessel (e.g., conical flask)
   • Stopwatch or timer
   • Delivery tube
   • Inverted measuring cylinder or gas syringe
   • Thermometer

2. Method:

   • Measure equal masses of zinc using the balance.
   • Prepare two bottles of dilute hydrochloric acid, one being double the concentration of the other.
   • Pour equal volumes of acid into two reaction vessels.
   • Record the initial temperature of the acid.
   • Add a piece of zinc to one of the vessels immediately after measuring the acid.
   • Start the timer when zinc is added, and place the delivery tube in the inverted measuring cylinder or gas syringe to collect the gas produced.
   • Measure the volume of hydrogen gas produced at intervals until the reaction ceases.
   • Record the final temperatures after the reaction has completed.
   • Repeat the procedure for the second concentration of hydrochloric acid maintaining other factors constant.
   • Analyze the gas volumes produced to compare the rates of reaction.