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Rate of Reaction · Acid & Metal IGCSE Experiment · Concentration
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IGCSE Experiment: Rate of Reaction (Acid and Metal)
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Conical Flask
Please select an acid concentration above to begin.

Theory & Details

Reaction Equation:

Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g)

Objective: Investigate how changing the concentration of acid affects the rate of chemical reaction.

Method: Add 30 cm³ of hydrochloric acid to the flask, drop in the magnesium ribbon, and time how long it takes for the solid to completely dissolve.

ExpAcidConc (M)Time (s)

Part B: Graph: Concentration vs Time

Part C: Interpolation

Use your graph to estimate the reaction time at a concentration of 1.3 mol dm⁻³.

Solution: The estimated time should be approximately 34 seconds. (Acceptable range usually between 30s to 38s depending on your specific curve of best fit).

Part D: Rate of Reaction Calculations

Calculate the average rate of reaction for Acid A using the formula: Rate = 5 cm ÷ time

Based on your results, which acid produced the slowest rate of reaction?

Solution:
1. Rate for Acid A = 5 ÷ (Time recorded for Acid A). Make sure to include units (cm/s or cm s⁻¹).
2. The slowest rate of reaction is produced by Acid E (0.5 M) because the lower concentration means fewer collisions per second, hence taking the longest time to dissolve the ribbon.

Part E: Experimental Evaluation

Explain why it is a good experimental practice to repeat the experiment for each concentration.

Solution: Repeating an experiment is crucial because it allows you to spot any anomalous (random error) results. You can then calculate a mean average (excluding anomalies), making your final data and conclusion much more reliable.

Part F: Temperature Control Investigation

Initial Temp (°C)Final Temp (°C)Change (ΔT)

Why is it important to keep the temperature constant when investigating the effect of concentration? Suggest a method to do this.

Solution: Temperature also affects the rate of reaction. If temperature is not controlled, it will not be a fair test, and you cannot be certain if a change in rate was caused by the concentration or the temperature change. You can control temperature by placing the reaction flask in a thermostatically controlled water bath.

Teacher Dashboard & Overview

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Developed by mrchemcoach / ajay shekhawat. All rights are reserved.

What this experiment shows

The rate of a reaction is how fast reactants are used up or products are made. Four things change it: concentration, temperature, surface area and a catalyst. Collision theory ties them together - a reaction only happens when particles collide with at least the activation energy and in the right orientation, so anything that raises the number of successful collisions per second raises the rate.

Na2S2O3 + 2HCl → 2NaCl + S + SO2 + H2O

What you need

  • Sodium thiosulfate solution and dilute hydrochloric acid
  • A conical flask and a printed cross on paper
  • A stopclock, measuring cylinders and a thermometer
  • A water bath, if temperature is the variable

How it is done

  1. Measure the thiosulfate into the flask and stand it on the cross.
  2. Add the acid, start the clock at the moment of mixing and swirl once.
  3. Look down through the flask and stop the clock when the cross disappears.
  4. Repeat with a different concentration, changing nothing else.
  5. Plot 1/time against concentration: 1/time is a measure of the rate.

What you should see

  • The mixture turns cloudy as solid sulfur forms.
  • A higher concentration makes the cross vanish sooner.
  • A 10 °C rise roughly doubles the rate for many reactions.
  • A graph of 1/time against concentration is close to a straight line through the origin.

Where marks are lost

  • Plotting time instead of 1/time. Time is not the rate - a longer time means a slower reaction.
  • Changing two things at once, so you cannot say which one caused the change.
  • Looking at the flask from the side. Always look down through the same depth of liquid.
  • Saying temperature works "because particles move faster". Say that more collisions have at least the activation energy.

Questions students ask

Why does concentration change the rate?
A more concentrated solution has more particles in the same volume, so collisions happen more often and more of them succeed each second.
Why 1/time?
The reaction always runs to the same end point - the same amount of sulfur hides the cross. A shorter time therefore means a faster rate, and 1/time is proportional to it.
Does a catalyst get used up?
No. It provides a different route with a lower activation energy and is chemically unchanged at the end, so a small amount works over and over.

Try these next

Written for Cambridge IGCSE Chemistry 0620 and CBSE Class 9-12 by Ajay Shekhawat, founder of MrChemCoach. Run the simulator above, then check yourself against the questions.