Chemistry · Simulation and virtual lab Free
Rate of reaction: magnesium and acid
Drop magnesium into hydrochloric acid, collect the hydrogen and compare how fast the reaction goes when you change one factor at a time.
- You will learn to
- Measure the volume of hydrogen against time with a gas syringe.
- Change one factor at a time: concentration, temperature, surface area.
- Explain the results with the collision theory.
- You will measure
- Volume of hydrogen (cm³) against time (s); initial rate in cm³/s.
- Time needed
- About 30–40 min
- Equipment
- Nothing extra. Real version: magnesium, dilute HCl, conical flask, bung and delivery tube, gas syringe, clamp stand, thermometer, stopwatch.
- Price
- Free: no payment, no account.
Virtual lab
Follow the steps with the simulation above (go back to the simulation ↑). Each time you tap Record, a row is added to the table and a point to the graph.
Aim
To find how concentration, temperature and surface area affect the rate of the reaction Mg + 2HCl → MgCl₂ + H₂.
What to do
- Look at the apparatus: 50 cm³ of acid in a conical flask, a bung with a delivery tube to a gas syringe, a thermometer and a stopwatch. Keep 1.0 mol/dm³ acid, 25 °C and a magnesium ribbon. Tap Drop the magnesium in. When the plunger stops, tap Keep this run.
- Change only the concentration to 2.0 mol/dm³ and run again. Then 0.5 mol/dm³. (Use “× 5 faster” if you wish.)
- Go back to 1.0 mol/dm³ and change only the temperature: 15, 35 and 45 °C.
- Go back to 25 °C and use small pieces, then powder.
- Compare the slopes at the start of the graphs and the times to finish. Fill in the conclusions in the questions.
- Watch the close-up: count how many collisions are successful (yellow) when the temperature is high.
Results
Questions
Why do all the curves end at the same volume of hydrogen?
The same mass of magnesium (0.05 g) is used and the acid is in excess, so the same amount of hydrogen forms: about 49 cm³ (0.05 ÷ 24.3 × 24 000 cm³).
Why is the graph steepest at the start?
At the start the concentration of acid and the amount of magnesium are greatest, so there are most collisions per second. As they are used up, the rate falls until the reaction stops.
Explain, using collisions, why a higher concentration gives a faster rate.
There are more acid particles in the same volume, so they collide with the magnesium more often: more successful collisions per second.
Explain why a rise in temperature of about 10 °C nearly doubles the rate.
Particles move faster and collide more often, and many more collisions have energy equal to or greater than the activation energy, so the fraction of successful collisions increases a lot.
Why does powder react faster than ribbon?
Powder has a much larger surface area, so more magnesium atoms are exposed to collisions with the acid at the same time.
Using your results, what is the order of reaction with respect to the acid?
Doubling the concentration doubles the initial rate, so the reaction is first order with respect to hydrochloric acid (in this model).
For teachers: expected results and how the model works
The model uses rate = k[HCl]·S·(1 − V/Vmax)^(2/3), with k following the Arrhenius equation (Ea = 45 kJ/mol), so +10 °C multiplies the rate by about 1.8. Ribbon, 1.0 mol/dm³, 25 °C gives about 0.8 cm³/s at the start and finishes in about 2.5 minutes. The particle close-up is a picture of the collision theory, not a measurement.
Exam practice Exam set
National-exam style questions on this simulation (16 marks). Try each one on paper first, then open the marking scheme.
Magnesium ribbon reacts with excess dilute hydrochloric acid. (a) Write the equation. (b) Describe how to measure the rate using a gas syringe. (c) Sketch the graph of volume against time and explain its shape. (7 marks)
Marking scheme: (a) Mg + 2HCl → MgCl₂ + H₂ (1). (b) Connect the flask to a gas syringe; add the magnesium, close quickly and start the stopwatch (1); read the volume every 10 s (1). (c) Curve rising steeply at first, then less steeply, then level (1); fastest at the start when the concentration is highest (1); slows as the reactants are used up (1); stops (horizontal) when the magnesium is used up (1).
Use the collision theory to explain why increasing the temperature increases the rate of reaction. (3 marks)
Marking scheme: Particles move faster, so they collide more often (1); more of the collisions have energy equal to or greater than the activation energy (1); so there are more successful collisions per second (1).
Why does powdered magnesium react faster than a ribbon of the same mass? (2 marks)
Marking scheme: The powder has a larger surface area (1), so more particles are exposed and there are more collisions per second with acid particles (1).
In an experiment 60 cm³ of hydrogen were collected in the first 20 s. Calculate the average rate in this time, and state the unit. (2 marks)
Marking scheme: Rate = 60 ÷ 20 = 3.0 (1) cm³/s (1).
Explain why the total volume of hydrogen does not change when only the temperature of the acid is increased. (2 marks)
Marking scheme: The amount (moles) of magnesium (the limiting reactant) is the same (1), so the same amount of hydrogen is produced; it is only produced faster (1).
Donat Sciences and MathsChemistry · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Rate of reaction: magnesium and acid
Aim: To find how concentration, temperature and surface area affect the rate of the reaction Mg + 2HCl → MgCl₂ + H₂.
Apparatus (real laboratory): magnesium, dilute HCl, conical flask, bung and delivery tube, gas syringe, clamp stand, thermometer, stopwatch.
What to do (with the simulation on www.donatstem.co.rw)
- Look at the apparatus: 50 cm³ of acid in a conical flask, a bung with a delivery tube to a gas syringe, a thermometer and a stopwatch. Keep 1.0 mol/dm³ acid, 25 °C and a magnesium ribbon. Tap Drop the magnesium in. When the plunger stops, tap Keep this run.
- Change only the concentration to 2.0 mol/dm³ and run again. Then 0.5 mol/dm³. (Use “× 5 faster” if you wish.)
- Go back to 1.0 mol/dm³ and change only the temperature: 15, 35 and 45 °C.
- Go back to 25 °C and use small pieces, then powder.
- Compare the slopes at the start of the graphs and the times to finish. Fill in the conclusions in the questions.
- Watch the close-up: count how many collisions are successful (yellow) when the temperature is high.
Results
| # | HCl (mol/dm³) | T (°C) | Magnesium | Rate in first 10 s (cm³/s) | Time to finish (s) | Total gas (cm³) |
|---|
| 1 | | | | | | |
| 2 | | | | | | |
| 3 | | | | | | |
| 4 | | | | | | |
| 5 | | | | | | |
| 6 | | | | | | |
| 7 | | | | | | |
| 8 | | | | | | |
Graph
Plot the volume of hydrogen (cm³) against time (s) for two conditions on the same axes. Draw a tangent at t = 0 to compare the initial rates.
Questions
- Why do all the curves end at the same volume of hydrogen? [2]
- Why is the graph steepest at the start? [2]
- Explain, using collisions, why a higher concentration gives a faster rate. [2]
- Explain why a rise in temperature of about 10 °C nearly doubles the rate. [2]
- Why does powder react faster than ribbon? [2]
- Using your results, what is the order of reaction with respect to the acid? [2]
- Magnesium ribbon reacts with excess dilute hydrochloric acid. (a) Write the equation. (b) Describe how to measure the rate using a gas syringe. (c) Sketch the graph of volume against time and explain its shape. [7]
- Use the collision theory to explain why increasing the temperature increases the rate of reaction. [3]
- Why does powdered magnesium react faster than a ribbon of the same mass? [2]
- In an experiment 60 cm³ of hydrogen were collected in the first 20 s. Calculate the average rate in this time, and state the unit. [2]
- Explain why the total volume of hydrogen does not change when only the temperature of the acid is increased. [2]
Donat Sciences and MathsChemistry · Virtual lab worksheet
School: ........................................ Name: ................................ Class: ........ Date: ............
Marking scheme: Rate of reaction: magnesium and acid
Expected results
The model uses rate = k[HCl]·S·(1 − V/Vmax)^(2/3), with k following the Arrhenius equation (Ea = 45 kJ/mol), so +10 °C multiplies the rate by about 1.8. Ribbon, 1.0 mol/dm³, 25 °C gives about 0.8 cm³/s at the start and finishes in about 2.5 minutes. The particle close-up is a picture of the collision theory, not a measurement.
Answers
- Why do all the curves end at the same volume of hydrogen? [2]
The same mass of magnesium (0.05 g) is used and the acid is in excess, so the same amount of hydrogen forms: about 49 cm³ (0.05 ÷ 24.3 × 24 000 cm³).
- Why is the graph steepest at the start? [2]
At the start the concentration of acid and the amount of magnesium are greatest, so there are most collisions per second. As they are used up, the rate falls until the reaction stops.
- Explain, using collisions, why a higher concentration gives a faster rate. [2]
There are more acid particles in the same volume, so they collide with the magnesium more often: more successful collisions per second.
- Explain why a rise in temperature of about 10 °C nearly doubles the rate. [2]
Particles move faster and collide more often, and many more collisions have energy equal to or greater than the activation energy, so the fraction of successful collisions increases a lot.
- Why does powder react faster than ribbon? [2]
Powder has a much larger surface area, so more magnesium atoms are exposed to collisions with the acid at the same time.
- Using your results, what is the order of reaction with respect to the acid? [2]
Doubling the concentration doubles the initial rate, so the reaction is first order with respect to hydrochloric acid (in this model).
- Magnesium ribbon reacts with excess dilute hydrochloric acid. (a) Write the equation. (b) Describe how to measure the rate using a gas syringe. (c) Sketch the graph of volume against time and explain its shape. [7]
(a) Mg + 2HCl → MgCl₂ + H₂ (1). (b) Connect the flask to a gas syringe; add the magnesium, close quickly and start the stopwatch (1); read the volume every 10 s (1). (c) Curve rising steeply at first, then less steeply, then level (1); fastest at the start when the concentration is highest (1); slows as the reactants are used up (1); stops (horizontal) when the magnesium is used up (1).
- Use the collision theory to explain why increasing the temperature increases the rate of reaction. [3]
Particles move faster, so they collide more often (1); more of the collisions have energy equal to or greater than the activation energy (1); so there are more successful collisions per second (1).
- Why does powdered magnesium react faster than a ribbon of the same mass? [2]
The powder has a larger surface area (1), so more particles are exposed and there are more collisions per second with acid particles (1).
- In an experiment 60 cm³ of hydrogen were collected in the first 20 s. Calculate the average rate in this time, and state the unit. [2]
Rate = 60 ÷ 20 = 3.0 (1) cm³/s (1).
- Explain why the total volume of hydrogen does not change when only the temperature of the acid is increased. [2]
The amount (moles) of magnesium (the limiting reactant) is the same (1), so the same amount of hydrogen is produced; it is only produced faster (1).