Jeffrey Ip
Molar Mass of Hydrogen Lab: Reflection
What curriculum expectations does this lab meet?
SCH3U Unit F: Gases and Atmospheric Chemistry
F2.1 use appropriate terminology related to gases and atmospheric chemistry, including, but no limited
to: standard temperature, standard pressure, molar volume, and ideal gas
F2.3 solve quantitative problems by performing calculations based on Boyle's law, Charles's law, GayLussac's law, the combined gas law, Dalton's law of partial pressures, and the ideal gas law
F2.4 use stoichiometry to solve problems related to chemical reactions involving gases (e.g., problems
involving moles, number of atoms, number of molecules, mass, and volume)
F2.5 determine, through inquiry, the molar volume or molar mass of a gas produced by a chemical
reaction (e.g., the molar volume of hydrogen gas from the reaction of magnesium with hydrochloric
acid)
What safety instructions would you give students before/during and after the lab?
The main potential hazard in this lab is the hydrochloric acid. So, prior to the lab I would warn students
of this and remind them to keep goggles and gloves on and to tie back long hair. They should also
know where the eye wash station is, and in advance I would advise them not to wear contact lenses that
day. Then I would emphasize that they should always pour acid into water and never water into acid; if
they pour water into acid they may get splash back and they do not want acid to get onto your skin.
They would also be working with glassware and I would warn them to handle glassware with care.
During the lab I would circulate and watch out for anyone who is pouring water into acid. I would stop
them and have them do it properly (acid into water). After the lab I would advise them about safe
disposal of materials.
What prior knowledge do you need to be able to lead the lab?
Students would require prior knowledge about gas laws including experience solving quantitative
problems using the ideal gas equation and Dalton's law of partial pressure. Students should also have
experience solving quantitative stoichiometry problems. They should also be familiar with single
displacement reactions and be able to write the following balanced equation for the lab reaction:
Mg(s) + 2 HCl(aq) → MgCl2(aq) + H2(g)
Students also need to know that molar volume is the volume occupied by one mole of a substance at a
particular temperature and pressure, and may benefit by being familiar with calculating molar volume
M
Vm =
d .
using the equation molar volume equals molar mass over density,
We would also review the sample calculations given at the beginning of the lab instructions so that
students understand the steps in the calculations.
What is the purpose of the lab? Is it to introduce a concept? Reinforce? Lab skills? etc.
Jeffrey Ip
The purpose of the lab is to give students lab experience working with a eudiometer to carry out a
chemical reaction between magnesium and hydrochloric acid. By doing so they learn about molar
volume, and apply their gas law knowledge to a new context. They also get to use what they've learned
in the problem sets they've completed for homework and apply it in calculations for this lab.
How will you assess this lab? (Please make specific reference to KICA)
Knowledge and Understanding
Students will demonstrate their knowledge and understanding by providing the correct answers to the
prelab and discussion questions. The knowledge and understanding marks for each question are given
below.
Prelab Questions
1) What is present in the eudiometer (gas collection tube) above the liquid phase, once the reaction in
this experiment is complete? Explain your answer. (1 mark)
2) What is the reaction that is taking place in this experiment? Indicate all reactants and products with
subscripts. (1 mark)
magnesium would be used to produce 75.0 mL of hydrogen gas? Show all calculations clearly. (1
mark)
4) What is the volume of water vapour if 65.0 mL of hydrogen gas are produced? Explain your answer.
(1 mark)
5) Explain what equalizing the pressure of the gas in the eudiometer means. (1 mark)
6) Why must the pressure in the eudiometer be equalized after the reaction is complete? Explain your
answer. (1 mark)
7) Why is copper wire a good choice for the cage to hold magnesium? (1 mark)
8) What would the volume of hydrogen be from the electrolysis of 0.0600 mol of water? Show all of
your work. (1 mark)
9) Prepare a flowchart of the procedure and a data table for the experiment (1 mark)
Discussion Questions
1) Calculate the number of moles of magnesium used. Show all calculations. (1 mark)
2) Calculate the pressure exerted by the dry hydrogen gas. Show all calculations. (1 mark)
3) Calculate the volume that the dry hydrogen would have occupied at STP. Show all calculations. (1
mark)
4) What is the volume of 1 mol of hydrogen (the molar volume) at STP as determined by this
experiment? (1 mark)
5) Calculate the percent difference between your answer and the accepted value for the molar volume
of hydrogen gas at STP. (1 mark)
Thinking and Investigation
Students will be marked on their problem solving skills. Focus will be given to how they solve
problems, the steps they take, the reasoning behind their explanations, and generally their process and
strategies. Thinking and investiagion marks are shown below.
Prelab Questions
1) What is present in the eudiometer (gas collection tube) above the liquid phase, once the reaction in
Jeffrey Ip
this experiment is complete? Explain your answer. (1 mark)
2) What is the reaction that is taking place in this experiment? Indicate all reactants and products with
subscripts. (1 mark)
magnesium would be used to produce 75.0 mL of hydrogen gas? Show all calculations clearly. (2
mark)
4) What is the volume of water vapour if 65.0 mL of hydrogen gas are produced? Explain your answer.
(1 mark)
5) Explain what equalizing the pressure of the gas in the eudiometer means. (1 mark)
6) Why must the pressure in the eudiometer be equalized after the reaction is complete? Explain your
answer. (1 mark)
7) Why is copper wire a good choice for the cage to hold magnesium? (1 mark)
8) What would the volume of hydrogen be from the electrolysis of 0.0600 mol of water? Show all of
your work. (1 mark)
9) Prepare a flowchart of the procedure and a data table for the experiment (1 mark)
Discussion Questions
1) Calculate the number of moles of magnesium used. Show all calculations. (2 marks)
2) Calculate the pressure exerted by the dry hydrogen gas. Show all calculations. (2 marks)
3) Calculate the volume that the dry hydrogen would have occupied at STP. Show all calculations. (2
marks)
4) What is the volume of 1 mol of hydrogen (the molar volume) at STP as determined by this
experiment?
5) Calculate the percent difference between your answer and the accepted value for the molar volume
of hydrogen gas at STP. (1 mark)
Communication
Students will be marked on the clarity and organization of their lab report, the proper use of notation
and conventions. Communication marks are shown below.
Prelab Questions
2) What is the reaction that is taking place in this experiment? Indicate all reactants and products with
subscripts. (1 mark)
9) Prepare a flowchart of the procedure and a data table for the experiment (2 marks)
Overall clarity and organization (including spelling and grammar) (3 marks)
Application
By successfully completing the lab and related calculations, students apply their gas law knowledge to
a new context. Therefore, application marks will be reflected in the knowledge and understanding and
thinking and investigation marks given for this lab. No separate application marks will be given.
How could you modify this lab for enriched students? students with IEPs? ELL? etc.
I would have enriched students prepare in advance the sample calculations at the beginning of the lab
handout. This would challenge them to figure out how to do these calculations on their own prior to the
lab.
Jeffrey Ip
For students with IEPs I would work with them on the lab or have them work with a support teacher. I
would also provide a more detailed sample calculation sheet for them.
For ELL students I would give them a handout showing gas law terminology, and provide a detailed
calculation sheet with guidance in plain English. I would also pair them with someone who speaks their
first language, or if that is not possible then with someone who is a native English speaker that they get
along with. And, I would not consider spelling and grammar in their lab.
What will the students gain from participating in this activity?
Students will gain a practical interactive example of how gas laws and related equations are applied in
a chemical lab setting. They will also gain lab experience, which means they will learn how carefully
handle materials, to observe patiently and take detailed notes, and to problem solve on their feet, and to
work effectively with others.