Embedded Files
Objectives
Objectives
Calculate stoichiometric reacting masses
A reminder to please only use your IGCSE periodic table for stoichiometry.
Mass and Molar Mass calculations
Mass and Molar Mass calculations
You must memorize this triangle. It is quicker with the symbols if you can.
Mass, m (g)
Molar Mass, M (g/mol)
Number of moles, n (mol)
Lesson Starter
Lesson Starter
Google tells us that there are 200 billion trillion stars in the universe. That's 200,000,000,000,000,000,000,000. Your challenge is to measure the mass of water that contains the same number of water molecules as there are stars in the universe
Hints:
Put the number in standard form. What fraction of a mole is it?
Calculate the relative molecular mass of water
You can now use the formula triangle from last lesson
Answer
Answer
m = 6g!
Calculations with moles
Calculations with moles
Aluminium metal reacts with oxygen in the air to form aluminium (iii) oxide. How many moles of aluminium (iii) oxide are produced if 8.0 mol of aluminium are used?
Hints:
Write word and symbol equation
Balance equation. Write what you know and need.
Determine the factor needed to scale the chemical equation to what you need.
Answers
Answers
Write word and symbol equation
aluminium + oxygen → aluminium (iii) oxide
Al + O2 → Al2O3
Balance equation. Write what you know and need.
4Al + 3O2 → 2Al2O3
n=8.0mol n=?
Determine the factor needed to scale the chemical “recipe” to what you need.
4Al + 3O2 → 2Al2O3
↓x2 ↓x2 ↓x2
8Al 6O2 4Al2O3
Answer: 4 mol of Al2O3 will be made
More calculations with moles
More calculations with moles
Consider the same reaction above: Aluminium metal reacting with oxygen in the air to form aluminium (iii) oxide.
How many moles of aluminium (iii)oxide are produced if 1.0 mol of aluminium are used?
How many moles of aluminium (iii) oxide are produced if 6.2 mol of aluminium are used?
I desire 5 moles of aluminium (iii) oxide. How many moles of each reactant are required?
What mass of each reactant is required?
Answers
Answers
0.5 moles of aluminium (iii) oxide are produced if 1.0 mol of aluminium is used
3.1 moles of aluminium (iii) oxide are produced if 6.2 mol of aluminium are used?
I desire 5 moles of Aluminium (iii) oxide. 10 mol Al and 7.5 mol O2 are required?
10 moles of Al has mass = 270g. 7.5 moles of O2 has a mass of 240g.
Calculations with masses
Calculations with masses
Let’s go back to our original reaction with aluminium and oxygen from before, but change it a little bit.
Aluminium metal reacts with oxygen in the air to form aluminium (iii) oxide. How many moles of aluminium oxide are produced if 9.2g of aluminium are used?
Hints:
Write word and symbol equation
Balance equation. Write what you know and need.
Convert mass of aluminium to moles using knowledge of molar mass.
Determine the factor needed to scale the chemical equation to what you need.
Answers
Answers
Write word and symbol equation
aluminium + oxygen → aluminium oxide
Al + O2 → Al2O3
Balance equation. Write what you know and need.
4Al + 3O2 → 2Al2O3
m=9.2g n=?
Convert mass of aluminium to moles using knowledge of molar mass.
n(Al) = 9.2g = 0.34mol
27g/mol
Determine the factor needed to scale the chemical “recipe” to what you need.
4Al + 3O2 → 2Al2O3
↓x0.085 ↓x0.085 ↓x0.085
0.34Al 0.26O2 0.17Al2O3
ANSWER: 0.17 mol of Al2O3 will be produced.
Practice calculations with masses
Practice calculations with masses
Nitrogen and hydrogen gas react to form ammonia (NH3).
What mass of ammonia can be produced from 3.5g of H2?
How many grams of nitrogen are needed to produce 7.9g of ammonia?
Magnesium reacts with hydrochloric acid (HCl) to form magnesium chloride and hydrogen gas.
You want to produce 6.1g of H2. How many grams of magnesium do you need?
10.2g of magnesium is reacted. How many grams of magnesium chloride would be produced?
Answers
Answers
Nitrogen and hydrogen gas react to form ammonia (NH3).
20g ammonia can be produced from 3.5g of H2.
6.5g of nitrogen are needed to produce 7.9g of ammonia.
Magnesium reacts with hydrochloric acid (HCl) to form magnesium chloride and hydrogen gas.
You want to produce 6.1g of H2. 73 grams of magnesium are needed
10.2g of magnesium is reacted. 40 grams of magnesium chloride would be produced
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