Starter quiz
- A beaker contains six pens. Three pens are black, two are red and one is green. Which of the follow ratios are correct?
- The ratio of black pens to green pens is 1 : 3
- The ratio of red pens to green pens is 2 : 1 ✓
- The ratio of green pens to black pens is 1 : 3 ✓
- The ratio of red pens to black pens is 3 : 2
-
- Which empirical formula shows a metal to non-metal ratio of 1 : 2?
- CuCl₂ ✓
- H₂O
- Na₂O
- NaCl
-
- True or false? The unit for relative atomic mass is grams.
- True
- False ✓
- State the unit for amount of substance.
- Mole ✓
- Avogadro's constant
- Relative atomic mass
- Kilogram
- Weight
-
- When a chemical is __________ there will always be some left over at the end of the reaction.
- in excess ✓
- limiting
- a reactant
-
- Calculate the relative formula mass of ammonium nitrate, NH₄NO₃. Relative atomic masses: N = 14; H = 1; O = 16.
- '80' ✓
Exit quiz
- The formula for sulfuric acid is H₂SO₄. What is the ratio of oxygen to sulfur in the formula?
- '4 : 1' ✓
- Which of the following chemical equations shows a similar molar ratio to the reaction?: Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O
- 2Ca(OH)₂ + 4HNO₃ → 2Ca(NO₃)₂ + 4H₂O ✓
- 2Ca(OH)₂ + 2HNO₃ → 2Ca(NO₃)₂ + 2H₂O
- Ca(OH)₂ + 4HNO₃ → Ca(NO₃)₂ + 4H₂O
- 4Ca(OH)₂ + 2HNO₃ → 4Ca(NO₃)₂ + 2H₂O
-
- 6 moles of calcium hydroxide, Ca(OH)₂, react with excess nitric acid, HNO₃. How many moles of water are formed in the reaction? Ca(OH)₂ + 2HNO₃ → Ca(NO₃)₂ + 2H₂O
- '12' ✓
- 0.5 g of magnesium reacts with oxygen to form 0.8 g of magnesium oxide. Calculate the number of moles of magnesium oxide formed during the reaction. Relative atomic masses: Mg = 24; O = 16.
- 0.8
- 0.02 ✓
- 0.01
- 0.5
-
- What is the reacting ratio when 12.0 g of magnesium, Mg, reacts with 8.0 g of oxygen, O₂, to produce magnesium oxide?
- Mg : O₂ = 2 : 1 ✓
- Mg : O₂ = 1 : 2
- Mg : O₂ = 3 : 2
- Mg : O₂ = 1.5 : 1
-
- It is possible to determine the balanced symbol equation of a reaction from the molar ratios using the following step. Place the steps into the correct order.
- 1⇔Write down the chemical formula for each reactant and product.
- 2⇔Calculate the relative formula mass for each substance.
- 3⇔Calculate the number of moles for each substance.
- 4⇔Find the unitary ratio (one ratio value should be 1).
- 5⇔Find the molar ratio (these should be whole numbers).
- 6⇔Convert the molar ratio to a balanced symbol equation.
Worksheet
Presentation
Video
Lesson Details
Key learning points
- The stoichiometry of a chemical reaction is the molar ratio of each substance in a balanced symbol equation.
- Stoichiometric values can be calculated using masses found by experiment.
- Subscript values in chemical formula indicate the ratio of atoms/ions in a molecule/formula unit.
Common misconception
Some pupils incorrectly interpret subscript and stoichiometric values in a balanced symbol equation.
Both subscript and stoichiometric values represent ratios. Subscripts indicate ratios *within* substances; stoichiometry. Molar ratios *between* substances in a reaction. Much practice distinguishing between/ interpreting these is time well spent.
Keywords
Balanced symbol equation - Describes a reaction using a symbol equation with coefficients, which ensure there are equal numbers of atoms of each element on both sides of the symbol equation.
Stoichiometry - Refers to the molar ratio of the reactants and products in a chemical reaction.
Mole - A mole of something is 6.02 × 10²³ of it. The mass of a mole of a substance is its relative mass expressed in grams.
Ratio - Ratio can be used to determine the size of one quantity in relation to another.