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Topic 5- Stoichiometry
1. Complete the table
Name Formula Name Formula
Magnesium Fluoride
Magnesium hydroxide
Lithium Chloride
Calcium phospahte
Calcium Chloride
Aluminium nitrate
Copper (I) Iodide
Copper (II) nitrate
Potassium Bromide
Lead(II)Chloride
Aluminum Oxide
Ammonium nitrate
Iron(II) Oxide
Potassium carbonate
Aluminum Sulfide
Lead (II) nitrate
Sodium Chloride
Sulfuric Acid
Barium Chloride
Nitric acid
Iron (II) Sulfate
Hydrochloric acid
Iron (III) Sulfide
Phosphoric acid
Sodium Hydroxide
Ammonia
Ammonium Bromide
Potassium manganate (VII)
Potassium Sulfate
Calcium hydroxide
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2. Write a balanced chemical equation for the following reactions
a) Sodium reacting with oxygen to form sodium oxide
b) Aluminum reacts with fluorine to form Aluminium fluoride
c) Calcium metal reacts with hydrochloric acid to form calcium chloride and hydrogen gas
d) Potassium bromide reacts with chlorine gas to form potassium chloride and bromine
e) Aluminum metal reacts with iron (II) oxide powder to produce aluminum oxide solid and iron metal.
Mole concept
1. Calculate relative molecular mass (RMM or Mr) using Ar values form the periodic table
a) CaO b) Mg(OH)2 c) Na2O
d) Na2O e) (NH4)2 SO4 f) Na2SO4
2. Calculating percentage by mass
𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑜𝑜𝑜𝑜 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎𝑎
Percentage by mass calculations = 𝑥𝑥 100
𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚
Calculate the percentage by mass of the elements given in bold
a) K2O b) Al2O3
b) c) (NH4)3PO4 d) Mg(OH)2
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3. Mole calculations
a) Calculate the amount of moles in 6g of Calcium (Ca).
b) Calculate the mass of 0.56 moles of MgO
c) Calculate the moles in 400 cm3 of hydrogen gas
d) Calculate the amount of moles in 0.6dm3 of oxygen gas
e) Calculate the moles in 2 dm3 of carbon dioxide
f) Calculate the volume of 0.05 moles of hydrogen gas.
4. Avogadro’s Constant
a) What is Avogadro’s constant.
………………………………………………………………………………………………………………………………………………………………………
……………………………………………………………………………………………………………………………………………………………………..
b) Calculate number of molecules in 0.05 moles of water
c) Calculate number of atoms in 0.125 moles of calcium
d) Calculate the number of atoms in 0.05 moles of carbon dioxide.
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e) Calculate number of ions in 0.012 moles of sodium chloride.
f) Calculate number of ions in 0.015 moles of Magnesium chloride.
5. Concentration of solutions
a) Calculate concentration in mol/dm3 of solution containing 0.012 moles in 25 cm3 of solution.
b) Calculate the number of moles of NaOH solution with concentration of 0.6mol/dm3 and volume of 50cm3
c) Calculate the volume of solution containing 0.045 moles of HCl in 0.5mol/dm3 solution.
d) Calculate the concentration in g/dm3 of solution containing 8g of NaCl dissolve in 50 cm3 of water.
More Complex mole calculations
1. Sodium hydrogencarbonate is found in baking powder. When sodium hydrogencarbonate is heated it forms three
products
Calculate the volume of carbon dioxide formed at room temperature and pressure when 12.6g of NaHCO3 is heated using
the following steps:
• determine the mass of one mole of NaHCO3
.............................. g
• calculate the number of moles of NaHCO3 used
.............................. moles
• determine the number of moles of carbon dioxide formed
.............................. moles
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• calculate the volume of carbon dioxide formed at room temperature and pressure.
.............................. dm3
2. Some salts can be made by titration. In a titration experiment, 20.0cm3 of aqueous sodium hydroxide reacts exactly with
25.0cm3 of 0.100mol/dm3 dilute sulfuric acid to make sodium sulfate.
Calculate the concentration of the aqueous sodium hydroxide in g/dm3 using the following steps.
● Calculate the number of moles of dilute sulfuric acid used.
.............................. mol
● Determine the number of moles of sodium hydroxide which react with the dilute sulfuric acid.
.............................. mol
● Calculate the concentration of the aqueous sodium hydroxide in mol/dm .3
.............................. mol/dm3
● Calculate the concentration of the aqueous sodium hydroxide in g/dm3 .
.............................. g/dm3
3. The equation for the decomposition of hydrogen peroxide is shown.
2H2O2(aq) → 2H2O(l) + O2(g)
25.0cm3 of aqueous hydrogen peroxide forms 48.0cm3 of oxygen at room temperature and pressure (r.t.p.). Calculate the
concentration of aqueous hydrogen peroxide at the start of the experiment using the following steps.
● Calculate the number of moles of oxygen formed.
……………. moles
● Deduce the number of moles of hydrogen peroxide that decomposed.
……………. moles
● Calculate the concentration of hydrogen peroxide in mol/dm3.
……………. Mol/dm3
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4. The equation for the reaction between powdered zinc carbonate and dilute nitric acid is shown.
ZnCO3 + 2HNO3 → Zn(NO3)2 + H2O + CO2
A student found that 2.5 g of zinc carbonate required 20cm3 of dilute nitric acid to react completely.
Calculate the concentration of dilute nitric acid using the following steps:
● calculate the mass of 1 mole of ZnCO3
● calculate the number of moles of ZnCO3 reacting
● determine the number of moles of HNO3 reacting
● calculate the concentration of HNO3.
5. Calcium reacts with water as shown from the chemical equation.
Ca + 2H2O Ca(OH)2 + H2
Calculate the volume of hydrogen gas produce when 2.5g of calcium is used.
6. Some sulfates are hydrated. When hydrated sodium sulfate crystals, Na2SO4•xH2O, are heated, they give off water
In an experiment, 1.61g of Na2SO4•xH2O is heated until all the water is given off. The mass of Na2SO4 remaining is 0.71g.
[Mr : Na2SO4,142; H2O,18]
Determine the value of x using the following steps.
● Calculate the number of moles of Na2SO4 remaining.
.............................. mol
● Calculate the mass of H2O given off.
.............................. g
● Calculate the number of moles of H2O given off.
.............................. mol
● Determine the value of x.
x = ..............................
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Excess and limiting reagent
1. For the reaction
2S(s) + 3O2(g) → 2SO3(g)
if 6.3 g of S is reacted with 10.0 g of O2 show by calculation which one will be the limiting reactant.
2. Consider the reaction
Mg2Si + 4H20 → 2Mg(OH)2 + SiH4
Which of the reactants is in excess if we start with 50.0 g of each reactant?
7. Sodium and water react according to the reaction
2Na(s) + 2H20(l) → 2NaOH(aq) + H2(g)
What number of moles of H2 will be produced when 4g Na is added to 2g H2O?
Molecular formula & Empirical formula
1. A compound was found to have 82% nitrogen and 18% hydrogen. Find its empirical formula.
2. Cryolite is an ore of aluminium, used in the extraction of aluminium from bauxite; it was found to have 33% sodium,
13% aluminium and 54% fluorine. Find its empirical formula?
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3. Many organic compounds, such as alcohols, carboxylic acids and esters, contain the elements carbon, hydrogen and
oxygen only.
(a) Compound R has the following composition by mass: C, 60.00%; H, 13.33%; O, 26.67%.
Calculate the empirical formula of compound R.
empirical formula = .............................. [2]
(b) Compound S has the empirical formula C2H4O and a relative molecular mass of 88.
Calculate the molecular formula of compound S.
4. Iodine forms an oxide which has the composition by mass: I, 76.0%; O, 24.0%.
Use this information to determine the empirical formula of this oxide of iodine.
5. Many organic compounds contain carbon, hydrogen and oxygen only.
(a) An organic compound V has the following composition by mass. C, 48.65%; H, 8.11%; O, 43.24% Calculate the
empirical formula of compound V.
empirical formula = ..............................
(b) Compound W has the empirical formula CH4O and a relative molecular mass of 32. Calculate the molecular
formula of compound W.
molecular formula = ..............................
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Percentage yield
1) CaCO3 → CaO + CO2
24.8 grams of Calcium Carbonate decomposes. Calculate the percent yield if you obtain 13.1 grams in the laboratory.
2) Iron(II) sulfate decomposes when heated strongly.
2FeSO4(s) → Fe2O3(s) + SO2(g) + SO3(g)
15.20 g of FeSO4(s) was heated and formed 4.80 g of Fe2O3(s).
[Mr, FeSO4 = 152; Mr, Fe2O3 = 160]
Calculate the percentage yield for this reaction.
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