Chemical calculations
Chemical calculations
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Chemistry
Chemical calculations
Chemical Calculations
Relative atomic mass (Ar): this is the mass of one atom of the element compared with the mass of one atom of Hydrogen
On the relative atomic mass scale the atomic mass of Hydrogen = 1
Use a Periodic table to help you answer these questions.
- How many times heavier is one atom of Sodium (Na) than one atom of Hydrogen?
- How many times heavier is one atom of Oxygen (O) than one atom of Hydrogen?
- How many atoms of Nitrogen (N) are needed to equal the mass of one atom of Iron (Fe)?
Relative formula mass (Mr): this is the mass of all the relative atomic masses of all the atoms in the formula of the compound
Use a periodic table to help you work out the relative formula masses of these compounds. An example has been done to help show you how.
E.g. (NH4)2 CO3 N x 2 = 14 x 2 = 28
H4 x 2 =(H x 8) = 1 x 8 = 8
C x 1 = 12 x 1 = 12
O x 3 = 16 x 3 = 48
Total = 96
- CO2
- SO2
- NaOH
- KCl
- Ca(OH)2
- HNO3
- CuCO3
- NH4NO3
- CuSO4 . 5H2O
- Mg(HCO3)2
Moles: M - the amount of a substance that contains Avogadros number of particles of the substance is called one mole of substance
The amount of substance in moles = Mass of substance
Mass of 1 mole of substance
E.g. what is the amount of Iron present in 196 g of Iron (Fe)
Ar of Iron = 56
Amount of Iron = Mass of Iron
Mass of 1 mole of Iron
Amount of Iron = 196g = 3.5 mol
56g
Use a periodic table to work out how much of each substance is present
- 1 mol of sodium atoms Na
- 2 mol of bromine molecules Br2
- 0.25 mol of nitrogen molecules N2
- 0.5 mol of sulphur atoms S
- 0.25 mol of sulphur molecules S8
- Moles of sodium in 46 g of sodium Na
- Magnesium in 0.6 g of magnesium Mg
- Oxygen molecules in 32 g of Oxygen O2
- 1 mol of sulphur dioxide molecules SO2
- 2 mol of calcium carbonate CaCO3
Reactions in solutions: Molar solutions
A molar solution is a solution containing 1 mole of a substance made up to one liter (1 dm3) of solution.
E.g. A molar solution of sodium hydroxide (NaOH) contains 1 mol of NaOH in 1 dm3 (1000 cm3) of solution.
This is equal to 40g of NaOH (23 + 16 +1) in 1000cm3 of solution
OR
20g of NaOH in 500cm3 of solution
OR
10 g of NaOH in 250cm3 of solution
OR
80 g of NaOH in 2000cm3 of solution
They are all the same … a 1 molar solution
Molarity = number of grams of solute dissolved x 1000 cm3 of solvent
mass of 1 mole of solute x volume of solvent it is dissolved in
E.g. Molarity of 9.8g of Sulphuric acid H2SO4 dissolve in 100cm3 is: -
1 mole of H2SO4 = 2x1 + 1x32 + 16x4 = 98g
9.8g x 1000 cm3 = 1 M
98g x 100 cm3
- Calculate the molarity of a solution containing 20g of sodium hydroxide (NaOH) dissolved in 200cm3 of solution
- Calculate the molarity of a solution containing 126 g of nitric acid (HNO3) dissolved in 500cm3
Concentration is measured in moles per liter = amount of solute in moles
volume of solution in liters
Calculate the concentration of a solution that was made by dissolving 60g of sodium hydroxide (NaOH) and making the solution up to 1 liter
Mass of 1 mole of NaOH = 23 + 16 + 1 = 40g/mol
Amount in moles of sodium hydroxide = 60g = 1.5 mol
40g/mol
Volume of solution = 1 liter
Amount of mols/volume in liters = 1.5 mol/ liter
Calculate the concentration of the following solutions:
1. 5.6g of potassium hydroxide (KOH) in 500cm3 of solution
2. 7.3 g of hydrogen chloride (HCl) in 250 cm3 of solution
Find the amount of solute dissolved in the following solutions:
- 250 cm3 of a solution of sodium hydroxide of concentration 2.0 mol/liter
- 500 cm3 of a solution of Sulphuric acid of concentration 0.12 mol/liter
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Chemical calculations
Chemical calculations
Chemical calculations
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