Calculating gas volumes and concentrations of solutions d. calculate the amount of substance in a solution of known concentration (excluding titration calculations at this stage) in mol dm-3 use chemical equations to calculate volumes of gases and vice versa using the concepts of amount of substance and molar volume of gases Connector: When 10g of zinc powder was added to a solution of copper(II) sulphate a displacement reaction took place and copper metal was formed along with zinc sulphate solution. Write the balanced symbol equation including states of matter for this reaction. What is the maximum mass of copper that could be formed? What is the atom efficiency with respect to copper?

1 mole of any gas occupies 24dm3. Moles of gases At room temperature (25oC) and pressure (1 atmosphere) (RTP) 1 mole of any gas occupies 24dm3. (1dm3 = 1000cm3) e.g.1 How many moles of hydrogen gas are there in 24cm3 of hydrogen gas? moles = volume/24,000 = 24/24,000 = 0.001mole V M 24

Some example calculations using moles and volumes How many moles of gas molecules are there in a) 24dm3 of chlorine, b) 6dm3 of hydrogen c) 2.4dm3 of oxygen, d) 120cm3 of nitrogen? a= 1mole, b= 0.25mole, c= 0.1mole, d= 0.005mole 2. What volume of gas does 0.1 mole of oxygen occupy at room temperature pressure (RTP)? V = moles x 24 = 0.1 x 24 = 2.4dm3 3. What volume is occupied by these gases at RTP? a) 3 moles of H2, b) 5 moles of Cl2, c) 0.1mole of N2, d) 0.001 mole of H2S e) 0.005 mole of CO2. a= 72dm3, b= 120dm3, c= 2.4dm3, d= 0.024dm3 or 24cm3, e= 0.12dm3 or 120cm3

Some example calculations masses and volumes 4. What volume does 8g of O2 gas occupy at RTP? (RAM O= 16) Work out the number of moles of O2 Moles = mass/RFM = 8/32 = 0.25mole Now work out the volume of gas vol. = moles x 24dm3 = 0.25 x 24 = 6dm3 5. What volume is occupied by these gases at RTP? a) 4g of H2, b) 8g of CH4, c) 3.55g of Cl2, d) 0.002g of He e) 8.8g of CO2. a) 48dm3, b) 12dm3, c) 1.2dm3, d) 0.012dm3, e) 4.8dm3

Calculating products and reactants Consider the reaction: CaCO3 CaO + CO2 The equation is balanced, this means that when 1 mole of calcium carbonate is heated it decomposes to form 1 mole of calcium oxide and 1 mole of carbon dioxide. If 10g of calcium carbonate was used, what mass of what volume of carbon dioxide (measured at RTP) would be released? (RAMs Ca= 40, C=12, O=16) CaCO3 = 100 = 1 mole So 10g = 0.1 mol and so 0.1 mol of CO2 made 1 mol of CO2 occupies 24dm3 So 0.1 mol occupies 2.4dm3

Concentration is measured in mol dm-3 Moles in solutions Concentration is measured in mol dm-3 How many moles of NaCl are there in 100cm3 of a 2 mol dm-3 solution? How many moles of NaCl are there in 22cm3 of a 2 mol dm-3 solution? What mass of sodium nitrate must be dissolved in 250cm3 of water to make a 1 mol dm-3 solution? (RAMs Na= 23, Cl= 35.5, N= 14, O= 16)