Do Now Write the general equation for the following reactions: Acid + metal Metal oxide + acid Metal hydroxide + acid Metal carbonate + acid Metal hydrogencarbonate + acid 2. Complete the following equations and balance where necessary: Mg + HCl  CuO + H2SO4  Zn(OH)2 + H2SO4  NaOH + H3PO4  Li2CO3 + HCl  Sodium hydrogencarbonate + citric acid 

Calculation of Reacting Volumes of Gases Targets Calculating reacting volumes of gases from chemical equations using the concept of molar volume of gases Homework: Read pages 144 – 149 and make notes. You will be tested on it next lesson. Due: Next Friday (17th Nov) Test: Topic 1 and 5 – Soon!

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Molar Volume The volume of gas that contains one mole of that gas. Molar volume is approximately the same for all gases, but its value varies with temperature and pressure. The value most often used is for gases at room temperature and pressure (RTP). Room temperature – 298K Standard pressure – 101325Pa (1 atm) The value is usually quoted as 24.0dm3 or 24000cm3. Vm = 24.0dm-3 mol-1 at RTP

Molar Volume (Vm) The molar volume (Vm) is the volume occupied by 1 mole of gas. It depends on the temperature and pressure (so it is important that these are stated). Unless you are told otherwise, you should assume that Vm is measured at RTP: PV=nRT V= nRT P So Vm at STP = 1x 8.31 x298 1x105 = 0.024m3 or 24 dm3 RTP 273.15 K 1.01325x105 Pa Molar volume can be used to work out the volume of gas produced in a reaction at STP

Rearrange the equation Vm = 24.0 = ? Vm = 24000 = ? Volume in dm3 = ? Volume in cm3 = ? Amount in mol = ?

Have a go… What is the amount, in moles, of Co is 3.80dm3 of carbon dioxide? What is the amount, in moles, of CO2 in 500cm3 of carbon dioxide? What is the volume of 0.356mol of hydrogen?

Have a go… What is the amount, in moles, of Co is 3.80dm3 of carbon dioxide? 0.158mol What is the amount, in moles, of CO2 in 500cm3 of carbon dioxide? 0.0208mol What is the volume of 0.356mol of hydrogen? 8.54dm3

Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) Worked Example What volume of hydrogen is produced at STP when 1.7g of magnesium ribbon reacts completely with excess hydrochloric acid? Mg (s) + 2HCl (aq) → MgCl2 (aq) + H2 (g) Moles of Mg = mass Ar = 1.7 = 0.07 mol 24.3 Mole ratio of Mg:H2 = 1:1 so 0.07 mol of H2 is produced. Volume of hydrogen at STP = 0.07 x 24 = 1.68 dm3

CaCO3(s) + 2HNO3(aq)  Ca(NO3)2(aq) + H2O(l) + CO2(g) Worked Example Calcium carbonate reacts with nitric acid to form calcium nitrate, water and carbon dioxide, as shown in the equation: CaCO3(s) + 2HNO3(aq)  Ca(NO3)2(aq) + H2O(l) + CO2(g) In a reaction 100cm3 of carbon dioxide is formed. What mass of calcium carbonate is needed for this?

(NH4)2SO4(s) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l) + 2NH3(g) Have a go… Ammonium sulfate reacts with sodium hydroxide solution to form sodium sulfate, water and ammonia, as shown in the equation below. (NH4)2SO4(s) + 2NaOH(aq)  Na2SO4(aq) + 2H2O(l) + 2NH3(g) What volume of ammonia is formed by reacting 2.16g of ammonium sulfate with excess sodium hydroxide solution?

Check Your Understanding ... 1. Hydrogen and chlorine react to produce hydrogen chloride gas: H2(g) + Cl2(g) → 2HCl (g) What volume of chlorine will react completely with 100 cm3 of hydrogen? What volume of hydrogen chloride will be produced when 100 cm3 of chlorine reacts completely with hydrogen? What volume of hydrogen chloride will be produced in the reaction between 50 cm3 of hydrogen and 100 cm3 of chlorine? 2. Airbags in cars contain sodium azide, NaN3. In a crash, this is ignited electrically. It decomposes rapidly to produce sodium and nitrogen 2NaN3(s) → 2Na(s) + 3N2 (g) The nitrogen gas inflates the bag within about 20 ms. What mass of sodium azide is needed to produce 40 dm3 of nitrogen at STP?

Check Your Understanding ... 1. Hydrogen and chlorine react to produce hydrogen chloride gas: H2(g) + Cl2(g) → 2HCl (g) What volume of chlorine will react completely with 100 cm3 of hydrogen? 100 cm3 What volume of hydrogen chloride will be produced when 100 cm3 of chlorine reacts completely with hydrogen? 200 cm3 What volume of hydrogen chloride will be produced in the reaction between 50 cm3 of hydrogen and 100 cm3 of chlorine? 100 cm3 2. Airbags in cars contain sodium azide, NaN3. In a crash, this is ignited electrically. It decomposes rapidly to produce sodium and nitrogen 2NaN3(s) → 2Na(s) + 3N2 (g) The nitrogen gas inflates the bag within about 20 ms. 77.4 g What mass of sodium azide is needed to produce 40 dm3 of nitrogen at STP? Q2 ans: Moles of N2 at STP = vol N2/22.4 = 40/22.4 = 1.7857 mol. Molar ratio = 2:3 Mol o fNaN2 = 2/3x1.7857 = 1.190 mol Mass = molx Mr = 1.190 x 65 = 77.4g

Task Chemsheets Amount of Substance Booklet Task 15