Credits: Thanks to Nicholas for contributing the questions! Q1. A mixture of CuSO45H2O and MgSO47H2O is heated until a mixture of the anhydrous salt is obtained. If 5.00g of the mixture gives 3.00g of the anhydrous salts, what is the percentage by mass of CuSO45H2O in the mixture? Solution CuSO45H2O (s) è CuSO4 (s) + 5H2O (s) Let the mass of CuSO45H2O be x g MgSO47H2O (s) è MgSO4 (s) + 5H2O (s) Total mass of solid after heating = 3.00g [ (x/249.6) x 159.6 + ((5-x)/246.4) x 120.4 ] = 3 Q2. Solid aluminium sulfide reacts with water to give aluminium hydroxide and hydrogen sulfide gas. Write a balanced equation for this reaction. What is the maximum mass of H2S that can form when 158g of aluminium sulfide reacts with 131g of water? Which is the limiting reactant? Calculate the number of moles of excess reagent remaining at the end of the reaction. Solution Al2S3 (s) + 6H2O (l) è 2Al(OH)3 (s) + 3H2S (g) Number of moles of Al2S3 = 158/150.3 Number of moles of H2O = 131/18 Stoichiometric Coefficient is 1:6:2:3 Therefore, Al2S3 is the limiting reactant.
Q3. What is the percentage yield of a reaction in which 41.5g of Tungsten(VI) Oxide reacts with excess hydrogen gas to produce metallic tungsten and 9.50ml of water (density = 1.00gml-1) Solution WO3 (s) + 3H2 (g) è W (s) + 3H2O (l) WO3 is the limiting reactant. Q4. A mixture of 10cm3 of methane and 10cm3 of ethane was sparked with an excess of oxygen. After cooling to room temperature, the residual gas was passed through aqueous potassium hydroxide. What volume of gas was absorbed by the alkali? Solution CH4 (s) + 2O2 (g) è CO2 (g) + 2H2O (l) Volume of CO2 produced is 10cm3 Stoichiometric Coefficient is 2:7:4:6 Volume of CO2 produced is 20cm3
Q5. 20cm3 of a gaseous hydrocarbon was mixed with 100cm3 if oxygen so that the hydrocarbon was completely burnt. The volume of gas remaining at the end of combustion was 70cm3. After passing over potassium hydroxide, this volume was reduced to 10cm3. All gases were measured at 25ºC and at the same pressure. What is the formula of the hydrocarbon? CXHy + [x+(y/4)] O2 è xCO2 + (y/2) H2O (l)
Solution By comparing coefficients of CxHy and CO2, By comparing coefficients of O2 and CxHy, Because x = 3, Q6. 10cm3 of a gaseous hydrocarbon was exploded with an excess of oxygen. A contraction of 25cm3 in volume occurs after the combustion. On passing the gaseous products through aqueous sodium hydroxide, a further contraction of 30cm3 occurs. Deduce the formula of the hydrocarbon. (All volumes were measured at r.t.p. CXHy + [x+(y/4)] O2 è xCO2 + (y/2) H2O (l)
Solution Total initial volume – Total final volume = 25cm3 By comparing coefficients of O2 and CxHy, Because x = 3, |
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