2. Atoms, molecules and stoichiometry
A section of Chemistry, 9701
Listing 10 of 208 questions
Defi ne the term mole. 10 cm3 of a gaseous hydrocarbon, CxHy, was reacted with 100 cm3 of oxygen gas, an excess. The fi nal volume of the gaseous mixture was 95 cm3. This gaseous mixture was treated with concentrated, aqueous sodium hydroxide to absorb the carbon dioxide present. This reduced the gas volume to 75 cm3. All gas volumes were measured at 298 K and 100 kPa. Write an equation for the reaction between sodium hydroxide and carbon dioxide. Calculate the volume of carbon dioxide produced by the combustion of the hydrocarbon. volume of CO2 produced = cm3 Calculate the volume of oxygen used up in the reaction with the hydrocarbon. volume of O2 used = cm3 Use your answers to and , together with the initial volume of hydrocarbon, to balance the equation below. CxHy + O2  CO2 + zH2O Deduce the values of x, y and z in the equation in . x = y = z = Another hydrocarbon, W, with the formula C4H8, reacts with hydrogen bromide, HBr, to give two products X and Y. X and Y are structural isomers of molecular formula C4H9Br. Reaction of X with aqueous alkali produces an alcohol, Z, that has no reaction with acidifi ed dichromate(. Give the structures and names of the compounds W, X, Y, and Z W X Y Z When W reacts with hydrogen bromide, more X than Y is produced. Explain why.
9701_s14_qp_23
THEORY
2014
Paper 2, Variant 3
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A white powder is known to be a mixture of magnesium oxide and aluminium oxide. 100 cm3 of 2 mol dm–3 NaOHis just sufficient to cause the aluminium oxide in x grams of the mixture to dissolve. The reaction occurring is Al 2O3 + 2OH– + 3H2O → 2Al (OH)4 –. 800 cm3 of 2 mol dm–3 HCl is just sufficient to cause all of the oxide in x grams of the mixture to dissolve. The reactions occurring are Al 2O3 + 6H+ → 2Al 3+ + 3H2O and MgO + 2H+ → Mg2+ + H2O. How many moles of each oxide are present in x grams of the mixture?
9701_s16_qp_11
MCQ
2016
Paper 1, Variant 1
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Questions Discovered
208