2. Atoms, molecules and stoichiometry
A section of Chemistry, 9701
Listing 10 of 208 questions
Combustion data can be used to calculate the empirical formula, molecular formula and relative molecular mass of many organic compounds. Define the term relative molecular mass. T is an alcohol, CxHyO. A gaseous sample of T occupied a volume of 20 cm3 at 120 °C and 100 kPa. The sample was completely burned in 200 cm3 of oxygen (an excess). The final volume, measured under the same conditions as the gaseous sample, was 250 cm3. Under these conditions, all water present is vaporised. Removal of the watervapour from the gaseous mixture decreased the volume to 170 cm3. Treating the remaining gaseous mixture with concentrated alkali, to absorb carbon dioxide, decreased the volume to 110 cm3. The equation for the complete combustion of T can be represented as shown. CxHyO + zO2 xCO2 + y 2H2O Use the data given to calculate the value of x. x = Use the data given to calculate the value of y. y = If you were unable to calculate values for x and y then use x = 4 and y = 10 for the remaining parts of this question. These are not the correct values. Complete the equation for the complete combustion of the alcohol, T. + O2 CO2 + H2O Give the skeletal formulae for two possible structures of T. Name each alcohol. Use the general gas equation to calculate the mass of T present in the original 20 cm3 gaseous sample, which was measured at 120 °C and 100 kPa. Give your answer to three significant figures. Show your working. mass = g
9701_s17_qp_21
THEORY
2017
Paper 2, Variant 1
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The apparatus shows a cell which can be used to determine a value of the Avogadro constant, L. X power supply silver electrodes electrolyte Y variable resistor Name component X. Suggest a suitable electrolyte Y. In an experiment, a current of 0.200 A was passed through the cell for 40.0minutes. The mass of the silver cathode increased by 0.500 g. The charge on the electron is –1.60×10–19 C. Calculate the: ● ● number of moles of silver deposited on the cathode ● ● number of coulombs of charge passed ● ● number of electrons passed ● ● number of electrons needed to deposit 1 mol of silver at the cathode.  
9701_m18_qp_42
THEORY
2018
Paper 4, Variant 2
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A student decided to determine the value of the Faraday constant by an electrolysis experiment. The following incomplete diagram shows the apparatus that was used. Apart from connecting wires, what two additional pieces of equipment are needed for this experiment? Complete the diagram, showing additional equipment connected in the circuit, and showing the powerpack connected to the correct electrodes. List the measurements the student would need to make in order to use the results to calculate a value for the Faraday constant. Using an equation, state the relationship between the Faraday constant, F, the Avogadro constant, L, and the charge on the electron, e. The value the student obtained was: 1 Faraday = 9.63 × 104 Coulombs Use this value and your equation in to calculate the Avogadro constant (take the charge on the electron to be 1.60 × 10–19 Coulombs) hydrogen being collected power pack inert electrodes – + dilute H2SO4
9701_s05_qp_4
THEORY
2005
Paper 4, Variant 0
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Questions Discovered
208