.
1. (a) Define the term relative atomic mass.
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(2)
(b) How would you calculate the mass of one mole of atoms from the mass of a single atom? ……………………………………………………………………………………. (1)
(c) Sodium hydride reacts with water according to the following equation.
NaH (s) + H2O (l) → NaOH (aq) + H2 (g)
A 1.00 g sample of sodium hydride was added to water and the resulting solution was diluted to a volume of exactly 250 cm3
(i) Calculate the concentration in moldm-3, of sodium hydroxide solution formed.
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(ii) Calculate the volume of hydrogen gas evolved, measured at 293 K and 100 kPa.
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(iii) Calculate the volume of 0.112 M hydrochloric acid which would react exactly with a 25.0 cm3 sample of sodium hydroxide solution.
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(8)
[TOTAL 11 marks]
2. (a) Sodium carbonate forms a number of hydrates of general formula Na2CO3.xH2O A 3.01 g sample of one of these hydrates was dissolved in water and the solution made up to 250 cm3.
In a titration, a 25.0 cm3 portion of this solution required 24.3 cm3 of 0.200 mol–1 dm–3 hydrochloric acid for complete reaction. The equation for this reaction is shown below.
Na2CO3 + 2HCl 2NaCl + H2O + CO2
(i) Calculate the number of moles of HCl in 24.3 cm3 of 0.200 mol dm–3 hydrochloric acid.
...........………………………………………………………………………….
(ii) Deduce the number of moles of Na2CO3 in 25.0 cm3 of the Na2CO3 solution.
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(iii) Hence deduce the number of moles of Na2CO3 in the original 250 cm3 of solution.
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(iv) Calculate the Mr of the hydrated sodium carbonate.
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(5)
(b) In an experiment, the Mr of a different hydrated sodium carbonate was found to be 250.
Use this value to calculate the number of molecules of water of crystallisation, x, in this hydrated sodium carbonate, Na2CO3.xH2O
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(3)
(c) A gas cylinder, of volume 5.00 × 10–3 m3, contains 325 g of argon gas.
(i) Give the ideal gas equation.
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(ii) Use the ideal gas equation to calculate the pressure of the argon gas in the cylinder at a temperature of 298 K.
(The gas constant R = 8.31 J K–1 mol–1)
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(4)
[Total 12 marks]
3. (a) A sample of ethanol vapour, C2H5OH (Mr = 46.0), was maintained at a pressure of
100 kPa and at a temperature of 366K.
(i) State the ideal gas equation.
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(ii) Use the ideal gas equation to calculate the volume, in cm3, that 1.36 g of ethanol vapour would occupy under these conditions.
(The gas constant R = 8.31 J K–1 mol–1)
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