IDEAL GAS EQUATION
1. (a) Define the term relative molecular mass.
(2)
(b) The mass of one atom of
12C is 1.993 × 10–23 g. Use this mass to calculate a value
for the Avogadro constant (L) showing your working.
(c) The following equation is not balanced.
MgI2(s) + Fe3+(aq) → Mg2+(aq) + I2(s) + Fe2+(aq)
(i) In what way is the equation unbalanced?
(ii) Write the balanced equation.
(2)
(d) A 153 kg sample of ammonia gas, NH3, was compressed at 800 K into a cylinder of volume 3.00 m3.
(i) Calculate the pressure
in the cylinder assuming that the ammonia remained
as a gas.
(ii) Calculate the pressure in the cylinder when the temperature is raised to 1000K.
(iii) Calculate the molarity of the solution formed by dissolving this mass of ammonia in water to make 1.0 m3 of solution.
(7)
(Total 12 marks)
2. (a) The mass of one atom of 12C is 1.99 × 10–23 g. Use this information to calculate a value for the Avogadro constant. Show your working.
(2)
(b) Give the meaning of the term empirical formula.
(c) Define the term relative molecular mass.
(2)
(d) The empirical formula of a compound is CHO and its relative molecular mass has the value 174. Determine the molecular formula of this compound and show your working.
(2)
(e) A compound with molecular formula CH4O burns in air to form carbon dioxide and water. Write a balanced equation for this reaction.
(Total 8 marks)
3. Ammonium nitrate can be prepared by the reaction between ammonia and nitric acid:
NH3 + HNO3 → NH4NO3
(a) The concentration of a nitric acid solution is 2.00 mol dm–3. Calculate the volume of this solution which would be required to react with exactly 20.0 g of ammonia.
(4)
(b) A sample of ammonium nitrate decomposed on heating as shown in the equation below.
NH4NO3 → 2H2O + N2 + ½O2
On cooling the resulting gases to 298 K, the volume of nitrogen and oxygen together was found to be 0.0500 m3 at a pressure of 95.0 kPa.
(i) State the ideal gas equation and use it to calculate the total number of moles of nitrogen and oxygen formed. (The gas constant R = 8.31 J mol–1 K–1)
(ii) Using your answer to part (b)(i), deduce the number of moles of ammonium nitrate decomposed and hence calculate the mass of ammonium nitrate in the sample.
Moles of ammonium nitrateANSWER
Mass of ammonium nitrateANSWER
(6)
(Total 10 marks)
4. (a) Define the term relative molecular mass.
(2)
(b) Give the meaning of the
term empirical formula.
(c) Compound X contains 32.9% by mass of carbon and 1.40% by mass of hydrogen; the remainder is oxygen.
(i) Calculate the
empirical formula of X.
(ii) The relative molecular mass of X is 146. Deduce its molecular formula.
(4)
(d) A 1.0 kg sample of methane was burned in air. It reacted as follows:
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O(g)
(i) Calculate the number of moles in 1.0 kg of methane.
(ii) Calculate the volume of oxygen gas, measured at 298 K and 100 kPa, which would be required for the complete combustion of 1.0 kg of methane.
(6)
(Total 13 marks)
5. (a) What is the name given to the number of molecules in one mole of carbon dioxide?
(b) (i) State the ideal gas equation.
(ii) Calculate the volume
of 1.00 mol of carbon dioxide gas at 298 K and 100 kPa.
(The gas constant R = 8.31 J mol–1 K–1)
(iii) Calculate the mass of carbon dioxide gas at 273 K and 500 kPa contained in a cylinder of volume 0.00500 m3.
(7)
(c) Hydrogen can be made by the reaction of hydrochloric acid with magnesium according to the equation
2HCl +
Mg → MgCl2 + H2
What mass of hydrogen is formed when 100cm3 of hydrochloric acid of concentration 5.0 mol dm–3 reacts with an excess of magnesium?
(3)
(d) A compound of iron contains 38.9% by mass of iron and 16.7% by mass of carbon, the remainder being oxygen.
(i) Determine the empirical formula of the iron compound.
(ii) When one mole of this iron compound is heated, it decomposes to give one mole of iron(II) oxide, FeO, one mole of carbon dioxide and one mole of another gas. Identify this other gas. (The molecular formula of the iron compound is the same as its empirical formula.)
(4)
(Total 15 marks)
6. (a) Give the meaning of the term mole as used in the phrase 'one mole of molecules'.
(b) Nitromethane, CH3NO2, burns in oxygen forming three gases.
2CH3NO2(l) + 1
O2(g) → 2CO2(g) + 3H2O(g) + N2(g)
(i) A 100g sample of nitromethane was completely burned in oxygen. Calculate the number of moles of nitromethane that were burned and also calculate the total volume of gaseous products at 400K and l00kPa.
Moles of nitromethane.ANSWER
Total volume of gaseous products.ANSWER
(ii) The combustion reaction is very exothermic and heats the products to a temperature of 1000 K. Calculate the total volume of gaseous products at this temperature and 100 kPa.
(7)
(c) Carbon dioxide gas can be absorbed by sodium hydroxide solution, as shown by the following equation.
2NaOH(aq) + CO2(g) → Na2CO3(aq) + H2O(l)
Calculate the concentration in mol dm–3 of sodium carbonate in a solution formed by dissolving 2.00g of carbon dioxide in 200 cm3 (an excess) of aqueous sodium hydroxide.
(2)
(d) Calculate the empirical formula of an oxide of nitrogen which contains 25.9% of nitrogen by mass.
(3)
(e) The molecular formula of the oxide in part (d) is the same as its empirical formula. The oxide decomposes on warming to produce nitrogen dioxide and oxygen. Write an equation for the decomposition reaction.
(Total 14 marks)