10. Chemical Calculations

1.The structure of a silicone polymer is shown.   Which element in the polymer is present in the highest percentage by mass?

2. On heating ammonium nitrate, NH4NO3, decomposes to form dinitrogen oxide and water. NH4NO3 →  N20 + 2H2O   When 80 g of an impure sample of ammonium nitrate is heated, 27 g of water is formed, Which expression shows the number of grammes of ammonium nitrate in the impure sample?

3. Compound X has the molecular formula Fe2O3. The following Statements were made about compound X. 1.Iron is present in compound X as the Fe2+ ion 2.One mole of compound X contains 112 g of iron and 48 g of oxygen 3.The empirical formula of compound X is Fe2O3 4.Three moles of oxygen molecules are needed to make one mole of X Which statements are correct?

4. When heated, two moles of X give one mole of oxygen and two moles of chlorine. What is the molecular formula of X?

5. What is the ratio of the volume of 2 g of hydrogen to the volume of 16 g of methane, when both volumes are at room temperature and pressure?

6. Each of the following solutions has a concentration of 1 mol/dm^3. Which solution contains the greatest number of ions in | dm^3 of solution?

7. Different volumes of aqueous solutions of hydrochloric acid and silver nitrate were mixed in beakers. In each case, a precipitate of silver chloride was formed. In which beaker would the greatest mass of silver chloride be formed?

8. Element Q has an electronic structure 2,4. Element R has an electronic structure 2,8,6. What would be the formula of the compound formed between Q and R?

9. In the electrolysis of molten sodium chloride, 46 g of sodium is formed at the cathode. How many moles of chlorine gas are formed at the anode?

10. An aqueous solution of hydrochloric acid has a concentration of 2.0mol/dm^3. Different volumes of the acid are added to different volumes of aqueous sodium hydroxide. NaOH + HCL →  Nacl + H2O   The maximum temperature of each mixture is measured. The grapg shows the results.   What is the concentration of the aqueous sodium hydroxide?

11. What is the volume of hydrogen produced at room temperature and pressure, When 0.2 mol of sodium is reacted with an excess of water? [1 mol of gas occupies 24 dm' at room temperature and pressure.] 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)  

12. A carbohydrate has the formula (CH2O) 6. One mole of this carbohydrate is burned in excess oxygen and the gas formed is collected. What volume of gas, measured at room temperature and pressure, is collected?

13. On adding 50 g of impure limestone, CaCO3 (M(r) = 100), to excess hydrochloric acid, 6.0 dm^3 of CO2 was evolved at room temperature and pressure. What is the purity of the limestone? 

14. An excess of dilute sulfuric acid was added separately to the following. 1. 1.2 g of magnesium 2. 2.0 g of magnesium oxide, then warmed 3. 4.2 g of magnesium carbonate Which statement is correct?  A. The number of moles of magnesium sulfate formed would be greatest in reaction 1 B. The number of moles of magnesium sulfate formed would be greatest in reaction 2. C. The number of moles of magnesium sulfate formed would be greatest in reaction 3. D. The number of moles of magnesium sulfate formed would be the same in all three reactions.    

15. The formula of an oxide of element Y is Y203. 8.0 g of Y2 O3 contains 5.6 g of Y. How many moles of Y does 5.6 g of the element contain?  

16. In the reaction between 23 g of ethanol and excess hydrogen bromide, the mass of bromoethane obtained is 27 g. C2H5OH + HBr → C2H5Br + H2O What is the percentage yield of bromoethane ? [M(r): C2H5OH,46;C2H5Br,109]  

17. When 42.0 g of sodium hydrogen carbonate, NaHCO3 (M(r) = 84), was strongly heated. 3.00 dm^3 of carbon dioxide gas, measured at room temperature and pressur, was released. 2NaHCO3 → Na2CO3+ H2O + CO2 What was the percentage yield of carbon dioxide?

18. The equations for the action of heat on four nitrates are given below.   A 10 g sample of each nitrate was heated until there was no further change. Which nitrate produced the greatest mass of nitrogen dioxide, NO2?

19. 28 g of gaseous hydrocarbon X has a volume of 12 dm^3 at room temperature amd pressure. What is the molecular formula of X?

20. The equations show the reactions involved in the formation of nitric acid, HNO3, from nitrogen. N2 + 02 →2NO 2NO + 02 → 2NO2 4NO2 + 2H20 + 02 → 4HNO3 How many moles of nitric acid are formed from 0.50 moles of nitrogen?

21. 1.0 g of each of the metals calcium, iron, magnesium and zinc was placed in separate test-tubes, each containing excess dilute hydrochloric acid. The gas evolved from each test-tube was collected and its volume was measured. Which metal produced the greatest volume of gas on completion of the reaction?

22. Sodium hydroxide reacts with sulfuric acid. The equation for the reaction is shown. 2NaOH + H2SO4 → Na2SO4+ 2H20 Which volume of 0.20 mol/dm^3 sodium hydroxide reacts completely with a solution containing 0.49 g of sulfuric acid? [M(r): H2SO4,98]

23. Bromobutane, C4H9Br, can be made from butanol using the reaction shown. C4H9OH + HBr → C4H9Br + H2O  In an experiment, 10 g of butanol produced 12 g of bromobutane What is the percentage yield of bromobutane? [M(r): C4H9OH, 74; C4H9Br, 137] 

24. Magnesium reacts with dilute sulfuric acid to form magnesium sulfate and hydrogen Mg +H2SO4 → MgSO4+H2 2.4 g of magnesium react with exactly 100 cm^3 of 1 mol/dm^3 sulfuric acid to give 2.4 dm^3 of hydrogen, at room temperature and pressure. Which row would give 4.8 dm^3 of hydrogen at room temperature and pressure?    

25. 4.00 g of a metal oxide, XO2, is reduced to form 3.15 g of metal X. What is the identity of X?