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Lower Six 2011

Some Questions on The Mole Concept :

<u>'''''Please try the questions really, give them a real try'''''</u

1. (a) Magnesium nitride reacts with water to form magnesium hydroxide and ammonia.
         (i) Balance the equation, given below, for the reaction between magnesium nitride and water.

                                              Mg3N2 + H2O  -->  Mg(OH)2 + NH3

         (ii) Calculate the number of moles, and hence the number of molecules, of NH3 in 0.263 g of ammonia gas.
                  (The Avogadro constant L = 6.02 × 1023 mol–1)


    (b) Sodium carbonate is manufactured in a two-stage process as shown by the equations below.

                                            NaCl + NH3 + CO2 + H2O --> NaHCO3 + NH4Cl

                                           2NaHCO3  --> Na2CO3 + H2O + CO2
Calculate the maximum mass of sodium carbonate which could be obtained from 800 g of sodium chloride.


2. Calculate the mass of H2O required to react completely with 5.0 g of SiCl4:

                                           SiCl4 + 2H2O --> SiO2 + 4HCl

3. Calculate the mass of phosphorus required to make 200 g of phosphine, PH3, by the reaction:

                                           P4(s) + 3NaOH(aq) +3H2O(l) --> 3NaH2PO4(aq) + PH3(g)

4. Lead (IV) oxide reacts with concentrated hydrochloric acid as follows:

                                          PbO2(s) + 4HCl(aq) --> PbCl2(s) + Cl2(g) + 2H2O(l)

What mass of lead chloride would be obtained from 37.2g of PbO2, and what mass of chlorine gas would be produced?

5. When copper (II) nitrate is heated, it decomposes according to the following equation:

                                           2Cu(NO3)2(s) --> 2CuO(s) + 4NO2(g) + O2(g).

When 20.0g of copper (II) nitrate is heated, what mass of copper (II) oxide would be produced? What mass of NO2 would be produced?