1)  Non metal X can be identified from its relative isotopic masses.  The table below shows the abundances of the isotopes:

a)  Define relative atomic mass 

        The weighted mean mass of an atom of an element [1] compared with 1/12th of the mass of of an atom of carbon - 12 [1]

b)  Calculate the relative atomic mass of a sample of X.  Give your answer to 3 significant figures.  35.5  [1] answer  [1] 3sf

c)  Use your answer to (b) and the data sheet to identify element X  Cl  [1]

2)  A sample of gas was found to contain 1.630g of carbon and 0.272g of hydrogen by mass and an Mr of 28. 

     Calculate the molecular formula of this compound.

     Empirical formula = CH₂ [1]    Mr of Ef = 14.  Mr of molecule = 28.  Therefore molecular formula = C₂H₄  [1]

3)  A student added 2.74g of Barium to water according to the following reaction:

                                Ba_(s)    +    2H₂O_(l)    à    Ba(OH)_2(aq)    +    H_2(g)

     The resulting solution was then made up to 250cm³ with distilled water.

a)  Calculate how many moles of Ba reacted   

        Moles = mass / Ar    2.74 / 137.3  =  0.0199563 [1]      = 0.0200 3sf [1]

b)  Calculate the volume of hydrogen that would be produced assuming 1 mole of gas occupies 24dm³ 

        Molar ratio = 1:1, so 0.0200 moles H₂ made [1]  Vol = Moles x 24 = 0.48dm³  [1]

c)  Calculate the concentration of the Ba(OH)₂   

        Moles of Ba(OH)₂ = 0.0200 (1:1) ratio [1]  Conc = moles / vol,  0.0200 / 0.25  =  0.0800 mol dm^-3 [1]

d)  Using oxidation numbers identify which element has been oxidised.

        Ba  [1]  as its oxidation number has gone from 0 to 2+  [1]  showing electrons have been lost [1]

4)  A student added magnesium oxide to 25cm³ of 2.00 mol dm^-3 nitric acid until all the nitric acid reacted.

a)  Write a balanced chemical equation for the above reaction, include state symbols.

                                MgO_(s)    +    2HNO_3(aq)    à    Mg(NO₃)_2(aq)    +    H₂O_(l)                  [1] All formulas  [1] Balanced  [1] state symbols

b)  How would the student know when the reaction was complete?

        No more MgO would react / dissolve away [1]

c)  Calculate how many mole of nitric acid was used in the reaction.

        Moles = C x V,    2.00 x 0.025  =  0.0500 moles  [1] answer   [1] 3sf

d)  Deduce the number of moles of magnesium oxide that reacted with this amount of nitric acid.

        2 : 1 ratio, therefore 0.0500 / 2 = 0.0250  moles

e)  Calculate the mass of magnesium oxide reacted with the nitric acid, give your answer to the nearest whole number [3]

        Mr = 40.3 [1]    Mass = moles x Mr,    0.025 x 40.3 = 1g [1]  whole number  [1]

5)  A 2.95g sample of the hydrated crystal CoI₂.nH₂O was heated until there was no further change in mass. 

     The final mass of the anhydrous crystals was 2.190g.

a)  Calculate n and give the formula of the salt.

                                                                                                                            CoI₂.6H₂O [1]

b)  Write an equation for the change that took place.  Include state symbols in your answer.

                                CoI₂.nH₂O_(s)     à    CoI_2(s)    +    6H₂O_(g)                  [1] Balanced equation  [1] state symbols