Review your understanding  /33

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

Isotope Isotope 1 Isotope 2
Relative isotopic mass 37 35
% abundance 25.0 75.0

a)  Define relative atomic mass [2]

b)  Calculate the relative atomic mass of a sample of X.  Give your answer to 3 significant figures.  [2]

c)  Use your answer to (b) and the data sheet to identify element X  [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.  [4]


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

                                Ba(s)    +    2H2O(l)        Ba(OH)2(aq)    +    H2(g)

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

a)  Calculate how many moles of Ba reacted [2]

b)  Calculate the volume of hydrogen that would be produced assuming 1 mole of gas occupies 24dm[2]

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

d)  Using oxidation numbers identify which element has been oxidised. [3]


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 [3]

b)  How would the student know when the reaction was complete?  [1]

c)  Calculate how many mole of nitric acid was used in the reaction  [2]

d)  Deduce the number of moles of magnesium oxide that reacted with this amount of nitric acid [1]

e)  Calculate the mass of magnesium oxide reacted with the nitric acid [3]


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 2.19g.

a)  Calculate n and give the formula of the salt [3]

b)  Write an equation for the change that took place.  Include state symbols in your answer [2]