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|
a) Define relative atomic mass 
b) Calculate the relative atomic mass of a sample of X. Give your answer to 3 significant figures. 
c) Use your answer to (b) and the data sheet to identify element X 
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. 
3) A student added 2.74g of Barium to water according to the following reaction:
Ba(s) + 2H2O(l) à 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 
b) Calculate the volume of hydrogen that would be produced assuming 1 mole of gas occupies 24dm3 
c) Calculate the concentration of the Ba(OH)2 
d) Using oxidation numbers identify which element has been oxidised. 
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 
b) How would the student know when the reaction was complete? 
c) Calculate how many mole of nitric acid was used in the reaction 
d) Deduce the number of moles of magnesium oxide that reacted with this amount of nitric acid 
e) Calculate the mass of magnesium oxide reacted with the nitric acid 
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 
b) Write an equation for the change that took place. Include state symbols in your answer