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:

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)    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 [2]

b)  Calculate the volume of hydrogen that would be produced assuming 1 mole of gas occupies 24dm³  [2]

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