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Calculating volume

A mixture of 20cm3 of oxygen and 60 cm3 of hydrogen is sparked continuously. What is the final minimum volume ?

A gaseous organic compund X was burnt in an excess of oxygen. A o.244 dm3 sample of X measured at s.t.p, produced 2.2 g of carbon dioxide. How many carbon atoms are there in one molecule of X ?

Reply 1

e-n-i-g-m-a

hey i really need to get an answer for these questiosn !!

Reply 2

oxymoron

If the H2 and O2 are reacting together to form H2O, then the 20cm3 of O2 will react with 40cm3 of H2 leaving 20cm3 of H2 remaining (because I can treat volumes as molar quantities when dealing with gases).

2.2g CO2 ---> 2.2/44 moles CO2 = 0.05 moles CO2

moles of X burned = 0.244/24 = 0.0102

so 0.01 mol X ---> 0.05 mol CO2
1 mol X --> 5 mol CO2

so X contains 5 carbon atoms

Reply 3

e-n-i-g-m-a

okay one last question :biggrin:

10cm3 of 0.1 mol/dm3 K2XO4 will just react with 40cm3 0.1 mol/ dm3 iron(II) sulphate solution. If Fe2+ is oxidised to Fe3+ by K2XO4 what is the final oxidation state of X?

Reply 4

oxymoron

moles K2XO4 reacting ---> 0.001

moles Fe2+ reacting ---> 0.004

so 4 molecules of Fe2+ react with one of K2XO4, so oxidation state change of X is 4 times bigger, so it decreases by 4

oxidation state of X in K2XO4 = +6 so final oxidation state is +2