The Student Room Group

stuck on 4 chemistry hw questions

got stuck 4 of my chem. homework questions which I have been trying to do for the past 3 hours
here they are;


2
a) Calculate the expected mass of one mole of 31^P atoms that the avogadro constant equals 6.0225 x10^23, the mass of one electron equals 9.1091x10^-28g, the mass of one proton equals 1.6725x10^-24g and the mass of one nuetron equals 1.6748x10^-24g.

b) The actual mass of one mole of 31^P atoms is 30.9738g. Try to account for the difference between this valueand your answer in (a).

3.
A mixture of MGS04 and CuSO4.7H20 is heated at 120(degrees C) until a mixture of the anhydrous compounds is produced. If 5.00g of the mixture gave 3.00g of the anhydrous compounds, calculate the percentage by mass of MGSO4.7H20 in the mixture.

4.
1 mole of a hydrocarbon formula CnH2n was burned completely in oxygen producing carbon dioxide and water vapour only. It requires 192g of oxygen. Work out the formula of the hydrocarbon.

5. When 15cm^3 of gaseous hydrocarbon was exploded with 60cm^3 of oxygen (an XS), the final volume was 45cm^3. This decreased by 15cm^3 on treatment with NaOH solution ( removes C02 ). What was the formula of the hydrocarbon (all measuremnets were made at room temp. and pressure, & water produced is liquid)

6.
A fertilser contains ammonuim sulphate and pottasuim sulphate. A samply of 1.455g of the fertilise was warmed with 25cm^3, 0.2moddm^-3 NaOH solution giving of ammonia gas. The remaining NaOH that was not used requireed 28.7cm^3 of 0.100moldm^-3 HCl acid for nuetrulisation. Calculate the % by mass of ammonuim sulphate in the sample.
Reply 1
Take it step by step, write it out in "table" form. I ain't giving you any answers you lazy git lol
Reply 2
lol john171
just out of interest did u get 72% for no. 6


i understand wat u mean by not given me answers but for real i dont no how to do no. 2 3 4

can u point me in right direction please
Reply 3
papz, is this AS?
Reply 4
Is this from the CI book,m if so i may have done it therefore i may be able to help.
Reply 5
my chem teacher said it was AS but he added bits of A2 work so they wud challenge us more

so i guess a bit of AS and a bit of A2
Reply 6
papz_007
my chem teacher said it was AS but he added bits of A2 work so they wud challenge us more

so i guess a bit of AS and a bit of A2
Ahh that's a relief! :smile: Saying that we've only had 6 lessons of chem (3 of atomic structure, 1 of redox and 2 of organic) so we've barely started! :eek:
Reply 7
@Nutchopper -- dont no were its from teacher gave it to us on a sheet off paper
Reply 8
2a. 31.258g
b. something to do with theoretical value always being greater than actual?
c. i got 19.5% which is prob wrong.
4. C4H8 Definitely
5. CH4
6. 9.66% Definitely
Reply 9
vinney i got C6H8 for no.4

how did u get C4H8??