1 What is the concentration of hydrogen ions in 0.05mol/dm3
sulfuric acid?
I will present you my working. Not sure if I'm right, but please
point out the error.
H2SO4 ----> 2H+ + SO4 2-
Assuming that volume of acid is 1 dm3,
No. of mols of H2SO4 = concentration X vol
=
0.05 X 1
= 0.05 mols
Comparing mole ratio, we know that no. of moles of H+ ions is
0.10 mol
so concentration is 0.10 mol/dm3
concentration in mol/dm3 = concentration of g/dm3 / relative Mr
of substance
concentration of H+ ions (in g/dm3) = 0.10 mol/dm3 X 1
= 0.10 g/dm3 (final
answer) - please verify
the answer is correct, but not sure if my working is correct or
not.
I multiply by 1 since Ar of hydrogen is 1.
2. Propane burns completely in oxygen according to the equation
shown
C3H8 + 5O2 ----> 3CO2 + 4H2O
If 0.1 mol of propane gas is burnt completely, which volume of
gaseous product is obtained, measured at r.t.p?
A 0.1 dm3 B 0.3dm3
C 2.4 dm3 D 7.2 dm3
My answer is D. TYS answer is A. I compared the mole ratio of
propane to CO2 gas, so we have 0.3 mol of CO2 being produced. 0.3 X
24 dm3 = 7.2dm3
3. This is the part where I need serious help. Can't do this
question at all.
Which ion is present in the highest concentration in a 2mol/dm3
aqueous solution of sodium sulfate?
The choices are hydrogen ions, hydroxide ions, sodium ions, and
sulfate ions.
4 All ammonium salts on heating with NaOH produce NH3 gas. From
which ammonium salt can the greatest mass of ammonia be
obtained?
0.5 mol (NH4)3PO4
0.5 mol (NH4)2SO4
1.0 mol NH4Cl
1.0 mol NH4NO3
Don't really know how to go about calculating this.
lastly, which fertilizer provides the most nitrogen per
mole?
NH4NO3 OR (NH4)3PO4 OR NaNO3
OR (NH4)2SO4
If I calculate using %tage composition, my answer would be
NH4NO3. If I simply look at the no. of Nitrogen atoms from the
formula given, my answer is (NH4)3PO4. Answer is (NH4)3PO4. I think
they look at the no. of nitrogen atoms. Is this method
accepted?
*****Alas, the MOST IMPORTANT questions are 3 and 4 cuz I have
totally no clue how to sovle them... the rest, i merely need you
guys to check my working. *****
Thanks
Hi Bonkysleuth,
Do have a look at JM's post for a solution for question 3.
http://www.simplechemconcepts.com/o-levels-chemistry-questions-mole-concepts-mole-calculations/
Cheers.