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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Chemistry => Topic started by: d0minicz on March 16, 2010, 01:50:49 pm

Title: Chem Q's
Post by: d0minicz on March 16, 2010, 01:50:49 pm
1.   24.0 g of a compound, XH3 reacts with carbon dioxide to form water and 42.3 g of H2XCOXH2.
Calculate the relative atomic mass and hence the identity of X.

2. 12 kg sample containing a mixture of CaO and CaCO3 is heated and 1.8 kg of carbon dioxide is released. Determine the % by weight of the CaCO3 in the original mixture.

3.  Boron naturally occurs in two isotopic forms, 10B and 11B. If the atomic mass 10.81 amu what is the approximate ratio of 10B to 11B?[/s]

4.      A mixture of ZnSO4  and ZnSO4.6H20 has a mass of 36.5 g. Upon heating the water is driven off and the mass of the ZnSO4 remaining is 28.1 g. Determine the % by weight of the ZnSO4.6H20 in the original mixture.

added a couple more.

thanks
Title: Re: Chem Q's
Post by: simonhu81292 on March 16, 2010, 04:39:41 pm
i think ques 3 is
10B is 19% abundance and 11B is 81% abundance
is that what you're asking?
Title: Re: Chem Q's
Post by: d0minicz on March 16, 2010, 04:45:53 pm
yee forgot to cross that off
thanks for clarification =]

still need clarification for others
Title: Re: Chem Q's
Post by: simonhu81292 on March 16, 2010, 04:52:40 pm
the second question the answer should be 29%
CaCO3 ----> CaO + CO2
so find the mole of CO2 and then find the mass of CaCO3 ..
is that right?
Title: Re: Chem Q's
Post by: d0minicz on March 16, 2010, 04:57:12 pm
hmm i got 34% for that one
Title: Re: Chem Q's
Post by: simonhu81292 on March 16, 2010, 05:02:06 pm
yep ...you're right..
i used the wrong molar mass..
sorry
Title: Re: Chem Q's
Post by: kenhung123 on March 16, 2010, 05:06:34 pm
blame anna
Title: Re: Chem Q's
Post by: physics on March 16, 2010, 07:44:55 pm
Quote from: kenhung123 on March 16, 2010, 05:06:34 pm
blame anna
thats nice...why r u blaming me for D:

anyway i did question4 and i think i did it right???!

equation : ZnSO4 + ZnSO4.6H20---> 2ZnSO4 (bleh water disappears)

u know that m(after) = 28.1 g
so u find the mol and i got 0.174mol
mole ratio is n(ZnS)4.6H20) / n(ZnSO4) = 1/2 therefore  1/2 * 0.174 mol = 0.08699mol
multiply that by the molar mass to get the mass and i got 23.45 g


23.45 /36.5  *100 = 64.23%


i attempted question 2 but it was too hard so i gave up after trying 3 times :P
Title: Re: Chem Q's
Post by: chem-nerd on March 16, 2010, 08:51:52 pm
Quote from: d0minicz on March 16, 2010, 01:50:49 pm
2. 12 kg sample containing a mixture of CaO and CaCO3 is heated and 1.8 kg of carbon dioxide is released. Determine the % by weight of the CaCO3 in the original mixture.

4.      A mixture of ZnSO4  and ZnSO4.6H20 has a mass of 36.5 g. Upon heating the water is driven off and the mass of the ZnSO4 remaining is 28.1 g. Determine the % by weight of the ZnSO4.6H20 in the original mixture.

added a couple more.

thanks

Q2

calculate n(CO2) from the 1.8 kg

this all came from the CaCO3 (1:1 ratio), thus you have n(CaCO3)

calculate m(CaCO3)

use this with the 12 kg of total mixture to get the %

Q4

similar process as Q2

m(H2O) = 36.5 - 28.1g

calculate n(H2O)

calculate n(ZnSO4.6H2O) (remember to use ratio 6:1)

calculate m(ZnSO4.6H2O)

use total mixture mass of 36.5 to calculate %

Title: Re: Chem Q's
Post by: physics on March 16, 2010, 08:56:39 pm
Quote from: chem-nerd on March 16, 2010, 08:51:52 pm
Quote from: d0minicz on March 16, 2010, 01:50:49 pm
2. 12 kg sample containing a mixture of CaO and CaCO3 is heated and 1.8 kg of carbon dioxide is released. Determine the % by weight of the CaCO3 in the original mixture.

4.      A mixture of ZnSO4  and ZnSO4.6H20 has a mass of 36.5 g. Upon heating the water is driven off and the mass of the ZnSO4 remaining is 28.1 g. Determine the % by weight of the ZnSO4.6H20 in the original mixture.

added a couple more.

thanks

Q2

calculate n(CO2) from the 1.8 kg

this all came from the CaCO3 (1:1 ratio), thus you have n(CaCO3)

calculate m(CaCO3)

use this with the 12 kg of total mixture to get the %

Q4

similar process as Q2

m(H2O) = 36.5 - 28.1g

calculate n(H2O)

calculate n(ZnSO4.6H2O) (remember to use ratio 6:1)

calculate m(ZnSO4.6H2O)

use total mixture mass of 36.5 to calculate %


i suppose i was wrong then :"( 
Title: Re: Chem Q's
Post by: simonhu81292 on March 16, 2010, 09:05:37 pm
yeah...that's right....
confirmed already ...
Title: Re: Chem Q's
Post by: d0minicz on April 22, 2010, 10:15:19 pm
hey

Assign R or S configuration to each chiralty center for both of the pictures given

thank you
Title: Re: Chem Q's
Post by: fady_22 on April 23, 2010, 04:53:34 pm
I think they are both S.