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Chemistry: Post your doubts here!

h4rriet

h4rriet

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kingos3111 said:
guys the initial moles of h2o is not given how can i multip;y it with 0.8 help
Click to expand...

HERE YOU GO:
MaNdToC.jpg

Tell me if you still don't understand; I'll try and make it more clear.
 
h4rriet

h4rriet

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Student12 said:
HEEEEELLLLLLLLLLLLLLLLLLLLLLLLP !

A few questions i'm not able to solve on Moles..
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w02_qp_1.pdf Q1 (C)http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w05_qp_1.pdf Q1(C)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf Q1,Q2,Q4
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s03_qp_1.pdf Q2
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s05_qp_1.pdf Q2(why is it not 1.5?)
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s08_qp_1.pdf Q2
Click to expand...

1. Construct balanced equations for the combustion of 1 mole (10 cm3) of methane and ethane. Take the moles to be the volume. CO2 will be a product; it'll react with KOH, so you can minus the moles of CO2 from the total volume of the products (i.e. volume of CO2 + H2O).
1. Construct a balanced equation.
1. Construct a balanced equation and use mole ratios.
2. Just take the moles to be the volume. SO2 and CO2 react with NaOH, so you'll minus their volumes from the total volume.
4. Count the electrons!
2. 1 C=C bond will take 1 mole of H2 when it becomes saturated. Count the number of C=C bonds initially, and the number of C=C bonds left after the reaction. Subtract the second from the first to get the number of moles of H2 used.
2. Because NaN3 decomposes to give Na also, which in turn reacts to give more N2. So technically this new N2 is actually coming because of the NaN3. You have to take it into consideration as well.
2. 100 grams of fertiliser contains 15 g of N2. So 14 grams will contain x moles. c=x/v.
 
K

kingos3111

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ooooooo is it becaause 1 mole of h2o gives 1 mole of hydrogen and half moles of 02 but isnt that principle only applies to kc not kp help thanx luk
 
Student12

Student12

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h4rriet said:
1. Construct balanced equations for the combustion of 1 mole (10 cm3) of methane and ethane. Take the moles to be the volume. CO2 will be a product; it'll react with KOH, so you can minus the moles of CO2 from the total volume of the products (i.e. volume of CO2 + H2O).
1. Construct a balanced equation.
1. Construct a balanced equation and use mole ratios.
2. Just take the moles to be the volume. SO2 and CO2 react with NaOH, so you'll minus their volumes from the total volume.
4. Count the electrons!
2. 1 C=C bond will take 1 mole of H2 when it becomes saturated. Count the number of C=C bonds initially, and the number of C=C bonds left after the reaction. Subtract the second from the first to get the number of moles of H2 used.
2. Because NaN3 decomposes to give Na also, which in turn reacts to give more N2. So technically this new N2 is actually coming because of the NaN3. You have to take it into consideration as well.
2. 100 grams of fertiliser contains 15 g of N2. So 14 grams will contain x moles. c=x/v.
Click to expand...
Could you please show the working in detail i knw the methods..
 
Jiyad Ahsan

Jiyad Ahsan

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Alice123 said:
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
Q30
isnt it supposed to be 25 %?? :(
n also Q39 h4rriet Jiyad Ahsan or anyone
thanks
Click to expand...

Q 30!
okay here goes, so you know when we find the yield in an ester rxn we use the acid right?
so the mass of the ethanoic acid given is 30, which divided by the mr of the acid
30/60 = 0.5 moles
and in the end the ester formed has mass 22g while its mr is 88, moles of ester formed,
22/88 = 0.25 moles
so if 0.5 moles of acid produces o.25 moles of the ester, we have
(0.25/0.5) x 100 = 50%

hope you got it, dnt mind asking if u didnt.
i'll just do 39 and post it up in a bit
 
h4rriet

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Alice123

Alice123

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Jiyad Ahsan said:
Q 30!
okay here goes, so you know when we find the yield in an ester rxn we use the acid right?
so the mass of the ethanoic acid given is 30, which divided by the mr of the acid
30/60 = 0.5 moles
and in the end the ester formed has mass 22g while its mr is 88, moles of ester formed,
22/88 = 0.25 moles
so if 0.5 moles of acid produces o.25 moles of the ester, we have
(0.25/0.5) x 100 = 50%

hope you got it, dnt mind asking if u didnt.
i'll just do 39 and post it up in a bit
Click to expand...

Thankyou sooo much :)
i did understand :D
Best of luck fr yr exam(y)


h4rriet said:
30. (30+30)-18 (mass of water)=the mass of ester we're supposed to get.
39. The compounds in 1 and 2 are made from C3H7 free radicals. The compound in 3 is made from C2H5 and C4H9 free radicals.
Click to expand...
Thanks:)
 
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