Chemistry: Post your doubts here!

[sitooon]

I use the Cambridge factsheets. (link)
or, Chemguide.

Mostly chemguide though. Lovely lovely stuff there.

I wish i had the link by begining of my A levels , now the time is up

 

[sitooon]

MgBr2 , what is the product at Anode using electrode potential ? it should be Oxygen , but the Answer given is Bromine !?

 

[ahmed abdulla]

iv-
The decomposition will complete when the plunger stops moving outwards. You'll heat and reheat till the point comes when the plunger stops moving outwards.

v- You've to record the volume of gas collected. You've already calculated how much volume of gas a fixed mass of copper carbonate will give you. You've to simply relate the two here and state that whichever volume is equal, or close enough, to the theoretical value for the given mass (calculated in iii) shows you which equation it is following.

3d
I haven't completed the table so idk if any of the other calculated densities are 1.154. If they are, simply equate the ratio of H2SO4/H2O (or the other way round) in terms of water added to the one which has 1.154.
I mean, (40+X)/60 = Volume of water that makes 1.154 from the table/volume of H2SO4 that makes 1.154 from the table.

If there's no valuee 1.154 in the table, do this:
Calculated Density = Mass of H2O + H2SO4 / Total Volume
Equate this to 1.154


1.154 = (60+X)/32.859+(1.003X)
Solve for X. I simple plugged it into my calculator saving me the time and got X = 140.23
X - volume originally added = volume required
140.23 - 40.00 = 100.23 cm3 required.

Please check the marking scheme and let me know if this is incorrect. The answer.


Explaining my 1.003X,

from the equation, we can see that 40g of H2O = 40.12cm3. So, 1g = 1.003 cm3.
Let me know if this doesn't make sense. I'm not good at explaining.

3e
mass error = 0.01/100 * 100 = 0.01%
volume error =
100g of H2SO4 = 54.765cm3
0.25/54.765*100 = 0.456%

Your answers are all right , Thanks

 

[AbbbbY]

I wish i had the link by begining of my A levels , now the time is up

Tis never too late!

And, I've posted that link on this thread several times!
Besides, believe in yourself. So what if you didn't have the link etc. You prepared for your exam using YOUR way. Good enough innit.

 

[sitooon]

Tis never too late!

And, I've posted that link on this thread several times!
Besides, believe in yourself. So what if you didn't have the link etc. You prepared for your exam using YOUR way. Good enough innit.

You are just awesome

 

[AbbbbY]

MgBr2 , what is the product at Anode using electrode potential ? it should be Oxygen , but the Answer given is Bromine !?

Br2 + 2e <=> 2Br- +1.07
O2 + 4H+ + 4e <=> 2H2O +1.23

The oxygen reaction will go forward, the Bromine reaction will go backwards. Br2(g) will be evolved.

 

[sitooon]

Br2 + 2e <=> 2Br- +1.07
O2 + 4H+ + 4e <=> 2H2O +1.23

The oxygen reaction will go forward, the Bromine reaction will go backwards. Br2(g) will be evolved.

Ok check this:
Fe2+ + 2e– ⇌ Fe -------------------- –0.44
O2 + 4H+ + 4e– ⇌ 2H2O --------- +1.23
first reaction will be reversed , so Fe2+ is produced not oxygen !

 

[Browny]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w04_qp_1.pdf

Can anyone please explain questions 5,7,12 and 18?

 

[Browny]

Who's doing chemistry paper 33?

 

[robinhoodmustafa]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w04_qp_1.pdf

Can anyone please explain questions 5,7,12 and 18?

5. The state with the most parallel spins is the lowest energy configuration. Refer "Hund's rule" Answer is C

7. Forces act between two molecules or atoms as a result of their size.this force increases with the increase in size of the particle. we wont choose any other option because it involves the sharing and donating of electron and form a strong bond between the molecule and that is the reason it reacts to form a new bond . answer

 

[Young Stunner]

1- N is going from +3 to 0
2- NaOCl is a bleach
3- NaCl will give you a ppt with AgNO3. P3 review!

Thanks but how is Nitrogen undergoing a REDOX reaction. I can see a reduction only?
And do we have to memorize all the reactions from P3

 

[Jinosupreme]

Guys need help, I get A why it is coplanar, but not B,C,D,E? Why??

 

[AbbbbY]

Guys need help, I get A why it is coplanar, but not B,C,D,E? Why??

Good lord! This is the fifth time I've seen this question here in the last 10 days.

I'll just quote a previous response of mine.

ON09 42 Q5a.
I've answered this before a day or two ago but I'll do it again anyway.
Look. This stuff isn't in the syllabus or taught. This is precisely why it has shown you the 4 figures above the actual question. The examiner wants you to analyze those figures, see whats going on, and apply THAT to the question.

The question shows that all carbons in Benzene can be made to lie on the same plane, but not in cyclohexane. The question also shows that butane Carbons can be made to lie on the same plane, but methylpropane, also an alkane, cannot.
This tells us that if a compound has a ring, OR branching, it cannot be made to lie on the same plane.

All of them are co-planer apart from B.

C is coplaner because you don't have to consider the Oxygen atoms. The others are unbranched and two individual chains lying on the same plane.
Get it?

 

[sitooon]

on Which cases we put the product at anode ?
E0 is not always true ! check!

 

[itallion stallion]

Plz help me with this question
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_43.pdf Q3 part eiv.
Thanks!

 

[Haya Ahmed]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_12.pdf


Question 20

Someone help me !

 

[♣♠ Magnanimous ♣♠]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_12.pdf


Question 20

Someone help me !

There are definatly only 4 C=C in the aliphatic side chain, which is what the question implies it wants the answer to.... However if you include the C=C in the cyclohene ring then you get 5 C=C in the molecule. So I'd answer is 5 C=C
and now for cis the R1 and R2 comes on horizontal and not diagonal.

 

[Namehere]

I use the Cambridge factsheets. (link)
or, Chemguide.

Mostly chemguide though. Lovely lovely stuff there.

Do you have anything like that but for physics?

 

[goodluckayesha]

Good lord! This is the fifth time I've seen this question here in the last 10 days.

I'll just quote a previous response of mine.

i also was going to ask this doubt thnx to alredy explained... umm i i have 2 more doubts pls kindly explain them also
http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w09_qp_42.pdf
Q3c and Q4c

 

[itallion stallion]

i also was going to ask this doubt thnx to alredy explained... umm i i have 2 more doubts pls kindly explain them also
http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w09_qp_42.pdf
Q3c and Q4c

Q3c take electrode potential equation from data booklet and simply balance the electrons on both sides and u will get the equation.for the oxidation state like for example Mno4- the oxidation state of Mn will be (X-8=-1)just change the sign of the value of X after calculating value of X.
Q4c bond breaking energy-bong making energy=total energy of reaction.
Cl-Cl and 3F-F bond will break to form 6 Cl-F bond as in one mole of ClF3 there are 3Cl-f bond.
3(158)+244-6Cl-F=-328.
Solve it and u will get the answer.