Chemistry: Post your doubts here!

[hihi]

oh! i get it XD
thanks ^^

can u please help me with these :
34) A student puts 10 cm3 of 0.100 mol dm–3 sulfuric acid into one test-tube and 10 cm 3 of 0.100 mol dm–3 ethanoic acid into another test-tube. He then adds 1.0 g (an excess) of magnesium ribbon to each test-tube and takes suitable measurements. Both acids have the same starting temperature.
Neither reaction is complete after 2 minutes, but both are complete after 20 minutes.
Which statements are correct?
1 After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2 After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
3 After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
(answer: 1,2,3)


39) Use of the Data Booklet is relevant for this question.
In an organic synthesis, a 62% yield of product is achieved.
Which of these conversions are consistent with this information?
1 74.00g of butan-2-ol → 44.64 g of butanone
2 74.00g of butan-1-ol → 54.56 g of butanoic acid
3 74.00g of 2-methylpropan-1-ol → 54.56 g of 2-methylpropanoic acid
(answ: 1,2,3)

40)
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
(answ: 1only)

 

[user]

Assalamoalaikum wr wb!!

some more...

@momin, where're ur doubts?
JazakAllah 4 solving the others.. didnt get Q:35 from the prev ones i posted so posting again...

 

[mominzahid]

can u please help me with these :
34) A student puts 10 cm3 of 0.100 mol dm–3 sulfuric acid into one test-tube and 10 cm 3 of 0.100 mol dm–3 ethanoic acid into another test-tube. He then adds 1.0 g (an excess) of magnesium ribbon to each test-tube and takes suitable measurements. Both acids have the same starting temperature.
Neither reaction is complete after 2 minutes, but both are complete after 20 minutes.
Which statements are correct?
1 After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2 After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
3 After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
(answer: 1,2,3)


39) Use of the Data Booklet is relevant for this question.
In an organic synthesis, a 62% yield of product is achieved.
Which of these conversions are consistent with this information?
1 74.00g of butan-2-ol → 44.64 g of butanone
2 74.00g of butan-1-ol → 54.56 g of butanoic acid
3 74.00g of 2-methylpropan-1-ol → 54.56 g of 2-methylpropanoic acid
(answ: 1,2,3)

40)
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
(answ: 1only)

In 34 all 1 and 2 are obviously correct because sulphuric acid is a more reactive acid. and 3 is correct because sulphuric acid is a stronger acid. this means that it ionises more in water i.e. it gives more H+ ions. Organic acids are weak acids they do not ionise as much. So at the end sulphuric acid would have produced more gas when the reaction is complete because it gave more H+ ions to the reaction.

39 is a moles related question. make equation for each statement and using the mass to mass ratio find out the mass that should be produced for each statement. then find out the 62% of that mass.. it should be equal to the mass stated of the products.

40. answer is D 1 only. this is because the energy profile shows that an intermediate is formed in the reaction. that is only the case for statement No. 1.
Good Luck.

 

[Oliveme]

Question 14-

EDIT: I meant moles of CO2 formed, not burned, sorry.
Question 16-
Write out all the products of the electrolysis. You have H2 gas, CL2 gas, and NaOH. Since they are constantly stirred, the ions are added back to the solutions, so you have H+ Cl-, Na+ and OH-
The anions react to give you a chlorate ion (CLO3-), with oxidation number 1, since both have the oxidation number 1. This reacts with the sodium to give you sodium chorate (I). I do not understand why H2 gas has formed and not water, though. However since there are no options with water in it. B seems the most reasonable option.

I'll take my time with question 9, it looks hard, and long.

Thank you very much.
yeah, question 9 is the main problem I have. but thank you, that cleared a lot of things.

 

[thunderingthunder]

yield increases with an increase in temp...??? so u think 400 is a greater temp than 500...????

ohh sorry my bad..actually the yield actually increases with an increase in pressure!!
SoorRR y!!

 

[Oliveme]

Please answer and explain question 40
http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

 

[leosco1995]

Please answer and explain question 40
http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w03_qp_1.pdf

Hydrolyze the ester to get CH3OH and CH3CH2CH2CO2H (so 3 is obviously wrong). Product #2 will be formed, but it doesn't distill off so you only have the alcohol in the distillate. It's also worth noting that if there was another option - CH3CHH2CH2CO2H in the question, that wouldn't be found in the distillate either because all of it would have been converted into the salt.

The answer is D.

 

[Student12]

QP http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
Q 4, 11, 14 ? Can someone xplain & solve ?

 

[umarashraf]

ohh sorry my bad..actually the yield actually increases with an increase in pressure!!
SoorRR y!!

haha... this is again not a perfect reason... increase in pressure favours the side where there are less number of moles..
3H2 + N2 ---> 2NH3... reactants have 3+1 = 4 moles while products have only 2 moles.... so reaction proceeds to the side with less no of reacting moles...

 

[leosco1995]

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_s06_qp_1.pdf

please explain the ans to question 12 ^^

The temperature is being increased, so the vertical height of the curve becomes smaller and the width slightly longer, because the area has to be the same. That means A, B and D are all wrong.

 

[leosco1995]

QP http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w06_qp_1.pdf
Q 4, 11, 14 ? Can someone xplain & solve ?

Construct balanced equations for combustion for each of the first 4 alkanes and figure out how much volume you obtain. I'll do one of them to show you how it's like:

CH4 + 2O2 -> CO2 + 2H2O

10 cm^3 of CH3 will react with 20 cm^3 of oxygen, leaving 50 behind as residual gas. You also have 10 cm^3 of CO2, so thte total volume left is 60 cm^3.

You would also do this for the other alkanes, but since the only graph that starts with 60 cm^3 is D, you don't have to bother will the others.

I will do 11 and 14 later because they're quite long. #14 is mainly math though, just balance the equations for each metal and use ratio to figure out which one is the right answer.

 

[mominzahid]

Assalamoalaikum wr wb!!

some more...

@momin, where're ur doubts?
JazakAllah 4 solving the others.. didnt get Q:35 from the prev ones i posted so posting again...



View attachment 8498View attachment 8499View attachment 8500View attachment 8501View attachment 8502View attachment 8503

I posted them again on this page check please.
Your doubts :
In 34 cant be MgO because it has a very high temperature.. i mean like VERY VERY high.. it is an ionic compound. it cant be decomposed on heating with a bunsen flame as the heat would never be enough.
In 32, the brackets represent the concentration. Now the concentration of H+ is always high because it is being produced in both reactions. 2 and 3 are incorrect because concentration of so4 is low. this is derived from the part where he said hso4 is a weak acid. this means that it ionises very less thus if it ionises less how can so4 ions produced be greater in concentration. 3rd can be derived from this both the concentrations cant be equal as so4 ions have very less concentration.
In 7, MgO is an ionic compound.. it relates to the question as in a furnace the temperature gets very high so a very high melting point compund is required so the compound should have strong forces of attraction in order to have a high melting point. and since it is an electrical furnace we dont want current leaking out so the compound should be an electrical insulator and MgO meets all three requirements.
40 i dont know
in 35, when magnesium burns in oxygen, it forms MgO.. Only if nitrate ions are present it doesnt mean that magnesium will necessarily react with them. and just in case it does we all know group 2 nitrates decompose easily so due to the heat produced the nitrate will decompose eventually forming Mgo again.. Hope that clears it up.

 

[mominzahid]

People please helpp..

 

[KurayamiKimmi]

can u please help me with these :
34) A student puts 10 cm3 of 0.100 mol dm–3 sulfuric acid into one test-tube and 10 cm 3 of 0.100 mol dm–3 ethanoic acid into another test-tube. He then adds 1.0 g (an excess) of magnesium ribbon to each test-tube and takes suitable measurements. Both acids have the same starting temperature.
Neither reaction is complete after 2 minutes, but both are complete after 20 minutes.
Which statements are correct?
1 After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2 After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
3 After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
(answer: 1,2,3)


39) Use of the Data Booklet is relevant for this question.
In an organic synthesis, a 62% yield of product is achieved.
Which of these conversions are consistent with this information?
1 74.00g of butan-2-ol → 44.64 g of butanone
2 74.00g of butan-1-ol → 54.56 g of butanoic acid
3 74.00g of 2-methylpropan-1-ol → 54.56 g of 2-methylpropanoic acid
(answ: 1,2,3)

40)
http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf
(answ: 1only)

Answer for question 35
the reactions will be
Mg + 2 CH3COOH <=> Mg(CH3COO)2+ H2(g)
Mg + H2SO4 → MgSO4 + H2


1 After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2 After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
this is because the sulfuric acid is a stronger oxidising agent and therefore will be quicker in forming the magnesium sulfate and hydrogen than ethanoic acid .and when it does form , bond forming is exxothermic and so it is at an higher temperature
3 After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
This is because the reaction between ethanoic acid and magnesium is in equilibrium which means the reaction never reaches completion.Moreover , the stoichichemtry of the equilibrium shows us that more reactants are present than products (reactants =3m products =2m)

 

[leosco1995]

[huge image]
People please helpp..

26) Draw all of the structures of C5H10 that have a double or triple bond I think (pi bond means double or triple). There's 6 of them in total.

17) D is the answer because bromine is a weaker oxidizing agent than H2SO4 (H2SO4 is a stronger oxdizing agent than bromine and everything below it in group 7). Also it's an acid because it donates a proton to make HBr.

14) There' an answer posted here.

12) Beryllium because it has a 3+ charge and so does Aluminium, the rest have a +2 charge.

 

[mominzahid]

26) Draw all of the structures of C5H10 that have a double or triple bond I think (pi bond means double or triple). There's 6 of them in total.

17) D is the answer because bromine is a weaker oxidizing agent than H2SO4 (H2SO4 is a stronger oxdizing agent than bromine and everything below it in group 7). Also it's an acid because it donates a proton to make HBr.

14) There' an answer posted here.

12) Beryllium because it has a 3+ charge and so does Aluminium, the rest have a +2 charge.

how does beryllium has +3 charge? it is in group 2.. :/
And thanks aloott for the answers u cleared my problems.

 

[leosco1995]

how does beryllium has +3 charge? it is in group 2.. :/
And thanks aloott for the answers u cleared my problems.

Oh, sorry I was wrong there, it does have a +2 charge. :\ Actually, all of the other elements are larger but beryllium is the only one which has the same charge density as Al. You can figure that out from the data booklet, that's why it said "use of the data booklet is relevant to this question".

 

[hihi]

In 34 all 1 and 2 are obviously correct because sulphuric acid is a more reactive acid. and 3 is correct because sulphuric acid is a stronger acid. this means that it ionises more in water i.e. it gives more H+ ions. Organic acids are weak acids they do not ionise as much. So at the end sulphuric acid would have produced more gas when the reaction is complete because it gave more H+ ions to the reaction.

39 is a moles related question. make equation for each statement and using the mass to mass ratio find out the mass that should be produced for each statement. then find out the 62% of that mass.. it should be equal to the mass stated of the products.

40. answer is D 1 only. this is because the energy profile shows that an intermediate is formed in the reaction. that is only the case for statement No. 1.
Good Luck.

It is very helpfull. Thanks very much Are you doing AS Chemistry exam in May??

 

[hihi]

Answer for question 35
the reactions will be
Mg + 2 CH3COOH <=> Mg(CH3COO)2+ H2(g)
Mg + H2SO4 → MgSO4 + H2


1 After 2 minutes, the sulfuric acid is at a higher temperature than the ethanoic acid.
2 After 2 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
this is because the sulfuric acid is a stronger oxidising agent and therefore will be quicker in forming the magnesium sulfate and hydrogen than ethanoic acid .and when it does form , bond forming is exxothermic and so it is at an higher temperature
3 After 20 minutes, the sulfuric acid has produced more gas than the ethanoic acid.
This is because the reaction between ethanoic acid and magnesium is in equilibrium which means the reaction never reaches completion.Moreover , the stoichichemtry of the equilibrium shows us that more reactants are present than products (reactants =3m products =2m)

Thank you so much!

 

[gary221]

Hey does sum1 know how 2 solve this??
For 19..ans is D, for 20...C