Chemistry MCQ thread...

[Xthegreat]

optical isomers
- always look for C=C or anything with double bond, and eliminate them
- when given a long chain, you'll just have to check all the C atoms one by one
- if both sides of the C are not symmetrical, then they are considered different groups ( look at the pic for reference )
* well, if symmetrical then, of course, they are considered the same group.

 

[MHHaider707]

in 15, u don need to calculate Mr of CO2!!!!
its the fact as un Q. it says '[One mole of any gas occupies 24dm3 at room temperature and pressure.]'

in 16 use oxidation no. to deduce whether Ag is oxidized or reduced!!!
before reaction oxidation no. of Ag is same as after the reaction...so neither reduced nor oxidized!!

in 26, A n C are both primary alcohols so will be oxidized to aldehyde first and then to carboxylic acid n therefore gives two oxidized products!!

 

[kakarocks]

Guys October November 2005 . Question 25 . Need help quick . Explain your answer please!

Answer is D.....

It says that only one of them reacts with 2,4-DNPH so it means only one of them have carbonyl group...this eliminates B n C!!!

It also states that they all react with PCl3....

In A Y has two aldehyde groups which does not react with PCl3....
and in D Y has one carboxylic group and one carbonyl group so it will react with PCl3 so answer is D!!

Wait a Second! Isnt 2,4 DPH a test for C double bond o ? so it should be positive in Carboxylic acids as well shouldn't it? i get that pcl3 reacts with oH so no reaction with Carbonyl compounds!

 

[Anonymousx3]

Guys October November 2005 . Question 25 . Need help quick . Explain your answer please!

Answer is D.....

It says that only one of them reacts with 2,4-DNPH so it means only one of them have carbonyl group...this eliminates B n C!!!

It also states that they all react with PCl3....

In A Y has two aldehyde groups which does not react with PCl3....
and in D Y has one carboxylic group and one carbonyl group so it will react with PCl3 so answer is D!!

Wait a Second! Isnt 2,4 DPH a test for C double bond o ? so it should be positive in Carboxylic acids as well shouldn't it? i get that pcl3 reacts with oH so no reaction with Carbonyl compounds!

Nope. 2,4 -DNPH only forms a precipitate with aldehydes and ketones. Other classes of organic compounds (such as carboxylic acids or esters) do not form precipitates. It's just something you gotta learn.

 

[kakarocks]

Thanks

 

[ismailkhan]

umm the answer for the question regarding which compouds will react with H2SO4 and Kmn04. the ans is B

 

[Saturation]

These questions!: ( I just want to know the answers, since these qs were from a mixed up mock exam!)

1) What will react differently with the two isomeric alcohols, (CH3)3CCH2OH and (CH3)2CHCH2CH2OH?

A acidified aq potassium manganate (VII)
B conc. H2SO4
C PCl5
D Na

2) What is formed when propanone is refluxed with a solution of NaBH4?

A propanal
B propan 1 ol
C propan 2 ol
D propane

3) When an isomer Y of molecular formula C4H9Br undergoes hydrolysis in aq. alkali to form an alcohol C4H9OH, the rate of reaction is found to be unaffected by changes in concentration of the OH- ions present. Which is the most likely molecular structure of Y?

A CH3CH2CH2CH2Br
B CH3CH2CHBrCH3
C (CH3)2CHCH2Br
D (CH3)3CBr

4) Which isomer of C4H10 O forms 3 alkenes on dehydration? (please explain this one! I think it's B? )

A butan 1 ol
B butan 2 ol
C 2-methlypropan 1 ol
D 2-methlypropan 2 ol

5) Which of the following would be suitable for use in a fire extinguisher?
1 CBrF3
2 CH3(CH2)5CH2Br
3 HCl

Finally, can someone answer this:

For the Haber process, does the [Kp} increase with pressure?

 

[xHazeMx]

These questions!: ( I just want to know the answers, since these qs were from a mixed up mock exam!)

1) What will react differently with the two isomeric alcohols, (CH3)3CCH2OH and (CH3)2CHCH2CH2OH?

A acidified aq potassium manganate (VII)
B conc. H2SO4
C PCl5
D Na

2) What is formed when propanone is refluxed with a solution of NaBH4?

A propanal
B propan 1 ol
C propan 2 ol
D propane

3) When an isomer Y of molecular formula C4H9Br undergoes hydrolysis in aq. alkali to form an alcohol C4H9OH, the rate of reaction is found to be unaffected by changes in concentration of the OH- ions present. Which is the most likely molecular structure of Y?

A CH3CH2CH2CH2Br
B CH3CH2CHBrCH3
C (CH3)2CHCH2Br
D (CH3)3CBr

4) Which isomer of C4H10 O forms 3 alkenes on dehydration? (please explain this one! I think it's B? )

A butan 1 ol
B butan 2 ol
C 2-methlypropan 1 ol
D 2-methlypropan 2 ol

5) Which of the following would be suitable for use in a fire extinguisher?
1 CBrF3
2 CH3(CH2)5CH2Br
3 HCl

Finally, can someone answer this:

For the Haber process, does the [Kp} increase with pressure?

Q 1 .. its B
Q 2 .. its C
Q 3 .. not sure but i think its D
Q 4 .. its D ( draw the structure and u will figure it out easily )
Q 5 .. i think its B ( 1 and 2 )
about the Haber process, no it does not because the yield is already high so a little pressure is needed to push the gases into the system.

 

[Vanto1994]

I'd be grateful if someone provides me with an explanation for this question >

2 Use of the Data Booklet is relevant to this question.
A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15 g : 30 g :15 g per 100 g of fertiliser. The recommended usage of fertiliser is 14 g
of fertiliser per 5 dm3 of water.
What is the concentration of nitrogen atoms in this solution?
A 0.03 mol dm–3
B 0.05 mol dm–3
C 0.42 mol dm–3
D 0.75 mol dm–3

It is May/June 2008 Q.2
Thanks in advance

 

[Saturation]

Number 4 is NOT D and Number 5 is NOT B ! ( Cause these where the same answers I wrote, and they are wrong!) And number 3: I think it's D aswell!

Number 5: I think it has to be D ( 1 only) , since chloroflourocarbons are used in fire extinguishers, so it must be only the 1st one.

Can anyone confirm this!?

 

[xHazeMx]

I'd be grateful if someone provides me with an explanation for this question >

2 Use of the Data Booklet is relevant to this question.
A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15 g : 30 g :15 g per 100 g of fertiliser. The recommended usage of fertiliser is 14 g
of fertiliser per 5 dm3 of water.
What is the concentration of nitrogen atoms in this solution?
A 0.03 mol dm–3
B 0.05 mol dm–3
C 0.42 mol dm–3
D 0.75 mol dm–3

It is May/June 2008 Q.2
Thanks in advance

its A
no of mole of nitrogen in 100 g of fertilizer = 15/14 =mass/mr = 1.07

no of moles in 14g of fertilizer = 1.07 X 14 / 100 =0.1498

now these are no of moles in 5 dm3 so in 1 dm3 = .1498/5 =.02996 ~ 0.03 !

 

[Mobeen]

@ saturation
1 is B
2 is C
3 is D
4 is B
5 is B

 

[abdullah181994]

please please please answer this and explian your working

 

[xHazeMx]

Number 4 is NOT D and Number 5 is NOT B ! ( Cause these where the same answers I wrote, and they are wrong!) And number 3: I think it's D aswell!

Number 5: I think it has to be D ( 1 only) , since chloroflourocarbons are used in fire extinguishers, so it must be only the 1st one.

Can anyone confirm this!?

are u sure question 4 is correct? because i think it has to be 2 methyl butan-2-ol

 

[abdullah181994]

please answer my above question.

 

[Saturation]

I'd be grateful if someone provides me with an explanation for this question >

2 Use of the Data Booklet is relevant to this question.
A typical solid fertiliser for use with household plants and shrubs contains the elements N, P, and
K in the ratio of 15 g : 30 g :15 g per 100 g of fertiliser. The recommended usage of fertiliser is 14 g
of fertiliser per 5 dm3 of water.
What is the concentration of nitrogen atoms in this solution?
A 0.03 mol dm–3
B 0.05 mol dm–3
C 0.42 mol dm–3
D 0.75 mol dm–3

It is May/June 2008 Q.2
Thanks in advance

In 100g of fertiliser there are 15g of Nitrogen, so In 14g of fertilser, there must be 2.1g of Nitrogen (ratios!)
number of moles of nitrogen = 2.1/14 = 0.15mol ( we divide by 14 because the qs says it's the Nitrogen element, so it isn't N2)
concentration= 0.15/5= 0.03, so it must be A.

 

[Mobeen]

Number 4 is NOT D and Number 5 is NOT B ! ( Cause these where the same answers I wrote, and they are wrong!) And number 3: I think it's D aswell!

Number 5: I think it has to be D ( 1 only) , since chloroflourocarbons are used in fire extinguishers, so it must be only the 1st one.

Can anyone confirm this!?

bromine is used in fire extinguishers .

 

[abdullah181994]

please answer question # 2 of 9701 O/N 11 paper 1

 

[Mobeen]

please answer question # 2 of 9701 O/N 11 paper 1

o/n 11 ? lol

 

[Saturation]

@ saturation
1 is B
2 is C
3 is D
4 is B
5 is B

Thanks, but for 5 is put B, but it's wrong! :/

Number 4 is NOT D and Number 5 is NOT B ! ( Cause these where the same answers I wrote, and they are wrong!) And number 3: I think it's D aswell!

Number 5: I think it has to be D ( 1 only) , since chloroflourocarbons are used in fire extinguishers, so it must be only the 1st one.

Can anyone confirm this!?

bromine is used in fire extinguishers .

Number 4 is NOT D and Number 5 is NOT B ! ( Cause these where the same answers I wrote, and they are wrong!) And number 3: I think it's D aswell!

Number 5: I think it has to be D ( 1 only) , since chloroflourocarbons are used in fire extinguishers, so it must be only the 1st one.

Can anyone confirm this!?

are u sure question 4 is correct? because i think it has to be 2 methyl butan-2-ol

Yeah, the questions are right!