Chemistry MCQ thread...

[Hateexams93]

WHY NOT A ?

ans is D
explanation: pv is constant so b and c are wrong, in case of A, graph is also direct relationship, with negative slope ( for inversely proportion check book)

A shows inverse proportion , when V increases P decreases .. so why its wrong ?

 

[Mobeen]

because a straight line shows a direct relation ..

 

[Hateexams93]

Mobeen is it always a curve ? and r u sure about it ?

 

[Mobeen]

yes . a straight line represent a direct relationship and a curve represents a inverse relation

 

[kshumaila52]

the graph for inverse proportion is always a curve .. because i think there is a limit when the curve becomes horizontal .. but a straight line would cut the x-axis .. but the presure cant be zero right ? thats my logic for why it cant be a straight line .. but i do know that for every inverse graph it is a curve ..

graph between T and V (direct relation ) on extrapolation cut x axes, so fact is that straight line indicate direct relationship, if it is decreasing as in A, it means slop is negative.

 

[Mobeen]

@kshumaila ur right .. straight line will represent a direct relation with only the gradient negative or positive.

 

[Hateexams93]

Inverse variations are in the form y = k/x, so they will never touch y=0 or x=0. Yes, they are curved, but they have the characteristic that as one coordinate increases, the other decreases. That eliminates A. LOL sometimes its easier to google

 

[Mobeen]

good that u understood it.. and googles the best ! i sometimes copy paste whole questions and it shows me in results if some is talking on that question on some forum !

 

[Hateexams93]

Use of the Data Booklet is relevant to this question.
The combustion of fossil fuels is a major source of increasing atmospheric carbon dioxide, with a
consequential rise in global warming. Another significant contribution to carbon dioxide levels
comes from the thermal decomposition of limestone, in the manufacture of cement and of lime for
agricultural purposes.
Cement works roast 1000 million tonnes of limestone per year and a further 200 million tonnes is
roasted in kilns to make lime.
What is the total annual mass output of carbon dioxide (in million tonnes) from these two
processes?
A 440 B 527 C 660 D 880
getting the wrong answer again :/

 

[Hateexams93]

stupid me -.- forgot to include values from the further 200 , omg i'm so careless :/

 

[Mobeen]

whats the answer ?

 

[Hateexams93]

B. 440+88 =528 ( but their its 527 ) anyways its close to that value ))

 

[Mobeen]

yeah .. some questions have answers of approximation ..

 

[Hateexams93]

or may be we are doing it in a wrong way and getting the same answer ))that happens to me sometimes

 

[Mobeen]

could be but i have seen some questions which dont have acurate answers and u have to aproximate it ..

 

[Hateexams93]

try this

 

[Hateexams93]

OR
Ethanal, CH3CHO, can be reduced using an aqueous methanolic solution of NaBH4 as the
reducing agent.
This is a nucleophilic addition reaction.
What could be the first step of this mechanism?
A attack of an H+ ion at the carbon atom of the carbonyl group
B attack of an H+ ion at the oxygen atom of the carbonyl group
C attack of an H– ion at the carbon atom of the carbonyl group
D attack of an H– ion at the oxygen atom of the carbonyl group

 

[kshumaila52]

try this

D
because if before dehydration it was tertiary alcohol, which can not oxidize( simple way is add water to all, will be structure of each before dehydration)

 

[kshumaila52]

OR
Ethanal, CH3CHO, can be reduced using an aqueous methanolic solution of NaBH4 as the
reducing agent.
This is a nucleophilic addition reaction.
What could be the first step of this mechanism?
A attack of an H+ ion at the carbon atom of the carbonyl group
B attack of an H+ ion at the oxygen atom of the carbonyl group
C attack of an H– ion at the carbon atom of the carbonyl group
D attack of an H– ion at the oxygen atom of the carbonyl group

C, as H- i s nucleophile and due top electronegativity difference, there is partial positive charge on carbon, so nucleophiole will approach to it.

 

[Hateexams93]

12
© UCLES 2008 9701/01/M/J/08
30 Compound X, C6H12O, is oxidised by acidified sodium dichromate(VI) to compound Y.
Compound Y reacts with ethanol in the presence of a little concentrated sulphuric acid to give
liquid Z.
What is the formula of Z?
A CH3(CH2)2CH=CHCO2H
B CH3(CH2)4CH2COCH2CH3
C CH3(CH2)4CO2CH2CH3
D CH3CH2CO2(CH2)4CH3