Chemistry and Physics AS paper 12 MCQS

[snowbrood]

http://papers.xtremepapers.com/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_s07_qp_1.pdf

Q no 9 10 12 13 14 16 18 20 22 26 34 37 39 n 40 pleasee

for Q9
let X2=A
Y2=B
X2y=C
C^2/(A^2)*B=2
C^2=2*(A^2)*B
SQUARE ROOT BOTH SIDES WE GET
C=(2^0.5)*A*(B^0.5) anything raised to 0.5 means it is square rooted ok
now for equation 2 we have
A*(B^0.5)/C
PUT IN VALUE OF C
WE GET A*(B^0.5)/(2^0.5)*A*(B^0.5)
thus we get 1/(2^0.5) as required by question

 

[IGCSEstudent2012]

Which reaction would not give propene as one product?
A adding an excess of concentrated sulfuric acid to propan-1-ol
B adding warm aqueous sodium hydroxide to 2-bromopropane
C adding warm ethanolic sodium hydroxide to 1-bromopropane
D passing propan-2-ol vapour over heated aluminium oxide
pls anyone??:/

 

[Mairaxo]

B?

Which reaction would not give propene as one product?
A adding an excess of concentrated sulfuric acid to propan-1-ol
B adding warm aqueous sodium hydroxide to 2-bromopropane
C adding warm ethanolic sodium hydroxide to 1-bromopropane
D passing propan-2-ol vapour over heated aluminium oxide
pls anyone??:/

 

[IGCSEstudent2012]

B?

yes but pls explain how?:/

 

[Mairaxo]

yes but pls explain how?:/

in A H2SO4 is dehydrating so removal of water will take place and a double bond will form forming propene.
in B NaOH(aq) is used. it will only substitute Br with OH so propanol forms not propene.
in C NaOH in ethanol will remove the Br and form a double bond instead so propene form.
in D Al2O3 is also used as dehydrating agent catalyst so it removes OH and adds double bond.

 

[cute97]

try to complete the paper on time!

hahhahahhaha thnxx i complete the first 25 on time

 

[IGCSEstudent2012]

hahhahahhaha thnxx i complete the first 25 on time

LOL!...same with me

 

[IGCSEstudent2012]

in A H2SO4 is dehydrating so removal of water will take place and a double bond will form forming propene.
in B NaOH(aq) is used. it will only substitute Br with OH so propanol forms not propene.
in C NaOH in ethanol will remove the Br and form a double bond instead so propene form.
in D Al2O3 is also used as dehydrating agent catalyst so it removes OH and adds double bond.

Mairaxo you are the bessstt!..thanks alot

 

[IGCSEstudent2012]

Compound X changes the colour of warm acidified sodium dichromate(VI) from orange to green.
1mol of X reacts with 2mol of HCN in the presence of KCN.
What could X be?
A CH3CH2CH2CHO
B CH3COCH2COCH3
C H2C=CHCH2CHO
D OHCCH2CH2CHO

can someone explain me this or how to solve ques like these:/?

Mairaxo pls if u can?...thanks fr yr time

 

[Mairaxo]

Mairaxo pls if u can?...thanks fr yr time

C?

 

[cute97]

LOL!...same with me

thanks you raise moral

 

[Mairaxo]

Oh wait .. D has two CHO groups right? Or is that an OH ?

 

[IGCSEstudent2012]

n

C?

no its D:/

 

[Mairaxo]

Mairaxo pls if u can?...thanks fr yr time

A just has one CHO group so only 1 mole of HCN needed
B needs 2 mol HCN but as it is a ketone it doesnt get oxidised so no colour change
C also needs only one mol HCN as it has only one CHO group
D has 2 CHO groups so 2 mol of HCN needed and CHO gets oxidised to acid so colour will also chnage so its D

 

[IGCSEstudent2012]

Oh wait .. D has two CHO groups right? Or is that an OH ?

its OH group

 

[Mairaxo]

its OH group

No its a CHO according to what you wrote!

 

[IGCSEstudent2012]

A just has one CHO group so only 1 mole of HCN needed
B needs 2 mol HCN but as it is a ketone it doesnt get oxidised so no colour change
C also needs only one mol HCN as it has only one CHO group
D has 2 CHO groups so 2 mol of HCN needed and CHO gets oxidised to acid so colour will also chnage so its D

thanku :* :')

 

[IGCSEstudent2012]

No its a CHO according to what you wrote!

lol yeah..its like ive frogotten chem:/

 

[Mairaxo]

thanku :* :')

your welcome

 

[Mairaxo]

lol yeah..its like ive frogotten chem:/

Lol no problem! Its hard to remember all this but the more you solve the easier it becomes and the more you remember