P1 MCQ's preparation thread for chemistry ONLY!!!!

[Aries_95]

when k2cr2o7 is used in oxidation product is always aldehyde not carboxlic acid

Primary alcohols are oxidised to aldehyde which is then further oxidised to carboxylic acid so it is a product of oxidation.

 

[HubbaBubba]

Can anybody explain this to me? It's q1 in May June 2004..

1 Which of these samples of gas contains the same number of atoms as 1g of hydrogen (Mr: H2 = 2)?
A) 22g of carbon dioxide (Mr: CO2, 44)
B) 8g of methane (Mr: CH4, 16)
C) 20g of neon (Mr: Ne, 20)
D) 8g of ozone (Mr: O3, 48)

Aren't A and B the same answer?

 

[magnesium]

Can some please explain Winter 2005 Q24 to me?

this is elimination reaction...butan 2 ol converts to butene...3 products are formed...but 1 en, but 2 ene ...this has 2 isomers... cis n trans

 

[studen12345]

Can anybody explain this to me? It's q1 in May June 2004..

1 Which of these samples of gas contains the same number of atoms as 1g of hydrogen (Mr: H2 = 2)?
A) 22g of carbon dioxide (Mr: CO2, 44)
B) 8g of methane (Mr: CH4, 16)
C) 20g of neon (Mr: Ne, 20)
D) 8g of ozone (Mr: O3, 48)

Aren't A and B the same answer?

i am also confused wid dis question
plz somebody enlighten us

 

[HubbaBubba]

i am also confused wid dis question
plz somebody enlighten us

The answer is C??? WHYYYY XD

 

[itallion stallion]

the

Why can we not oxidise this compound? It has OH group so it should be oxidised which is written in 2. Summer 2005, Q39.
View attachment 28630

OH groups present are secondary so they will oxidise to ketone and ketone dont oxidise to carboxylic acid.

 

[itallion stallion]

.is t

mcq 2) B is not the ans cz p=9, n=19-9=10 nd e=10 nd the qts says all shud b different...
mcq 10) u need to check using electronegativities...
mcq 33) 1 is correct h2so4 is a strong acid nd will release high conc. of H+ ions....SO4 ^2- ions r not in high conc.b/c the HSO4- is a weak acid...so 2 is incorrect in dis way u dont need to think of 3...so D is correct...

as we go across a period electronrgativity increases. Down a grp electronegativity decreases.is this correct??

 

[Aries_95]

i am also confused wid dis question
plz somebody enlighten us

The question says the mass of HYDROGEN ATOMS, we take the mr to be 1 and the mass is 1g which give us 1 mole.
Since Ne has mr of 20, and the mass is 20, the moles will be equal to 1. the no of atoms are thus same to that of 1 g of HYDROGEN ATOMS.
Hope you understand

 

[itallion stallion]

http://papers.xtremepapers.com/CIE/... AS Level/Chemistry (9701)/9701_w10_qp_12.pdf plz help me with q13,q33.thanks alot!!

 

[SYED ALI ARIZ]

ANY1 WITH ACCURATE N PRECISE PHYSICS CHEMISTRY NOTES??? POST THM.....DO REVISION GUIDDES WORK WELL????

 

[magnesium]

Primary alcohols are oxidised to aldehyde which is then further oxidised to carboxylic acid so it is a product of oxidation.

thanks.. bt i thought that aldehydes can only b made by using K2Cr207?!

 

[HubbaBubba]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_s06_qp_1.pdf

Can somebody explain q10 and q38

 

[angel456]

h

Q21- Substitute n by numbers 1 to 4. then find all isomers. There will be 7.
Q37- In 2 there will be only one ketone and one acid as there is one primary and one secondary C atom. In 3 a ketone and a dibasic acid will b produced. Only one has 2 secondary C atoms so it will produce 2 ketones.
Q39- H2SO4 will dehydrate the compounds. 1 on dehydration will produce an alkene which reacts with KMnO4. 2 also forms an alkene. 3 is an acid so it wont react with H2SO4.

in Q2 how 7 please explain

 

[Aries_95]

thanks.. bt i thought that aldehydes can only b made by using K2Cr207?!

Yes aldehydes are made but you can say that they are the initial products of oxidation of primary alcohol..the final product is carboxylic acid

 

[magnesium]

Yes aldehydes are made but you can say that they are the initial products of oxidation of primary alcohol..the final product is carboxylic acid

Can they b made using KMnO4?

 

[Aries_95]

Can they b made using KMnO4?

Yes since KMNO4 is also used for oxidation

 

[Aries_95]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w10_qp_12.pdf plz help me with q13,q33.thanks alot!!

Q.33
In a triple or a double bond, there is only ONE SIGMA BOND, the rest are PI bonds hence option 1 is wrong
the pi-bond cannot itself rotate hance the rotation can only take place along the sigma bond axis.
since option 2 and 3 are correct, the answer is C.

 

[magnesium]

Yes since KMNO4 is also used for oxidation

if aldehyde is reacted with cold kmno4 wat will b the product?

 

[Aries_95]

if aldehyde is reacted with cold kmno4 wat will b the product?

when aldehydes are oxidised using acidified KMNO4, carboxylic acids are produced and when oxidised using alkaline KMNO4, salt of carboxylic acids are produced.

 

[magnesium]

when aldehydes are oxidised using acidified KMNO4, carboxylic acids are produced and when oxidised using alkaline KMNO4, salt of carboxylic acids are produced.

Will not the condition effect the product? i mean hot / cold oxidising agent?