Chemistry: Post your doubts here!

[Falconwing]

How is this B??

 

[qwertypoiu]

The Sarcastic Retard qwertypoiu I need help in this question ...

Here i have posted the link for the question paper and my doubt is in question no 21 ....
I have even posted the explanation for Q21 which was answered previously .... My doubt is I don't get what they are trying to say in the part where i have highlighted ... so can one of you clarify it to me further.. Thanks in advance

https://docs.google.com/viewer?a=v&...sLm9yZ3x0ZWFjaGVyc3xneDoxYmI0OTYwOWIyZDRmNWVj

If the compound was an alkane and had no rings or double bonds, number of H atoms present = 2n+2 = 2(20)+2 = 42

Now, every time there're 2H less, you'll either have a double bond or a ring. The question states that there's one aldehyde (C=O) and 1 ring structure which has 1 C=C so this accounts for 6 missing Hydrogens, thereby leaving you with 8 missing Hydrogens.

8/2 = 4 Hydrogens in the aliphatic side chain.

However, total C=C are 5 because you have to include the C=C from the cyclohexene + cis formation hence A

I will assume you have understood the parts you did not highlight. So there would have been 42 hydrogen atoms, if it were just a straight chain alkane. We wish for only 28 to be left.
6 hydrogen atoms are accounted for by the presence of aldehyde and ring structure. So 42-6 = 36 we'd expect now.
However we wish for 28. We need to eliminate 36-28= 8 more hydrogen atoms.
Every time a double bond is added to a saturated chain, 2 hydrogen atoms are gotten rid of.
Therefore, 8/2 = 4 double bonds required to satisfy our condition.

 

[Falconwing]

Aluminium carbide, Al 4C3, reacts readily with aqueous sodium hydroxide. The two products of the

reaction are NaAlO2 and a hydrocarbon. Water molecules are also involved as reactants.

What is the formula of the hydrocarbon?

A CH4
B C2H6
C C3H8
D C6H12
someone explain this plz the answer is A

Reaction => Al4C3 + 4NaOH + 4H2O --> 4NaAlO2 + 3CH4. You'll end up at this if you try to balance the equation.

 

[mohhef3]

Use of the Data Booklet is relevant to this question.

A sample of potassium oxide, K2O, is dissolved in 250cm3 of distilled water. 25.0cm3

solution is titrated against sulfuric acid of concentration 2.00moldm–3. 15.0 cm3 of this

acid is needed for complete neutralisation. of this sulfuric

Which mass of potassium oxide was originally dissolved in 250cm3 of distilled water?

A 2.83g
B 28.3g
C 47.1g
D 56.6g

 

[qwertypoiu]

Use of the Data Booklet is relevant to this question.

A sample of potassium oxide, K2O, is dissolved in 250cm3 of distilled water. 25.0cm3

solution is titrated against sulfuric acid of concentration 2.00moldm–3. 15.0 cm3 of this

acid is needed for complete neutralisation. of this sulfuric

Which mass of potassium oxide was originally dissolved in 250cm3 of distilled water?

A 2.83g
B 28.3g
C 47.1g
D 56.6g

K2O + H2SO4 ----> K2SO4 + H2O
Moles of acid = 15/1000*2 = 0.03mol
Moles of K2O in 25cm3 = 0.03mol, due to ratio.
Moles of K2O in 250cm3, = 0.03*10 = 0.3mol
Mass = (39.1*2+16)*0.3 = 28.26g

 

[mohhef3]

K2O + H2SO4 ----> K2SO4 + H2O
Moles of acid = 15/1000*2 = 0.03mol
Moles of K2O in 25cm3 = 0.03mol, due to ratio.
Moles of K2O in 250cm3, = 0.03*10 = 0.3mol
Mass = (39.1*2+16)*0.3 = 28.26g

oh i didnt multiply it by 10 he wanted it in the distilled solution.thx mate what r u studing?a levels or as

 

[qwertypoiu]

oh i didnt multiply it by 10 he wanted it in the distilled solution.thx mate what r u studing?a levels or as

Welcome. Doing AS this year

 

[shazmina]

I will assume you have understood the parts you did not highlight. So there would have been 42 hydrogen atoms, if it were just a straight chain alkane. We wish for only 28 to be left.
6 hydrogen atoms are accounted for by the presence of aldehyde and ring structure. So 42-6 = 36 we'd expect now.
However we wish for 28. We need to eliminate 36-28= 8 more hydrogen atoms.
Every time a double bond is added to a saturated chain, 2 hydrogen atoms are gotten rid of.
Therefore, 8/2 = 4 double bonds required to satisfy our condition.

Thanks alot JazakAllah khairan

 

[mohhef3]

someone help me out with que 30,28 and 23
http://maxpapers.com/syllabus-materials/chemistry-9701-a-level/attachment/9701_w14_qp_12/
and in que 32 what will differ in my calculations when i see that dot

 

[princess Anu]

how is 2 important in helping to reduce atmospheric pollution? :/

 

[princess Anu]

Is there an easier way to find out the number of isomers? and for this question how many are there?? Please help!!

It's 9701/13/0/N/14

whats the answer

 

[Abdel Moniem]

View attachment 54707 how is 2 important in helping to reduce atmospheric pollution? :/

Oxygen in the air reacts with sulphur dioxide to form sulphur trioxide which then reacts with calcium oxide to form calcium sulphate.

 

[princess Anu]

so this way both the pollutants i.e So3 & so2 quantities get reduced?

Oxygen in the air reacts with sulphur dioxide to form sulphur trioxide which then reacts with calcium oxide to form calcium sulphate.

 

[princess Anu]

why is C wrong?

 

[princess Anu]

how do we read the benzene rings? why is C chiral and not D?

 

[BhaiArshad]

View attachment 54717 how do we read the benzene rings? why is C chiral and not D?

Every Carbon in Benzene ring has a double bond so none of the carbons in a benzene ring are chiral. C is chiral because Central C atom is Connected to the following groups:
1) OH
2) CH3
3) Benzene Ring
4) OH Benzene Ring

4 different groups so it is chiral. Central Atom C in part D is connected to:
1) OH
2) CO2CH2CH3
3) OH Benzene Ring
4) OH Benzene Ring

 

[princess Anu]

hey you missed out the OH group attached to the benzene ring in option C (it wasn't printed properly ) .. look at the question again

 

[BhaiArshad]

hey you missed out the OH group attached to the benzene ring in option C (it wasn't printed properly )View attachment 54722 .. look at the question again

In C the Rings are different since OH is attached to different Carbon.

 

[qwertypoiu]

View attachment 54716 why is C wrong?

Pressure cannot affect Kc. Only temperature does.

 

[nehaoscar]

Why D?