Chemistry: Post your doubts here!

[Metanoia]

Use of the Data Booklet is relevant to this question.
Ethyl ethanoate can be obtained from ethanoic acid and ethanol by the following reaction.
CH3CH2OH + CH3CO2H = CH3CO2CH2CH3 + H2O (where the = is the double arrow arrow)
Ethanol (30 g) and ethanoic acid (30 g) are heated under reflux together, and 22 g of ethyl
ethanoate are obtained.
What is the yield of the ester?
A. 25%
B. 38%
C. 50%
D. 77%

Answer is C, I need the explanation or workout for the calculations please!

Convert the masses of ethanol and ethanoic acid to moles to figure out the limiting reagent.

Limiting reactant is acid, 0.5 moles. Expected moles of ester is thus 0.5 moles, 44g.

%yield = 22/44 = 50%

 

[The Sarcastic Retard]

Use of the Data Booklet is relevant to this question.
Ethyl ethanoate can be obtained from ethanoic acid and ethanol by the following reaction.
CH3CH2OH + CH3CO2H = CH3CO2CH2CH3 + H2O (where the = is the double arrow arrow)
Ethanol (30 g) and ethanoic acid (30 g) are heated under reflux together, and 22 g of ethyl
ethanoate are obtained.
What is the yield of the ester?
A. 25%
B. 38%
C. 50%
D. 77%

Answer is C, I need the explanation or workout for the calculations please!

n of alcohol = 30/46
n of acid = 30/60
limiting reagent is acid since its no of mole is smaller
so mass of theoretical yield of ester - 30/60 x 88 = 44
percentage = 22/44 x 100% = 50%

 

[nehaoscar]

One on the CH3 group on the far left, one on the CH2 beside it, the other on either one of the CH3 groups attached to the central carbon atom.

Oh! It can also join on the CH2 besides the CH3? Thanks!

 

[nehaoscar]

Thanks a lot everyone especially Mathemagical and qwertypoiu for your explanations! They really helped

 

[Mathemagical]

Thanks a lot everyone especially Mathemagical and qwertypoiu for your explanations! They really helped

No worries, always glad to help.

 

[princess Anu]

I can't find the answers for these questions so can somebody check my answers & see if they seem correct, please?
8B 9B 1D 6 D??

I

 

[nehaoscar]

Why A? Why not D?

 

[Mathemagical]

View attachment 54264
Why A? Why not D?

Ammonia has hydrogen bonding, which is the strongest intramolecular bond, so it is the least ideal.

 

[Mathemagical]

I can't find the answers for these questions so can somebody check my answers & see if they seem correct, please?
8B 9B 1D 6 D??

IView attachment 54261View attachment 54262 View attachment 54263

Yes, I got the same answers too. Where did you get these questions from?

 

[nehaoscar]

Why not D?

 

[Mathemagical]

View attachment 54265
Why not D?

A nucleophile is a chemical species which donates an electron pair to an electrophile. Therefore, it must have a lone pair of electrons to do this.

 

[nehaoscar]

.
How are 2 and 3 correct?

Cl stays -1 all through right?
And N goes from +5 to 0 right?
So N is reduced....

 

[nehaoscar]

Why are 2 and 3 wrong?

 

[nehaoscar]

Why is 3 wrong ... it reacts with Na so shouldn't it be an alcohol?

 

[Mathemagical]

View attachment 54266.
How are 2 and 3 correct?

Cl stays -1 all through right?
And N goes from +5 to 0 right?
So N is reduced....

In NH4ClO4, the oxidation state of chlorine is +7, so it is reduced to -1 in AlCl3.
N increases from -3 to 0.

Remember that in the ammonium ion, NH4+, the oxidation state of N is -3 and that of H is +1.

 

[Mathemagical]

View attachment 54267
Why are 2 and 3 wrong?

Option 2: Halogenoalkanes have less H atoms because they are replaced by halogens, so they form hydrogen bonds less readily.

Option 3: Alkanes cannot undergo addition polymerisation.

Therefore, they are both wrong.

 

[Metanoia]

View attachment 54265
Why not D?

Nucleophiles contain lone pairs, but are not necessary negatively charged.

Examples of commonly encountered neutral nucleophiles are H2O and NH3.

 

[qwertypoiu]

View attachment 54265
Why not D?

H2O, for example, is a nucleophile. Because it has a lone pair it can attack with. However, water molecules are not negatively charged.

 

[Mathemagical]

View attachment 54268
Why is 3 wrong ... it reacts with Na so shouldn't it be an alcohol?

Option 3 is wrong because it could either be an alcohol or a carboxylic acid. There is no observation which confirms either of these, so we cannot assume that it is an alcohol definitely.

 

[qwertypoiu]

My teacher says you can conclude the answer is C simply because Al3+ and C4- can only form Al4C3 based on their valency.

However I think there must be a reason behind the other numbers given, if there is a method which utilises the given information please help. Thanks.