Chemistry: Post your doubts here!

[Rizwan Javed]

I thought only the CH3 which is near to OH was the only chiral center, because it was the only one which was sp3 hybridizied and had four different groups attached but how is the answer D?? View attachment 59774

I think these all are the chiral centers for this molecule.

 

[Eugene99]

View attachment 59775
I think these all are the chiral centers for this molecule.

Can you please explain why? Shouldn't the chiral centers have four different substituent groups attached?

 

[Rizwan Javed]

View attachment 59773

So I can understand that carvone is a ketone and 2-4 DNPH is a test for carbonyl group, but how will I know that what amount of molecules react with 2,4 DNPH??

After the reaction with Concentrated, Hot, KMnO4 you get a molecule as shown above.

There're 4 carbonyl groups. 1 molecule of 2,4 DNPH reacts with 1 carbonyl. As there're are 4 carbonyl groups, so you'll need 4 molecules of 2,4 DNPH.
2,4 DNPH reacts with a carbonyl group like this:

 

[sj0007]

It can never be 6, because if you divide 6 Carbons into two molecules, each molecule will have 3 Carbons. You can't make any non-cyclic isomer out of propane. So 6 is not an option.

Ohhhhh RIGHT!
How stupid of me! XD
Thnx!

 

[Eugene99]

View attachment 59776
After the reaction with Concentrated, Hot, KMnO4 you get a molecule as shown above.

There're 4 carbonyl groups. 1 molecule of 2,4 DNPH reacts with 1 carbonyl. As there're are 4 carbonyl groups, so you'll need 4 molecules of 2,4 DNPH.
2,4 DNPH reacts with a carbonyl group like this:
View attachment 59777

thanks! I get that

 

[Eugene99]

View attachment 59776
After the reaction with Concentrated, Hot, KMnO4 you get a molecule as shown above.

There're 4 carbonyl groups. 1 molecule of 2,4 DNPH reacts with 1 carbonyl. As there're are 4 carbonyl groups, so you'll need 4 molecules of 2,4 DNPH.
2,4 DNPH reacts with a carbonyl group like this:
View attachment 59777

wait, can you tell me which reaction was that when ketone reacted with potassium manganate solution?
why was carbondioxide produced? I don't remember reading about any such reaction??

 

[Rizwan Javed]

RCH=CH2
If a terminal carbon atom, like shown in red above, is bonded to two hydrogen atoms we get oxidation to a CO2 molecule.

 

[Abdullahassan_99]

First write the Kc expression for this reaction:
Kc = [HI]^2 / [I2]*[H2]

We know Kc = 60 at the specified temperature.

Assume a container of 1dm^3 for simplicity:
[H2] = 2
[I2] = 0.3
Kc = 60
[HI] = sqrt(Kc*[I2]*[H2]) = sqrt(60*0.3*2) = sqrt(36) = 6mol/dm^3

Thank you SO much

 

[Eugene99]

Reaction of aldehyde with Tollen's reagent makes silver mirror inside the test tube. But when I mixed Tollen's reagent with aldehyde, and heated it up, only black precipitate appeared, no silver mirror, why?

 

[Rizwan Javed]

Reaction of aldehyde with Tollen's reagent makes silver mirror inside the test tube. But when I mixed Tollen's reagent with aldehyde, and heated it up, only black precipitate appeared, no silver mirror, why?

First, a black ppt is formed, but if you shake the test-tube gently, you'll see that silver mirror.

 

[Eugene99]

First, a black ppt is formed, but if you shake the test-tube gently, you'll see that silver mirror.

it just forms a blackish water after mixing could my aldehyde be stale since I have it for almost a year, Tollen's reagent I just bought recently

 

[Rizwan Javed]

it just forms a blackish water after mixing could my aldehyde be stale since I have it for almost a year, Tollen's reagent I just bought recently

It doesn't make a difference, i guess. You can see a black ppt, it is an enough indication that aldehyde is present.

 

[qwertypoiu]

It doesn't make a difference, i guess. You can see a black ppt, it is an enough indication that aldehyde is present.

Do you know what compound is causing this black ppt?

 

[Rizwan Javed]

Do you know what compound is causing this black ppt?

I think that color is due to the formation of Ag (s).

 

[Bhaijan]

9701_w03_qp1
Ans is B
I dont understand how to solve this question
pls help!!!

 

[Mohammed Elatta]

View attachment 59786
9701_w03_qp1
Ans is B
I dont understand how to solve this question
pls help!!!

From the data given to us we know that 30% of the fertiliser mass is P2O5. Get the mass of the fertiliser.
In 100g of the fertiliser there is 30% of it P2O5 therefore mass of fertiliser is
(100/30) x 142= 473.3g
to know the percent by mass of phosporus in fertiliser calculate the mass of phosphorus as we have 2 atoms within each molecule of P205 in 1 mole the mass of phosporus is 31x2=62 calculate the percentage now
62x100/473.3= 13.1

 

[Bhaijan]

From the data given to us we know that 30% of the fertiliser mass is P2O5. Get the mass of the fertiliser.
In 100g of the fertiliser there is 30g P2O5 therefore mass of fertiliser is
(100/30) x 142= 473.3g
to know the percent by mass of phosporus in fertiliser calculate the mass of phosphorus as we have 2 atoms within each molecule of P205 in 1 mole the mass of phosporus is 31x2=62 calculate the percentage now
62x100/473.3= 13.1

wow thnks i didnt think to find the mass of fertilizer

 

[holoholo]

When preparing a solution of a fixed concentration from a given parent solution of concentration , say, 2.0 mol/dm3

A. We are required to prepare a solution of concentration of 1.0 mol/dm3 with volume 250 cm3 ( the concn cannot be greater than 2 !!!!!!!!!!!!!!)
a. Add 100 cm3 of the parent solution to a volumetric flask of marking at 250 cm3
b. Top off with water to the mark of 250 cm3. Use a wash bottle for this purpose to have greater control over the addition process


Shouldn't we add 125cm^3 of the parent solution not 100 cm^3 ?

 

[holoholo]

Also in this
When required to prepare 250 cm3 of 0.5 mol/dm3 solution of a crystal of Mr 50g

First realize that we need only 250 cm3, not 1 dm3
Now in 250 cm3 there will be: 50/4 = 12.5 g of the solid

Shouldn't it be 6.25 g ?

 

[qwertypoiu]

When preparing a solution of a fixed concentration from a given parent solution of concentration , say, 2.0 mol/dm3

A. We are required to prepare a solution of concentration of 1.0 mol/dm3 with volume 250 cm3 ( the concn cannot be greater than 2 !!!!!!!!!!!!!!)
a. Add 100 cm3 of the parent solution to a volumetric flask of marking at 250 cm3
b. Top off with water to the mark of 250 cm3. Use a wash bottle for this purpose to have greater control over the addition process


Shouldn't we add 125cm^3 of the parent solution not 100 cm^3 ?

If you want to prepare 250cm3 of 1mol/dm3 solution from 2mol/dm3 solution, you need to use 125 of it yes. Then 125 of water. So that the concentration is halved.