Author Topic: Edexcel CHEMISTRY DOUBTS!!!! (Read 253533 times)

Amii · « **Reply #825 on:** March 25, 2011, 07:32:06 pm »

Number of moles = Concentration X Volume

=2 X (25/1000) [1dm3=1000cm3)
=0.05 moles of ammonia

NH3 : (NH4)2SO4
2 : 1
0.05 : x

x = 0.05/2 = 0.025 moles of ammonium sulfate

Molar mass of (NH4)2SO4 = 132.1 g mol-1

Mass = 132.1 X 0.025
=3.3025 g

Blizz_rb93 · « **Reply #826 on:** March 25, 2011, 08:17:27 pm »

Thank you!!! =)
Really appreciate it!

+rep

Amii · « **Reply #827 on:** March 26, 2011, 06:33:52 am »

Quote from: Blizz_rb93 on March 25, 2011, 08:17:27 pm

Thank you!!! =)
Really appreciate it!
+rep

No problem

Blizz_rb93 · « **Reply #828 on:** March 26, 2011, 01:41:58 pm »

a) Aluminium is extraced by electrolysis of Al2O3. What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?

b) If the yield of the electrolysis plant is 90%, what mass of the oxide must be used to produce 1 tonne of aluminium?

how do we find out in (a) the percentages of each element in the compound??

elemis · « **Reply #829 on:** March 26, 2011, 01:51:38 pm »

Quote from: Blizz_rb93 on March 26, 2011, 01:41:58 pm

a) Aluminium is extraced by electrolysis of Al2O3. What is the maximum mass of the metal that could be obtained from 1 tonne of the oxide?

b) If the yield of the electrolysis plant is 90%, what mass of the oxide must be used to produce 1 tonne of aluminium?

how do we find out in (a) the percentages of each element in the compound??

2Al₂O₃ ----> 4Al + 3O₂

1 tonne of bauxite = 9.80 * 10^-3 moles

Hence, 1 tonne of bauxite gives 0.0196 moles of Al metal i.e. 0.529 tonnes of Aluminum.

elemis · « **Reply #830 on:** March 26, 2011, 01:57:38 pm »

Using actual yield/theoretical yield * 100 = percentage yield

1/x = 0.9

x = 1.11 tonnes of Al.

Now use the molar ratios to find the mass of bauxite. Make sure to convert 1.11 tonnes of Al to moles when using the ratio !

Blizz_rb93 · « **Reply #831 on:** March 26, 2011, 02:06:44 pm »

how did you find out the moles of bauxite?? :S I dont understand

elemis · « **Reply #832 on:** March 26, 2011, 02:19:37 pm »

Quote from: Blizz_rb93 on March 26, 2011, 02:06:44 pm

how did you find out the moles of bauxite?? :S I dont understand

First, I wrote the equation. Then I balanced it.

We are told we want 1 tonne of the metal.

Thus, moles = mass/molar mass

moles = 1/molar mass of bauxite

moles = 9.80 * 10^-3 moles

Blizz_rb93 · « **Reply #833 on:** March 26, 2011, 02:33:08 pm »

oh okay i get it now! xD
i figured out i was making a mistake in the calculations :p
for the molar mass, instead of putting 27 for the Al, i used 23 xD mixed it up with sodium for some reason :p
anyways thank you!!

RoRo · « **Reply #834 on:** April 01, 2011, 06:03:19 pm »

I have a question in Organic Chemistry - addition reactions of alkenes.

If we're asked to give all the possible products of the following reaction:

CH3CH=CH2 ----Br2 [on top of the arrow] and NaCl [at the bottom of the arrow]---->

What would the answer be? According to my teacher's explanation it should be like this: CH3CH(Br)CH2(Br) and CH3CH(Cl)CH2(Br) but what I wrote in my book in the class was this: CH3CH(Br)CH2(Br) and CH3CH(Br)CH2(Cl), so I wanted to confirm which one is right?

Thanks in advance!

elemis · « **Reply #835 on:** April 01, 2011, 06:09:44 pm »

Quote from: The Secret on April 01, 2011, 06:03:19 pm

I have a question in Organic Chemistry - addition reactions of alkenes.

If we're asked to give all the possible products of the following reaction:

CH3CH=CH2 ----Br2 [on top of the arrow] and NaCl [at the bottom of the arrow]---->

What would the answer be? According to my teacher's explanation it should be like this: CH3CH(Br)CH2(Br) and CH3CH(Cl)CH2(Br) but what I wrote in my book in the class was this: CH3CH(Br)CH2(Br) and CH3CH(Br)CH2(Cl), so I wanted to confirm which one is right?

Thanks in advance!

You are both correct.

RoRo · « **Reply #836 on:** April 01, 2011, 06:56:46 pm »

Quote from: Ari Ben Canaan on April 01, 2011, 06:09:44 pm

You are both correct.

How come?
See, that's what I understood, correct me if I'm wrong!

In CH₃CH=CH₂, the alkyl group is present on the LHS so it electrons are pushed to the RHS due to the Induction effect, so a carbocation is formed at the LHS and so Br⁺ which is more reactive than Na⁺ will attach to the slightly negatively charged carbon atom i.e. the one of the RHS and now what's left is the Br^- and the Cl^-, so they'll have to attach to the carbocation which is positively charged since they are negatively charged, right? & not on the RHS where the carbon atom is negatively charged.

& also, another question:

What was the original alkene before it got oxidised in the presence of hot acidic KMnO₄ and produced CO₂ + CH₃COCH₂CH₃ + CH₃COCH₃ + CH₃COOH + H₂O?

The Golden Girl =D · « **Reply #837 on:** April 02, 2011, 10:12:22 am »

I know that ethanol is an inert solvent so it would be the reaction which is taking place with Most ease.

About ethanoic acid ,I'm not sure.

Water and sodium is the Most vigorous reaction here Since Na is in group 1 and all metals in group 1 react vigorously with water.

I hope I helped

RoRo · « **Reply #838 on:** April 02, 2011, 04:27:42 pm »

Quote from: ~ The Golden Girl ~ on April 02, 2011, 10:12:22 am

I know that ethanol is an inert solvent so it would be the reaction which is taking place with Most ease.

About ethanoic acid ,I'm not sure.

Water and sodium is the Most vigorous reaction here Since Na is in group 1 and all metals in group 1 react vigorously with water.

I hope I helped

Actually the answer according to my teacher was that it's easier with the acid, then with water then with alcohol, she had even told us the reasoning, but I haven't noted it down clearly! :/

RoRo · « **Reply #839 on:** April 03, 2011, 10:31:20 am »

& my 4th questions is: Do we need to learn the wavenumbers for the different bonds in the different functional groups in IR mass spectroscope?

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