Chemistry: Post your doubts here!

[qwertypoiu]

Doubt it. Calcium carbonate decomposes into calcium oxide and carbon dioxide when heated above 840°C, so gentle heating from a Bunsen burner would not be sufficient.

Oh I see.
I have a question. Would it melt or thermally decompose? Is there a way to make it do one and not the other based on what we wish?

 

[nehaoscar]

Why D? why not C?

 

[nehaoscar]

How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

 

[qwertypoiu]

View attachment 54234

How is it B? when does it increase and then decrease??

2O2- - 4e- ----> O2
This is oxidation. Electrons are lost. Oxidation state was -2, then became 0. So it increased by 2.

C + O2 ---> CO2
Oxygen is first 0, then becomes -2.

 

[nehaoscar]

How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

 

[Mathemagical]

View attachment 54235

How is it 3? i can only see 2...?

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.

 

[Mathemagical]

View attachment 54238
How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

Ethanoic acid dissociates into CH3COO- and H+ ions. Calcium forms Ca2+ ions, so 1 mol of Ca2+ ions will combine with 2 moles of CH3COO- ions.

 

[qwertypoiu]

View attachment 54235

How is it 3? i can only see 2...?

A hydrogen atom must be broken off from the organic compound by homolytic fission. Depending on from where this is done, a different resulting free radical will be formed.

The three methane groups are treated as same. From the ethyl group there are two carbons from which the hydrogen may be stolen

 

[Mathemagical]

View attachment 54237
How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

That's correct. Carbon has 2 electrons in the p-orbital and the chloride ion has 4 electrons in the p orbital. However, both have 2 unpaired electrons in the orbital, so Option 3 is correct.

 

[qwertypoiu]

View attachment 54236

Why D? why not C?

An OH and H next to it must be given off for dehydration of alcohol. There is no way C can be formed this way. The OH is below so how can the double bond form there?

The correct answer D is confusing at first, but it's flipped to the left. Imagine it flipped back and you'll see how it could be formed.

 

[Mathemagical]

View attachment 54236

Why D? why not C?

Check the structure carefully. The compound is not symmetrical so C would not be the same.

 

[qwertypoiu]

View attachment 54237
How is 3 also correct? C has 2 in p and Cl+ has 4 in p right?

C has two. They're both unpaired.
Cl+ has 4. Two of them are paired, the other two are unpaired.

 

[qwertypoiu]

View attachment 54238
How is only number 1 correct?
Ethanoic acid has only 2 Carbons which is less than the empirical formula!?

Ca has a vacancy of +2. It would form Ca(OH)2, for example.
When Na reacts with acid it's simply like CH3COONa. But Ca will join with two of the anions.
Ca2+ ( CH3COO- )2

Thus the empirical formula has 4 carbon atoms.

 

[fantastic girl]

Assalamu Alaikum
http://studentbounty.com/pastpapers...l/Chemistry (9701)/2007 Nov/9701_w07_qp_1.pdf
Can someone explain me statement 1 of Q33 :/

http://studentbounty.com/pastpapers.../Chemistry (9701)/2012 Jun/9701_s12_qp_11.pdf
Q18 - iam confused...plz help :/

Thanks in advance

 

[Studydayandnight]

Since this is obviously a decomposition reaction, we can conclude that one mole of N2F4 decomposes into 2 moles of NF2. Therefore, only the N-N bond in the middle is broken, and not the N-F bonds. Option 1 is incorrect.

Option 2 states that the enthalpy change of the reaction is +160kJ/mol. This is the approximate bond enthalpy of the N-N bond, so this is correct.

Since we have concluded that X is NF2, we can now begin to inspect it in detail. A nitrogen atom has 5 valence electrons, and 2 of these are involved in bonding. This leaves 3 other electrons in the valence shell, unbonded. Therefore, the molecule is non-linear. Option 3 is correct.

Since Options 2 and 3 are correct, the answer is C.

Thank you!!

 

[qwertypoiu]

Assalamu Alaikum
http://studentbounty.com/pastpapers/Cambridge International Examinations (CIE)/International AS and A Level/Chemistry (9701)/2007 Nov/9701_w07_qp_1.pdf
Can someone explain me statement 1 of Q33 :/

http://studentbounty.com/pastpapers/Cambridge International Examinations (CIE)/International AS and A Level/Chemistry (9701)/2012 Jun/9701_s12_qp_11.pdf
Q18 - iam confused...plz help :/

Thanks in advance

It says pressure inside will be greater than atmospheric pressure outside. This is not true. Rather, they must be equal because the gas has stopped expanding. If the pressure inside were greater, the gas would continue pushing against the plunger and expanding.

Q 18: X - the fumes produced are HCl. If it's dissolved in aqueous potassium iodide solution, nothing happens. It dissolves. So the solution is colourless.
Y - any silver chloride solid that precipitates would dissolve in the ammonia solution, by forming Ag(NH3)2Cl. So again colourless.

 

[fantastic girl]

It says pressure inside will be greater than atmospheric pressure outside. This is not true. Rather, they must be equal because the gas has stopped expanding. If the pressure inside were greater, the gas would continue pushing against the plunger and expanding.

Q 18: X - the fumes produced are HCl. If it's dissolved in aqueous potassium iodide solution, nothing happens. It dissolves. So the solution is colourless.
Y - any silver chloride solid that precipitates would dissolve in the ammonia solution, by forming Ag(NH3)2Cl. So again colourless.

Thankyew soo much

but see in Y- first it forms the complex Ag(NH3)2Cl then its being added to silver nitrate so wont their be a ppt now ?

 

[qwertypoiu]

Thankyew soo much

but see in Y- first it forms the complex Ag(NH3)2Cl then its being added to silver nitrate so wont their be a ppt now ?

You said first it forms the complex... How? Ag+ ions are introduced from the silver nitrate solution LATER as you said.

But I understand what you mean, that they are adding the reagents the other way around. First they made the chloride ions dissolve in ammonia solution. Then they added the silver ions. This does not make any difference. The solution now has silver ions that will attempt to precipitate with chloride ions, only to be joined by the ammonia molecules also present, thus forming the complex. Hope that made sense

 

[fantastic girl]

You said first it forms the complex... How? Ag+ ions are introduced from the silver nitrate solution LATER as you said.

But I understand what you mean, that they are adding the reagents the other way around. First they made the chloride ions dissolve in ammonia solution. Then they added the silver ions. This does not make any difference. The solution now has silver ions that will attempt to precipitate with chloride ions, only to be joined by the ammonium ions also present, thus forming the complex. Hope that made sense

Ohh yea...I completely forgot ammonia was still in the complex xP
Thanks alot...I got it now =)

 

[Xaptor16]

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!