Chemistry: Post your doubts here!

[Lola_sweet]

How do you do Q 5 and 6?
View attachment 59613

Q5)
it cant be A as the protons and electrons are same in number.
it cant be B as the number of neutrons and electrons are same (remember chlorine is gaining an electron here)
it cant be C as the number of neutrons and protons are the same
its D because number of neutrons is 20, number of protons is 19 and number of electrons is 18 (K loses an electron)

for Q6) im gonna end up giving a crap explanation
so its best someone else explains it sorry abt tht :3

 

[drowning-in-studies]

A solution of Sn2+ ions will reduce an acidified solution of MnO4 – ions to Mn2+ ions. The Sn2+ ions are oxidised to Sn4+ ions in this reaction. How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is added to an excess of acidified KMnO4 solution?
A 0.010 B 0.020 C 0.050 D 0.125
Can someone pls help me with this??

 

[drowning-in-studies]

Q5)
it cant be A as the protons and electrons are same in number.
it cant be B as the number of neutrons and electrons are same (remember chlorine is gaining an electron here)
it cant be C as the number of neutrons and protons are the same
its D because number of neutrons is 20, number of protons is 19 and number of electrons is 18 (K loses an electron)

for Q6) im gonna end up giving a crap explanation
so its best someone else explains it sorry abt tht :3

Okay thanks

 

[drowning-in-studies]

Q5)
it cant be A as the protons and electrons are same in number.
it cant be B as the number of neutrons and electrons are same (remember chlorine is gaining an electron here)
it cant be C as the number of neutrons and protons are the same
its D because number of neutrons is 20, number of protons is 19 and number of electrons is 18 (K loses an electron)

for Q6) im gonna end up giving a crap explanation
so its best someone else explains it sorry abt tht :3

hehehe.. okay, Q 5 is very easy but sometimes i just freak out

 

[Lola_sweet]

hehehe.. okay, Q 5 is very easy but sometimes i just freak out

hahaha yeah it is easy but i feel the same way
sometimes the basic qs seem the most complicated ones xD but thats A-levels for you

 

[Dark Destination]

Does anyone have the latest revision guide that is according to the 2016 syllabus? Is it released?

 

[Eugene99]

ans is D but I get 0.003 or something...help!

 

[My Name]

View attachment 59614
ans is D but I get 0.003 or something...help!

pV=nRT
so converting them to the specific units we get:
103000 x 5.37x10^-3=mass/16 (which is the Mr( x 8.31 x 333
so then multiply the p,V and Mr and you get 8849.76.
Divide that by the RT which is 2767.23.
And you get 3.198 which is aprox 3.2.

In other words equation for finding mass equation becomes:
mass=pV Mr/RT.

Did you get it? :3

 

[Eugene99]

pV=nRT
so converting them to the specific units we get:
103000 x 5.37x10^-3=mass/16 (which is the Mr( x 8.31 x 333
so then multiply the p,V and Mr and you get 8849.76.
Divide that by the RT which is 2767.23.
And you get 3.198 which is aprox 3.2.

In other words equation for finding mass equation becomes:
mass=pV Mr/RT.

Did you get it? :3

Got it! Actually I didn't convert kPa into Pa, that made my answer wrong
Mr is 15 not 16 which means we get exactly 3.2, no need to round off
thank you

 

[My Name]

Got it! Actually I didn't convert kPa into Pa, that made my answer wrong
Mr is 15 not 16 which means we get exactly 3.2, no need to round off
thank you

Ohkay
It is methane it should be 16.
Welcome.

 

[Zoha Ali]

http://papers.xtremepapers.com/CIE/...d AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

Question 19? how can the 3rd one have an optically active isomer?

 

[Rizwan Javed]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w07_qp_1.pdf

Question 19? how can the 3rd one have an optically active isomer?

For the III one, this is the optical isomer possible, with the C with asterisk being the chiral carbon.

 

[drowning-in-studies]

A solution of Sn2+ ions will reduce an acidified solution of MnO4 – ions to Mn2+ ions. The Sn2+ ions are oxidised to Sn4+ ions in this reaction. How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is added to an excess of acidified KMnO4 solution?
A 0.010 B 0.020 C 0.050 D 0.125

 

[drowning-in-studies]

Lactic acid (2-hydroxypropanoic acid), CH3CH(OH)CO2H, is found in sour milk. Which reaction could occur with lactic acid?
A CH3CH(OH)CO2H + CH3OH → CH3CH(OCH3)CO2H + H2O
B CH3CH(OH)CO2H + HCO2H → CH3CH(O2CH)CO2H + H2O
C CH3CH(OH)CO2H + NaHCO3 → CH3CH(ONa)CO2H + H2O + CO2
D CH3CH(OH)CO2H + Cl 2 → CH3CH(Cl)CO2H + HOCl

 

[drowning-in-studies]

Use of the Data Booklet is relevant to this question.
2.30g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The reaction mixture was then boiled under reflux for one hour. The desired organic product was then collected by distillation. The yield of product was 60.0%. What mass of product was collected?
A 1.32g B 1.38g C 1.80g D 3.20g

 

[Saad the Paki]

Use of the Data Booklet is relevant to this question.
2.30g of ethanol were mixed with an excess of aqueous acidified potassium dichromate(VI). The reaction mixture was then boiled under reflux for one hour. The desired organic product was then collected by distillation. The yield of product was 60.0%. What mass of product was collected?
A 1.32g B 1.38g C 1.80g D 3.20g

Oxidation of ethanol under reflux will give us ethanoic acid as our product. CH3CH2OH+[O]-->CH3COOH.
Now we know one mole of ethanol gives one mole of ethanoic acid. So moles of ethanol: 2.3/46=0.05 moles. This is also the moles of ethanoic acid. Now we can find the theoretical yield: Mr×moles=0.05×60=3G
The formula for yield is: (practical yield/theoretical yield)
Yield is given in the question,we found the theoretical yield and we need the practical yield
Therefore : 60%×3g=1.8g. Ans is C

 

[Saad the Paki]

A solution of Sn2+ ions will reduce an acidified solution of MnO4 – ions to Mn2+ ions. The Sn2+ ions are oxidised to Sn4+ ions in this reaction. How many moles of Mn2+ ions are formed when a solution containing 9.5 g of SnCl 2 (Mr: 190) is added to an excess of acidified KMnO4 solution?
A 0.010 B 0.020 C 0.050 D 0.125

The only difficult thing here is to form the equations, which u have to do by balancing the oxidation numbers.
Once the equation is there, find the moles of Sn2+, and then do the ratio thing.

 

[Saad the Paki]

Lactic acid (2-hydroxypropanoic acid), CH3CH(OH)CO2H, is found in sour milk. Which reaction could occur with lactic acid?
A CH3CH(OH)CO2H + CH3OH → CH3CH(OCH3)CO2H + H2O
B CH3CH(OH)CO2H + HCO2H → CH3CH(O2CH)CO2H + H2O
C CH3CH(OH)CO2H + NaHCO3 → CH3CH(ONa)CO2H + H2O + CO2
D CH3CH(OH)CO2H + Cl 2 → CH3CH(Cl)CO2H + HOCl

The first reaction is wrong as the alcohol will only react with CO2H group to form ester, it can't react with another alcohol.
Third reaction is wrong again as only carboxylic acids react with carbonates to release CO2, not alcohols.
Fourth is wrong cuz alcohols do not react with elemental chlorine, they react with chlorine compounds like HCL,PCL3 etc.
The ans is therefore B, because the second reaction is an esterification, the OH has been replaced by part of the carboxylic acid.

 

[drowning-in-studies]

Oxidation of ethanol under reflux will give us ethanoic acid as our product. CH3CH2OH+[O]-->CH3COOH.
Now we know one mole of ethanol gives one mole of ethanoic acid. So moles of ethanol: 2.3/46=0.05 moles. This is also the moles of ethanoic acid. Now we can find the theoretical yield: Mr×moles=0.05×60=3G
The formula for yield is: (practical yield/theoretical yield)
Yield is given in the question,we found the theoretical yield and we need the practical yield
Therefore : 60%×3g=1.8g. Ans is C

Thank you That was a nice explanation! Do you know if this is out of the syllabus?

 

[drowning-in-studies]

The first reaction is wrong as the alcohol will only react with CO2H group to form ester, it can't react with another alcohol.
Third reaction is wrong again as only carboxylic acids react with carbonates to release CO2, not alcohols.
Fourth is wrong cuz alcohols do not react with elemental chlorine, they react with chlorine compounds like HCL,PCL3 etc.
The ans is therefore B, because the second reaction is an esterification, the OH has been replaced by part of the carboxylic acid.

Oh...okay thanks