Chemistry: Post your doubts here!

[MShaheerUddin]

X is a salt of one of the halogens chlorine, bromine, iodine, or astatine (proton number 85).
The reaction scheme shows a series of reactions using a solution of X as the starting reagent.

X HNO3/ AgNO3 a precipitate excess NH3(aq) colorless solution

excess HNO3

precipiate



What could X be?

A sodium chloride
B sodium bromide
C potassium iodide
D potassium astatide

 

[Hamnah Zahoor]

X is a salt of one of the halogens chlorine, bromine, iodine, or astatine (proton number 85).
The reaction scheme shows a series of reactions using a solution of X as the starting reagent.

X HNO3/ AgNO3 a precipitate excess NH3(aq) colorless solution

excess HNO3

precipiate



What could X be?

A sodium chloride
B sodium bromide
C potassium iodide
D potassium astatide

When x is added to silver nitrate a precipitate is formed which then dissolves in excess ammonia this dissolving shows that it will be a soluble halogen ....which means chloride. This is the main thing to be focused ...on reading the last step you might get confused but in excess of HNO3 it is actually the ammonia in the complex solution of Silver chloride that reacts to form ammonium nitrate and Silver chloride is left as precipitate.

 

[Hinafatima]

Kindly solve these
May June 2017/11 q#20,24

 

[Hamnah Zahoor]

Kindly solve these
May June 2017/11 q#20,24

For question 24

acid catalyst is added when dehydration is being done ....considering the diagram divide it into two parts from the upper oxygen to the lower right branch and similar division on the left side and then draw the structural formula for it will match the compound in part C.

 

[Hinafatima]

got it thanks

 

[Hinafatima]

Thanks, got it, any idea of question 20?

For question 24

acid catalyst is added when dehydration is being done ....considering the diagram divide it into two parts from the upper oxygen to the lower right branch and similar division on the left side and then draw the structural formula for it will match the compound in part C.

 

[Hamnah Zahoor]

Thanks, got it, any idea of question 20?

This is from the examination report
Question 20
The most commonly chosen incorrect answer was C. C, pentan-3-one, would be reduced to pentan-3-ol. This will dehydrate to give cis and trans pent-2-ene; two isomers. B, butanone, would be reduced to butan-2-ol. This will dehydrate to give cis and trans but-2-ene and but-1-ene, three isomers.

Apart from above statement you have to focus on the statement ....Generating one product or mixture of products in case of option A one product is produced, in option B the product produced shows cis-trans isomerism which are in total three thus producing the most isomers..... same goes for the rest of the options.

 

[Hinafatima]

This is from the examination report
Question 20
The most commonly chosen incorrect answer was C. C, pentan-3-one, would be reduced to pentan-3-ol. This will dehydrate to give cis and trans pent-2-ene; two isomers. B, butanone, would be reduced to butan-2-ol. This will dehydrate to give cis and trans but-2-ene and but-1-ene, three isomers.

Apart from above statement you have to focus on the statement ....Generating one product or mixture of products in case of option A one product is produced, in option B the product produced shows cis-trans isomerism which are in total three thus producing the most isomers..... same goes for the rest of the options.

JazakAllah Khairan kaseera
Actually i didn't have the examiner report so couldn't get any clue,thanks once again

 

[Hamnah Zahoor]

JazakAllah Khairan kaseera
Actually i didn't have the examiner report so couldn't get any clue,thanks once again

My pleasure.

 

[feliciablack2000]

Dinitrogen tetroxide dissociates into nitrogen dioxide on heating.
N2O4⇌2NO2
In an experiment the partial pressures of the gases at equilibrium were found to be NO2 , 0.33 atm; N2O4, 0.67 atm
What is the numerical value of Kp at the temperature of the experiment?
A 0.16
B 0.49
C 0.65
D 2.03
If anyone is generous enough to help me solve this question, i would really appreciate it!

 

[Hamnah Zahoor]

Dinitrogen tetroxide dissociates into nitrogen dioxide on heating.
N2O4⇌2NO2
In an experiment the partial pressures of the gases at equilibrium were found to be NO2 , 0.33 atm; N2O4, 0.67 atm
What is the numerical value of Kp at the temperature of the experiment?
A 0.16
B 0.49
C 0.65
D 2.03
If anyone is generous enough to help me solve this question, i would really appreciate it!

Kp=(0.33)^2/0.67=0.16 .....option A

 

[feliciablack2000]

Thankyou so much!

 

[Holmes]

Guys If anyone is struggling with the ORGANIC CHEMISTRY and other topics as well. Try the link below it's very useful. I got A grade just because of the notes provided on this website.
http://www.khizarchemistry.com/book.html

 

[mehran46]

Hi there I am new to this site. Still trying to get familiar with it.
Wanted the reason for the answer of question 9
thanks

 

[kuetian]

Hydroxyethanal, HOCH2CHO, is heated under reflux with an excess of acidified potassium
dichromate(VI) until no further oxidation takes place.
What is the skeletal formula of the organic product?

 

[kuetian]

ans:a,b,c

 

[Hamnah Zahoor]

In the manufacture of sulfuric acid the reaction 2SO2(g) + O2(g) 2SO3(g) usually takes place at 400 °C and 1 atm pressure. In one industrial plant, it is decided to change the pressure to
20 atm

What will be the consequences of this change
1 increased running costs
2 an increased percentage of sulfur trioxide in the equilibrium mixture
3 the rate of the backward reaction increases

The answer is A which 1,2 and 3 are correct
But how the rate of the backward reaction increases? I thought it should be decreases?

This question is a bit confusing one
From the examination report
Question 35: The correct answer was A. The most commonly chosen incorrect answer was B. This suggests that for most candidates their choice of answer rested on the truth or otherwise of choice 3. If the operating pressure is increased for a process in which all reactants and products are gases then both the rate of the forward reaction and the rate of the backward reaction will increase, although by different amounts.

 

[Haroon Ahmed]

Can anyone kindly answer the question below(and explain why he/she chose the staement).
Q.Two bulbs R and S, connected by a mercury manometer, are held in a thermostat, as shown. The volume of R is twice that of S. R contains gas, X, at the same pressure as the nitrogen in S.When the temperature is increased, which gases in bulb R would cause the mercury level in the right-hand limb of the manometer to rise? 1. an equilibrium mixture N2F4(g) to 2NF2(g); ∆H positive. (PAST PAPER REFERENCE;M-J/2007/PAPER 1/Q34.)

 

[Hamnah Zahoor]

Hydroxyethanal, HOCH2CHO, is heated under reflux with an excess of acidified potassium
dichromate(VI) until no further oxidation takes place.
What is the skeletal formula of the organic product?

Answer is B....first draw the skeletal formula of HOCH2COH heating it under reflux will result in OH on both sides being oxidised to Acid i.e CO2H on both sides in option b There are two carbons with acis groups on each side.In option A there are three carbons while in option C and D no acid formed is shown.

 

[Hamnah Zahoor]

Hi there I am new to this site. Still trying to get familiar with it.
Wanted the reason for the answer of question 9
thanks

Same groups or atoms on the opposite side of the double bond having same elctronegativites tends to cancel out the effect of each other thus reducing the overall dipole to a great extent.