Biology; Chemistry; Physics: Post your doubts here!

[zeeshma]

11) all ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
a) 0.5 mol (NH4)3 PO4
B) 0.5 mol (NH4)2 S03
C) 1.0 mol NH4Cl
D) 1.0 mol NH4NO3

How do we get to the answer?

Kindly help. Thankyou in advance.

convert moles into mass for all salts
a ad b can give two moles of ammonia
c and d can gve one mole of ammnia
find massof all the salts
divide mass of moles produd=ced by each salt divided by total mass f the salt and multiply it with mass of salts given in the questin(u already have conv
erted mles into mass in first step

 

[Yazka Shathir]

Can someone explain the re absorption of water. When it occurs? Plus why does re-absorption increase when sweat production increase?

 

[Ram97]

11) all ammonium salts on heating with sodium hydroxide produce ammonia gas. From which ammonium salt can the greatest mass of ammonia be obtained?
a) 0.5 mol (NH4)3 PO4
B) 0.5 mol (NH4)2 S03
C) 1.0 mol NH4Cl
D) 1.0 mol NH4NO3

How do we get to the answer?

Kindly help. Thankyou in advance.

Answer is A

Multiply the number of moles by the molecules of ammonia
For A (0.5 x 3) = 1.5 mol
For B (0.5 x 2)= 1 mol
For C (1 x 1)= 1 mol
For D (1 x 1)= 1 mol

So you divide the no. of moles by Mr/Ar
As A has the greater no. of moles, therefore, it has greater mass of ammonia present

 

[Al-Anoud]

http://papers.xtremepapers.com/CIE/...and AS Level/Physics (9702)/9702_s05_qp_1.pdf
AS Level, Physics. Q3. Don't understand it.. Please help.

 

[Saad Mughal]

http://papers.xtremepapers.com/CIE/Cambridge International A and AS Level/Physics (9702)/9702_s05_qp_1.pdf
AS Level, Physics. Q3. Don't understand it.. Please help.

Estimation questions are always confusing since you will seldom get 'exact' answers.
Let's just consider this question, the average speed for an athlete can range from 15-20 mph, i.e. 6.5-9 m/s.
Kinetic Energy = 1/2(m)(v^2)
Kinetic Energy = 1/2(80)(9^2) (You may take any value from 6.5-9 m/s).
Kinetic Energy = 3240 J.
Now, this is 3.2 * 10^3 J. If you take 6.5 m/s, the value will be something around 1.6 * 10^3 J.
The answer is B, because:
- The best estimates of the kinetic energy using the 'average' speed of an athlete will always be '10^3'.
- The other values, i.e. 400 J, 40000 J or 400000 J can only be there if the runner has a speed of around 5-10 mph OR 20-40 mph, which is quite slow/fast for an average athlete.

All estimation questions need you to be able to use sensible estimations of quantities; I advise you to go through the estimates of such quantities (e.g. mass of an apple, average speed of marathon runner/athlete, mass of a human head, etc.)


P.S. Remember to post such questions in the 'Physics' thread in the A'level forum next time, you'll get better help.

 

[Al-Anoud]

Estimation questions are always confusing since you will seldom get 'exact' answers.
Let's just consider this question, the average speed for an athlete can range from 15-20 mph, i.e. 6.5-9 m/s.
Kinetic Energy = 1/2(m)(v^2)
Kinetic Energy = 1/2(80)(9^2) (You may take any value from 6.5-9 m/s).
Kinetic Energy = 3240 J.
Now, this is 3.2 * 10^3 J. If you take 6.5 m/s, the value will be something around 1.6 * 10^3 J.
The answer is B, because:
- The best estimates of the kinetic energy using the 'average' speed of an athlete will always be '10^3'.
- The other values, i.e. 400 J, 40000 J or 400000 J can only be there if the runner has a speed of around 5-10 mph OR 20-40 mph, which is quite slow/fast for an average athlete.

All estimation questions need you to be able to use sensible estimations of quantities; I advise you to go through the estimates of such quantities (e.g. mass of an apple, average speed of marathon runner/athlete, mass of a human head, etc.)


P.S. Remember to post such questions in the 'Physics' thread in the A'level forum next time, you'll get better help.

Ahan, Jazak Allah khair! I get it... Thank you very much!

Sure...
One more question... Are the estimates of such quantities given anywhere? Or shud i google them?

 

[asadalam]

How to draw the best fit lines in ATPs?I can never seem to get them drawn neat.Any tips?

 

[Saad Mughal]

Ahan, Jazak Allah khair! I get it... Thank you very much!

Sure...
One more question... Are the estimates of such quantities given anywhere? Or shud i google them?

I saw a thread which contained a majority of the estimates in the A'level forum but I forgot to bookmark it. Search for it there, you'll find it.

 

[Saad Mughal]

How to draw the best fit lines in ATPs?I can never seem to get them drawn neat.Any tips?

- Equal points above the line and below the line.
- Neat, thin straight lines, no curvy lines.
- Proper scale taken that fills at least 1/2 the graph paper/area.
- For certain quantities/instruments, the graph must pass through the origin.

 

[asadalam]

- Equal points above the line and below the line.
- Neat, thin straight lines, no curvy lines.
- Proper scale taken that fills at least 1/2 the graph paper/area.
- For certain quantities/instruments, the graph must pass through the origin.

But isnt it supposed to be curved?like this:

Instead of joining the points in straight lines.

 

[Al-Anoud]

I saw a thread which contained a majority of the estimates in the A'level forum but I forgot to bookmark it. Search for it there, you'll find it.

okay thank you!

 

[Saad Mughal]

But isnt it supposed to be curved?like this:

Instead of joining the points in straight lines.

For a best fit 'line', it is never supposed to be curved.
For a best fit 'curve', it is, obviously, meant to be curved.

 

[asadalam]

For a best fit 'line', it is never supposed to be curved.
For a best fit 'curve', it is, obviously, meant to be curved.

Thanks.I see its written best fit curve in most Q's

 

[Saad Mughal]

Thanks.I see its written best fit curve in most Q's

Yeah, it is mostly best fit 'curve'. The best way to draw such graphs is by looking at the pointers given in the mark schemes; draw exactly as stated in the mark scheme and you will score full.

 

[333333*]

Is wine production and beer formation are included in bio syllabus ?????????????????????????????

 

[tdk]

When a car turns round a corner at a constant speed, what causes the car to accelerate as it turns the corner?

 

[Iridescent]

When a car turns round a corner at a constant speed, what causes the car to accelerate as it turns the corner?

Change in the direction.

 

[Ram97]

Chemistry (5070): Marking scheme needed for June & November 2003

 

[asadalam]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s03_er.pdf

It contains MS of P1.You can also se comments on many Q's.If needed you can consult classified book for proper answers.

 

[Ram97]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Chemistry (5070)/5070_s03_er.pdf

It contains MS of P1.You can also se comments on many Q's.If needed you can consult classified book for proper answers.

Thanks for the suggestion