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Biology; Chemistry; Physics: Post your doubts here!

Dream.Eater

Dream.Eater

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Awesome12 said:
yup I think mentioning such stuff might give you the edge above other candidates.
Click to expand...

But are you going to get the same marks as those who write the usual test?
I noticed that 4 marks were allocated for the USUAL nitrate ion test. This was in MJ 2011 paper 4 mark scheme. There was nothing mentioned about the brown ring test.
So, by mentioning that test won't the examiner find it difficult to give the correct marks. 4 marks is quite a lot and missing it because of a simple thing is a waste....
 
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Awesome12

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Dream.Eater said:
But are you going to get the same marks as those who write the usual test?
I noticed that 4 marks were allocated for the USUAL nitrate ion test. This was in MJ 2011 paper 4 mark scheme. There was nothing mentioned about the brown ring test.
So, by mentioning that test won't the examiner find it difficult to give the correct marks. 4 marks is quite a lot and missing it because of a simple thing is a waste....
Click to expand...
Yes I agree, but what I meant was more of like this. If you use terms such as for electroylsis, both ions go to the elctrodes but only ------ ion is discharged. So this will give you the upper hand
 
Dream.Eater

Dream.Eater

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Awesome12 said:
Yes I agree, but what I meant was more of like this. If you use terms such as for electroylsis, both ions go to the elctrodes but only ------ ion is discharged. So this will give you the upper hand
Click to expand...

So what you meant was the wordings......
That's 100% correct since you could show the examiner you know the concepts very well.
 
Dark Destination

Dark Destination

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They usually ask observations about when Potassium or Sodium is added to water.
What to write in such questions?
In the marking scheme they tell about flame colors. Like when sodium is added their is YELLOW FLAME. When potassium is added, there is LILAC flame? What does this mean?
 
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Awesome12

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Dark Destination said:
They usually ask observations about when Potassium or Sodium is added to water.
What to write in such questions?
In the marking scheme they tell about flame colors. Like when sodium is added their is YELLOW FLAME. When potassium is added, there is LILAC flame? What does this mean?
Click to expand...
The easiest answer
Metal floats on the surface
Violent bubbling
Metal melts due to heat of reaction

For the more reactive metals, the metal shoots across the water, and catches fire , giving its distinct flame colour
 
Dream.Eater

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Awesome12 said:
Maximum mass of ppt obtained was 2.33
The Mr of BaSO4 is 233
Moles gives us 0.01

The volume of K needed was 8.0 cm^3
Moles = Vol * Con.c
0.01 = (8.0/1000) * conc.
conc. = 1.25
Click to expand...

Thanks
But they didn't give Mr of baso4 even though its a paper 4 question
 
Dream.Eater

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funky brat said:
Is diode ( Physics) part of our syllabus? I saw an MCQ related to this is 2012 O/N variant.
http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w12_qp_11.pdf
See 3oth MCQ. Why is the answer D? Does diode work on an alternating current?
Click to expand...

Yes,diode is part of the syllabus.
Ans is D since it clearly states RECTIFYING diode so only AC can be used in the rectification process so that's why A is wrong. The purpose of a diode is to allow current to pass only when its forward biased so even DC can pass.
When AC passes, a forward biased diode blocks the 'negative/backward' part of the current while allowing only the 'forward/positive' part to go through. This process is called rectification.
Hope this helps!
 
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sid2333

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funky brat

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Dream.Eater said:
Yes,diode is part of the syllabus.
Ans is D since it clearly states RECTIFYING diode so only AC can be used in the rectification process so that's why A is wrong. The purpose of a diode is to allow current to pass only when its forward biased so even DC can pass.
When AC passes, a forward biased diode blocks the 'negative/backward' part of the current while allowing only the 'forward/positive' part to go through. This process is called rectification.
Hope this helps!
Click to expand...
Are you sure it's there in the syllabus? I mean my teacher told me that this diode thing is no more in the syllabus. I had no idea what 'rectification' meant. Thanks, btw.
 
funky brat

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sid2333 said:
The correct answer to this question is Option "D". As hydrogen gas has a very less molecular mass (2), therefore, it will cause an increase in the water level. As the water rises, it remains at the increased level. It won't fall back.
Click to expand...
Umm the correct answer is A. You may confirm from the MS. Thanks, anyways.
 
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Awesome12

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sid2333 said:
The correct answer to this question is Option "D". As hydrogen gas has a very less molecular mass (2), therefore, it will cause an increase in the water level. As the water rises, it remains at the increased level. It won't fall back.
Click to expand...
You are wrong. Please do go back to the previous pages for the correct explanation
 
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