Physics, Chemistry and Biology: Post your doubts here!

[sultan ahmed]

Same here, Jeddah!

im frm dammam

 

[Student of the year]

One difficult Q (I understand it, I just want to show it to u in case a similar one comes in the exam!):
View attachment 12841
From O level!

the ans is B-Ca , bcz Al & Zn are soluble & NH4 does not produce ppt

 

[Rahma Abdelrahman]

is it Ca2+?

B?

Yes, it is B Ca2+...
How did u get it?
Student of the year , it's B!

 

[Rahma Abdelrahman]

One difficult Q (I understand it, I just want to show it to u in case a similar one comes in the exam!):
View attachment 12841
From O level!

The answer is B

 

[thats_me]

Yes, it is B Ca2+...
How did u get it?
Student of the year , it's B!

Because, the question says wat is NOT present
and AL3+ and Zn2+ being Amphoteric react with NaOH and no ppt is formed
NH4+ doesnot form a ppt just ammonia is released

 

[Rahma Abdelrahman]

the ans is B-Ca , bcz Al & Zn are soluble & NH4 does not produce ppt

Right!

 

[FATIMAH]

One difficult Q (I understand it, I just want to show it to u in case a similar one comes in the exam!):
View attachment 12841
From O level!

WHAT IS THE ANSWER ???

 

[FATIMAH]

which years paper?

ITS FROM O LEVELS NOV 09

 

[Rahma Abdelrahman]

Because, the question says wat is NOT present
and AL3+ and Zn2+ being Amphoteric react with NaOH and no ppt is formed
NH4+ doesnot form a ppt just ammonia is released

According to cations tests, they should form white ppt that is sol. in excess!

the ans is B-Ca , bcz Al & Zn are soluble & NH4 does not produce ppt

 

[Rahma Abdelrahman]

ITS FROM O LEVELS NOV 09

I haven't solved nov 09, but i got it from june 2011

 

[always-smile :)]

Right!

i didn't get it

 

[fishcook]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w03_qp_1.pdf
Q21.. please help!

 

[Just Smie :)]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w03_qp_1.pdf
Q21.. please help!

it's going to be D because u can never mix to alkalis and have a result with a PH of an acid...

 

[Rahma Abdelrahman]

i didn't get it

First, ammonium ion doesn't form a ppt..
Second, zinc and aluminium ions are soluble in excess, so they may have formed and then dissolved!
Moreover, the Q says: no ppt was formed because no ppt formed as NaOH WAS ADDED TOO QUICKLY not because of dissolving!
So answer must surely be Ca2+ as its ppt is insol. in excess which did not form as NaOH WAS ADDED TOO QUICKLY!!

 

[FATIMAH]

I haven't solved nov 09, but i got it from june 2011

WHICH BOARD ?????

 

[always-smile :)]

First, ammonium ion doesn't form a ppt..
Second, zinc and aluminium ions are soluble in excess, so they may have formed and then dissolved!
Moreover, the Q says: no ppt was formed because no ppt formed as NaOH WAS ADDED TOO QUICKLY not because of dissolving!
So answer must surely be Ca2+ as its ppt is insol. in excess which did not form as NaOH WAS ADDED TOO QUICKLY!!

thnx .. got it

 

[Rahma Abdelrahman]

WHICH BOARD ?????

O level... http://www.xtremepapers.com/papers/...l O Level/Chemistry (5070)/5070_s11_qp_11.pdf

 

[slayer]

Hello, guyss pleaaasee aia need some help! how do we know if the specific given acid reacts with the metal or not plzzzzzzzzz

 

[Rahma Abdelrahman]

Hello, guyss pleaaasee aia need some help! how do we know if the specific given acid reacts with the metal or not plzzzzzzzzz

i think you have to take it as ALL Acids, as we are not supposed to have knowledge of the reactivity of different acids...which paper is this from?

 

[slayer]

i think you have to take it as ALL Acids, as we are not supposed to have knowledge of the reactivity of different acids...which paper is this from?

This question came in most of the PP but its not in a direct way if u know what I mean anyway thank you