All chemistry Doubts here :)

[HyDraZin3]

You all can post your doubts in this single thread so that others can view and answer your questions and this will help all of us in our upcoming chemistry exam (paper 1 and paper 3) :wink:

 

[HyDraZin3]

Guys i have a doubt in this paper
http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf
Question 30

Plz help me

 

[xIshtar]

Well, the distillate is what collects in the beaker. So the NaOH, will become more concentrated, meaning that the pH of whats left in the flask will be higher than what it was before. (Alkaline)
In addition, thinking logically, if it becomes more concentrated, the pH of the distillate must be mostly water, etc, and thus the pH will be lower..

So the answer is C.

 

[Yoyo1994]

Hello mate, I've got a doubt here: viewtopic.php?f=24&t=8919&p=95296
I've only got one answer and it was of much help, can you please help me? Thanks!
I also posted another doubt regarding the same matter beneath the unhelpful answer, so can you please answer that? Thanks!

 

[HyDraZin3]

so water is the distillate and NaOH remains in the flask?

 

[xIshtar]

so water is the distillate and NaOH remains in the flask?

Hmm, it was the way I saw it.

Hello mate, I've got a doubt here: viewtopic.php?f=24&t=8919&p=95296
I've only got one answer and it was of much help, can you please help me? Thanks!
I also posted another doubt regarding the same matter beneath the unhelpful answer, so can you please answer that? Thanks!

When no oxidation state is given, just assume it from knowledge.. I have never seen Zinc (ii) given, only zinc, which is always 2+

So as you said Zn(OH)2 -> ZnO + H2O

 

[Yoyo1994]

so water is the distillate and NaOH remains in the flask?

Hmm, it was the way I saw it.

Hello mate, I've got a doubt here: viewtopic.php?f=24&t=8919&p=95296
I've only got one answer and it was of much help, can you please help me? Thanks!
I also posted another doubt regarding the same matter beneath the unhelpful answer, so can you please answer that? Thanks!

When no oxidation state is given, just assume it from knowledge.. I have never seen Zinc (ii) given, only zinc, which is always 2+

So as you said Zn(OH)2 -> ZnO + H2O

Ok thanks for that tip, but I have another concern. When you're not given an oxidation state, do transition metals always have a valency of 2? Or is it only Zinc? Usually they would say Zinc (II) or Copper (II) but if they don't how can I assume or determine the valency? Would transition metals usually have a valency of 2?

 

[HyDraZin3]

No, transition metals will not always have the valency of 2
Is it like if we add water to NaOH the ph will remain the same (original ph of NaOH) and if we add NaOH to water the PH will increase?

 

[HyDraZin3]

I have one more doubt :bad:
http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf
Question 3 and question 21

In question 21 can someone explain me the answer by writing reactions?

 

[themathshater]

i think u need to know ion tests for dis so chk dem up i guess and ull kno da answr

 

[Yoyo1994]

I have one more doubt :bad:
http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf
Question 3 and question 21

In question 21 can someone explain me the answer by writing reactions?

This was on the examiners report:
This was found to be very hard although the discrimination was satisfactory. About half of all candidates chose B, instead of the key C. The left-hand diagram relates to the release of ammonia from its salts by the action of alkali but the damp red litmus paper “stays” red. It is the reduction of the nitrate ion that results in the release of ammonia. Careful reading of the question required.

 

[Yoyo1994]

No, transition metals will not always have the valency of 2
Is it like if we add water to NaOH the ph will remain the same (original ph of NaOH) and if we add NaOH to water the PH will increase?

Lol okay but just to make sure, how is one supposed to know the oxidation number/valency if it is not provided for transition metals?

 

[HyDraZin3]

I saw the examiners report but can someone write the reaction and explain that question to me?
Its quite easy to determine the valency.
For example:- if it is ZnO it means that the valency of Zn is 2 because valency of oxygen is 2 always.
I think u must be knowing that the copper has 2 valencies one is 1 and other is 2.The valency of the copper depends on the question.For example:-if it is CuO, then the valency of the copper is 2 in this question and if is Cu2O then the valency of copper is 1 in this question
I hope that u have understood what i said

 

[Yoyo1994]

I saw the examiners report but can someone write the reaction and explain that question to me?
Its quite easy to determine the valency.
For example:- if it is ZnO it means that the valency of Zn is 2 because valency of oxygen is 2 always.
I think u must be knowing that the copper has 2 valencies one is 1 and other is 2.The valency of the copper depends on the question.For example:-if it is CuO, then the valency of the copper is 2 in this question and if is Cu2O then the valency of copper is 1 in this question
I hope that u have understood what i said

Yeah I think I understand. Thanks.

 

[Keeemoman]

I saw the examiners report but can someone write the reaction and explain that question to me?
Its quite easy to determine the valency.
For example:- if it is ZnO it means that the valency of Zn is 2 because valency of oxygen is 2 always.
I think u must be knowing that the copper has 2 valencies one is 1 and other is 2.The valency of the copper depends on the question.For example:-if it is CuO, then the valency of the copper is 2 in this question and if is Cu2O then the valency of copper is 1 in this question
I hope that u have understood what i said

Hey man you can see the test for nitrate ion and you will find out that the right test-tube is the test but instead its aluminium powder and they kept aluminium powder instead.

 

[HyDraZin3]

http://www.xtremepapers.me/CIE/Cambridg ... 7_qp_1.pdf
Question 12th, this is a very tough question and i didnt understand the question after reading the examiners report

 

[PUSHPAK1321]

http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_w07_qp_1.pdf
Question 12th, this is a very tough question and i didnt understand the question after reading the examiners report

R u sure it is a hard question????
Okay, as you know anode is a positive electrode. Now the second what type of element is formed (they does'nt mean the characteristic change). They simply want the element that is attracted to anode, and being a positive electrode it attract negative ions, so this mean it is a non metal.

 

[PUSHPAK1321]

http://www.xtremepapers.me/CIE/Cambridge%20IGCSE/0620%20-%20Chemistry/0620_w07_qp_1.pdf
Question 12th, this is a very tough question and i didnt understand the question after reading the examiners report

R u sure it is a hard question????
Okay, as you know anode is a positive electrode. Now the second what type of element is formed (they does'nt mean the characteristic change). They simply want the element that is attracted to anode, and being a positive electrode it attract negative ions, so this mean it is a non metal.

Because non metal are able to form negative ions.

 

[Keeemoman]

Come on this is easy nothing to worry about
You firstly have know which element goes and this is of course a non-metal
But then you have to know what is charge of the anode, it should be positive in order to be able to neutralize the non metal ion by, when give an electron to the anode this =positive+negative=neutral

 

[HyDraZin3]

I asked the wrong question,the paper is same but i want the answer for the 11th question srry guys i posted the wrong question number