Chemistry doubt(Urgent)-(0620)

[Shamu M]

Can someone please explain me this question's answer:
32) Dry air is passed over hot copper until all the oxygen has reacted.
The volume of gas at the end of the reaction is 120cm3.
What is the starting volume of dry air?
A )132cm cube
B)150cm cube
C) 180cm cube
D) 600cm cube
(You could refer to the question paper for the diagram-0620-October/November-2011-Paper-12,Question 32).

 

[white rose]

Can someone please explain me this question's answer:
32) Dry air is passed over hot copper until all the oxygen has reacted.
The volume of gas at the end of the reaction is 120cm3.
What is the starting volume of dry air?
A )132cm cube
B)150cm cube
C) 180cm cube
D) 600cm cube
(You could refer to the question paper for the diagram-0620-October/November-2011-Paper-12,Question 32).

150cm is the correct ans.

 

[Shamu M]

But how,explain it,I didn't understand it?????

 

[сᴏᴏʟ сяуѕтᴀʟѕ]

Can someone please explain me this question's answer:
32) Dry air is passed over hot copper until all the oxygen has reacted.
The volume of gas at the end of the reaction is 120cm3.
What is the starting volume of dry air?
A )132cm cube
B)150cm cube
C) 180cm cube
D) 600cm cube
(You could refer to the question paper for the diagram-0620-October/November-2011-Paper-12,Question 32).

Assalam-o-alaikum wr wb...
Well what is the % of oxygen in air? 20%
when all the oxygen is used up..what volume remains? 80%
total volume of air is 100%

we need to cross multiply..
Volume of air remaining = 120 cm3 % of air remaining = 80%
Total volume = ? Total % = 100...

cross multiply! (120*100)/80 = 150 cm3....

hope you get it!

 

[Shamu M]

Thanks a lot for ur help!!!!!!

 

[Shamu M]

Thank you white rose,even u helped

 

[Shamu M]

20) An alloy contains copper and zinc.
Some of the zinc has become oxidised to zinc oxide.
What is the result of adding an excess of dilute sulfuric acid to the alloy?
A ) A blue solution and a white solid remains.
B ) A colourless solution and a pink /brown solid remains.
C ) The alloy dissolves completely to give a blue solution.
D ) The alloy dissolves completely to give a colourless solution.

 

[Shamu M]

Can someone explain this one too,why is the answer "B"?:S

 

[Warrior66]

@coolcrystals, AOA! Thank you for your explanation, it helped me a lot too! JazakAllah! I have seen you a numerous times helping out people and Allah will give you the reward for this. Inshallah! But from my side....all I could do was like the response! Hope u success in this world and in the Hereafter! Ameen!

 

[сᴏᴏʟ сяуѕтᴀʟѕ]

Thanks a lot for ur help!!!!!!

Yout welcome

 

[Skynox]

20) An alloy contains copper and zinc.
Some of the zinc has become oxidised to zinc oxide.
What is the result of adding an excess of dilute sulfuric acid to the alloy?
A ) A blue solution and a white solid remains.
B ) A colourless solution and a pink /brown solid remains.
C ) The alloy dissolves completely to give a blue solution.
D ) The alloy dissolves completely to give a colourless solution.

Okay so you are adding sulfuric acid to zinc oxide producing zinc sulfate which is colourless..Copper doesnt react with sulfuric acid so reddish brown solid remains

 

[IGCSE O/L student]

20) An alloy contains copper and zinc.
Some of the zinc has become oxidised to zinc oxide.
What is the result of adding an excess of dilute sulfuric acid to the alloy?
A ) A blue solution and a white solid remains.
B ) A colourless solution and a pink /brown solid remains.
C ) The alloy dissolves completely to give a blue solution.
D ) The alloy dissolves completely to give a colourless solution.

copper cannot replace hydrogen so it will remain in it's solid form
zinc oxide will dissolve in the sulfuric acid. so the answer is B

 

[сᴏᴏʟ сяуѕтᴀʟѕ]

@coolcrystals, AOA! Thank you for your explanation, it helped me a lot too! JazakAllah! I have seen you a numerous times helping out people and Allah will give you the reward for this. Inshallah! But from my side....all I could do was like the response! Hope u success in this world and in the Hereafter! Ameen!

Walaikumassalam wr wb...
Your welcome and Wa eyyakum...
Inshallah...Aameen! Your prayers actually mean a lot to me
May Allah give you more than what you desire, protect you from the evil whispers of shaytaan and give you success in this world as well as the Hereafter..Aameen!

 

[IGCSE O/L student]

Walaikumassalam wr wb...
Your welcome and Wa eyyakum...
Inshallah...Aameen! Your prayers actually mean a lot to me
May Allah give you more than what you desire, protect you from the evil whispers of shaytaan and give you success in this world as well as the Hereafter..Aameen!

Aameen!

 

[pk1947]

can sum1 PLEASEEEEEEEEEE post evryyythinnngg that we need to noe for chem p1????? PLEASEEEE ​

 

[meriama]

guys what about the thermometer question in may/june 2007?? can someone help me out with that.
thanks

 

[IGCSE O/L student]

guys what about the thermometer question in may/june 2007?? can someone help me out with that.
thanks

it has to be below 100. 84.5 isn't right because the marker cannot show that reading. if it was 84.5 the marker should have been lower. so it has to be 75.5

 

[meriama]

ahhaa thank you very much for your concern Good luck

 

[IGCSE O/L student]

anytime!!!
thanks and same to you too!

 

[nosschem]

Can yu give me important points about chem paper 12??