Biology; Chemistry; Physics: Post your doubts here!

[Khadija_1234]

you have to balance the charges on both sides too, so you put a 2 before the Cu on the right side, so that the total charge is 4+ like on the left hand side

That doesn't make any sense, from what I've studied, there is no charge on an ATOM. Only ions have charge

 

[sourov97]

Because there was O2 on the left so to balance oxygen on the right we had to put a 2 before H2O and that meant there were 4 hydrogen now so thats why

finally its same - u wrote 4H+ to balance 2H2O...then why cant u write 2Cu as reactant for Cu2+

 

[usama321]

That doesn't make any sense, from what I've studied, there is no charge on an ATOM. Only ions have charge

When you put the 4 before the hydrogen ion on the left, the charge on the left side became +4. Now to balance that charge, you put a 2 before the Cu2+ ion on the right hand side. And then to balance Cu atom, you put a 2 before it on the left hand side........ ok?

 

[Khadija_1234]

what about june 06 p2 Q A1 (c)....the answer is Al2O3,,how?

Non metals form either neutral or acidic oxides, so there can be no non metal as the answer. All metals apart from amphoteric form basic oxides so they can't be the answer. Only amphoteric form both oxides and aluminum is amphoteric

 

[sourov97]

When you put the 4 before the hydrogen ion on the left, the charge on the left side became +4. Now to balance that charge, you put a 2 before the Cu2+ ion on the right hand side. And then to balance Cu atom, you put a 2 before it on the left hand side........ ok?

what...if i put 4H+ for 2H2 then i sould put 2Cu for Cu2+....but ms says 2Cu and 2Cu2+

 

[Khadija_1234]

When you put the 4 before the hydrogen ion on the left, the charge on the left side became +4. Now to balance that charge, you put a 2 before the Cu2+ ion on the right hand side. And then to balance Cu atom, you put a 2 before it on the left hand side........ ok?

But then why is there a 2Cu2+ in the mark scheme?

 

[usama321]

what...if i put 4H+ for 2H2 then i sould put 2Cu for Cu2+....but ms says 2Cu and 2Cu2+

2Cu + O2 + 4H+ = 2Cu2+ + 2H2O

first of all this equation is right. The thing is you have to balance the charges as well as the atoms on both sides. Now when we put the 2 before water, we had to put 4 before the H ion on the left side to balance the atoms H. Now, there is a total charge of 4+ on the left hand side. To balance this, we put a 2 before the Cu2+ ion, so that the total charge becomes 4+ here too. Now, as we increased the Cu ions on the right side to two, we have to put a 2 before the Cu atom on the left side

 

[sourov97]

my question is

Non metals form either neutral or acidic oxides, so there can be no non metal as the answer. All metals apart from amphoteric form basic oxides so they can't be the answer. Only amphoteric form both oxides and aluminum is amphoteric

my question is, why Al2O3 (unreactive) reacts with O2..syllabus doesnt include learning about the out comes when a metal oxide reacts again with O2

 

[Khadija_1234]

2Cu + O2 + 4H+ = 2Cu2+ + 2H2O

first of all this equation is right. The thing is you have to balance the charges as well as the atoms on both sides. Now when we put the 2 before water, we had to put 4 before the H ion on the left side to balance the atoms H. Now, there is a total charge of 4+ on the left hand side. To balance this, we put a 2 before the Cu2+ ion, so that the total charge becomes 4+ here too. Now, as we increased the Cu ions on the right side to two, we have to put a 2 before the Cu atom on the left side

Thank you so much!!

 

[usama321]

my question is
my question is, why Al2O3 (unreactive) reacts with O2..syllabus doesnt include learning about the out comes when a metal oxide reacts again with O2

i think the answer should have been simply Al. there is something wrong with the mark scheme. Cuz the question specifically asks which ELEMENT, not COMPOUND. So, aluminium reacts with air to form an amphoteric oxide. Understand?

 

[Khadija_1234]

my question is
my question is, why Al2O3 (unreactive) reacts with O2..syllabus doesnt include learning about the out comes when a metal oxide reacts again with O2

It doesn't
The mark scheme Has written the answer with respect to the question, the answer is Aluminum not aluminum oxide

 

[TheStallion-Reborn]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_11.pdf
can any1 plx help me with question 8,10,12,13.. usama321 u up?

 

[sourov97]

i think the answer should have been simply Al. there is something wrong with the mark scheme. Cuz the question specifically asks which ELEMENT, not COMPOUND. So, aluminium reacts with air to form an amphoteric oxide. Understand?

let me write the qs:
an element that reacts with oxygen to give acidic oxide .... and the answer is aluminium oxide..
what u have to say about this?

 

[sourov97]

It doesn't
The mark scheme Has written the answer with respect to the question, the answer is Aluminum not aluminum oxide

check part (c) clearly aluminium oxide

 

[Khadija_1234]

check part (c) clearly aluminium oxide

View attachment 26499

That is what usmam said! There may be something wrong with the mark scheme or they must have written the complete answer. They have asked for an element
The answer is aluminum now please just accept it

 

[usama321]

http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_s10_qp_11.pdf
can any1 plx help me with question 8,10,12,13.. usama321 u up?

hmm 8 would be taking moments, the weight is acting at 30 cm mark, so

30*x = 60 *15
x=30N divide by 10 you get 3 kg

for 10, the more the area the less the pressure, so C or D (m not sure)

12 D as potential energy is decreasing and K.E is constant

13 power = energy/time

 

[sourov97]

That is what usmam said! There may be something wrong with the mark scheme or they must have written the complete answer
The answer is aluminum now please just accept it

whooo! never mind its sorted out

 

[usama321]

check part (c) clearly aluminium oxide

View attachment 26499

k one thing, i have been repeatedly telling you that they are asking for an ELEMENT. the CIE is not the god, they can make mistakes too

 

[Khadija_1234]

whooo! never mind its sorted out

Sorry I didn't mean to be rude.

 

[sourov97]

k one thing, i have been repeatedly telling you that they are asking for an ELEMENT. the CIE is not the god, they can make mistakes too

thanks and sorry bro