chemistry pp1 help !

[irlzs95]

hii guyz
plz help me with these qs ..


http://www.xtremepapers.me/CIE/Cambridg ... 3_qp_1.pdf
q13 , why is it A? why cant its be c ???

http://www.xtremepapers.me/CIE/Cambridg ... 3_qp_1.pdf
q16 ??

http://www.xtremepapers.me/CIE/Cambridg ... 4_qp_1.pdf
q29 ??

http://www.xtremepapers.me/CIE/Cambridg ... 5_qp_1.pdf
q11 , why it isnt part c ??

http://www.xtremepapers.me/CIE/Cambridg ... 6_qp_1.pdf
q16 , btw wen they say redox , they mean that both reduction nd oxidation occured in same equation or only one thing ??
nd plz explain the ques.

http://www.xtremepapers.me/CIE/Cambridg ... 7_qp_1.pdf
q20 and 21

:$

http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_1.pdf
q20 nd 21


http://www.xtremepapers.me/CIE/Cambridg ... _qp_12.pdf
q14


im sorry i asked ALOT


thx in advance

 

[irlzs95]

guyz plz help , dont let me down , the exam is tmrw =/

 

[JmCullen]

hii guyz
plz help me with these qs ..


http://www.xtremepapers.me/CIE/Cambridg ... 3_qp_1.pdf
q13 , why is it A? why cant its be c ???


http://www.xtremepapers.me/CIE/Cambridg ... 8_qp_1.pdf
q20 nd 21

ok.
im seriously sleepy over here.. it's 12am. sorry..
so, i'll just help some of it.

13) A because calcium is more reactive than copper

20) B, salt forms, pH become neutral, so increase. all chloride is soluble. so no ppt form

21) D because barium sulphate will form, which is insoluble. that's why ppt forms.

sorry..
i'll stop here..

good luck for tomorrow.

 

[CaptainDanger]

13. C (You read that wrong I guess)

16. B (Lead II Oxide is reduced to lead so at X there is a decrease and at Y due to excess hydrogen there is increase)

29. C (Oxygen in air is 21% so the 30 cm^3 volume when decreased is due to all the oxygen used up in the reaction... 21% of 150 = 31.5 so its C....)

11. It cannot be C because they are asking for the manufacture of magnesium... In electrolysis it is reduced to pure metal....

16. D (As they have mentioned an "excess" of Barium Hydroxide which is an alkali will increase the pH from about 1 to 14 when poured into HCl & yes they mean both reduction and oxidation... )

0620_w07_qp_1.pdf

20. B (Carbon + Oxygen ----> CO2 released so mass decreases... While Copper + Oxygen ----> Copper Oxide which is a powder so it increases the mass)

21. C (The reagent in test 1 is wrong one... It needs to be Sodium Hydroxide... For the result to be blue ppt when copper is present... The 2nd test is done for the presence of Chloride ions... It gives white ppt when chloride ions are present... So its correct...)

0620_w09_qp_12.pdf

D (Chlorine is going out.... The indicator is in the solution... So it won't turn red... It will be colorless... At cathode when Hydrogen is released the solution will be left with OH ions... So due to OH ions it will turn blue or purple... So the answer is D...

The question I left are answered by the sleepy person...

 

[irlzs95]

thaaaaank you both veery much
gd luck in ur exams !!


but i hav one tiny qs ,
"16. B (Lead II Oxide is reduced to lead so at X there is a decrease and at Y due to excess hydrogen there is increase)"

as far as i know that most of these oxides dont get reduced by heating except for mercury and silver , so hw come lead is reduced ??

thaaaanks again

 

[CaptainDanger]

There lead is reduced by Hydrogen... Not just the heat...

 

[SmartNour]

guys check this may/june 2008 q26
in marking scheme its D
why?? please any1 help
http://www.xtremepapers.me/CIE/index.ph ... 8_qp_1.pdf

 

[CaptainDanger]

Its D (Rubidium forms positive ions) 36 is inert gas... 35 and 34 forms negative ions.... Check in the periodic table according to proton number...

 

[Ramosk95]

There lead is reduced by Hydrogen... Not just the heat...

but how isn't hydrogen below pb in the rs ?if 'm r8 then i think that hydrogen combines with oxygen because of thermal decomposition then it will be vapour bcz of heat so the mass at x is decreased and the mass in y is more bcz water condensed there!

 

[CaptainDanger]

Yes your explanation is right...