Physics, Chemistry and Biology: Post your doubts here!

[Rahma Abdelrahman]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf q15, why 20 deg. C?

Less water absorbs less heat energy so temperature decrease is doubled.
!

 

[Rahma Abdelrahman]

w09_qp11 q4 http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_11.pdf
if u c d periodic tbl, atomic no goes(4 noble gases): 2,8,18,36.... 18 & 36 have a diff of 18 n not 8, so it could b ne option
same grp should b ticked, but i dnt think unreactive ... plz help

sm ppr q20

Firstly, Atomic no. goes 2, 10, ....(not 8).
Secondly, it is a fact that noble gases are all unreactive, the Question says: Which students CAN be correct? so it is just a suggestion; it may be right or wrong!
For Q.20, answer is A because barium sulfate and silver chloride are formed which are both insoluble and form precipitates.
Any further doubt ?

 

[thats_me]

do v need 2 learn d reactivity series 4 metals? plz say no

do it this way
metals :
Please(potassium) stop(sodium) calling(calcium) my(magnesium) aunt(aluminium) carol(carbon) zine(zinc) inanimate(iron) things(tin) like(lead) honey(hydrogen) comb(copper) sugar(silver) goey(gold) plop(platinum)
non-metals :
FAther (flourine)of (oxygen)carol(chlorine) brother(Bromine) naughty(nitrogen) sister(sulphur) idiot(iodine) parents(phosphorus) called(carbon) home(hydrogen)

 

[122]

Well i think i hve them but only as a hard copy..if u want u can tell me a question and i will give u its answer

oh thanks . can u tell me the answer for may 1998 question no. 18,21,37

 

[Ahmed Khider]

oh thanks . can u tell me the answer for may 1998 question no. 18,21,37

Ok the answer for qno 18 is A, no 21 is B, no 37 is A.

 

[Abu mota]

w09_qp11 q4 http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w09_qp_11.pdf
if u c d periodic tbl, atomic no goes(4 noble gases): 2,8,18,36.... 18 & 36 have a diff of 18 n not 8, so it could b ne option
same grp should b ticked, but i dnt think unreactive ... plz help

sm ppr q20

idk if anyone answered u yet, but for Q.4 it says which can be correct and so if u start with already a noble gas and moved 8 protons u will also end up with a noble gas and so it will be unreactive and will be in the same group and also atomic number is 2 then 10 then 18, i guess ur periodic table is wrong.
for Q.20 it is B because sulfuric acid contains sulfate ions and adding barium chloride is actually the test for sulfates (it makes white precipitate) hydrochloric acid doesnt contain sulfate ions and so there is no effect.

 

[Abu mota]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w08_qp_1.pdf q15, why 20 deg. C?

if u halved the volume, all of the heat will be concentrated in a small area and so the temperature increases but if u increased the area the heat will spread everywhere reducing the temperature

 

[Rahma Abdelrahman]

do it this way
metals :
Please(potassium) stop(sodium) calling(calcium) my(magnesium) aunt(aluminium) carol(carbon) zine(zinc) inanimate(iron) things(tin) like(lead) honey(hydrogen) comb(copper) sugar(silver) goey(gold) plop(platinum)
non-metals :
FAther (flourine)of (oxygen)carol(chlorine) brother(Bromine) naughty(nitrogen) sister(sulphur) idiot(iodine) parents(phosphorus) called(carbon) home(hydrogen)

Is the reactivity series of non-metals in our syllabus?

 

[AAnsarii]

Firstly, Atomic no. goes 2, 10, ....(not 8).
Secondly, it is a fact that noble gases are all unreactive, the Question says: Which students CAN be correct? so it is just a suggestion; it may be right or wrong!
For Q.20, answer is A because barium sulfate and silver chloride are formed which are both insoluble and form precipitates.
Any further doubt ?

jazakillah, if i have ne, will iA post it here. jazakillah again

 

[Ahmed Khider]

Is the reactivity series of non-metals in our syllabus?

I dont think so

 

[thats_me]

Is the reactivity series of non-metals in our syllabus?

I don't really knw but i hav them in my notes so i learned it

 

[Rahma Abdelrahman]

What is the chemical formula of sodium aluminate ?
NaAlO2 or Na3AlO3.

 

[Abu mota]

What is the chemical formula of sodium aluminate ?
NaAlO2 or Na3AlO3.

NaAlO2, i dont think we have to know that though

 

[Rahma Abdelrahman]

NaAlO2, i dont think we have to know that though

Are you sure?!

 

[Abu mota]

Are you sure?!

yes ,pretty sure

 

[GorgeousEyes]

please someone explain , Nov99 , no.36 , no.40 .

 

[Abu mota]

please someone explain , Nov99 , no.36 , no.40 .

biology or chemistry?

 

[GorgeousEyes]

Chemistry .

 

[Abu mota]

Chemistry .

for Q.36 it is D u need to memorize the structures of all hydrocarbons, it cant be explained :/
for Q.40 it is D also because u need to memorize the conditions of the reactions u take, none of these questions can be explained, it can only be memorized

 

[Yousif Mukkhtar]

Guys, can you explain to me q 19 and q 22:
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s08_qp_1.pdf