Chemistry Doubts: IGCSE Paper 3

[Sajal mehta]

ok thank u soo much! one more
d- the formula of an acid is either of the type HY or H2Y.How could you find out which one is correct by using Aq.solutions of the acid and of sodium hydroxide. Assume that both solutions have the same concentration, 0.1 mol/dm3
please help!

which paper is that???

 

[Beedo]

ok explain 7b & 2c & 5b only please

please someone explain to me

 

[gelato]

Hey guys, can anyone tell me what to focus on? So we've got organic chemistry annnd what else?

 

[Rhea_daga]

can someone please tell me all the names of the catalysts used in the various manufacturing processes? I always get confused !

 

[kanishk]

can someone please tell me all the names of the catalysts used in the various manufacturing processes? I always get confused !

i think you should just remember iron for haber process and vanadium pentaoxide for contact process

 

[Tekno-M]

Can someone explain to me the structure of fats and its monomers, and proteins too?

 

[Rhea_daga]

i think you should just remember iron for haber process and vanadium pentaoxide for contact process

thanks! ..Are you sure they wouldn't ask for anything else?

 

[Shivashree]

another problem help me on this
c) A 5.00 g sample of impure lead(II) nitrate was heated. The volume of oxygen formed was
0.16dm3 measured at r.t.p. The impurities did not decompose.
Calculate the percentage of lead(II) nitrate in the sample.
2Pb(NO3)2 → 2PbO + 4NO2 + O2
Number of moles of O2 formed = .......................................
Number of moles of Pb(NO3)2 in the sample = .......................................
Mass of one mole of Pb(NO3)2 = 331 g
Mass of lead(II) nitrate in the sample = ....................................... g
Percentage of lead(II) nitrate in sample = .....................................
tell me how you got each too please

• no. of moles of O2= 0.16/24 =0.0067 moles'''
• 1 mole O2 gives 2 moles Pn(NO3)2 .....therefore 0.067 moles O2 will give 2 * o.o067 = 0.0133 moles
• mass of lead nitrate = 0.0133 * 331 =4.4g
• %of lead nitrate in the sample= (4.4/5)*100= 88.7%

 

[omglaigcse]

HELPHELPHELP.
how do you know a gas is more dense or less dense than air?
what molecular mass are you comparing when you say "air"
is it oxygen or what?

 

[SB29597]

Hehe yeah.. but CIE is quite unpredictable! Check dis out; qn. 5 (b).. http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s07_qp_3.pdf

yeah dude- when i read that i was like What?! The part about titanium not rusting

 

[Mozmozil]

One H2O is H-O-H. If u break that up, u get (H-O)(H-O). So one H2O = 2(H-O).. and 2H2O = 4(H-O). CH4 is just 4(C-H). Hope this helped!

thanks ^_^

 

[kanishk]

• no. of moles of O2= 0.16/24 =0.0067 moles'''
• 1 mole O2 gives 2 moles Pn(NO3)2 .....therefore 0.067 moles O2 will give 2 * o.o067 = 0.0133 moles
• mass of lead nitrate = 0.0133 * 331 =4.4g
• %of lead nitrate in the sample= (4.4/5)*100= 88.7%

thanks man but why cant moles of lead nitrate be mass/molecular mass? can you tell me why thats wrong? and what concept have you used for it? that 1 mole gives 2 mole thingy

 

[Maz]

thanks man but why cant moles of lead nitrate be mass/molecular mass? can you tell me why thats wrong? and what concept have you used for it? that 1 mole gives 2 mole thingy

It is mass/molecular mass, only thing is that the subject has been changed.
From: moles= mass/molecular mass.
to: moles*molecular mass= mass.(since we have to find the mass).

 

[imperial]

got what you mean thanks a lot,

can you answer this?
which group nitrates are stable? give nitrite? give nitrogen dioxide?
thanks
i think its group 1, group 2, others
need confirming

 

[Tariqig7]

how can we get ethene form erhane and under what conditioned

 

[Dinuka Malith]

Brilliant fuel cell

 

[Maz]

got what you mean thanks a lot,

can you answer this?
which group nitrates are stable? give nitrite? give nitrogen dioxide?
thanks
i think its group 1, group 2, others
need confirming

All nitrates decompose when heated.
Sodium and potassium nitrates decompose to nitrite and oxygen.
Nitrates of lesser reactive metals decompose to their oxides, nitrogen dioxide and oxygen.

 

[imperial]

All nitrates decompose when heated.
Sodium and potassium nitrates decompose to nitrite and oxygen.
Nitrates of lesser reactive metals decompose to their oxides, nitrogen dioxide and oxygen.

awesome thanks ^^

 

[IsraJ]

can someone please tell me all the names of the catalysts used in the various manufacturing processes? I always get confused !

catalyst - process
amylase or dilute HCl - hydrolysis of starch
aluminium oxide or chromium oxide - cracking
phosphoric acid- alcohol fermentation
conc. sulfuric acid - esterification
nickel - steam reforming
iron - ammonia
vanadium oxide- sulfuric acid

 

[Yousif Mukkhtar]

Can some one explain to me 9 c)
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s09_qp_3.pdf