Chemistry: Post your doubts here!

[Soldier313]

Asslamu Alikum, now you have three versions..!!
Soldier313

Wa alaykum salaam, haha yes...

PhyZac littlecloud11 iKhaled
Thanx a million guyss......it really helped...alhamdulillah ^_^

 

[PhyZac]

Asslamu Alikum Wa Rahmatullahi Wa Barakatoho.......

Can anyone please explain this?

 

[littlecloud11]

Asslamu Alikum Wa Rahmatullahi Wa Barakatoho.......

Can anyone please explain this?

Ka is for the acid. The acid contains H2PO4- ion hence, NaH2PO4 is the acid.
PH = pKa + log [salt]/[acid]
PH = -log(6.3*10^-8) + log [.1]/[.2]
PH = 6.89

 

[PhyZac]

Ka is for the acid. The acid contains H2PO4- ion hence, NaH2PO4 is the acid.
PH = pKa + log [salt]/[acid]
PH = -log(6.3*10^-8) + log [.1]/[.2]
PH = 6.89

JazakAllah khairan........thank you so much for your help!! Alhamdulilah i got it now..! May Allah grant you and your family with Jannah tul firdous..!!

 

[Oliveme]

Can someone pleasee explain me the the following paper 1 questions
o/n 05 Q1
m/j 05 Q1 & 2
o/n 04 Q3
m/j 04 Q3
o/n 03 Q1
:/

Question 1 2003 october

there are 3 x 10^-21 moles of amino acids. we need the molecules that this amount of amino acids contains.
1 mole = 6.02 x 10^23 particles (whether its atoms or molecules)
so 3 x 10^-21 moles would be 1806 molecules because we multiply 6.02 x 10^23 by 3 x 10^-21.
1806 is closest to the answer 1800.
do not get confused because they gave you Mr as 200, that's extra information designed to distract you and confuse you.

Question 3 2004 may june

2NaN3 ----> 3N2 + 2Na there are 50 grams of NaN3 - from this we can find the moles

moles = mass/Mr ------> 50/ 23 +(3 x 14) = 0.77 moles of NaN3
now, let's look at the mole ratio of NaN3 to N2 from the equation (big yellow numbers)------>

NaN3 : N2
2 : 3
0.77 : x ------------> find x = (0.77 x 3)/ 2 = 1.155 moles of N2
volume of N2, use the equation ----> moles (only for gases)= volume/24

so, volume = 1.155 moles x 24 =27.7 dm^-3
the answer is C.

Hope this helped, sorry I couldn't help with the other questions.
Please keep in mind, next time give links to the questions, makes it much easier.

 

[MaRyy xD]

Chem paper 2 . MJ 2011 v 1
Q 3 d
I don't understand this answer. Why should we use any soluble sulfates.

 

[PhyZac]

Chem paper 2 . MJ 2011 v 1
Q 3 d
I don't understand this answer. Why should we use any soluble sulfates.

Asslamu Alikum Wa Rahmatullahi Wa Barakatoho..

See, u need to form CaSO4 . It is generally insoluble....and can be formed by precipitation process ( which is mixing two soluble salts forming a precipitate)
Since Calcium nitrate is soluble u add another soluble sulphate like Sodium sulphate. And CaSO4 is formed!

 

[ashiqbal]

does anyone know any thread where chem p3 tips are given? especially the salt part...if someone has made any sort of notes can u please upload them?

 

[Alool]

The elements phosphorus, sulphur, and chlorine are regarded as having simple molecular structures
what are the molecular formulae of each of these three elements?
Why is the answer for phosphorous P4 and for sulphur S8 ?

 

[daredevil]

The elements phosphorus, sulphur, and chlorine are regarded as having simple molecular structures
what are the molecular formulae of each of these three elements?
Why is the answer for phosphorous P4 and for sulphur S8 ?

its just the way they r.... S8 and P4 are just their simple molecular formulae and u have to remember it... the reasons are not needed in a levels and my teacher was not too keen to answer when i asked -_-

 

[Alool]

its just the way they r.... S8 and P4 are just their simple molecular formulae and u have to remember it... the reasons are not needed in a levels and my teacher was not too keen to answer when i asked -_-

owh hahah so im not the only one... okay thanks a lot.. i thought it was part of the syllabus and i missed it

 

[daredevil]

owh hahah so im not the only one... okay thanks a lot.. i thought it was part of the syllabus and i missed it

np and no not part of the syllabus
at least not in A1... can't say about A2

 

[strangerss]

hello everyone , al salam alaykom. Can any one help me out in question 15 year Oct/Nov 2012 p1? I tried to find the number of moles of the compound then divided the mass with it to get the Mr of the compound but it was wrong , what am I supposed to do? And in question 3 is what the shape pf the sodium borohydride ion? I also failed solving question 23 and 24 (apparently I'm a failure ) oh and question 17 too

 

[snowbrood]

why is ethanoic acid stronger acid than ethanol explain the above statement please use the concepts of as level to explain this

 

[Silent Hunter]

Asalamualikum... can anybody tell how much of AS organic is needed to be revised and memorised ? JazakAllah

 

[daredevil]

Asalamualikum... can anybody tell how much of AS organic is needed to be revised and memorised ? JazakAllah

just learn the reactions and mechanisms if u don't have much time. understand wats happeining and u'l b gud to go hopefully

 

[daredevil]

explain this pls -_-

 

[littlecloud11]

why is ethanoic acid stronger acid than ethanol explain the above statement please use the concepts of as level to explain this

For ethanoic acid in the -COOH structure the electron density is shifted towards the doubly bonded oxygen atom and away from the hydrogen atom due to it's high electronegativity. This results in the weakening of the -OH bond so that hydrogen can be lost more easily to the water molecules.
In ethanol there is no extra electron withdrawing atom as a result the -OH bond is much stronger and making H less available to the H2O molecules. So ethanoic acid is a much stronger acid.

 

[littlecloud11]

explain this pls -_-

Vacuum tube means there is no air resistance, so the feather is supposed to accelerate at the value of 'g' until it reaches the ground.
s= ut+ 1/2 at^2
if the feather is dropped from rest u=0
s= 0 + 1/2 g t^2
s= 1/2 * 10 * .5^2
s= 1.25
approx. 1.3
so the answer is A.

PS. Is this a chem question?

 

[ashiqbal]

Q: why is HCl a stronger acid in aqueous ammonia then in water?

its a MCQ, and the answer is that pH of ammonia is higher than water..but how does this relate?