Biology; Chemistry; Physics: Post your doubts here!

[usama321]

ohk, just searched on google. Zn(OH)2 solubility in water is extremely low. And i was confusing it dissolving in the cation test with it dissolving in water. It actually dissolves in the excess NaOH, thanks everyone

 

[papajohn]

ohk, just searched on google. Zn(OH)2 solubility in water is extremely low. And i was confusing it dissolving in the cation test with it dissolving in water. It actually dissolves in the excess NaOH, thanks everyone

 

[Suchal Riaz]

Koi BAAP ka DADA hai to explain this MCQ..
Energy, Work and Power MCQ 50

http://books.google.com.pk/books?id...=gbs_selected_pages&cad=3#v=onepage&q&f=false

not a difficult but need little bit of vector manipulation.
do u know about component vectors?
see this. Saad Mughal u would understand it easily coz u know about component vectors:
i hope i made no silly mistake in calculation.

 

[Sijal Mirza]

can u please tell me what topics from physics come in the ATP paper? (O-level) like in chemistry its mainly just Acids, Bases n Salts , Rate of reaction and Moles..
PLEASE HELP!

 

[Saad Mughal]

not a difficult but need little bit of vector manipulation.
do u know about component vectors?
see this. Saad Mughal u would understand it easily coz u know about component vectors:
i hope i made no silly mistake in calculation.
View attachment 23991

Yeah, I got it. Simple enough (but the thought of applying component vectors in this question didn't occur to me). Good try!
Haris Bin Zahid also solved this with another method.
Logically, both methods are right. Well done, geniuses.

 

[Suchal Riaz]

Yeah, I got it. Simple enough (but the thought of applying component vectors in this question didn't occur to me). Good try!
Haris Bin Zahid also solved this with another method.
Logically, both methods are right. Well done, geniuses.

can u show me how he solved it?

 

[Saad Mughal]

can u please tell me what topics from physics come in the ATP paper? (O-level) like in chemistry its mainly just Acids, Bases n Salts , Rate of reaction and Moles..
PLEASE HELP!

P.S. I do not own any of the notes.

 

[Saad Mughal]

can u show me how he solved it?

The 5 kg block falls by a height of 0.1 m. So the loss in its g.p.e was (0.1 * 5 * 10) = 5 J
The 1 kg block also moves by a distance of 0.1 m.....
.... So the work done against friction = F * d = 10 * 0.1 =1 J
By using trigonometry, we can find out that the height of the 1 kg block increased by 5 cm (0.05m)......
......So its increase in g.p.e = mgh = 1 * 10 * 0.05 = 0.5 J
The loss in g.p.e of 5 kg mass was converted to heat energy (due to friction), g.p.e of 1 kg block and kinetic energy of whole system.
We have calculated the work done against friction and increase in g.p.e of 1 kg block....
....so kinetic energy of system = 5 - 1 - 0.5 =3.5 J
Both, the 1 kg block and 5 kg block are moving with the same velocity, but the 5 kg block has 5 times more kinetic energy than the 1 kg block because of its mass being greater by 5 times.....so.....
x + 5x = 3.5
x = 7 /12 - which is kinetic energy of the 1 kg block.
use k.e. = 0.5 * m *v^2
By substituting m=1, you get
v= 1.08 =1.1 m/s

 

[Kamihus]

16
Which statement about catalysts is correct for a typical equilibrium reaction?
A A catalyst can be either an inorganic or an organic species.
B A catalyst does not take part in the reaction.
C A catalyst only speeds up the forward reaction.
D A catalyst provides the energy required to start a reaction.
Why in the world is the answer A and NOT B

catalysts form temporary compounds with reactants and then react again to form products

 

[zeekay132]

Test for iodide ion.What is the meaning of the red underlined line???

 

[ijlalm]

not a difficult but need little bit of vector manipulation.
do u know about component vectors?
see this. Saad Mughal u would understand it easily coz u know about component vectors:
i hope i made no silly mistake in calculation.
View attachment 23991

Dimagh ki dahi ban gai but good... you solved it finally...Thank GOD
PS: I might have used the component velocity but i thought it was not in the syllabus..

 

[ijlalm]

Small pieces of a silver coloured metal, X, were added to concentrated nitric acid. A brown
gas, Z, and a colourless solution containing salt Ywere formed.
Analysis of a 0.0914 mol sample of Zshowed it contained 1.28 g of nitrogen and 2.93 g of
oxygen.
The small sample of the colourless solution was diluted with water and then divided into two
portions.
• To one portion, aqueous sodium hydroxide was added drop by drop until it was in
excess. A white precipitate, W, was formed that redissolved in the excess sodium
hydroxide.
• To the other portion, aqueous ammonia was added drop by drop until it was in
excess. A white precipitate, W, was formed that redissolved in the excess ammonia.
(a) (i) Name the white precipitate, W.
............................................................................................................................. [1]
(ii) Construct the ionic equation, with state symbols, for the formation of W.
............................................................................................................................. [2]
(b) Name Xand Y.
Xis ...................................................................................................................................
Yis .............................................................................................................................. [2]
(c) (i) Calculate the relative formula mass, Mr, for gas Z.
Mr
= ................................................. [2]
(ii) Determine the molecular formula for Z.
molecular formula is ................................................. [2]
[Total: 9]

 

[ijlalm]

Could also anyone can tell me what is a repeat unit in a polymer..??

 

[Suchal Riaz]

Could also anyone can tell me what is a repeat unit in a polymer..??

show the structure of polymer first.
the monomer(single molecules) which combine to create polymer are called repeat unit as they are repeated again and again in polymer.

 

[Suchal Riaz]

Dimagh ki dahi ban gai but good... you solved it finally...Thank GOD
PS: I might have used the component velocity but i thought it was not in the syllabus..

my teacher taught us this that component vectors are used to deduce the force acting downwards so it must be in syllabus. although i managed to remember it coz i have used component vectors many times in addmaths.
although method of Haris Bin Zahid seems more 'o level' method. a normal o level physics student will not get idea of using components in physics unless he has done hard vector question.
all i can advice u is that whenever u are asked to add or subtract two things first see are they vectors or scalars. if they are vectors then u should do it by triangle-rule(head-to-tail) or parallelogram rule to add/subtract them. such as here in Q1 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w10_qp_22.pdf we must subtract the velocity as vectors to get correct answer.

 

[Saad Mughal]

Small pieces of a silver coloured metal, X, were added to concentrated nitric acid. A brown
gas, Z, and a colourless solution containing salt Ywere formed.
Analysis of a 0.0914 mol sample of Zshowed it contained 1.28 g of nitrogen and 2.93 g of
oxygen.
The small sample of the colourless solution was diluted with water and then divided into two
portions.
• To one portion, aqueous sodium hydroxide was added drop by drop until it was in
excess. A white precipitate, W, was formed that redissolved in the excess sodium
hydroxide.
• To the other portion, aqueous ammonia was added drop by drop until it was in
excess. A white precipitate, W, was formed that redissolved in the excess ammonia.
(a) (i) Name the white precipitate, W.
............................................................................................................................. [1]
(ii) Construct the ionic equation, with state symbols, for the formation of W.
............................................................................................................................. [2]
(b) Name Xand Y.
Xis ...................................................................................................................................
Yis .............................................................................................................................. [2]
(c) (i) Calculate the relative formula mass, Mr, for gas Z.
Mr
= ................................................. [2]
(ii) Determine the molecular formula for Z.
molecular formula is ................................................. [2]
[Total: 9]

(a) Zinc Hydroxide
(ii) Zn (2+)(aq.) + OH (-1)(aq.) -----> Zn(OH)2 (s), the numbers in bracket show charge.
(b) X is Zinc.
Y is Zinc Nitrate , Zn(NO3)2
(c) The gas Z is Nitrogen Dioxide (brown color)
Therefore, Mr = 12+(2*16) = 44 g/mol.
(ii) NO2

 

[Saad Mughal]

Could also anyone can tell me what is a repeat unit in a polymer..??

 

[asma tareen]

not a difficult but need little bit of vector manipulation.
do u know about component vectors?
see this. Saad Mughal u would understand it easily coz u know about component vectors:
i hope i made no silly mistake in calculation.
View attachment 23991

MJE NE SAMJH AAYA

 

[scouserlfc]

my teacher taught us this that component vectors are used to deduce the force acting downwards so it must be in syllabus. although i managed to remember it coz i have used component vectors many times in addmaths.
although method of Haris Bin Zahid seems more 'o level' method. a normal o level physics student will not get idea of using components in physics unless he has done hard vector question.
all i can advice u is that whenever u are asked to add or subtract two things first see are they vectors or scalars. if they are vectors then u should do it by triangle-rule(head-to-tail) or parallelogram rule to add/subtract them. such as here in Q1 http://papers.xtremepapers.com/CIE/Cambridge International O Level/Physics (5054)/5054_w10_qp_22.pdf we must subtract the velocity as vectors to get correct answer.

Im amazed a bit You did it the alevel way, Congratz you actually covered almost whole of A level physics vectors
And by the way make sure if u try this method in exam u get credit because CIE never liked when people did extra stuff more than required but anyways ask your sir ! But i think you know both methods and this method of yours helps a lot in Add maths,those having troubles abt how he broke the vector into pieces think about the i and j vectors from add maths or just think that vector which is given can be broken into two parts one a horizontal and the other vertical these are called vector components,but plz dont get disappointed or sad just because he knows the method and you dont use the parallelogram law or head to tail rule the most easiest one for O levels and added advantage of using in A level too later on so its very good if u know these rules and not those components !!

 

[Saad Mughal]

Im amazed a bit You did it the alevel way, Congratz you actually covered almost whole of A level physics vectors
And by the way make sure if u try this method in exam u get credit because CIE never liked when people did extra stuff more than required but anyways ask your sir ! But i think you know both methods and this method of yours helps a lot in Add maths,those having troubles abt how he broke the vector into pieces think about the i and j vectors from add maths or just think that vector which is given can be broken into two parts one a horizontal and the other vertical these are called vector components,but plz dont get disappointed or sad just because he knows the method and you dont use the parallelogram law or head to tail rule the most easiest one for O levels and added advantage of using in A level too later on so its very good if u know these rules and not those components !!

I think almost everyone is taught component vectors in relative velocity. It's just about applying them correctly. Credits to Suchal Riaz for applying them in a Physics Mcq correctly.