Chemistry: Post your doubts here!

[MysteRyGiRl]

the general equation for combustion of hydro carbon is CxHy+x(y/4)O2----->XCO2+(y/2)H2O
in such question volume ratio is molar ratio .........1 mol of hydrcarbon produces 3 mol of CO2 thus the carbon atoms are three......... 10cm3of hydrocarbon:50cm3 oxygen(70-20)
thus it is 1:5 if we put 5 in the general equation we get..... x+(y/4)=5 futhur solve t it is y=8.....
thus CxHy=C3H8

umm thnx bt i didnt get the x+(y/4) thing??

 

[MysteRyGiRl]

I'm on it! Give me a minute

sory u can help me if u have a dfrnt method plz

 

[angelgirl:)]

wht is the Q

dont add Ag(s) in in kc value as kc is used only for aques medium...

 

[Muhammad Asif]

umm thnx bt i didnt get the x+(y/4) thing??

 

[TheMan123]

Can someone help?

Aqueous sodium chloride (brine) is electrolysed by using inert electrodes in a cell which is stirred
so that products of electrolysis react with each other. The cell is kept cold.
Which pair of substances is among the major products?
A hydrogen and chlorine
B hydrogen and sodium chlorate(I)
C hydrogen and sodium chlorate(V)
D sodium hydroxide and chlorine

http://www.xtremepapers.com/papers/... AS Level/Chemistry (9701)/9701_w11_qp_13.pdf
Q17
I chose D but the answer is B. I know that sodium chlorate and hydrogen is made, therefore B is right but isnt D also right because NaOH and Cl2 is also made?

 

[Muhammad Asif]

Can someone help?

Aqueous sodium chloride (brine) is electrolysed by using inert electrodes in a cell which is stirred
so that products of electrolysis react with each other. The cell is kept cold.
Which pair of substances is among the major products?
A hydrogen and chlorine
B hydrogen and sodium chlorate(I)
C hydrogen and sodium chlorate(V)
D sodium hydroxide and chlorine

http://www.xtremepapers.com/papers/CIE/Cambridge International A and AS Level/Chemistry (9701)/9701_w11_qp_13.pdf
Q17
I chose D but the answer is B. I know that sodium chlorate and hydrogen is made, therefore B is right but isnt D also right because NaOH and Cl2 is also made?

The products of the electrolysis are Cl2 and H2 and NaOH...but when the products are mixed there is a reaction between NaOH and Cl2.....since the conditions are cold the products are NaClO+H2+NaCl+H2O

 

[bumble26]

please help me with Q20 with explanation.

 

[MysteRyGiRl]

thank u soo soo soo mch

 

[angelgirl:)]

An aqueous solution was prepared containing 1.0mol of AgNO3 and 1.0mol of FeSO4 in 1.00 dm3
of water. When equilibrium was established, there was 0.44mol of Ag+(aq) in the mixture.
Ag+(aq) + Fe2+(aq) --> Ag(s) + Fe3+(aq)

What is Kc?

A. 0.35 B. 0.62 C. 1.62 D. 2.89

I got C as my answer but the correct one is D, can anyone explain how to get D?

Edit: Oops I missed out the question! I just added it

dont add Ag(s) in calculating kc value as kc is used only for aques medium...

 

[Amaryllis]

one more question
how to differentiate between permanent and induced dipoles ...i know that in permanent there is a difference in the electronegativities ..but how to know which have the higher electronegativity?

 

[Muhammad Asif]

thank u soo soo soo mch

welcome

 

[MysteRyGiRl]

for hydrogen halides,there is hydrogen bonding onlyn widn HF??

 

[étudiante]

for hydrogen halides,there is hydrogen bonding onlyn widn HF??

yes!

 

[MysteRyGiRl]

one more question
how to differentiate between permanent and induced dipoles ...i know that in permanent there is a difference in the electronegativities ..but how to know which have the higher electronegativity?

the difernce in the + and the - charge .higher the dfrnce higher the electronegativity

 

[MysteRyGiRl]

yes!

oki thnx

 

[étudiante]

oki thnx

ur welcum ^_^

 

[Muhammad Asif]

for hydrogen halides,there is hydrogen bonding onlyn widn HF??

yes.....hydrogen bonding occurs with only threee elements F O N.....

 

[MysteRyGiRl]

On collision, airbags in cars inflate rapidly due to the production of nitrogen.
The nitrogen is formed according to the following equations.
2NaN3----->2Na+3N2
10Na+2KNO3----->K2O+5Na2O+N2
How many moles of nitrogen gas are produced from 1 mol of sodium azide?
A 1.5 B 1.6 C 3.2 D 4.0


hows it B?

 

[TheMan123]

please help me with Q20 with explanation.

Well the molecule is a cis-molecule so its either A or C
it has a formula of C20H28O, which is also CnH2n-12O. It has some double bonds, an aldehyde group and a cyclohexene ring
Lets start of with an alkane and change it into the molecule in question
An alkane has a formula of CnH2n+2
If you could change it into an aldehyde, you lose 2hydrogens and gain one Oxygen
so now its CnH2nO
If you could make part of it into a ring, adding a cyclohexane ring, you reduce number of hydrogens by 2. Noticed I added cyclohexane isntead of cyclohexene. We'll take care of double bonds later
now its CnH2n-2O
So now the only group we haven't considered is alkene. Each alkene reduces the H number by 2, so if there are 5 alkenes,
the formula would be CnH2n-12O, which is our molecule

So answer is A

EDIT: Fixed up some mistakes, you should reread it if you read it already

 

[Muhammad Asif]

On collision, airbags in cars inflate rapidly due to the production of nitrogen.
The nitrogen is formed according to the following equations.
2NaN3----->2Na+3N2
10Na+2KNO3----->K2O+5Na2O+N2
How many moles of nitrogen gas are produced from 1 mol of sodium azide?
A 1.5 B 1.6 C 3.2 D 4.0


hows it B?

1 moll of NaN3 produces 1.5N2 according 2 equation....but it also produces 1 mol Na which gives 0.1mol of N2 so in total it is 1.6mol of N2