Chemistry: Post your doubts here!

[smartangel]

Remember this: Bond breaking is endothermic(positive) and Bond making is exothermic(negative)
Enthalpy changes:
P=+193 Br-Br bond broken
Q=-244 Cl-Cl made
R=-340 C-Cl made
S=+410 C-H broken
Answer C. RQPS

thamks. plz see if u can explain 21 of the same paper as well!

 

[MysteRyGiRl]

10 cm3 of hydrocarbon is burned in 70cm3 of oxygen(excess) the funal gaseous mixture contains 30cm3 of ccarbon dioxide n 20 cm3 of unreacrted oxygen.whats the formula of hydrocarbon?
a) C2H5 b)C3H6 c)C3H8 d)C4H10
hows it c? these r supoosed 2 be easy questions bt cant get the answers

can any1 help em out here??

 

[TheMan123]

thanks..could you please solve 21 of the same paper?

The Cl radical can bond to any CH3 or CH2 carbons by substituting a hydrogen. There are 5 such carbons here, however there are 3 CH3 groups bonded directly to the alpha central carbon. If the Cl radical bonds to any three of this, you get the same molecule. The 3 CH3 groups form only one type of molecule. There are another two carbons which Cl can bond to, which makes 3 Chloroalkanes in total.
Answer: C. 3 (I checked)
Sorry for the messy explanation, not very good at this, ask me to clarify if needed
EDIT: Fixed typo

 

[Muhammad Asif]

thanks..could you please solve 21 of the same paper?

the answer is C as the 2 CH3 groups are the side chain on same parent chain carbon thus makes no difference but if Cl substitutes any other H in parent chain it gives rise to 2 pther forms thus in total 3

 

[Muhammad Asif]

http://www.xtremepapers.com/papers/CIE/Cambridge%20International%20A%20and%20AS%20Level/Chemistry%20(9701)/9701_w08_qp_1.pdf
what would be the equation in question no 1???????

 

[TheMan123]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
what would be the equation in question no 1???????

The full equation isnt really too important, you just need to know this:
FeTiO3-->TiO2 + other stuff
What you need to know is that 1 mole of FeTiO3 gives one mole of TiO2

 

[MysteRyGiRl]

somebodyyyyy???

 

[TheMan123]

http://www.xtremepapers.com/papers/...d AS Level/Chemistry (9701)/9701_w08_qp_1.pdf
what would be the equation in question no 1???????

Anyway this is how you do it:
FeTiO3=151.7grams per mol
TiO2=79.9 grams per mol

Therefore the same moles of TiO2 as FeTiO3 will weigh 79.9/151.7 times as FeTiO3

so 79.9/151.7 * 19 tonnes= 10 tonnes

A

 

[Muhammad Asif]

can any1 help em out here??

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

 

[TheMan123]

somebodyyyyy???

I'm on it! Give me a minute

 

[TheMan123]

I'm on it! Give me a minute

Nvm seems that Muhammad Asif is on a roll!

 

[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...