sos, may day! help

[lacoste]

Some questions that I don't quite get... more will be coming  

Q3).
Copper metal can be oxidised by nitric acid according to the following half-equations
Cu (s) ---> Cu2+ (aq) + 2 e–
NO3– (aq) + 4 H+ (aq) + 3 e– ---> NO (g) + 2 H2O (l)
The number of moles of nitrate ions reduced by one mole of copper is closest to
A.   0.33
B.   0.67
C.   1.5
D.   2.0

[lacoste]

Question 5
A chemist working for a mining company found that a mineral sample contained 67% zinc.
A possible chemical formula for the mineral sample is
A.   ZnO
B.   Zn2S
C.   ZnS
D.   FeZnS

What is your working out?

THANKS!!!!!!!!!!!

[TrueTears]

(Did not put in states because I cbf lol)





Add those 2





Answer is B

[TrueTears]

Question 5
A chemist working for a mining company found that a mineral sample contained 67% zinc.
A possible chemical formula for the mineral sample is
A.   ZnO
B.   Zn2S
C.   ZnS
D.   FeZnS

What is your working out?

THANKS!!!!!!!!!!!

Answer is C

Molar mass of

% of Zn is

[lacoste]

Why is it 1:0.67?

[TrueTears]

Why is it 1:0.67?

We require n(Cu) to be 1.

So we know

divide both by 3 yields:

[lacoste]

Thanks Truetears! you are great!!!!!!!!!!!!!!!!!!!

[lacoste]

Question 12
The volume of 0.20 mol L-1 KOH needed to neutralise the weak acid is
A.   100 mL
B.   50 mL
C.   10 mL
D.   5.0 mL

[TrueTears]

Question 12
The volume of 0.20 mol L-1 KOH needed to neutralise the weak acid is
A.   100 mL
B.   50 mL
C.   10 mL
D.   5.0 mL

What is the weak acid?

[lacoste]

Questions 11 and 12 refer to the following information.
A 100 mL sample of an aqueous solution of a weak monoprotic acid has a concentration of 0.10 mol L-1 and a pH of 2.0.


I got the answer, thanks, true tears again. I was looking at the MC question by itself without referring to the above given info.
LOL. No wonder I had no clue at first. I thought i was going nuts




next q.
Question 19
In which of the following reactions is sulfuric acid, H2SO4, acting as an oxidant?
A.   H2SO4 (aq) + CuO (s) ---> CuSO4 (aq) + H2O (l)
B.   2 H2SO4 (aq) + Cu (s) ---> CuSO4 (aq) + SO2 (g) + H2O (l)
C.   H2SO4 (aq) + CaCO3 (s) ---> CaSO4 (aq) + CO2 (g) + H2O (l)
D.   H2SO4 (aq) + 2 NaCl (s) ----> 2 HCl (g) + Na2SO4 (aq)

How do you know that in B, H2SO4 goes to CuSO4 or SO2?

[TrueTears]

Questions 11 and 12 refer to the following information.
A 100 mL sample of an aqueous solution of a weak monoprotic acid has a concentration of 0.10 mol L-1 and a pH of 2.0.


I got the answer, thanks, true tears again. I was looking at the MC question by itself without referring to the above given info.
LOL. No wonder I had no clue at first.




next q.
Question 19
In which of the following reactions is sulfuric acid, H2SO4, acting as an oxidant?
A.   H2SO4 (aq) + CuO (s) ---> CuSO4 (aq) + H2O (l)
B.   2 H2SO4 (aq) + Cu (s) ---> CuSO4 (aq) + SO2 (g) + H2O (l)
C.   H2SO4 (aq) + CaCO3 (s) ---> CaSO4 (aq) + CO2 (g) + H2O (l)
D.   H2SO4 (aq) + 2 NaCl (s) ----> 2 HCl (g) + Na2SO4 (aq)

How do you know that in B, H2SO4 goes to CuSO4 or SO2?

Oxidation number of from left to right is : +1 , +6 and -2

In Oxidation numbers from left to right is : +4 , -2

Now acting as an oxidant means must be reduced. This means it's oxidation number must decrease.

In was +6 but in it changed to +4

Hence it decreased it acts as an oxidant

As you can see in , the oxidation of S does not change, hence it must go to

[lacoste]

Question 2
Natural gas consisting of the alkanes containing one to four carbon atoms can undergo thermal cracking in a cracker.
 
Why is steam added into the cracker?

[TrueTears]

Hydrocarbons ranging from 1 - 4 carbon atoms are gases. I think using steam helps carry the gases up the cracker. It kind of acts like a "carrier".

[lacoste]

Thanks Truetears again, wish i could + karma you again.

Would it be wise to go through every MC option A to D and check for the oxidation numbers, or go through until you get one ie like B the one above and then stop and say its B?    

So if it doesnt change we just move onto the other "SO2 option" and find a decrease?

Cheers!!!

[lacoste]

Hydrocarbons ranging from 1 - 4 carbon atoms are gases. Using steam heaps carry the gases up the cracker. It kind of acts like a "carrier".

I like your answer as it makes more sense than the solution.

the solution is:(a)   Steam is added to the thermal cracker to reduce carbon build-up during thermal cracking.   
[The chemical equation for the process is: H2O (g) + C (s) ---> CO (g) + H2 (g)]

What does it mean by reduce carbon build up?


actually your answer answers this i think, helps carry the gases c1 to c4 hydrocarbons up