Few questions about molarity (1 Viewer)

[Dragonmaster262]

Q1) How many moles of Hydrogen are needed to form 40 moles of ammonium?

Q2) What mass of zinc is formed when 0.2 mole zinc oxide reacts with excess carbon?

Q3) Copper is extracted from chalcocite (copper(1) sulfide) by roasting the ore in the air. When 15.3 g chalcocite was so treated, 11.3 g copper was obtained. What is the percentage yield?

Q4) What mass of sodium would be obtained from the electrolysis of 1 tonne of molten sodium chloride if the process had a percentage yield of 92%?

 

[shady145]

1) write an eq for the formatio of ammonium
4H2 + N2 ------>2NH4^+

balance it like i have.
multiply everything by 40
therefore 160 moles of hydrogen gas
haha embaracing i didnt balance it correctly

 

[shady145]

2)
couldnt be bothered searching for a periodic table/searching the net for the mass of zinc
ANYWAY write a balanced eq.
ZnO + C--------->Zn + CO
it will not form CO2 becasue there is excess of carbon
molar ratios of 1:1
therefore 0.2 moles of Zn are formed
mass=molesxmolecular mass
=0.2xMm of zinc u can do that

 

[annabackwards]

2/
2ZnO + C → 2Zn + CO2
n(ZnO) = n(Zn) = 0.2 moles
n = mass/molar mass
mass = n x molar mass
=0.2 x 65.38 (used wiki's value, just swap it for whatever one is on your periodic table)
=13.076g

I'm too tired to do the rest right now...

 

[shady145]

write another 'balanced' chem eq
Cu2S + air ------------->2Cu +S(air)
lol
we are only interested in the Cu2S and Cu anyway which we can balnce as done
first find moles of Cu2S
mass = 15.3
n=m/Mm
=15.3/159.17
=0.096
molar ratios of 1:2
therefore 2x0.096 moles of Cu should have been produced
=0.192 moles
mass of Cu=moles x Mm
=0.192x63.55
=12.22 gms
however only 11.3 gms were extracted therefore 0.92gms went out somewhere else
yeild percentage is then
(11.3/12.22)x 100
=92.5%

 

[shady145]

2/
2ZnO + C → 2Zn + CO2


I'm too tired to do the rest right now...

shouldnt it be just CO not CO2 because there is excess carbon, not excess oxygen, so the one oxygen atom coming off is straight away taken by a carbon and by the next oxygen atom there is already a heap of carbon atoms waiting to jump it lol. ooo family guys on

 

[shady145]

4)
chem eq
NaCl ---------->Na + Cl
moles of NaCl
=mass/Mm
change m to gms
moles=1000000/58.44
=17111.57 moles, ratio of 1:1 of NaCl to Na
therefore 17111.57 moles of Na
mass=molesxMm
=17111.57x22.99
=393395 gms of sodium, if 100% yeild however only 92 % so multiply by 0.92
=361923gms of sodium

 

[Dragonmaster262]

1) write an eq for the formatio of ammonium
4H2 + N2 ------>2NH4^+

balance it like i have.
multiply everything by 40
therefore 160 moles of hydrogen gas
haha embaracing i didnt balance it correctly

The answer says it's 60 moles of Hydrogen. The specific question says Nitrogen and Hydrogen combine to form NH3.

 

[Dragonmaster262]

2)
couldnt be bothered searching for a periodic table/searching the net for the mass of zinc
ANYWAY write a balanced eq.
ZnO + C--------->Zn + CO
it will not form CO2 becasue there is excess of carbon
molar ratios of 1:1
therefore 0.2 moles of Zn are formed
mass=molesxmolecular mass
=0.2xMm of zinc u can do that

The book says that the answer is 65.6 g but that's not what I get.

 

[shady145]

The answer says it's 60 moles of Hydrogen. The specific question says Nitrogen and Hydrogen combine to form NH3.

ahhh dammit lol, thought it was NH3 but i checked it on wiki and it said NH4+ but now i checked it again it says the ion fromed by NH3 lol
anyway
3(H2) + N2 ----------> 2(NH3)
now multpily both sides by 20 as there is already a 2 infront of the NH3 also looking back at my first post i didnt do this either XD
yea so 60 moles of H2

 

[shady145]

The book says that the answer is 65.6 g but that's not what I get.

dunno well me and anna got the same answer, what did u get?

 

[Dragonmaster262]

dunno well me and anna got the same answer, what did u get?

I got the same as you but the book says that the answer is 65.6 g.

 

[Dragonmaster262]

ahhh dammit lol, thought it was NH3 but i checked it on wiki and it said NH4+ but now i checked it again it says the ion fromed by NH3 lol
anyway
3(H2) + N2 ----------> 2(NH3)
now multpily both sides by 20 as there is already a 2 infront of the NH3 also looking back at my first post i didnt do this either XD
yea so 60 moles of H2

How do you know that you have to multiply it by 20?

 

[annabackwards]

shouldnt it be just CO not CO2 because there is excess carbon, not excess oxygen, so the one oxygen atom coming off is straight away taken by a carbon and by the next oxygen atom there is already a heap of carbon atoms waiting to jump it lol. ooo family guys on

Ah, you are correct. I shouldn't try to do questions when i'm tired XD

I got the same as you but the book says that the answer is 65.6 g.

Perhaps the equation is wrong... i'm going to work backwards to see what it should be.

n (Zn) = mass/molar mass

= 65.6 g/65.38
= 1.003 moles

Sine we are given that n(ZnO) = 0.2 moles then the ratio of n (Zn) to n(ZnO) is 1:0.2 = 5 : 1

So the equation should be something like

ZnO + C--------->5Zn + CO

But then that doesn't balance unless Zn solid is Zn1/5 lol ><"

I'm hoping that the answers is wrong

 

[shady145]

How do you know that you have to multiply it by 20?

the numbers infront of the chemical in a balanced eq are the molar ratios right.
so 3(H2) + N2--------->2NH3
so ratio of hydrogen to ammonium is 3:2
we want 40 for NH3, multiplying both sides by 20 will get that
the ratio is kept the same see. 60:40 = 3:2
and means 60 moles of H2 for 40 moles of NH3

 

[shady145]

Ah, you are correct. I shouldn't try to do questions when i'm tired XD


Perhaps the equation is wrong... i'm going to work backwards to see what it should be.

n (Zn) = mass/molar mass

= 65.6 g/65.38
= 1.003 moles

Sine we are given that n(ZnO) = 0.2 moles then the ratio of n (Zn) to n(ZnO) is 1:0.2 = 5 : 1

So the equation should be something like

ZnO + C--------->5Zn + CO

But then that doesn't balance unless Zn solid is Zn1/5 lol ><"

I'm hoping that the answers is wrong

haha yea lets take it as the answer is wrong =P
3 BoSers is good enough confirmation for me lol

 

[annabackwards]

haha yea lets take it as the answer is wrong =P
3 BoSers is good enough confirmation for me lol

It is official