# AS level chemistry- help!!

Watch
Announcements
#1
In an experiment, 3.425 g of lead oxide was reduced to form 3.105 g of lead.

The empirical formula of the lead oxide is

A PbO
B Pb3O2
C Pb3O4
D Pb4O3

The answer is C but I don't know-how. can someone explain this?
0
1 month ago
#2

What is the mass of oxygen that is lost during decomposition?
0
#3
(Original post by EierVonSatan)

What is the mass of oxygen that is lost during decomposition?
it's not given in the question so I suppose we have to subtract the mass of lead from lead oxide and get 0.32g
0
1 month ago
#4
(Original post by a.f.x.d)
it's not given in the question so I suppose we have to subtract the mass of lead from lead oxide and get 0.32g
Correct

So now you have the mass of oxygen: 0.32g
And the mass of lead: 3.105g

Can you now find the empirical formula from there?
0
#5
(Original post by EierVonSatan)
Correct

So now you have the mass of oxygen: 0.32g
And the mass of lead: 3.105g

Can you now find the empirical formula from there?
I'm getting A as the answer whereas it's C in the marking scheme. could you please explain?
0
1 month ago
#6
(Original post by a.f.x.d)
I'm getting A as the answer whereas it's C in the marking scheme. could you please explain?
mol of oxygen: mass/Mr = 0.32 / 16 = 0.02
mol of lead: mass/Mr = 3.105/207 = 0.015

Now, divide by the smallest (0.015) to get: Pb = 1 and O = 4/3

Multiply both by 3 to remove the fraction: Pb3O4

(I assume you've rounded 4/3 down to 1, which might be okay at GCSE but not A-level)
0
1 month ago
#7
try looking here, its gcse but will probably help

https://www.science-revision.co.uk/m...20formula.html
1
#8
(Original post by EierVonSatan)
mol of oxygen: mass/Mr = 0.32 / 16 = 0.02
mol of lead: mass/Mr = 3.105/207 = 0.015

Now, divide by the smallest (0.015) to get: Pb = 1 and O = 4/3

Multiply both by 3 to remove the fraction: Pb3O4

(I assume you've rounded 4/3 down to 1, which might be okay at GCSE but not A-level)
thank you so much!
0
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Feeling behind at school/college? What is the best thing your teachers could to help you catch up?

Extra compulsory independent learning activities (eg, homework tasks) (14)
6.64%
Run extra compulsory lessons or workshops (34)
16.11%
Focus on making the normal lesson time with them as high quality as possible (34)
16.11%
Focus on making the normal learning resources as high quality/accessible as possible (31)
14.69%
Provide extra optional activities, lessons and/or workshops (57)
27.01%
Assess students, decide who needs extra support and focus on these students (41)
19.43%