AS Chemistry- helping each other out!

Original post by purplefoot

Oh I see, thank you!

They would never do it that way though so I don't think you would need to know why.
The nitric acid is added first to make sure no ions interfere with the test with silver nitrate

Reply 2386

frozo123

12

Original post by ilovecake123

hi can someone help me with this question thanks

methanol starts to have toxic effects when it is present in blood at levels of above 200mg in 1000g
express this in parts per million

ppm= mass of solute (g) / mass of solution (g) x1000000

so lets fill in the places

milligrams means one thousandth of a gram so 200mg would be 0.2g because it's 200/1000

in 1kg you have 1000g
Now..
ppm= 0.2/1000 X1000000
= 200 ppm

If you have any further questions let me know :smile:

although someone called samb may be more suitable for help as I've forgotten half of AS chemistry lol

Reply 2387

Question about redox here
if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

i just can't get my head round it

Reply 2388

F1's Finest

21

Original post by samwillettsxxx

Question about redox here
if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

i just can't get my head round it

Remember this mnemonic.

OIL RIG

Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

:smile:

Reply 2389

Original post by James A

Remember this mnemonic.

OIL RIG

Oxidation Is Loss (of electrons), Reduction Is Gain (of electrons).

:smile:

Yes thank you I use that but I mean is the going up going down of numbers I wrote right?

Reply 2390

_NMcC_

15

Original post by samwillettsxxx

Question about redox here
if the atom ox state goes up e.g +2 to +3 it's lost electrons and therefore has been oxidised
and if the atom ox state goes down +1 to 0 then it's reduced - gained electrons????

i just can't get my head round it

Posted from TSR Mobile

You're right. When an atom/compound/molecule loses electrons, it is oxidised. E.g +1 -----> +2. That would mean 1 electron was lost by the atom/compound/molecule

When an atom/compound/molecule gains electrons, It is reduced. E.g 0 -----------> -3. That would mean that the atom/compound/molecule gained 3 electrons.

(edited 8 years ago)

Reply 2391

F1's Finest

21

Original post by samwillettsxxx

Yes thank you I use that but I mean is the going up going down of numbers I wrote right?

Yeah it is.

Just remember that an electron carries a negative charge (-1), so if you remove an electron (oxidation) then the number will increase on the atom that you are looking at.

e.g:

Fe(2+) -----------> Fe(3+) + e-

Reply 2392

Original post by _NMcC_

Posted from TSR Mobile

You're right. When an atom/compound/molecule loses electrons, it is oxidised. E.g +1 -----> +2. That would mean 1 electron was lost by the atom/compound/molecule

When an atom/compound/molecule gains electrons, It is reduced. E.g 0 -----------> -3. That would mean that the atom/compound/molecule gained 3 electrons.

Thank you

Reply 2393

Kloekayne

2

Who has already done their empa?

Posted from TSR Mobile

Reply 2394

TeaAndTextbooks

9

Could someone help me with this question please? Thank you :hmmm:

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Reply 2395

samb1234

13

Original post by TeaAndTextbooks

Could someone help me with this question please? Thank you :hmmm:

290. 10% reacts so because of the fact the mole ratios that 30cm3 becomes 20cm3 and you have 270 that never reacted

Posted from TSR Mobile

Reply 2396

C0balt

16

Original post by TeaAndTextbooks

Could someone help me with this question please? Thank you :hmmm:

As only 10% is decomposed 270cm3 of ozone is left.
30cm is converted to oxygen. In same temperature and pressure gases of same number of moles occupy the same volume. Ozone :redface:

xygen are in 3:2 ratio so you multiply 30cm3 by 2/3, which gives 20cm3
Add the volume of ozone left and it is 290cm3

Posted from TSR Mobile

Reply 2397

TeaAndTextbooks

9

That's so helpful thanks alot!! My teacher spent ages explaining this to me, but you just made it alot easier :smile: