Help with a chemistry question!

bump - I got 0.833... mol/dm3 when the answer is 0.3 :/

Reply 3

Mudas

OP

13

Figured it out!

0.1 x 0.2 = 0.02 moles of NaCl. Therefore, there are 0.02 moles of Na+ in the NaCl
0.1 x 0.2 = 0.02 moles of Na2C03. Therefore, there are 0.02 moles of Na2 in the Na2CO3 meaning there are 0.04 moles of Na+ in Na2CO3.
0.02 + 0.04 = 0.06 moles
The total volume is 200cm3.
0.06/ 0.02dm3 = 0.3mol/dm3

Reply 4

Original post by HarrisonGCSE

Figured it out!

0.1 x 0.2 = 0.02 moles of NaCl. Therefore, there are 0.02 moles of Na+ in the NaCl
0.1 x 0.2 = 0.02 moles of Na2C03. Therefore, there are 0.02 moles of Na2 in the Na2CO3 meaning there are 0.04 moles of Na+ in Na2CO3.
0.02 + 0.04 = 0.06 moles
The total volume is 200cm3.
0.06/ 0.02dm3 = 0.3mol/dm3

Thanks! I was stupid and when I saw there was 0.02 moles NaCl, I divided it by 2 to get 0.01 moles Na+ ( :colonhash:

) and used the same technique for the other solution :colondollar:

Reply 5

molly221

3

Can anyone help me with this question? Thanks

Reply 6

Rchilton

8

Original post by molly221

Can anyone help me with this question? Thanks

Vanillin has extra polar group, as water is a polar solvent you can deduce the relative solubility from that (think about like dissolves like). As for the volatility consider comparing boiling points, think about which is likely to be higher bearing in mind that hydrogen bonding will increase the boiling point and then how that would relate to the compounds volatility.

Posted from TSR Mobile

(edited 8 years ago)

Reply 7

Original post by HarrisonGCSE

Figured it out!

0.1 x 0.2 = 0.02 moles of NaCl. Therefore, there are 0.02 moles of Na+ in the NaCl
0.1 x 0.2 = 0.02 moles of Na2C03. Therefore, there are 0.02 moles of Na2 in the Na2CO3 meaning there are 0.04 moles of Na+ in Na2CO3.
0.02 + 0.04 = 0.06 moles
The total volume is 200cm3.
0.06/ 0.02dm3 = 0.3mol/dm3

Hi, I am really stuck on this question ! Could you please help?
1) Why is the mole of Na+ ions in NaCl 0.02mol? Isn't that the number of moles for NaCl?
2) I have also worked out that Na2CO3 is 0.02 moles but again I don't get why Na+ would also be 0.02 mol
3) I understand that the total volume is 200 but why did you get 0.02dm3 from? That's not the volume though...

Thanks in advance!

Reply 8

Original post by surina16

Thanks! I was stupid and when I saw there was 0.02 moles NaCl, I divided it by 2 to get 0.01 moles Na+ ( :colonhash:

) and used the same technique for the other solution :colondollar:

Hi, could you please explain to me how you solved this question? I still don't get it. Why is the mole of Na+ ions the same as the mole of NaCl? Thank you.

Reply 9

Rchilton

8

Original post by coconut64

Hi, could you please explain to me how you solved this question? I still don't get it. Why is the mole of Na+ ions the same as the mole of NaCl? Thank you.

You need one mole of Na+ and one mole of Cl- to make one mole of NaCl, so it follows that if you have 0.02 moles of NaCl you will have 0.02 moles of Na. Remember that all the mole unit represents is the number of atoms/molecules.

Reply 10

Original post by coconut64

Hi, could you please explain to me how you solved this question? I still don't get it. Why is the mole of Na+ ions the same as the mole of NaCl? Thank you.

If you have 1 mole of NaCl, it means that you have 1 mole of Na+ and 1 mole of Cl-, bonded together.
Therefore, if you have 0.02 moles of NaCl, you have 0.02 moles Na+ and 0.02 moles Cl- :smile:

Reply 11

Original post by surina16

If you have 1 mole of NaCl, it means that you have 1 mole of Na+ and 1 mole of Cl-, bonded together.
Therefore, if you have 0.02 moles of NaCl, you have 0.02 moles Na+ and 0.02 moles Cl- :smile:

Oh okay. So if the mole of Na2Co3 is 0.4 mol, the mole of Na2 would be 0.8mol?

(edited 8 years ago)

Reply 12

Rchilton

8

Original post by coconut64

3) I understand that the total volume is 200 but why did you get 0.02dm3 from? That's not the volume though...

Thanks in advance!

I think it's a typo and meant to be 0.2dm3. Which you get if you convert 200cm3 in to dm3. (10 cm in a dm, but as it's a volume it's 10^3 = 1000)

Posted from TSR Mobile

Reply 13

Original post by Rchilton

I think it's a typo and meant to be 0.2dm3. Which you get if you convert 200cm3 in to dm3. (10 cm in a dm, but as it's a volume it's 10^3 = 1000)

Posted from TSR Mobile

Thanks for the help. Actually one more quick question. Say if the mole of Na2Co3 is 0.4mol, will 1 Na+ ion be 0.2 mol?

(edited 8 years ago)

Reply 14

Original post by coconut64

Oh okay. So if the mole of Na2Co3 is 0.4 mol, the mole of Na2 would be 0.2mol?

No I think you would have 0.4 mol Na2 which therefore means you would have 0.8 mol Na+ :smile:

Spoiler

(edited 8 years ago)

Reply 15

Original post by surina16

No I think you would have 0.4 mol Na2 which therefore means you would have 0.2 mol Na :smile:

Spoiler

Really? But the OP mentioned that '0.1 x 0.2 = 0.02 moles of Na2C03. Therefore, there are 0.02 moles of Na2 in the Na2CO3 meaning there are 0.04 moles of Na+ in Na2CO3. ' So 0.02 mole for Na2. For all Na+ion, it will be 0.02*2. So if the mole of Na2CO3 is 0.4mole. Na2 ions will be 0.4 mole. All Na ions will be 0.8 right?

(edited 8 years ago)

Reply 16

Original post by coconut64

Really? But the OP mentioned that '0.1 x 0.2 = 0.02 moles of Na2C03. Therefore, there are 0.02 moles of Na2 in the Na2CO3 meaning there are 0.04 moles of Na+ in Na2CO3. ' So 0.02 mole for Na2. For all Na+ion, it will be 0.02*2. So if the mole of Na2CO3 is 0.4mole. Na2 ions will be 0.4 mole. All Na ions will be 0.8 right?

Oh yeah of course aha I meant to multiply by 2, not divide :colondollar:

Sorry for the confusion :tongue:

Reply 17