Help to understand the calulations pls?

Ericka

Hi folks, a little help would be great. I know this is very basic stuff to you lot, but I'm only starting out


Last week we were asked to prepare a 0.1% M solution of NaOH. Now I did the experiment, but I sort of winged it with the calculations. So I knew already that we'd have to use 1g of the pellets, and had to make up 250mls of it. Though I do have some doodles written down;

H = 1.0
Na = 23.0
O = 40.0


So I understand that ^^ and where it comes from.

1M = 40g to 1L

250mls x 4 = 1L


This is the bit where I get a bit fuzzy, if the rule here is 250mls is 1/4 litre, I'd assumably divide the 40g by four, giving me 10.

How did they get 1g from that?

craggles

NaOH

Na= 23

O = 16

H = 1

So NaOH is 40 grams per mole, but you know that already, that's good

So if you put 40g of NaOH pellets in a beaker and fill it up to 1L, that'll be a 1 mole per litre, or 1 molar, or 1M solution.

So if you used 4g instead of 40g in that one litre, that would be a 0.1 M solution.

Take 250 ml of that, and there'll be 1g of sodium hydroxide in there!

Does that clear it up?

Ericka

craggles wrote: »

NaOH

Na= 23

O = 16

H = 1

So NaOH is 40 grams per mole, but you know that already, that's good

So if you put 40g of NaOH pellets in a beaker and fill it up to 1L, that'll be a 1 mole per litre, or 1 molar, or 1M solution.

So if you used 4g instead of 40g in that one litre, that would be a 0.1 M solution.

Take 250 ml of that, and there'll be 1g of sodium hydroxide in there!

Does that clear it up?

Yes it does Craggy, I knew there was something I was over-looking

Thanks a million

Kevster

She said 0.1%M, but I assume she meant 0.1M, right? 0.1%M would be 0.04g of NaOH for 1 litre.

This question is a standard question though, and i know it's 0.1M!

Ericka

Thanks for replying Kevster.

Kevster wrote: »

She said 0.1%M, but I assume she meant 0.1M, right? 0.1%M would be 0.04g of NaOH for 1 litre.

Does the % not refer to the concentration of the solution? Or does it need to be in there at all?

This question is a standard question though, and i know it's 0.1M!

Smarty pants

Kevster

...yes, Im a smarty pants! :P

The 0.1% solution is the same as saying a 0.1M solution. Like, you can use either. Are you in IT Carlow by any chance? They seemed to love giving us those equations when I was there.

Kevin

Ericka

Kevster wrote: »

...yes, Im a smarty pants! :P

The 0.1% solution is the same as saying a 0.1M solution. Like, you can use either. Are you in IT Carlow by any chance? They seemed to love giving us those equations when I was there.

Kevin

Oh so its either / or, thanks for that

No, I'm not in Carlow. I'm doing a one year in Killester, and looking for either DIT or DCU after that. Never studied science in secondary, so when I say I'm new to it all!

I'm enjoying it though

Kevster

Science is fantastic... ...stay in it. I studied Cmputer Science after school for four years, and then Industrial Biology for four years after that. im now doing a PhD in Chemistry!! I did my leaving cert way back in 2000.

Ericka

Kevster wrote: »

Science is fantastic... ...stay in it. I studied Cmputer Science after school for four years, and then Industrial Biology for four years after that. im now doing a PhD in Chemistry!! I did my leaving cert way back in 2000.

Congrats, sounds like you found your calling

I'm class of 1997 :eek: So I'm a very late beginner! Its amazing the stuff that you learn along the way, that you may never have known unless you venture into chemistry. But when he started off telling us that everything was made of atoms, it was somewhat hard to visualise!

Thanks again btw for helping out with the calculations, you're a life saver :pac: