[audienne]

a Explain how to prepare 25 litres of a 0.10M  NACl Solutions starting with solid NaCl

Molar mass of 1 mole of  NaCl is 58.45g (  Na 23g + Cl 35.45g)

Therefore molarity of solid NaCl is 58.45g/L

0.1M of NaCl = 0.1 x 58.45g = 5.845g. Molarity 5.845g/L

Therefore to get 25 litres, will need to dilute 146.125g NaCl ( 25 x 5.845 g) and add 25 litres of water

b Specify the volume of the solution in (a)  needed to get 0.020 mol NaCl

0.020 mol NaCl = 0.020 x 58.45g= 1.169g


58.45g          =     1.169 g
1000ml                              Volume

Volume required = 20 ml



Do i get the logic right? Can you recommended a good website in relation to this topic?

Thanks heaps

[Astrokel]

Yes

[Borek]

Therefore molarity of solid NaCl is 58.45g/L

This is not molarity. Molarity is not mass per liter, it is moles/liter. Besides, we usually don't assign molarity to the pure solids. Molarity is a property of a solution.

And nitpickers, please don't add anything. She (?) seems to be already confused.

0.1M of NaCl = 0.1 x 58.45g = 5.845g. Molarity 5.845g/L

Same problem as above.

Therefore to get 25 litres, will need to dilute 146.125g NaCl ( 25 x 5.845 g) and add 25 litres of water

We will not dilute the solid, we will dissolve it.

Funny thing is that apart from using completely wrong nomenclature your logic is in a way correct and leads to the correct answer

b Specify the volume of the solution in (a)  needed to get 0.020 mol NaCl

0.020 mol NaCl = 0.020 x 58.45g= 1.169g


58.45g          =     1.169 g
1000ml                              Volume

Volume required = 20 ml

OK, although there is no need to use molar mass and convert to grams. C=n/V (by definition of molarity), so V=n/C. Put n (given) and C (known) into the formula and you have the volume.

http://www.chembuddy.com/?left=concentration&right=toc

[audienne]

Hi Borek

Thank you very much for explaining! It really helps!