June 04, 2020, 02:09:11 AM
Forum Rules: Read This Before Posting

### Topic: Molarity vs Molality  (Read 12820 times)

0 Members and 1 Guest are viewing this topic.

#### ARGOS++

• Sr. Member
• Posts: 1489
• Mole Snacks: +199/-56
• Gender:
##### Re: Molarity vs Molality
« Reply #15 on: December 01, 2008, 04:39:51 PM »
Dear student8607;

Use the Units for control!

And if you have corrected it, then calculate the final molaRity from it.

Good Luck!
ARGOS++

#### student8607

• Full Member
• Posts: 227
• Mole Snacks: +2/-3
##### Re: Molarity vs Molality
« Reply #16 on: December 01, 2008, 04:48:56 PM »
yeah i see that my calculations has way too many zeroes
but i doubled checked
density was given in g/mL

and we said 1kg for solvent. so that's 1000g + the 46.5g of solute from the molality

#### ARGOS++

• Sr. Member
• Posts: 1489
• Mole Snacks: +199/-56
• Gender:
##### Re: Molarity vs Molality
« Reply #17 on: December 01, 2008, 04:56:52 PM »
Dear student8607;

Please control again! (masstotal is ok!)

But I got:  1046.5g / 1.0173 g/ml = 1028.7 ml (= voltotal)
(If density is finally correct.)

Good Luck!
ARGOS++

#### student8607

• Full Member
• Posts: 227
• Mole Snacks: +2/-3
##### Re: Molarity vs Molality
« Reply #18 on: December 01, 2008, 05:49:01 PM »
oh you are right
it is mass over density not the other way around

so then 0.2588mol/1.028L = 0.251M

#### ARGOS++

• Sr. Member
• Posts: 1489
• Mole Snacks: +199/-56
• Gender:
##### Re: Molarity vs Molality
« Reply #19 on: December 01, 2008, 05:54:24 PM »
Dear student8607;

You did it!  -  Hard but ultimately!

Repeat the small conversion once again, to “get” really behind it!

Good Luck!
ARGOS++

#### student8607

• Full Member
• Posts: 227
• Mole Snacks: +2/-3
##### Re: Molarity vs Molality
« Reply #20 on: December 01, 2008, 05:58:11 PM »
YAY - thanks very much

so i got bold and tried another problem (molarity to molality)
and i failed

The density of a 0.500M solution of acetic acid in water is 1.0042g/mL. What is the molality?

Molar mass is 60.05g

#### student8607

• Full Member
• Posts: 227
• Mole Snacks: +2/-3
##### Re: Molarity vs Molality
« Reply #21 on: December 01, 2008, 05:59:33 PM »
0.5mol acetic acid = 30.025g of acetic acid

D times V = total mass
(1.0042g/mL)(1000mL from the 0.500M) = 1004g total

so i figured 1004-30.025 would be grams of solvent (0.974kg)

0.5mol / 0.974kg = 0.513?

#### student8607

• Full Member
• Posts: 227
• Mole Snacks: +2/-3
##### Re: Molarity vs Molality
« Reply #22 on: December 01, 2008, 06:04:09 PM »
oh wait, my fault, that WAS correct
0.513 is right
yay

#### ARGOS++

• Sr. Member
• Posts: 1489
• Mole Snacks: +199/-56
• Gender:
##### Re: Molarity vs Molality
« Reply #23 on: December 01, 2008, 06:06:41 PM »

Dear student8607;

Correct!

Good Luck!
ARGOS++

• Mr. pH