Molarity

[Temperature101]

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What is the molarity of a solution of KCl with specific gravity 1.007? (Molar mass of KCl is 74.6 g/mol)




0.06 M

0.01 M

0.6 M

0.1 M

The answer is 0.1 M ...Can someone explain?

 

[MedPR]

What is the molarity of a solution of KCl with specific gravity 1.007? (Molar mass of KCl is 74.6 g/mol)




0.06 M

0.01 M

0.6 M

0.1 M

The answer is 0.1 M ...Can someone explain?

Trying again.

Idk, I keep getting 13M lol.

Specific gravity of 1.007 means there are 1007 grams of KCl/Liter.

(1007g/L)(1mol/75g)=13mol/L=13M

 

[chiddler]

What is the molarity of a solution of KCl with specific gravity 1.007? (Molar mass of KCl is 74.6 g/mol)




0.06 M

0.01 M

0.6 M

0.1 M

The answer is 0.1 M ...Can someone explain?

1 L has 1007 grams

that means the extra 7 grams is KCl

35 + 40 = 75 is molar mass of KCl. lets just make it 70

7/70 = 0.1 mols in this one liter. 0.1 mol/L = 0.1 M.

 

[SaintJude]

So you mean:

density (KCl solution) = 1.007 x density (water) = 1.007 x 1 g/cm^3 = 1.007 g/cm^3

1.007 g/cm^3 x ( 1000 cm^3/1 L) = 1007 grams/1 L

How did you realize that only 7 grams represents KCL---not the entire 1007 ?!

Edit:
Found this elsewhere: Assuming we have 1 L.Therefore the mass of water = 1000 grams

The mass of solution ; M = DV = ( 1.007 g/ml ) ( 1000 ml ) = 1007 grams

The mass of KCL = mass of solution – mass of water = 1007 – 1000 = 7 grams

Molarity = moles/ solution = (7/70) / 1 = 0.1 M

 

[chiddler]

So you mean:

density (KCl solution) = 1.007 x density (water) = 1.007 x 1 g/cm^3 = 1.007 g/cm^3

1.007 g/cm^3 x ( 1000 cm^3/1 L) = 1007 grams/1 L

How did you realize that only 7 grams represents KCL---not the entire 1007 ?!

what's the density of water?

(1 kg/L)

this liter has how many grams?

(1007)

so how many grams are not due to water?

(7)

 

[SaintJude]

Take this 1 step further: What's the molality of this solution?

Molality= moles of solute 👎 / kilograms of solvent = 0.1 moles/ 1 kg = 0.1 m

Is that right?

 

[MedPR]

Ah I see. I missed that part about only 7grams being KCl. Makes sense now, thanks!

 

[chiddler]

Take this 1 step further: What's the molality of this solution?

Molality= moles of solute 👎 / kilograms of solvent = 0.1 moles/ 1 kg = 0.1 m

Is that right?

right.

hmm i never think about molality outside freezing point stuff. I wonder how an exam might throw it at us in some novel way.

 

[Temperature101]

right.

hmm i never think about molality outside freezing point stuff. I wonder how an exam might throw it at us in some novel way.

It was scary for me too when I see I couldn't solve a problem about molarity and I am about to sit for the mcat, which notably a test that throw every kind of sh... at you in some weird way.