Finding the concentration of X


by MagicMarker
Tags: concentration
MagicMarker
MagicMarker is offline
#1
Jun29-11, 09:34 PM
P: 1
1. The problem statement, all variables and given/known data
How do I find the Density of X (Part A) and how do I find the Concentration of X in a solution (Part B)?

Part A:
I have 4mL of X. The mass of 4mL of X is 10g. Calculate the density of X.

Part B:
I have 7g of X in 100mL of Water. Calculate the concentration of X.

The FINAL ANSWER must be written in BOTH "g/L" and as a percent (%).

2. Relevant equations
Density of X = Mass/Volume
Concentration of X = grams of solute/Litre of solution

3. The attempt at a solution
What did I do:
------------------
Part A:
I have 4mL of X. The mass of 4mL of X is 10g. Calculate the density.

Finding Density of X:
I have 10g of X. (10g is the mass)
I have 4mL of X. (I'm thinking that 4mL is the volume)

Density of X = Mass/Volume
Density of X = 10/4
Density of X = 2.5g/mL

Therefore, the density of X is 2.5g/mL.
------------------
Part B:
I have 7g of X in 100mL of Water. Calculate the concentration of X.

Finding Concentration of X:
I have 7g. (grams of solute)
I have 100mL of Water, which is 0.100L. (Solution in L)

Concentration of X = grams of solute/Litre of solution
[X] = 7/0.100
[X] = 70g/L

As a percentage:
70g/L = 70/1000 = 0.07 = 7%

Therefore, the concentration of 7g of X in 100mL of Water is 70g/L (7%).

-------------------------------------------

Thoughts:
You know how I calculated the density of X in Part A (2.5g/mL), don't I use that information to calculate the concentration of X in Part B?

Does the density of the solute matter when calculating the concentration of X? If so, how do I use 2.5g/mL (density of X) in order to calculate the concentration of X in 100mL of Water?

I hope you are able to help me.

Thank you!
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ehild
ehild is offline
#2
Jun29-11, 11:57 PM
HW Helper
Thanks
P: 9,818
Quote Quote by MagicMarker View Post

Thoughts:
You know how I calculated the density of X in Part A (2.5g/mL), don't I use that information to calculate the concentration of X in Part B?

Does the density of the solute matter when calculating the concentration of X? If so, how do I use 2.5g/mL (density of X) in order to calculate the concentration of X in 100mL of Water?

I hope you are able to help me.

Thank you!
No, the density of the solute does not influence its concentration if its mass is known. Think, before adding x to the solvent, it can be solid, and in the solution the molecules are dispersed. No sense to speak of the density of x.

You would need the density of x if its volume were given, to calculate the mass.

ehild


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