Finding the concentration of X

  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!
     
  2. jcsd
  3. ehild

    ehild 12,267
    Homework Helper
    Gold Member
    2014 Award

    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
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?
Similar discussions for: Finding the concentration of X
Loading...