# Finding the concentration of X

by MagicMarker
Tags: concentration
 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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P: 10,540
 Quote by MagicMarker 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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