Answer:
0.297 mol/L
Explanation:
<em>A chemist prepares a solution of potassium dichromate by measuring out 13.1 g of potassium dichromate into a 150 mL volumetric flask and filling the flask to the mark with water. Calculate the concentration in mol/L of the chemist's potassium dichromate solution. Be sure your answer has the correct number of significant digits.</em>
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Step 1: Calculate the moles corresponding to 13.1 g of potassium dichromate
The molar mass of potassium dichromate is 294.19 g/mol.
13.1 g × (1 mol/294.19 g) = 0.0445 mol
Step 2: Convert the volume of solution to L
We will use the relationship 1 L = 1000 mL.
150 mL × (1 L/1000 mL) = 0.150 L
Step 3: Calculate the concentration of the solution in mol/L
C = 0.0445 mol/0.150 L = 0.297 mol/L
We will use the expression for freezing point depression ∆Tf
∆Tf = i Kf m
Since we know that the freezing point of water is 0 degree Celsius, temperature change ∆Tf is
∆Tf = 0C - (-3°C) = 3°C
and the van't Hoff Factor i is approximately equal to 2 since one molecule of KCl in aqueous solution will produce one K+ ion and one Cl- ion:
KCl → K+ + Cl-
Therefore, the molality m of the solution can be calculated as
3 = 2 * 1.86 * m
m = 3 / (2 * 1.86)
m = 0.80 molal
False. A mixture represents elements or molecules which are not chemically combined.
