Solution Composition - Molarity, Mass And Volume Calculations
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Solution Composition - Molarity, Mass And Volume Calculations

Solutions are homogeneous mixtures. Solutions consist of solutes and solvents (the more voluminous substance into which the solute dissolves). Solution concentration measures the amount of solute per liter of the solvent. Molarity is a commonly used measure of solution concentration.

Calculate:
(a) The number of grams of solute in 0.250 L of 0.150 M KBr
(b) The molar concentration of a solution containing 4.75 g of Ca(NO3)2 in 0.200 L
(c) The volume of 1.50 M Na3PO4 in milliliters that contains 5.00 g of solute.

The strings: S7P1A15 (containership - mass).

The math:
Pj Problem of Interest is of type containership (mass).

(a) 0.150 M of KBr = 0.150 mol/L of KBr
O.250 L of KBr contains (0.150)(0.250) = 0.0375 mol of KBr.
Molar mass of KBr = 39 + 80 =119 g
So, 119(0.0375) = 4.46 g of solute.

(b) Molar mass of Ca(NO3)2 = 40 + 28 + 96 = 164 g
So, 4.75 g of Ca(NO3)2 = 4.75/164 = 0.0290 mol
0.200 L contains 0.0290 mol of Ca(NO3)2
So 1 liter contains 0.0290/0.200 = 0.233 mol
So, molar concentration = 0.145 M.

(c) Molar mass of Na3PO4 = 23x3 + 31 + 16x4 = 69 + 31 + 64 = 164
So, moles of 5 g of Na3PO4 = 5/164 = 0.0305 mol of Na3PO4
1.50 moles of Na3PO4 in 1 liter
So, 0.0305 mol is in 0.0305/1.50 = 0.0203 L = 20.3 mL of 1.50 M of Na3PO4.

Math

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