Question 9.14: The normal concentration of Ca^2+ in blood is 5.0 mEq/L. How...

Fundamentals of General, Organic, and Biological Chemistry

The normal concentration of $Ca^{2+}$ in blood is 5.0 mEq/L. How many milligrams of $Ca^{2+}$ are in 1.00 L of blood?
ANALYSIS We are given a volume and a concentration in milliequivalents per liter, and we need to find an amount in milligrams. Thus, we need to calculate the gram-equivalent for $Ca^{2+}$ and then use concentration as a conversion factor between volume and mass, as indicated in the following flow diagram:
BALLPARK ESTIMATE The molar mass of calcium is 40.08 g/mol, and the calcium ion carries a charge of 2+ . Thus, 1 g-Eq of $Ca^{2+}$ equals about 20 g/Eq or 20 mg/mEq. This means that the 5.0 mEq of $Ca^{2+}$ ions in 1.00 L of blood corresponds to a mass of 5.0 mEq $Ca^{2+} \times 20 mg/mEq = 100 mg Ca^{2+}$ .

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