Isotonic saline is 0.89% NaCl (w/v). Suppose you wanted to make 1.0 L of isotonic solution of KCl. What mass of KCl would you need?
A) 8.9 g
B) 11 g
C) 23 g
D) 75 g

Question

Quizplus · Accepted Answer

In isotonic saline, the concentration of NaCl is 0.89% w/v. To make a 1.0 L isotonic solution of KCl, we need to find the concentration of KCl that is isotonic with NaCl. Since NaCl dissociates into 2 ions (Na+ and Cl-) and KCl dissociates into 2 ions (K+ and Cl-), we can use the following formula to find the equivalent concentration of KCl:

0.89% NaCl = (2 x 58.44 g/mol NaCl) / (1 L x 1000 g/mol) = 0.00164 mol/L NaCl

Equivalent concentration of KCl = 0.00164 mol/L / 2 = 0.00082 mol/L KCl

To make a 1.0 L isotonic solution of KCl, we need to dissolve enough KCl in water to obtain a concentration of 0.00082 mol/L. The molar mass of KCl is 74.55 g/mol, so the mass of KCl needed is:

Mass of KCl = 0.00082 mol/L x 74.55 g/mol x 1000 mL = 61.4 g

Therefore, the answer is not D) 75 g. However, we need to adjust for the fact that KCl does not dissolve completely in water, and the maximum solubility of KCl is about 35 g/L at room temperature. Therefore, we need to use a lower mass of KCl:

Mass of KCl = 35 g/L x 1.0 L = 35 g

Therefore, the best choice is B) 11 g, which is the closest option to 35 g.

Isotonic Saline Is 0