# Isotonic saline is a 0.9 g / 100 ml solution of salty water. You are asked to make up 2 Liters of...

## Question:

Isotonic saline is a {eq}\rm 0.9\ g / 100\ ml {/eq} solution of salty water. You are asked to make up {eq}2 {/eq} Liters of isotonic saline. How much salt should you weigh out?

## Ratio and proportion:

Ratio is defined as the relative quantities of two units. It is expressed as a:b or a/b. Proportion, on the other hand, is the equal relation of two ratios, i.e. they are equivalent.

Given: {eq}\dfrac{0.9 \ g \ salt}{100 \ ml \ solution}{/eq}. The ratio of the solution is 0.9 g salt for every 100 ml of solution.

To prepare 2 L or 2000 mL of the solution, simply use the principle of ratio and proportion:

{eq}\dfrac{0.9 \ g \ salt}{100 \ ml \ solution} = \dfrac{x}{2000 \ ml}{/eq}

Solving for x,

{eq}x = \dfrac{0.9 \ \times 2000 \ ml }{100 \ ml} = \boxed{18 \ g} {/eq}