Scenario #3 For a lab, you need to make a 10 ml solution using 2.5 grams of salt dissolved in water. 1) List the lab equipment that will you need? 2) Choose the correct order of steps (procedure) from below that you will follow for weighing out the 2.5 g
of salt. 1. Add the salt to the weigh boat. 2. Measure 10 ml of water. 3. Put the empty weigh boat on the balance. 4. Put the salt
directly on the balance. 5. Press the tare or zero button on the balance. 6. Turn on the balance.

Explanation:

Using percentage by volume (v/v)

When the solute is a liquid, it is sometimes convenient to express the solution concentration as a volume percent.

Formula

The formula for volume percent (v/v) is: [Volume of solute (ml) / Volume of solution (ml)] x 100

Example

Make 1000ml of a 5% by volume solution of ethylene glycol in water.

Procedure

First, express the percent of solute as a decimal: 5% = 0.05

Multiply this decimal by the total volume: 0.05 x 1000ml = 50ml (ethylene glycol needed).

Subtract the volume of solute (ethylene glycol) from the total solution volume:

1000ml (total solution volume) - 50ml (ethylene glycol volume) = 950ml (water needed)

Dissolve 50ml ethylene glycol in a little less than 950ml of water. Now bring final volume of solution up to 1000ml with the addition of more water. (This eliminates any error because the final volume of the solution may not equal the calculated sum of the individual components).

So, 50ml ethylene glycol / 1000ml solution x100 = 5% (v/v) ethylene glycol solution.