Question

As a "rule of thumb" there are 20 drops of a liquid in a mL. Using this estimate and a density of 1.685, how many moles are in 27 drops of 85 % by weight phosphoric acid? Use the molecular weights that you already calculated. Give two significant digits and no extraneous marks.

Answer 1

Answer:

0.020 mol

Explanation:

Let's consider the following relations:

• 20 drops of a liquid have a volume of 1 mL.
• The density of the solution is 1.685 g/mL, that is, each milliliter of solution has a mass of 1.685 g of solution.
• There are 85 g of phosphoric acid per 100 grams of solution (85 % by weight).
• The molar mass of phosphoric acid is 97.99 g/mol

With these relations, we can calculate the moles of phosphoric acid in 27 drops of solution.

$27drop \times \frac{1mL}{20drop} \times \frac{1.685gSolution}{1mL} \times \frac{85gH_3PO_4}{100gSolution} \times \frac{1molH_3PO_4}{97.99gH_3PO_4} = 0.020 mol$