Study the reaction scheme below in which compound Y is produced by the reaction of compound X with water - Leaving Cert Chemistry - Question 8 - 2021

To express the concentration of isopropyl alcohol in moles per litre, follow these steps:

1. Determine the volume of isopropyl alcohol in the solution: Since it’s a 70% (v/v) solution, this means there are 70 cm³ of isopropyl alcohol per 100 cm³ of solution.

2. Scale it to one litre:
   [ 70 \text{ cm}^3 \text{ of isopropyl alcohol per } 100 \text{ cm}^3 \text{ of solution} ] leads to 700 cm³ of isopropyl alcohol in one litre (1000 cm³).

3. Convert the volume to mass using density:
   The density of isopropyl alcohol is given as 0.8 g cm³. Thus, [ 700 \text{ cm}^3 \times 0.8 \text{ g cm}^{-3} = 560 \text{ g of isopropyl alcohol} ]

4. Calculate moles of isopropyl alcohol: The molar mass (M) of isopropyl alcohol (C₃H₈O) can be calculated as follows:

   • C: 3 × 12.01 g/mol = 36.03 g/mol
   • H: 8 × 1.008 g/mol = 8.064 g/mol
   • O: 1 × 16.00 g/mol = 16.00 g/mol

   Therefore, [ M = 36.03 + 8.064 + 16.00 = 60.094 \text{ g/mol} ]

5. Calculate moles in one litre:
   [ \text{Moles of isopropyl alcohol} = \frac{560 \text{ g}}{60.094 \text{ g/mol}} \approx 9.3 \text{ moles} \text{ per litre} ]

Thus, the concentration of isopropyl alcohol in the hand sanitizer is approximately 9.3 moles per litre.