The degree of dissociation of hydrofluoric acid is 8%. Determine the number of acid molecules

The degree of dissociation of hydrofluoric acid is 8%. Determine the number of acid molecules not decayed into ions in 220 g of its 2% solution.

1. Let us determine the mass of pure acid in solution:
To begin with, we write down an expression to determine the mass fraction of a substance in a solution:
w (in-va) = (m (in-va) / m (solution)) * 100%.
Let us express from this expression the mass of a substance:
m (in-va) = (w (in-va) * m (solution)) / 100%.
Substitute the numerical values ​​and find the mass of the salt:
m (HF) = (w (HF) * m (solution)) / 100% = 2 * 220/100 = 4.4 g.
2. To determine how much acid has not disintegrated into ions, let’s make the proportion:
4.4 g – 100%.
x – 8%.
x = 4.4 * 8/100 = 0.352 g.
It turned out that 0.352 g did not disintegrate into ions.
3. Determine the amount of substance of non-decayed ions.
ν (in-va) = m (in-va) / M (in-va).
Find the molar mass of the acid:
M (HF) = 1 + 19-20 g / mol.
Substitute numerical values ​​into the formula for the amount of substance:
ν (HF) = m (HF) / M (HF) = 0.352 / 20 = 0.0176 mol.
Answer: 0.0176 mol of acid did not decompose into ions.