1.15 g of sodium was immersed in 40 ml water. Calculate the mass fraction of alkalis.

1. Let’s write down given:

m (Na) = 1.15 g.

V (H20) = 40 ml.

p (H2O) = 1 g / ml.

2. Let’s write down the reaction:

2Na + 2H20 = 2NaOH + H2

3. Let’s find the mass of water, its amount and the amount of sodium:

m (H2O) = V (H2O) * p (H2O) = 40 ml * 1 g / ml = 40 g.

n (H2O) = m (H2O) / M (H2O) = 40 g / 18 g / mol = 2.22 mol.

n (Na) = m (Na) / M (Na) = 1.15 g / 23 g / mol = 0.05 mol.

4. According to the equation, the amounts of sodium and water are equal, but according to the condition, sodium is less, which means we find the amount of alkali and hydrogen for sodium:

n (NaOH) = n (Na) = 0.05 mol.

m (NaOH) = n (NaOH) * M (NaOH) = 0.05 mol * 40 g / mol = 2 g.

n (H2) = 0.5n (Na) = 0.025 mol.

m (H2) = n (H2) * M (H2) = 0.025 mol * 2 g / mol = 0.05 g.

5. Find the mass of the entire solution. It should be borne in mind that hydrogen is a gas, so it left it:

m (solution) = m (Na) + m (H2O) – m (H2) = 1.15 g + 40 g – 0.05 g = 41.1 g.

6. Let’s find the mass fraction of alkali, it is equal to:

(m (NaOH) / m (solution)) * 100% = 4.87%.

Answer: 4.87%