By 400g. 5% solution of ferrous sulfate (3) poured 200 g. 3% sodium hydroxide solution.

By 400g. 5% solution of ferrous sulfate (3) poured 200 g. 3% sodium hydroxide solution. Calculate the mass of the formed oklad.

Given:

m (NaOH) = 200 g

w% (NaOH) = 3%

m (FeSO4) = 400 g

w% (FeSO4) = 5%

To find:

m (draft) -?

Decision:

Fe2 (SO4) 3 + 6NaOH = 3Na2SO4 + 2Fe (OH) 3, – we solve the problem using the composed reaction equation:

1) Find the mass of ferrous sulfate and sodium hydroxide in solutions:

m (Fe2 (SO4) 3) = 400 g * 0.05 = 8 g

m (NaOH) = 200 g * 0.03 = 6 g

2) Find the amount of ferrous sulfate and sodium hydroxide:

n (Fe2 (SO4) 3) = m: M = 8 g: 400 g / mol = 0.02 mol

n (NaOH) = m: M = 6 g: 40 g / mol = 0.15 mol

We start from a lower value to get more accurate calculations. We work with Fe2 (SO4) 3:

3) We compose a logical expression:

if 1 mol of Fe2 (SO4) 3 gives 2 mol of Fe (OH) 3,

then 0.02 mol Fe2 (SO4) 3 will give x mol Fe (OH) 3,

then x = 0.04 mol.

4) Find the mass of iron hydroxide precipitated during the reaction:

m (Fe (OH) 3) = n * M = 0.04 mol * 107 g / mol = 4.28 g.

Answer: m (Fe (OH) 3) = 4.28 g.