Calculate the m of the precipitate that is formed by the interaction of NaOH solutions, m = 20, the mass fraction

| September 7, 2021 | education

Calculate the m of the precipitate that is formed by the interaction of NaOH solutions, m = 20, the mass fraction of NaOH is 10% and the MgCl2 solution with a mass fraction of 5%.

Given:

m (NaOH) = 20 g

w% (NaOH) = 10%

Find:

m (draft) -?

Solution:

2NaOH + MgCl2 = Mg (OH) 2 + 2NaCl, – we solve the problem based on the composed reaction equation:

1) Find the mass of sodium hydroxide in the solution:

m (NaOH) = 20 g * 0.1 = 2 g

2) Find the amount of sodium hydroxide that has reacted:

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

3) We compose a logical expression:

If 2 mol of NaOH gives 1 mol of Mg (OH) 2,

then 0.05 mol of NaOH will give a mol of Mg (OH) 2,

then x = 0.025 mol.

4) Find the mass of magnesium hydroxide precipitated:

m (Mg (OH) 2) = n * M = 0.025 mol * 58 g / mol = 1.45 g.

Answer: m (Mg (OH) 2) = 1.45 g.



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