Calcium carbide weighing 12.8 g was dissolved in 174 ml of 20% hydrobromic acid (p = 1.12 g / ml).

Calcium carbide weighing 12.8 g was dissolved in 174 ml of 20% hydrobromic acid (p = 1.12 g / ml). Calculate the mass fraction of salt in the resulting solution.

Given:

m (CaC2) = 12.8g

V (HBr) = 174 ml

p (HBr) = 1.12 g / ml

w% (HBr) = 20%

To find:

m (salt) -?

Decision:

CaC2 + 2HBr = CaBr2 + C2H2, – we solve the problem, relying on the composed reaction equation:

1) Find the mass of the solution of hydrobromic acid:

m (HBr) = p * V = 1.12 g / ml * 174 ml = 194.88 g

2) Find the mass of acid in solution:

m (HBr) = 194.88 g * 0.2 = 38.976 g

3) Find the amount of acid and calcium carbide:

n (HBr) = m: M = 38.976 g: 81 g / mol = 0.48 mol

n (CaC2) = m: M = 12.8 g: 64 g / mol = 0.2 mol

We start from a lower value to get accurate calculations. We work with calcium carbide:

4) We compose a logical expression:

if 1 mol of CaC2 gives 1 mol of CaBr2,

then 0.2 mol CaC2 will give x mol CaBr2,

then x = 0.2 mol.

5) Find the mass of calcium bromide formed during the reaction:

m (CaBr2) = n * M = 0.2 mol * 200 g / mol = 40 g.

Answer: m (CaBr2) = 40 g.