Calculate the mass of calcium carbide containing 20% impurities required to obtain 28 liters of acetylene.

Given:

V (C2H2) = 28 l

w% (impurities) = 20%

Find:

m (CaC2) -?

Solution:

CaC2 + 2H2O = Ca (OH) 2 + C2H2, – we solve the problem, relying on the composed reaction equation:

1) Find the amount of acetylene obtained as a result of the reaction:

n (C2H2) = V: Vm = 28 L: 22.4 L / mol = 1.25 mol

2) We compose a logical expression:

if 1 mol of CaC2 gives 1 mol of C2H2,

then x mol CaC2 will give 1.25 mol C2H2,

then x = 1.25 mol.

3) Find the mass of pure calcium carbide that has reacted:

m (CaC2) = n * M = 1.25 mol * 64 g / mol = 80 g

4) we find the mass of calcium carbide containing 20% ​​impurities:

If the proportion of impurities is 20%, then the proportion of pure substance will be 80%,

then m (tech. CaC2) = 80 g: 0.8 = 100 g

Answer: m (tech. CaC2) = 100 g.