Question

 1. When heated, magnesium metal reacts with nitrogen from the air to form magnesium nitride. Write the balanced chemical equation (with phase symbols) for this reaction.  

 2. Chromium metal reacts vigorously with hydrochloric acid, producing a green solution of chromium(III) chloride and hydrogen gas. The balanced equation for this reaction is: 

2 Cr(s) + 6 HCI (aq) → 2 CrCl₃ (aq) + 3 H₂ (g)

 In an experiment, a 6.378 g piece of chromium is placed in a beaker containing excess HCI

 solution.

 a. What is the theoretical yield (in grams) of hydrogen gas for this reaction? 

 b. After the reaction, the hydrogen gas is collected and found to have a mass of 0.305 g. What is the percent yield for this reaction? 

Answer 1

Question 1

Magnesium metal reacts with nitrogen gas and produces powder of magnesium nitride.

Molecular equation : Mg (s) + N ₂ (g) Mg₃N₂ (s)

Balanced molecular equation : 3 Mg (s) + N ₂ (g) Mg₃N₂ (s)

Question 2

Mass of Cr = 6.378 g

Molar mass of Cr = 52.00 g/mol

Moles of Cr = Mass / Molar mass = 6.378 g / 52.00 g/mol = 0.12265 mol

Consider reaction, 2 Cr (s) + 6 HCl (aq) 2 CrCl ₃ (aq) + 3 H ₂ (g)  

According to reaction, 2 mole Cr produces 3 mole H ₂ gas.

Hence, moles of H ₂ gas produced from 0.12265 mol Cr would be

0.12265 mol Cr ( 3 mol H ₂ / 2 mol Cr ) = 0.18398 mol H ₂

Theoretical yield of H ₂ gas = 0.18398 mol

Theoretical yield of H ₂ gas in g = 0.18398 mol 2.01588 g/mol = 0.3709 g

ANSWER : Theoretical yield of H ₂ gas = 0.3709 g

We have , % yield of reaction = ( Practical yield of product / Theoretical yield of product ) 100

% yield of reaction = ( 0.305 g / 0.3709 g ) 100

= 82.24 %

ANSWER :  % yield of reaction = 82.2 %