Mass Calculation

Video on Mass to Mass Stoichiometry

Steps in Solving a Mass to Mass Stoichiometry Problem

STEP 1: Write and balance the chemical equation

STEP 2: Underline the compounds involved in the problem and calculate its molar masses

STEP 3: Using the mole ratio from the balanced chemical equation, solve the problem and

cross cancel units.

Example

Methane, CH₄, the major component of natural gas burns in the air to form carbon dioxide and water. What mass of water is formed in the complete combustion of 5.00 x 10¹³ g of CH₄?

STEP 1: Write and balance the chemical equation

CH₄ + 2O₂ ---> 2H₂O + CO₂

STEP 2: Underline the compounds involved in the problem and calculate its molar masses

CH₄ + 2O₂ ---> 2H₂O + CO₂

1 mol CH₄ = 16.04 g

1 mol H₂O = 18.02 g

STEP 3: Using the mole ratio from the balanced chemical equation, solve the problem and

cross cancel units. (mole ratio is boldfaced)

5.00 x 10¹³ g CH₄ x 1 mol CH₄ x 2 mol H₂O x 18.02 g H₂O = 1.12 x 10⁴ g H₂O

16.04 g CH₄ 1 mol CH₄ 1 mol H₂O

Exercises

1. For the reaction

CaCO₃(s) + 2 HCl(aq) ----> CaCl₂(aq) + CO₂(g) + H₂O(l)

how many grams of CaCl₂ could be obtained if 15.0g HCl is allowed to react with excess

CaCO₃?

2. Consider the reaction

Mg₂Si(s) + 2H₂O(l) ----> 2Mg(OH)₂(aq) + SiH₄(g)

Calculate the number of grams of silane gas, SiH₄, formed if 25.0 g of Mg₂Si reacts with excess

H₂O.

3. Fe₃O₄ reacts with CO according to the reaction

Fe₃O₄(s) + 4CO(g) ----> 4CO₂(g) + 3Fe(s)

If 234 g CO is reacted with excess Fe₃O₄, what mass of CO₂ will be produced?

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