mole concept and stoichiometry (part 2)

Question 1

Mg + 2HCl +–> MgCl2 + H2. How can this be interpreted?

Answer 1

1 mol of magnesium reacts with 2 moles of hydrochloric acid to form 1 mol of magnesium chloride and 1 mol of hydrogen gas.

Question 2

For calculations involving reacting masses, what is one essential step?

Answer 2

The given masses must be first converted to number of moles.

mass of a, known substance –> no. of moles of a –> no. of moles of b, unknown substance –> mass of b

Question 3

The mole ratio of gases is ___ to the volume ratio of gases.

Answer 3

The mole ratio of gases is equal to the volume ratio of gases.
(volume of gas a –> volume of gas b, using mole ratio)

Question 4

How to solve questions with limiting reagent?

Answer 4

1. Chemical equation (gas? volume ratio)
2. Calculate moles (from mass, from volume of gas, from volume x concentration)
3. Stoichiometry ratio (mole ratio)
4. Non-stoichiometry ratio
5. Determine limiting reagent
6. Use moles of LIMITING REAGENT for other calculations

Question 5

What is the formula for percentage yield?

Answer 5

% yield = actual yield / theoretical yield x 100%

Question 6

What is the formula for percentage purity?

Answer 6

% purity = mass of pure substance / mass of substance used in reaction