Stoichiometry

Question 1

What is stoichiometry?

Answer 1

This is the relationship between the amounts of reactants and products in a chemical reaction.

Question 2

Define Molarity (Molar concentration)

Answer 2

This is the amount of solute in moles dissolved in water to make one litre
(1000cm3) of solution.

The units for molarity are moldm-3 or moll-1 or simply M.

Question 3

Define Molality

Answer 3

This is the number of moles of a solute dissolved in 1000g of solvent.

Question 4

What is a Standard solution

Answer 4

A solution whose concentration is accurately known.

Question 5

State characteristics of a primary standard

Answer 5

• It should be readily available in a state of high purity.
• It should be of high relative formula mass to minimize weighing errors.
• Its reactions should be stoichiometric and practically instantaneous.
• It should not be chemically altered in air during the weighing process i.e. it should not be deliquescent, hygroscopic nor react with gases in air during weighing.
• It should be chemically stable (should not readily decompose).
• It should be readily soluble in water at room temperature and pressure.

Question 6

How is percentage purity calculated?

Answer 6

Mass of pure substance/ total mass x100%

Question 7

How is percentage yield calculated?

Answer 7

Experimental yield in grams/ Theoretical yield in grams x 100%

Question 8

What is a limiting reactant?

Answer 8

One that is used up during a chemical reaction

Question 9

Define a Primary standard

Answer 9

This is a substance of known high purity (analytically pure) and can be dissolved in a known volume of distilled water to form a standard solution.