G11 - UNIT 3 FLASHCARDS
What is a mole?
The mole is a base unit that is used to measure the amount of substance. A mole is
the amount of substance that contains 6.02 x 10^23 particles
What is the relationship between the atomic mass
of an element in atomic mass units and the atomic
molar mass of the same element in grams?
The mass of one atom of an element in atomic mass units has the same numerical value
as the mass of one mole of atoms of the same element in grams.
What is the difference between an empirical and
a molecular formula?
The empirical formula shows the smallest whole-number ratio of elements in a
compound. The molecular formula for a compound shows the number of atoms of each
element that make up a molecule of that compound.
When is the molecular formula of a compound
the same as its empirical?
If it’s an ionic compound or if it is a simple molecular compound that is the smallest
whole-number ratio e.g. water (H2O) or formaldehyde (CH2O)
Explain the difference between a hydrate and its
anhydrous form.
A hydrate is a compound that has a specific number of water molecules bound to each
formula unit. The anhydrous form does not have any water molecules bound to it.
Why is it important for chemists to know if they are
using a hydrate or the anhydrous form when they
are performing investigations?
Chemists need to know if it’s a hydrate because the water molecules are part of the
crystal structure and add mass to the compound.
What is stoichiometry?
Stoichiometry is the study of quantitative relationships in chemical reactions.
What important chemical information about the
reactants and products in a reaction is obtained
from the coefficients of a balanced chemical
equation?
The coefficients of a balanced chemical equation can be used to represent the relative
amounts (in moles) of particles (atoms, ions, molecules, or formula units)
Explain what is meant by the term “stoichiometric
amount”.
The reactants and products are in the exact molar amounts as predicted by the balanced
chemical equation
What is a limiting reactant? An excess reactant?
A limiting reactant is a reactant that is completely consumed during a chemical reaction,
limiting the amount of product that is produced. The excess reactant is the reactant that
remains after a reaction is over.
Explain the difference between experimental
yield and theoretical yield.
The theoretical yield is the amount of product that is predicted by stoichiometric
calculations. The experimental yield is the actual amount of product that is recovered
after a reaction is complete.
Why is the experimental yield usually lower than
the theoretical yield?
The difference can be caused by various factors:
● Poor laboratory techniques (e.g. loss of product while transferring from one
container to another)
● The reaction did not go to completion (e.g. not enough time allowed)
● Poor reaction conditions (e.g. temperature, pressure not optimal)
● Competing side reactions (i.e. other reactions occurring)
● The reactants themselves may have been impure
