General Chemistry Exam 2 Questions
and Answers
How to find the mass of a molecule? - correct answer-g molecule --> mol molecule -->
Avogadro's #
Example:
(1 mol CO.01g CO2)
x
(6.022 x 10^23 CO2 molecules / 1 mol CO2)
OR (to organize the equation/steps)
(44.01g CO mol CO2)
x
(1 mol CO.022 x 10^23 CO2 molecules)
Mass Percent Composition
(Mass Percent) - correct answer-(Mass of element X in 1 mol of compound /
Mass of 1 mol of the compound) x 100%
Example:
(2 x molar mass Cl / molar mass CCl2F2) x 100%
How to calculate the number of moles of each element that are present in each sample?
- correct answer-Example:
0.857g H x (1 mol H / 1.01 g H) = 0.849 mol H
6.86g O x (1 mol O / 16.00g O) = 0.429 mol O
[Divide each # of moles by fewest moles]
0.849 mol H / 0.429 = 1.98 => 2
0.429 mol O / 0.429 = 1
So, the empirical compound of Hydrogen and Oxygen is H2O
,How to calculate Molecular Mass [n]
(After finding Empirical Formula and given Molar Mass in the problem)? - correct
answer-Molecular Mass [n] =>
(molar mass / empirical formula molar mass)
Elemental Analysis - correct answer-A method of obtaining Empirical Formulas for
unknown compounds (containing C and H) by burning a sample of the compound in
pure oxygen and analyzing the products of the combustion reaction.
What must be in equilibrium in a "balanced" chemical reaction? - correct answer-1.) The
number of atoms
2.) The amount of mass
Organic Compounds - correct answer-A compound composed of C and H and other
elements: N, O, and S.
Example: Methane (CH4)
Hydrocarbons - correct answer-Organic Compounds composed of only C and H.
Alkanes, Alkenes, Alkynes (# of bonds)? - correct answer-Alkanes =>
Hydrocarbons with single-bonded carbons
Alkenes =>
Hydrocarbons with double-bonded carbons
Alkynes =>
Hydrocarbons with triple-bonded carbons
Base Names for Hydrocarbons - correct answer-meth = 1
eth = 2
prop = 3
but = 4
pent = 5
hex = 6
hept = 7
oct = 8
non = 9
dec = 10
The Greenhouse Effect - correct answer-Greenhouse gases in the atmosphere act as a
one-way filter.
They allow sunlight to pass through and warm Earth's surface.
, Prevent heat energy from radiating back out into space.
Stoichiometry - correct answer-The numerical relationships between the amount of
reactants and the amount of products in a balanced chemical equation.
Coefficients in a Chemical Reaction (function) - correct answer-The amounts (in moles)
of the reactants and the products in a chemical reaction.
Limiting Reactant (Reagent) - correct answer-The reactant that has the smallest
stoichiometric amount in a reactant mixture and hence limits the amount of product in a
chemical reaction.
The reactant that makes the least amount of product.
Completely consumed in a chemical reaction
NOTE:
- Also called "limiting reagent"
Excess Reactant (Reagent) - correct answer-The reactants that do not limit the amount
of product (in excess)
Usually greater than what is required to completely react with the limiting reactant.
Theoretical Yield - correct answer-The maximum possible amount (in grams) of product
that can be made in a chemical reaction based on the amount of limiting reactant.
TY = [Amount of product by limiting reactant]
x
[Molar mass of product]
Actual Yield - correct answer-The amount of product ACTUALLY produced by a
chemical reaction.
Always equal to or less than the Theoretical Yield because a small mount of product is
usually lost to other reactions or foes not form during a reaction.
Percent Yield - correct answer-The percentage of the Theoretical Yield that was actually
obtained.
Expressed as the ratio of the actual yield to the theoretical yield.
% Yield =
(Actual amount of product formed/
Maximum [possible] amount of product) x 100%
and Answers
How to find the mass of a molecule? - correct answer-g molecule --> mol molecule -->
Avogadro's #
Example:
(1 mol CO.01g CO2)
x
(6.022 x 10^23 CO2 molecules / 1 mol CO2)
OR (to organize the equation/steps)
(44.01g CO mol CO2)
x
(1 mol CO.022 x 10^23 CO2 molecules)
Mass Percent Composition
(Mass Percent) - correct answer-(Mass of element X in 1 mol of compound /
Mass of 1 mol of the compound) x 100%
Example:
(2 x molar mass Cl / molar mass CCl2F2) x 100%
How to calculate the number of moles of each element that are present in each sample?
- correct answer-Example:
0.857g H x (1 mol H / 1.01 g H) = 0.849 mol H
6.86g O x (1 mol O / 16.00g O) = 0.429 mol O
[Divide each # of moles by fewest moles]
0.849 mol H / 0.429 = 1.98 => 2
0.429 mol O / 0.429 = 1
So, the empirical compound of Hydrogen and Oxygen is H2O
,How to calculate Molecular Mass [n]
(After finding Empirical Formula and given Molar Mass in the problem)? - correct
answer-Molecular Mass [n] =>
(molar mass / empirical formula molar mass)
Elemental Analysis - correct answer-A method of obtaining Empirical Formulas for
unknown compounds (containing C and H) by burning a sample of the compound in
pure oxygen and analyzing the products of the combustion reaction.
What must be in equilibrium in a "balanced" chemical reaction? - correct answer-1.) The
number of atoms
2.) The amount of mass
Organic Compounds - correct answer-A compound composed of C and H and other
elements: N, O, and S.
Example: Methane (CH4)
Hydrocarbons - correct answer-Organic Compounds composed of only C and H.
Alkanes, Alkenes, Alkynes (# of bonds)? - correct answer-Alkanes =>
Hydrocarbons with single-bonded carbons
Alkenes =>
Hydrocarbons with double-bonded carbons
Alkynes =>
Hydrocarbons with triple-bonded carbons
Base Names for Hydrocarbons - correct answer-meth = 1
eth = 2
prop = 3
but = 4
pent = 5
hex = 6
hept = 7
oct = 8
non = 9
dec = 10
The Greenhouse Effect - correct answer-Greenhouse gases in the atmosphere act as a
one-way filter.
They allow sunlight to pass through and warm Earth's surface.
, Prevent heat energy from radiating back out into space.
Stoichiometry - correct answer-The numerical relationships between the amount of
reactants and the amount of products in a balanced chemical equation.
Coefficients in a Chemical Reaction (function) - correct answer-The amounts (in moles)
of the reactants and the products in a chemical reaction.
Limiting Reactant (Reagent) - correct answer-The reactant that has the smallest
stoichiometric amount in a reactant mixture and hence limits the amount of product in a
chemical reaction.
The reactant that makes the least amount of product.
Completely consumed in a chemical reaction
NOTE:
- Also called "limiting reagent"
Excess Reactant (Reagent) - correct answer-The reactants that do not limit the amount
of product (in excess)
Usually greater than what is required to completely react with the limiting reactant.
Theoretical Yield - correct answer-The maximum possible amount (in grams) of product
that can be made in a chemical reaction based on the amount of limiting reactant.
TY = [Amount of product by limiting reactant]
x
[Molar mass of product]
Actual Yield - correct answer-The amount of product ACTUALLY produced by a
chemical reaction.
Always equal to or less than the Theoretical Yield because a small mount of product is
usually lost to other reactions or foes not form during a reaction.
Percent Yield - correct answer-The percentage of the Theoretical Yield that was actually
obtained.
Expressed as the ratio of the actual yield to the theoretical yield.
% Yield =
(Actual amount of product formed/
Maximum [possible] amount of product) x 100%
