CHEM 103: EXAM 2 QUESTIONS
ANSWERS WITH COMPLETE
SOLUTIONS 100% CORRECT NEWLY
UPDATED 2026/2027
Question: How is "Atomic Mass" defined in relation to the isotopes of an
element?
Answer: ✔️✔️ Atomic mass represents the weighted average mass of all
naturally occurring isotopes of that element. It accounts for both the mass of
each isotope and its relative abundance in nature.
Question: What is the precise scientific definition of a "Mole" as it relates to
Carbon-12?
Answer: ✔️✔️ A mole is defined as the specific amount of a substance that
contains exactly the same number of elementary entities (atoms, molecules, or
ions) as there are atoms in 12.00 grams of carbon-12. This constant value is
known as Avogadro's number
What is Avogadro's number? -ANSWER ✔️✔️6.022*10^23 elements per mole
molar mass/ atomic mass (amu)/ molecular mass/ formula weight -ANSWER
✔️✔️mass of 1 mole of anything in grams (g/mol)
for any element, what does atomic mass (amu) equivalent to? -ANSWER
✔️✔️molar mass (grams)
molecular mass / molecular weight -ANSWER ✔️✔️the sum of the atomic masses
in a molecule
, formula mass -ANSWER ✔️✔️the sum of the atomic masses (in amu) in a
formula unit of an ionic compound
what is the percent composition of compounds used for? -ANSWER ✔️✔️-used
to find the purity of a compound
-to get the empirical formula
-to tell the mass of a certain element in a compound
what is the equation for percent composition of an element in a compound? -
ANSWER ✔️✔️n * molar mass of an element
--------------------------------- *100
molar mass of a compound
what does the n in the percent composition equation stand for? -ANSWER
✔️✔️the number of moles of an element in 1 mole of a compound
empirical formula -ANSWER ✔️✔️simplest, whole-number ratio of the atoms of
elements in a compound
what are the steps for obtaining the empirical formula? -ANSWER ✔️✔️1.
Convert the percentages to grams by assuming there is 100g of the compound
(skip if already in grams)
2. Convert grams to moles by using the molar mass os each element
3. Divide all by the smallest number of moles (if the result is within 0.1 of a
whole number, round to a whole number)
4. Multiply all mole ratios by a number to make a whole number
combustion analysis -ANSWER ✔️✔️a method of obtaining empirical formulas
for unknown compounds, especially those containing carbon and hydrogen, by
ANSWERS WITH COMPLETE
SOLUTIONS 100% CORRECT NEWLY
UPDATED 2026/2027
Question: How is "Atomic Mass" defined in relation to the isotopes of an
element?
Answer: ✔️✔️ Atomic mass represents the weighted average mass of all
naturally occurring isotopes of that element. It accounts for both the mass of
each isotope and its relative abundance in nature.
Question: What is the precise scientific definition of a "Mole" as it relates to
Carbon-12?
Answer: ✔️✔️ A mole is defined as the specific amount of a substance that
contains exactly the same number of elementary entities (atoms, molecules, or
ions) as there are atoms in 12.00 grams of carbon-12. This constant value is
known as Avogadro's number
What is Avogadro's number? -ANSWER ✔️✔️6.022*10^23 elements per mole
molar mass/ atomic mass (amu)/ molecular mass/ formula weight -ANSWER
✔️✔️mass of 1 mole of anything in grams (g/mol)
for any element, what does atomic mass (amu) equivalent to? -ANSWER
✔️✔️molar mass (grams)
molecular mass / molecular weight -ANSWER ✔️✔️the sum of the atomic masses
in a molecule
, formula mass -ANSWER ✔️✔️the sum of the atomic masses (in amu) in a
formula unit of an ionic compound
what is the percent composition of compounds used for? -ANSWER ✔️✔️-used
to find the purity of a compound
-to get the empirical formula
-to tell the mass of a certain element in a compound
what is the equation for percent composition of an element in a compound? -
ANSWER ✔️✔️n * molar mass of an element
--------------------------------- *100
molar mass of a compound
what does the n in the percent composition equation stand for? -ANSWER
✔️✔️the number of moles of an element in 1 mole of a compound
empirical formula -ANSWER ✔️✔️simplest, whole-number ratio of the atoms of
elements in a compound
what are the steps for obtaining the empirical formula? -ANSWER ✔️✔️1.
Convert the percentages to grams by assuming there is 100g of the compound
(skip if already in grams)
2. Convert grams to moles by using the molar mass os each element
3. Divide all by the smallest number of moles (if the result is within 0.1 of a
whole number, round to a whole number)
4. Multiply all mole ratios by a number to make a whole number
combustion analysis -ANSWER ✔️✔️a method of obtaining empirical formulas
for unknown compounds, especially those containing carbon and hydrogen, by
