Textbook Ch.3: Mass Relations in Chemistry; Stoichiometry

Question 1

Atomic mass

Answer 1

the way that the relative masses of atoms of different elements are expressed (often referred to as atomic weights)

• indicates how heavy, on the average, one atom of that element is compared with an atom of another element

Question 2

What isotope is the modern atomic scale base on?

Answer 2

carbon-12

Question 3

Atomic mass unit (amu)

Answer 3

a unit of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12

Question 4

Isotopic abundances

Answer 4

atom percents, the relative proportions of the stable isotopes of each element.

Question 5

Avogadro’s number

Answer 5

represents the number of atoms of an element in a sample whose mass in grams is numerically equal to the atomic mass of the
element
6.022 * 10²³

Question 6

Mole

Answer 6

the quantity represented by Avogadro’s number

6.022 * 10²³ of something

Question 7

Molar mass (MM)

Answer 7

in grams per mol (g/mol), is numerically equal to the sum of the masses (in amu) of the atoms in the formula

Question 8

Percent composition

Answer 8

specified by citing the mass percents of the elements present

Question 9

What do the subscripts in a formula represent?

Answer 9

• The atom ratio in which the different elements are combined
• The mole ratio

Question 10

Simplest / Empirical formula

Answer 10

gives the simplest whole-number ratio of the atoms present

Question 11

What do the coefficients of a balanced equation represent?

Answer 11

the numbers of moles of reactants and products

Question 12

Excess reactant

Answer 12

a reactant present in an amount in excess of that required to combine with all of the limiting reactant

Question 13

Limiting reactant

Answer 13

limits the amount of product formed

Question 14

Theoretical yield

Answer 14

the amount of product produced if the limiting reactant is completely consumed

Question 15

After you perform calculations with the two reactants, how do you know which one is the limiting reactant? What does that value
represent?

Answer 15

the smaller of the two amounts calculated represents the theoretical yield of the product

Question 16

How do you find out how much of the reactant in excess is used up in the reaction?

Answer 16

subtract the theoretical yield from the starting amount

Question 17

Experimental yield

Answer 17

the amount of product that was actually collected when a chemical reaction was performed, the limiting reactant is never 100% converted into a product as the theoretical yield would assume

Question 18

Percent yield

Answer 18

(experimental yield / theoretical yield) * 100

** Expected to be less than 100% **