Chapter 5

Question 1

What is the atomic mass of the elements in the periodic table based on?

Answer 1

carbon 12

Question 2

What is the atomic mass of carbon 12?

Answer 2

12 amu

Question 3

How do you calculate the atomic mass of an element?

Answer 3

atomic mass = (fractional abundance times the mass of the isotope 1 (percent written in decimal form) + (fractional abundance times the mass of the isotope 2 (percent written in decimal form))

Question 4

Sample Problem: Neon gas naturally exists as a mixture of 3 isotopes (20Ne, 21Ne, and 22Ne) and has an atomic mass of 20.1797 amu. What is the percent abundance of 22Ne (21.9914 amu)?
•91.84% 20Ne (19.9924 amu)
•0.47% 21Ne (20.9940 amu)

Answer 4

7.69 %

Question 5

What is a mole?

Answer 5

a mole is a number equal to the number of carbon atoms in exactly 12 grams of carbon 12

amount of any substance (like how dozen = 12, pair = 2)

Question 6

What does 1 mol equal?

Answer 6

6.022 x 10^23 molecules/atoms

Question 7

Sample problem: A copper wire is found to have a mass of 325g. Copper comes as an avg mass of 65.546 g

a) Calculate the number of moles of copper in the wire.
b) Calculate the number of copper atoms in the wire.

Answer 7

a) 1 mol Cu = 4.96

b) 2.98 x 10^24

Question 8

What do moles allow us to do?

Answer 8

moles allow us to express a chemical’s atomic mass in grams

Question 9

If an element has a mass of a certain amount, how many moles does that equal?

Answer 9

1 mol of that certain element

Question 10

Molar mass = ____ mass

Answer 10

molar mass = atomic mass x number of element type present (g/mol)

Question 11

What is the molar mass of oxygen gas?

Answer 11

15.999 x 2 = g/mol of O2

Question 12

If we are calculating the molar mass of a covalently bound molecule, we use what type of formula?

Answer 12

the molecular formula (C6H12O6)

Question 13

If we are calculating the molar mass of an ionic compound, we use what type of formula?

Answer 13

the formula unit (ex: CaCl2)

Question 14

How many water molecules are in a 500 mL amount of water?

Answer 14

1.67 x 10 ^25 water molecules

Question 15

Chalk is comprised of calcium carbonate. How many formula units of calcium carbonate are present in 20.0g of chalk?

Answer 15

1.20 x 10^23 formula units

Question 16

If you have the amount of a substance in moles, what do you use to figure out the number of particles?

Answer 16

Avogadro’s number

Question 17

If you have the amount of a substance in moles and you want to find the mass, what do you use?

Answer 17

the molar mass

Question 18

What can composition be described by?

Answer 18

1) the number of atoms of each element

2) the percentage (mass) of each element

Question 19

What do you do when you want to calculate the mass percent of a certain element in a compound?

Answer 19

mass percent = (mass of a particular element in a compound / total mass of a compound) x 100

Question 20

Sample Problem: Acetetopmenophene is C8H9NO2

a) calculate the molar mass
b) calculate each of the percentages

Answer 20

a) 151.165 g/mol

b) % C is 63.565, & H is 6.001%, % N is 9.266%, %O is 21. 168

Question 21

Sample Problem: C12H18Ox molecules have 75.69285% C, what’s the chemical formula?

Answer 21

C3H18O2

Question 22

What are empirical formulas?

Answer 22

simplest whole-number ratios of atoms in a compound (H2O, CO2, NaCl)

Question 23

What are molecular formulas?

Answer 23

formulas containing all atoms in a molecule (ex: C6H12O6)

Question 24

What type of formula do ionic compounds have?

Answer 24

always empirical formula

Question 25

When calculating empirical formulas from mass percentage, how many grams do you assume there are of the substance?

Answer 25

100g (so that something like 38.67 % C gets converted to 38.67 g of C)

Question 26

What are chemical reactions?

Answer 26

involve the rearrangement of atoms in one or more substances

Question 27

What are chemical equations used for?

Answer 27

used to represent and describe chemical reactions

Question 28

What info can you get from chemical equations?

Answer 28

natures of reactants and products and the ratio in which they react

Question 29

What level do chemical reactions happen?

Answer 29

the molecular level

Question 30

What is the sign for solid, liquid, gas?

Answer 30

s, l , g

Question 31

What is the sign for states in which the compound is dissolved in water?

Answer 31

aq

Question 32

How do you balance equations?

Answer 32

balance one element at a time
start by balancing the largest compound
if element exists by itself, balance it last
change only the coefficient, not the elements

Question 33

What is stoichiometry?

Answer 33

relates the measure of substance in a chemical reaction

Question 34

What is mass of oxygen is required to react completely with 20.0 g of methane?

Answer 34

79.8 g

Question 35

What is the mass of water produced given 20.0 g of methane?

Answer 35

44.9 g of H2O

Question 36

What are limiting reactants?

Answer 36

the substance that limits the amount of product that is made, it runs out first

Question 37

What is the first step in determining the limiting reactant?

Answer 37

making a balanced equation

Question 38

What is the second step in determining the limiting reactant?

Answer 38

convert reactants to moles

Question 39

What is the third step in determining the limiting reactant?

Answer 39

calculate the amount of product that each reactant can make

Question 40

What is the theoretical yield?

Answer 40

amount of product formed when limiting reactant is completely consumed

Question 41

What is the percent yield?

Answer 41

percentage of theoretical yield

Question 42

What is the equation for percent yield?

Answer 42

actual experimental yield/theoretical yield x 100