Moles, AMUs, & Conversions

Question 1

When can we argue that modern chemical science began?

Answer 1

We can argue that modern chemical science began when scientists started exploring the quantitative as well as the qualitative aspects of chemistry.

Question 2

What was Dalton’s atomic theory an attempt of?

Answer 2

Dalton’s atomic theory was an attempt to explain the results of measurements that allowed him to calculate the relative masses of elements combined in various compounds.

Question 3

How do we calculate the formula mass?

Answer 3

By summing the average atomic masses of all the atoms represented in the substance’s formula

Question 4

What is formula mass for covalent substances?

Answer 4

For covalent substances, the formula represents the numbers and types of atoms composing a single molecule of the substance which may be correctly referred to as molecular mass

Question 5

How do we calculate molecular mass?

Answer 5

Number of an atom x average atomic mass (repeat process for atoms then add up their totals for the mass of the entire molecule)

Question 6

How is formula mass calculated for an ionic compound?

Answer 6

The formula mass for an ionic compound is calculated in the same way as the formula mass for covalent compounds: by summing the average atomic masses of all the atoms in the compound’s formula (yet it may not be referred to as molecular mass)

Question 7

Try this: What is the formula mass (amu) of calcium phosphate?

Answer 7

310.18 amu

Question 8

Why is a mole important?

Answer 8

Provides a specific measure of the number of atoms or molecules in a bulk sample of matter

Question 9

What is the definition of a mole?

Answer 9

The amount of substance containing the same number of discrete entities (atoms, molecules, ions etc.) and the number of atoms in a sample of pure 12C with a mass of exactly 12g

Question 10

The mole provides a link between what?

Answer 10

Provides a link between an easily measured macroscopic property (bulk mass) and an extremely important fundamental property (number of atoms, molecules, etc)

Question 11

The number of entities composing a mole has been experimentally determined to be what value?

Answer 11

6.022141 × 1023 (more commonly 6.022 x 1023)

Question 12

What is the constant 6.022 x 1023 referred to/known as?

Answer 12

Avogadro’s number (NA)

Question 13

True or False: 1 mole of any element contains the same number of atoms as 1 mole of any other element.

Answer 13

True

Question 14

What is molar mass?

Answer 14

The mass in grams of 1 mole of that substance, a property expressed in units of grams per mole

Question 15

True or False: Extending this principle, the molar mass of a compound in grams is likewise numerically equivalent to its formula mass in amu

Answer 15

True

Question 16

What can the relationships between formula mass, the mole, and Avogadro’s number be applied to compute?

Answer 16

The relationships between formula mass, the mole, and Avogadro’s number can be applied to compute various quantities that describe the composition of substances and compounds.

Question 17

True or False: The elemental makeup of a compound defines its chemical identity, and chemical formulas are the most succinct way of representing this elemental makeup.

Answer 17

True

Question 18

How do we calculate the mass of an unknown compound’s formula?

Answer 18

When a compound’s formula is unknown, measuring the mass of each of its constituent elements is often the first step in the process of determining the formula experimentally.

Question 19

What is percent composition?

Answer 19

The percentage by mass of each element in the compound

Question 20

What do we do to calculate percent composition?

Answer 20

To calculate percent composition, we divide the experimentally derived mass of each element by the overall mass of the compound, and then convert to a percentage

Question 21

What else can percent composition be useful for in evaluating?

Answer 21

Relative abundance of a given element in different compounds of known formulas

Question 22

Where is percent composition derived from?

Answer 22

The percent composition of a compound is easily derived from its formula mass and the atomic masses of its constituent elements.

Question 23

True or False: Due to the use of the same reference substance in defining the atomic mass unit and the mole, the formula mass (amu) and molar mass (g/mol) for any substance are numerically equivalent (for example, one H2O molecule has a mass of 18 amu and 1 mole of H2O molecules has a mass of 18 g).

Answer 23

True

Question 24

What is the chemical identity of a substance defined by?

Answer 24

The types and relative numbers of atoms composing its fundamental entities (molecules in the case of covalent compounds, ions in the case of ionic compounds).

Question 25

What kind of information does a compound’s percent composition provide us with?

Answer 25

The mass percentage of each element in the compound

Question 26

What is the total mass (amu) of carbon in each of the following molecules?
1. CH4
2. C12H10O6

Answer 26

A. 12.01 amu
B. 144.12 amu

Question 27

Calculate the molecular or formula mass of each of the following:
1. P4
2. Ca(NO3)2

Answer 27

1. 123.896 amu
2. 164.086 amu

Question 28

Write a sentence that describes how to determine the number of moles of a compound in a known mass of the compound if we know its molecular formula.

Answer 28

Use the molecular formula to find the molar mass; to obtain the number of moles, divide the mass of compound by the molar mass of the compound expressed in grams.

Question 29

How are the molecular mass and the molar mass of a compound similar and how are they different?

Answer 29

The two masses have the same numerical value, but the units are different: The molecular mass is the mass of 1 molecule while the molar mass is the mass of 6.022 × 1023 molecules.

Question 30

A single atom is related to what?

Answer 30

Mass in g/mol