Question

get the gizmo ready:

• check that the equation is still:

fe₂o₃ + 3co → 2fe + 3co₂

• if not, click new equation until it reappears.

a mole is:
a) a mammal known for digging up gardens.
b) a small, dark spot on the skin.
c) a spy embedded within an enemy government.
d) 6.02 × 10²³ particles of a substance.
e) all of the above.

correct answer, of course, is e. in chemistry, the mole (mol) is defined as an amount of a substance that contains 6.022 × 10²³ particles of that substance. this number, called avogadros number, is special because the number of particles has a mass in grams that is equal to the mass (in unified mass units) of a single molecule of the substance.

question: how do scientists find the formula mass and molar mass of a substance?

calculate: the formula mass of a compound is the sum of the masses of each atom in the chemical formula. the unit of formula mass is the unified mass unit (u). formula mass is also called molecular mass if the compound is composed of molecules.

iron’s atomic mass is 55.85 u, carbon’s mass is 12.01 u, and oxygen’s mass is 16.00 u.

a. calculate the formula mass of carbon monoxide (co) by adding the atomic mass of carbon and the atomic mass of oxygen:

b. calculate the formula mass of carbon dioxide (co₂):

c. calculate the formula mass of iron (iii) oxide (fe₂o₃):

refer: a mole of a substance has a mass in grams that is equal to the formula mass. for example, a carbon atom has an average mass of 12.01 u. a mole of carbon has a mass of 12.01 g. based on their formula masses, list the molar mass of each substance. the unit for molar mass is g/mol, or grams per mole.

fe₂o₃ co fe co₂

check your answers on the gizmo by inspecting the middle row of tiles on the right side of the gizmo. these tiles show the units \1 mol\ on top and \g\ below.

practice: hydrogen has an atomic mass of 1.01 u. what is the molar mass of these substances? (remember to use the units g/mol.)

h₂o ch₄ h₂co₃ c₆h₁₂o₆

Explanation:

Step1: Calculate formula mass of CO

Formula mass of \(CO\) is sum of atomic mass of \(C\) and \(O\).
Atomic mass of \(C = 12.01u\), atomic mass of \(O=16.00u\)
\(12.01 + 16.00=28.01u\)

Step2: Calculate formula mass of \(CO_{2}\)

Formula mass of \(CO_{2}\) is sum of atomic mass of \(C\) and \(2\) times atomic mass of \(O\)
\(12.01+(2\times16.00)=12.01 + 32.00 = 44.01u\)

Step3: Calculate formula mass of \(Fe_{2}O_{3}\)

Formula mass of \(Fe_{2}O_{3}\) is \(2\) times atomic mass of \(Fe\) plus \(3\) times atomic mass of \(O\)
Atomic mass of \(Fe = 55.85u\)
\((2\times55.85)+(3\times16.00)=111.7+48=159.7u\)

Step4: Molar mass of \(Fe_{2}O_{3}\)

Since molar mass (g/mol) is equal to formula mass (u). Molar mass of \(Fe_{2}O_{3}=159.7g/mol\)

Step5: Molar mass of \(CO\)

Molar mass of \(CO = 28.01g/mol\)

Step6: Molar mass of \(Fe\)

Atomic mass of \(Fe = 55.85u\), so molar mass of \(Fe=55.85g/mol\)

Step7: Molar mass of \(CO_{2}\)

Molar mass of \(CO_{2}=44.01g/mol\)

Step8: Molar mass of \(H_{2}O\)

Atomic mass of \(H = 1.01u\), formula mass of \(H_{2}O=(2\times1.01)+16.00=2.02 + 16.00=18.02u\), molar mass of \(H_{2}O = 18.02g/mol\)

Step9: Molar mass of \(CH_{4}\)

Formula mass of \(CH_{4}=12.01+(4\times1.01)=12.01+4.04 = 16.05u\), molar mass of \(CH_{4}=16.05g/mol\)

Step10: Molar mass of \(H_{2}CO_{3}\)

Formula mass of \(H_{2}CO_{3}=(2\times1.01)+12.01+(3\times16.00)=2.02+12.01 + 48=62.03u\), molar mass of \(H_{2}CO_{3}=62.03g/mol\)

Step11: Molar mass of \(C_{6}H_{12}O_{6}\)

Formula mass of \(C_{6}H_{12}O_{6}=(6\times12.01)+(12\times1.01)+(6\times16.00)=72.06+12.12+96=180.18u\), molar mass of \(C_{6}H_{12}O_{6}=180.18g/mol\)

Answer:

A. \(28.01u\)
B. \(44.01u\)
C. \(159.7u\)
Molar mass: \(Fe_{2}O_{3}:159.7g/mol\), \(CO:28.01g/mol\), \(Fe:55.85g/mol\), \(CO_{2}:44.01g/mol\)
Practice: \(H_{2}O:18.02g/mol\), \(CH_{4}:16.05g/mol\), \(H_{2}CO_{3}:62.03g/mol\), \(C_{6}H_{12}O_{6}:180.18g/mol\)