Unit 5 Section 2: Percent Composition

Unit 5 Section 2: Percent Composition

Multiple Choice

How many atoms of iodine are in a mole of iodine?

• 53

• 63.55g

• 126.9

• 6.02 x 10²³

Multiple Choice

The number 6.02 x 10²³ is called...

• The Magic number

• Bohr's number

• The Molar number

• Avogadro's number

Fill in the Blank

What is the molar mass of C₂H₄O₂? Round to a Whole Number

Lesson Objectives

• Use molar mass to determine the percent composition of a compound

• Use a given mass of a compound to determine the percent composition of the whole compound

• Use Percent Composition to predict the amounts of individual elements in a compound

Chemical Ratios

• The Law of Definite Proportions: Every Compound has a fixed ratio of atoms that does not change

  • Water is always H₂O, 2 hydrogens, and 1 Oxygen

    • 2:1 Ratio

  • Carbon Dioxide always has 1 Carbon and 2 Oxygen

    • 1:2 Ratio

Dropdown

Sodium Chloride has the formula NaCl. It has a ratio of ​

Select answer

Na : ​

Select answer

Cl

Dropdown

Butane has the chemical C₄H₁₀. It has a chemical ratio of ​

Select answer

Carbon : ​

Select answer

Hydrogen

Percentage Composition

• Percentage Composition: the percentage by mass of each element in a compound​

  • It is sometimes useful to know how much of a particular element is in a compound

Percent Composition Sample Problem 1

• ​Find the percentage composition of copper(I) sulfide Cu₂S

• First step: find the total molar mass of the compound Cu₂S

  • ​2 Cu= 2 x 63.55

  • ​1 S= 1 x 32.07

Fill in the Blank

What is the total mass for Cu₂S (Round to 1 decimal place)

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Percent Composition Sample Problem 1

Find the percentage composition of Tin (IV) Oxide (SnO₄)

• ​​Identify the individual masses

  • 1*Tin: 118.710

  • 4*Oxygen:​ 4(16)

• Calculate the Total atomic Mass

Fill in the Blank

What is the atomic mass of Tin (IV) Oxide? Round to two decimal places

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Find the percentage composition of Tin (IV) Oxide (SnO₄)

Fill in the Blank

What is the percent composition of tin in Tin (IV) Oxide? Round to Two Decimal Places

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Fill in the Blank

What is the percent composition of Oxygen in Tin (IV) Oxide? Round to Two Decimal Places

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Fill in the Blank

What percentage of the total atomic mass of carbon monoxide (CO) is composed of carbon? Round to a whole Number

Fill in the Blank

What percentage of the total atomic mass of carbon monoxide (CO) is composed of oxygen? Round to a whole number

Fill in the Blank

What percentage of the total atomic mass of magnesium bromide (MgBr₂) is composed of magnesium? Round to a whole number

Fill in the Blank

What is the percent by mass of magnesium in MgO? Round to a whole number

Why Use Percentage Composition?

• Percent Composition can also be used to determine the formulation of ionic compounds based solely on the mass of a substance tested

  • By comparing the mass of one sample to the mass of the whole, you can determine the amount of other components in the compound

Percent Composition from mass sample 1

• When a 13.60 g sample of a compound containing only magnesium and oxygen decomposes, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

  • Step 1: Identify what you know

    • Total Mass: 13.60 g

    • Mass of Oxygen: 5.40

    • Mass of Magnesium: ?

  • Step 2: Find the mass of your unknown

    • Magnesium=Total-Oxygen= 13.60-5.40

Fill in the Blank

What is the mass of Magnesium in our sample? Round to 1 Decimal Place

Percent Composition from mass sample 1

• When a 13.60 g sample of a compound containing only magnesium and oxygen decomposes, 5.40 g of oxygen is obtained. What is the percent composition of this compound?

  • Known:

    • Total Mass: 13.60 g

    • Mass of Oxygen: 5.40

    • Mass of Magnesium: 8.20

  • Step 3: Plug your values into your percent composition equation

Fill in the Blank

When a 13.60 g sample of a compound containing only magnesium and oxygen decomposes, 5.40 g of oxygen is obtained. What is the percent composition of Oxygen in this compound? Round to 1 Decimal Place

Fill in the Blank

When a 13.60 g sample of a compound containing only magnesium and oxygen decomposes, 5.40 g of oxygen is obtained. What is the percent composition of Magnesium in this compound? Round to 1 Decimal Place

Using Percent Composition as a Conversion Factor

• You can use percent composition to calculate the number of grams of any element in a specific mass of a compound

•  If you have a 100 gram sample, the percent composition can tell you how much of each element is in that sample.

Using Percent Composition as a Conversion Factor #1

• Example: 11.11 % of water is hydrogen. How much hydrogen is in 20 grams of water?

Fill in the Blank

How many grams of hydrogen is in 20 grams of water? Round to 2 Decimal Places

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Percent Composition as a Conversion Factor #2

• Calculate the mass of carbon and the mass of hydrogen in 82.0 grams of propane (C₃H₈).

  • Step 1: Calculate your mass of propane

Fill in the Blank

Propane has the chemical formula C₃H₈. What is the molar mass of propane? Round to a whole Number

Percent Composition as a Conversion Factor #2

• Calculate the mass of carbon and the mass of hydrogen in 82.0 grams of propane (C₃H₈).

  • Step 1: Calculate your mass of propane

    • C₃H₈ =44 g/mol

  • Step 2: Identify the percent composition of both Carbon and Hydrogen in Propane

Fill in the Blank

Propane has the chemical formula C₃H₈. What is the percent composition of carbon in propane? Round to 2 decimal places

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Fill in the Blank

Propane has the chemical formula C₃H₈. What is the percent composition of Hydrogen in propane? Round to 2 decimal places

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Percent Composition as a Conversion Factor #2

• Calculate the mass of carbon and the mass of hydrogen in 82.0 grams of propane (C₃H₈).

  • Step 1: Calculate your mass of propane

    • C₃H₈ =44 g/mol

  • Step 2: Identify the percent composition of both Carbon and Hydrogen in Propane

    • C= 81.82 %, H= 18.18%

  • Step 3: Use the percent Composition to convert 82 grams of propane into grams of carbon and grams of hydrogen

Fill in the Blank

What is the Mass of Carbon in 82 grams of propane? Round to 2 Decimal Places

Fill in the Blank

What is the Mass of Hydrogen in 82 grams of propane? Round to 2 Decimal Places

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