Ch 7.3 Using Chemical Formulas

Ch 7.3 Using Chemical Formulas

Lesson Starter Ch 7.3 Using Chemical Formulas
The chemical formula for water is H2O. How many atoms of hydrogen and oxygen are there in one water molecule? How can you calculate the mass of a water molecule, given the atomic masses of hydrogen and oxygen? In this section, you will learn how to carry out these and other calculations for any compound.

Objectives Calculate the formula mass or molar mass of any given compound. Use molar mass to convert between mass in grams and amount in moles of a chemical compound. Calculate the number of molecules, formula units, or ions in a given molar amount of a chemical compound. Calculate the percentage composition of a given chemical compound.

A chemical formula indicates: the elements present in a compound the relative number of atoms or ions of each element present in a compound Chemical formulas also allow chemists to calculate a number of other characteristic values for a compound: formula mass molar mass percentage composition

Formula Masses Formula Masses The formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all atoms represented in its formula. example: formula mass of water, H2O average atomic mass of H: 1.01 amu average atomic mass of O: amu average mass of H2O molecule: 2.02 amu amu =18.02 amu

Formula Masses The mass of a water molecule can be referred to as a molecular mass. The mass of one formula unit of an ionic compound, such as NaCl, is not a molecular mass. The mass of any unit represented by a chemical formula (H2O, NaCl) can be referred to as the formula mass.

Molar Masses The molar mass of a substance is equal to the mass in grams of one mole (mol), or approximately 6.02 × 1023 particles (Avogadro’s Number), of the substance. example: the molar mass of pure calcium, Ca, is g/mol because one mole of calcium atoms has a mass of g. The molar mass of a compound is calculated by adding the masses of the elements present in a mole of the molecules or formula units that make up the compound.

One mole of water molecules contains exactly two moles of H atoms and one mole of O atoms. The molar mass of water is calculated as follows. molar mass of H2O molecule: 2.02 g/mol g/mol = g/mol A compound’s molar mass is numerically equal to its formula mass.

Practice: What is the molar mass of barium nitrate, Ba(NO3)2?

What is the molar mass of iron (III) sulfate?
What is the molar mass of strontium hydroxide?

Molar Mass as a Conversion Factor The molar mass of a compound can be used as a conversion factor to relate an amount in moles to a mass in grams for a given substance. To convert moles to mass multiply the amount in moles by the molar mass: Amount in moles × molar mass (g/mol) = mass in grams

MOLES DIVIDE MULTIPLY BY MASS MASS MOLAR MASS MOLAR MASS 1 mol
ATOMS IONS MOLECULES ATOMS IONS MOLECULES DIVIDE MULTIPLY BY 6.02 x 1023 6.02 x 1023 1 mol 6.02 x 10 23 6.02 x 1023 1 mol DIVIDE MULTIPLY BY VOL VOL 22.40 L 22.40 L For a gas only 1 mol 22.40 L 22.40 L 1 mol For a gas only

Sample Problem What is the mass in grams of 2.50 mol of oxygen gas?

Practice Problem: How many moles of carbon are in 26 g of carbon?

MOLES DIVIDE MULTIPLY BY MASS MASS MOLAR MASS MOLAR MASS ATOMS IONS
MOLECULES ATOMS IONS MOLECULES DIVIDE MULTIPLY BY 6.02 x 1023 6.02 x 1023 DIVIDE MULTIPLY BY VOL VOL 22.40 L 22.40 L For a gas STP For a gas STP

Practice Problem: How many molecules are in 2.50 mol of C12H22O11?

Practice Problem: How many mol are in molecules of C3H8?

Practice Problem: Find the volume of 2.1 mol of fluorine gas at standard temperature and pressure (STP).

Practice Problem: Find the number of mol of carbon dioxide gas in 8.1 L of carbon dioxide gas at standard temperature and pressure (STP).

Practice Problem: Find the mass of 2.1  1024 molecules of NaHCO3.

Sample Problem Ibuprofen, C13H18O2, is the active ingredient in many nonprescription pain relievers. Its molar mass is g/mol. If the tablets in a bottle contain a total of 33 g of ibuprofen, how many moles of ibuprofen are in the bottle? How many molecules of ibuprofen are in the bottle? What is the total mass in grams of carbon in 33 g of ibuprofen?

percentage composition of the compound
Ch 7.3 Using Chemical Formulas Percentage Composition The percentage of an element in a compound can be calculated by determining how many grams of the element are present in one mole of the compound. X 100 = percentage composition of the compound mass of element in one (1) mol of compound molar mass of compound The percentage by mass of each element in a compound is known as the percentage composition of the compound.

percentage composition of the compound
Ch 7.3 Using Chemical Formulas Ch 7.3 Using Chemical Formulas Percentage Composition The percentage of an element in a compound can be calculated by dividing the part by the whole and then multiply by 100 X 100 = percentage composition of the compound part whole

Percentage Composition Practice Problem: Find the percentage composition of each element in copper(I) sulfide. Given: Copper (I) Sulfide Unknown: percentage composition of Cu (I) and S Solution: Formula → molar mass → mass percentage of each element

Percentage Composition Practice Problem: Find the percentage composition of each element in calcium hydroxide.

Percentage Composition Practice Problem: Find the percentage composition of each element in sodium bicarbonate.

Percentage Composition Practice Problem: Find the percentage composition of each element in iron(III) nitrite.

Ch 7.3 Using Chemical Formulas

Similar presentations

Presentation on theme: "Ch 7.3 Using Chemical Formulas"— Presentation transcript:

Similar presentations

About project

Feedback

Log in

Auth with social network:

Ch 7.3 Using Chemical Formulas

Similar presentations

Presentation on theme: "Ch 7.3 Using Chemical Formulas"— Presentation transcript:

Similar presentations

About project

Feedback