Chemical Quantities Standards 3b. Students know the quantity of one mole is set by defining one mole of carbon-12 atoms to have a mass of exactly 12.

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Presentation transcript:

Chemical Quantities

Standards 3b. Students know the quantity of one mole is set by defining one mole of carbon-12 atoms to have a mass of exactly 12 grams. 3c. Students know one mole equals 6.02 x particles (atoms or molecules). 3d. Students know how to determine the molar mass of a molecule from its chemical formula and a table of atomic masses and how to convert the mass of a molecular substance to moles, number of particles, or volume of gas at standard temperature and pressure.

Objectives Know the meaning of the mole Know how to convert between moles, grams, and number or particles Know how to calculate the molar mass of a compound Know how to calculate percent composition Know how to determine empirical, molecular and hydrate formulas

Identity of some basic “particles” in chemistry Element Atom Molecule…diatomic elements

Compounds Covalent vs Ionic Covalent Compounds Are composed of molecules

Compounds Covalent vs Ionic Ionic Compounds Are composed of positive and negative ions; the representative particle is called a formula unit Formula unit: the simplest ratio of ions represented in an ionic compound

Mole Defn: a counting reference. A quantity chosen by chemists to represent the amount of a substance.  It is the number of representative particles in exactly 12 grams of pure carbon-12  The amount of a substance which contains “6.022 x particles” Particles can be: Atoms, molecules, formula units, ions, etc x is known as Avogadro’s Number 1 mole = the atomic mass of that element in grams...from the PT

Question Where do you find the atomic mass for an element? 12 grams of carbon contains the same # of atoms as 19 grams of fluorine or g of Se because they each contain 1 mole of particles 1 mole of He = ________g He g Ni = ________mole Ni

Atomic Mass Atomic Mass: the weighted average mass of the isotopes of an element …the value on the PT What is the atomic mass of hydrogen? g What is the atomic mass of Oxygen? g

Avogadro's Number Avogadro's Number is 6.022x10 23 which is the number of representative particles in a mole 6.022x10 23 “particles” = 1 mole

Mole Conversions Determine the “given” and the “get” Mini road map Set up equation with conversion factor(s) Cancel the units and calculate. Does your answer make sense? MOLES ↔ GRAMSMOLES ↔ ATOMS

Example 2.00 moles Boron = how many grams Boron?

How many moles of calcium are there in grams of calcium?

How many atoms are there in 5.25 moles of nitrogen gas?

Put the Moles in the Middle! GRAMS ↔ MOLES ↔ ATOMS “MOLES IN THE MIDDLE,” you gotta go through the MOLE!

Generic Mole Conversion Set-Up

Example How many atoms are there in g of aluminum?

How many grams are there in 6.7 x molecules of HF?

Molar Mass Defn: the sum of the atomic masses of all the elements in a compound/element

Calculating Molar Mass 1) Determine the atomic mass of each element in the compound The atomic mass is found on the periodic table 2) Add all the atomic masses together, this is your molar mass EX. What is the molar mass of water? H 2 O: 2 H = 2 ( g) 1 O = g/mol 2 ( g) g= g/mol

Question What is the molar mass of calcium sulfate?

Percent Composition The percent by mass of each element in a compound To determine the percent composition of a compound: 1) Determine the molar mass of the compound 2) Determine the molar mass of the element 3) Determine the percent of each element in the compound, using the % composition formula 4) Check to make sure percentages add up to 100% % El = (# atoms of El) (atomic mass El) x 100 molar mass of compound

Question What is the percent composition of H 2 O? % El = (# atoms of El) (atomic mass El) x 100 molar mass of compound % H = (2) ( g) x 100 = 11.2% H g % O =? =88.8%

Examples Calculate the percent composition of the following compounds: C 2 H 6 CO 2 NaHSO 4

CO 2

NaHSO 4

Empirical Formulas Defn: the formula with the smallest whole number mole ratio of elements in a compound If given percent composition, then: 1) Assume a 100 gram sample 2) Find the number of moles of each element 3) Divide each mole number by the smallest mole number 4) Write the formula If you come up with a decimal number, multiply the decimal number by a whole number to get a whole number Then multiply all other ratios by that same whole number

Example Given:94.11% O and 5.89% H Assume 100 g sample →

Given: 52.9% Cand 47.1% O Assume a 100 g sample →

Empirical Formulas If given the mass of a compound and the mass of the individual elements, then: 1) Determine how many grams of each element is present 2) Find the number of moles of each element 3) Divide each mole number by the smallest mole number 4) Write the formula If you come up with a decimal number, multiply the decimal number by a whole number to get a whole number Then multiply all other ratios by that same whole number

Question Analysis of 20.0 g of a compound containing only calcium and bromine indicates that 4.00 g of calcium are present. What is the empirical formula of the compound formed?

Molecular Formulas Defn: The actual number of atoms of each element in one molecule or formula unit of the substance You calculate a molecular formula from an empirical formula To find the molecular formula: 1) find molar mass of empirical formula 2) Divide molar mass (given) by empirical formula mass to get an “integer” Molar mass of compound = N (an integer) empirical formula mass 3) Multiply empirical formula by the “integer” (Molecular Formula) = (Empirical Formula)N… N distributes to all the subscripts

Example The molar mass of a compound is 42 g/mol. Its empirical formula is CH 2. What is the molecular formula for this compound?

What is the molecular formula for a compound with an empirical formula of OH and a molar mass of 34 g/mol?

Hydrate Formulas Defn:a solid which crystallizes with water molecules bonded to the compound in the crystalline lattice. Name of the hydrous compound: BaCl 2 2H 2 O → BaCl 2 (s) + 2 H 2 O (g)BaCl 2 x H 2 O → BaCl 2 (s) + x H 2 O (g)

To Name a hydrous compound: Name of the ionic compound + prefix hydrate… (the prefix corresponds to the coefficient in front of the water) Prefixes: 1-mono4-tetra7-hepta 2- di5-penta8-octa 3-tri6-hexa9-nona 10-deca

Finding a Hydrate Formula 1) Find the number of moles for each compound 2) Divide each mol number by the smallest mol number 3) Write the formula 4) Name the compound

Example A hydrate of CuSO4 is heated to drive off the water of crystallization. When 10.0 g of the hydrate is heated, 6.39 grams of solid residue remain. Find the hydrate formula.

The End