X Chemistry Unit 7The Mole

Problem Solving involving Chemical Compounds

Vocab: Molar Mass- the mass of 1 mole of a substance

Equal to the atomic mass for elementsFor a compound, the sum of the atomic

masses for all the atoms in a compoundUnits = grams/mole = g/mol

Mole - the amount of substance that is equal to 6.02x1023 particles of that substance

Vocab: Representative particle- the smallest particle of

a substance; defined by the type of substance:Element = atomCovalent compound = moleculeIonic compound = formula unitCharged atom = ion

Vocab: Avogadro’s Number- the number of particles

in 1 mole of any substanceAvogadro’s # = 6.02x1023

Molar Volume- the volume of 1 mole of ANY gas at STP (Standard Temperature and Pressure = 0°C and 1atm), 22.4 Liters

What is a Mole? Amedeo Avogadro (Italian Mathematician)

used Carbon as the basis for the masses of the other elements

devised a counting relationship between grams and moles

1 mole = 6.02x1023 atoms of any element1 mole of carbon = 12.0 g Carbon

(matches the atomic mass on the P.T.)

What is a Mole?(REAL WORLD EXAMPLE)Relationships:

1 dozen = 12 donuts just like 1 mole = 6.02x1023 atoms

BUT:1 dozen feathers = 0.015 grams

and1 dozen bricks = 32,400 grams!

Although the amount of particles is the same,

the weight is not necessarily the same!!

What is a Mole?The mass of 1 mole of any element will be different

than 1 mole of any other element!!What are the masses of 1 mole of the following elements?

Magnesium = 24.31 g/mol

Nitrogen = 14.01 g/mol

These values come from the periodic table!!

One-mole Amounts

Determining Molar Mass for a Compound:1. Write the symbols of the elements in the formula down

the left hand side of the paper.

2. Count the number of each atom of each element present.

3. Multiply the number of each atom by the molar mass of the corresponding element from the periodic table rounded to the tenths place.

4. Sum the products from step 3.

5. The units on your final answer are g/mol (grams per mole).

Determining Molar Mass: Examples:

CO2

(NH4)2SO4

Mole Conversions

Moles!

MassRepresentative

particles(atoms, molecules, formula

units, ions)

Mole Conversions

Use molar mass ( __ grams / 1 mole)

Use Avogadro’s # (6.02 x 1023

particles per

1 mole)

Mole Conversions Always start with the number given in the problem

If mass appears anywhere in the problem, you must use molar mass as a conversion!

If particles (atoms, molecules, ions) appear anywhere in the problem, you must use Avogadro’s number as a conversion!

Cross out units that cancel Stop when you get to the unit asked for in the

problem!

Converting between Moles and Mass (Grams): Dimensional Analysis!! Use molar mass

as conversion factor!

Moles to grams:

Grams to moles:

¿𝑜𝑓 𝑚𝑜𝑙𝑒𝑠×𝑀𝑜𝑙𝑎𝑟 𝑚𝑎𝑠𝑠 (𝑔 )1𝑚𝑜𝑙𝑒 =¿𝑜𝑓 𝑔𝑟𝑎𝑚𝑠

¿𝑜𝑓 𝑔𝑟𝑎𝑚𝑠× 1𝑚𝑜𝑙𝑒𝑀𝑜𝑙𝑎𝑟𝑚𝑎𝑠𝑠 (𝑔)

=¿𝑜𝑓 𝑚𝑜𝑙𝑒𝑠

Converting between Moles and Mass:Examples:How many moles of CCl4 are there in 523.4 g?

Converting between Moles and Mass:Examples: (cont.)How many grams of Na are there in 12.3 moles of Na?

Converting between Moles and Particles: Dimensional Analysis!! Use Avogadro’s

number as conversion factor!

Moles to particles:

Particles to moles:

¿𝑜𝑓 𝑚𝑜𝑙𝑒𝑠× 6.02 𝑥1023

1𝑚𝑜𝑙𝑒 =¿ 𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠

¿𝑜𝑓 𝑝𝑎𝑟𝑡𝑖𝑐𝑙𝑒𝑠× 1𝑚𝑜𝑙𝑒6.02 𝑥1023

=¿𝑜𝑓 𝑚𝑜𝑙𝑒𝑠

Conversions Between Moles & Particles: Use Avogadro’s Number!!

Examples:How many atoms of carbon are contained in

0.230 moles of C?

Conversions Between Moles & Particles

Examples:How many moles of sodium chloride are contained in 8.73 x 1022 molecules (formula units) of NaCl?

Conversions Between Moles & Particles

Challenge!!How many molecules of barium chloride are

contained in 1.07 grams of barium chloride?

Vocab: Percent composition – mass of the part

divided by mass of the whole times 100

Empirical Formula – the simplest whole number ratio of atoms in a compound

Molecular Formula- the true whole number ratio of atoms in a compound

Percent Composition Problems:

2 types:1. Using mass data about a specific sample

to find percentage of each component in the sample (More specific)

2. Using a chemical formula to find percentage of each element in a compound (More general)

Percent Composition Problems: Type 1: (just like the separation of a mixture lab!!)

% of element or component in a specific sample

mass of one component% composition 100%total mass of sample

Percent Composition Problems: Examples:If 20.55 g of sodium combines completely with 31.75 g of chlorine to form a compound, what is the % composition of each element in this compound?

Percent Composition Problems:

Type 2:Mass of each element in 1 mole of a

compound (1 mole use the molar mass!!)

mass of element from periodic table # of atom% composition 100%

molar mass of entire compound

Percent Composition Problems:

Example:What is the percent composition of each element in C12H22O11?

Empirical Formula vs. Molecular Formula

Molecular FormulaP3H6

C6H12O6

N6F8

Empirical FormulaPH2

CH2O

N3F4

Identify the following as empirical or molecular formulas

Ribose, C5H10O5, a sugar molecule in RNA.

Ethyl butanoate, C6H12O2, a compound with the odor of pineapple.

Chlorophyll, C55H72MgN4O5, part of photosynthesis.

DEET, C12H17ON, an insect repellent.

Oxalic acid H2C2O4, found in spinach and tea.