Introducing.. The Mole A Unit of Measurement

A Baking Analogy.. *A recipe calls for flour, chocolate chips, eggs, milk, vinegar, baking soda and sugar. Q. Which ingredients do you measure by counting? Q. What do you measure by volume/mass? Q. Why does the recipe not tell you exactly how many chocolate chips or grains of sugar you will need? Q. What units do you think the chocolate chips and sugar are given in?   *These units are used as a matter of convenience.

2 eggs + 3 mushrooms + 1 pepper  1 omelette *Advantage: Ingredients are all macroscopic; that is, they can be seen with the unaided eye. 2H2(g) + O2(g)  2H2O(l) *Entities are submicroscopic – cannot be seen clearly with the most powerful microscopes.

However, chemists have developed methods that allow them to predict, with great accuracy, the number of entities (atoms, ions, or molecules) that take part in chemical reactions. Chemists count atoms by organizing very large numbers of them into convenient, measurable groups.

What are some examples of convenient, measurable groups that are commonly used? 1 ream = 500 sheets (photocopy paper) 1 Astronomical Unit = 150,000,000 Km 1 goal (football) = 6 points 1 dollar = 100 cents 1 kilometre = 1000 metres 1 litre = 1000 ml 1 Kilobyte = 1024 bytes 1 megabyte = 1048576 bytes 1 carat (jewels) = 200 mg 1 horsepower = 746 watts (joule/sec) 1 pack or deck = 52 cards 1 light-year = 9,461,000,000,000 km 1 decade = 10 years A gold record = 1,000,000 copies sold 1 century = 100 years 1 octave = 12 notes 1 millennium = 1,000 years p = 3.1415926 1 Coulomb = 6 x 1024 electrons 1 Faraday = 9.65 x 104 Coulombs

1 mole = 6.02 x 1023 particles

*Amedeo Avogadro (1776 – 1856) One mole (1 mol) of a substance contains _____________particles (usually: atoms, molecules, formula units, ions or electrons) of the substance. This value is called the ____________ constant. Its symbol is NA. The mole is defined as the amount of substance that contains as many elementary entities as exactly 12 g of _________-12, (C).

C-12 From the periodic table, we know that a C-12 atom is 12 amu (atomic mass units). 1 amu = 1.6605 x 10-24 g 1 C-12 atom = 12 amu = 1.9926 x 10-23 g/atom In 12 g of C-12 there are: 12g/ 1.9926 x 10-23 g/atom = 6.022 x 10-23 atoms = 1 mole

NA = Avogadro’s Constant (6.02 x 1023) N = number of particles n = number of moles NA = Avogadro’s Constant (6.02 x 1023)

A sample contains 1.25 mol of nitrogen dioxide, NO2 How many molecules are in the sample?

Solution Given: NA = 6.02 x 1023 Therefore, there are molecules in 1.25 mol of NO2

Consider a sample containing 1. 2 x 1024 atoms of iron Consider a sample containing 1.2 x 1024 atoms of iron. How many moles of atoms do you have? (Ans: 2.0 mol) A sample of bauxite ore contains 7.71 x 1024 molecules of aluminum oxide, Al203. How many moles of aluminum oxide are in the sample? (Ans: 12.8 mol) A small pin contains 0.0178 mol of iron. How many atoms of iron are in the pin? (Ans: 1.07 x 1022 )

Why do you think the masses of 1 mol of sample is different?

Molar Mass The mass of 1 mol of substance is called the molar mass of the a substance. Molar Mass (Mx) units: g/mol Molar mass of C-12 (Mc) = 12.01 g/mol The molar mass can be found by looking at the periodic table. E.g. MS = MH20 =

m mass (g) n no. of moles (mol) M molar mass (g/mol)

Example: How many moles are in 36 g of carbon? Convert a mass of 1.5 kg of calcium carbonate to an amount in moles