THE MOLE WHY IS COMPOSITION IMPORTANT Molecular Mass

THE MOLE WHY IS COMPOSITION IMPORTANT?

Molecular Mass • Is the sum of the atomic masses of a given molecule. • These masses are always rounded up to whole numbers.

Unitary Formula Mass • Ionic compounds don’t have a molecular mass. – Not a real bond – Only electrostatic attraction – They have a UNITARY FORMULA MASS • The sum of the ions using 2 decimals.

Avogadro´s Number • An honorary name that gives how many atoms, molecules, etc. are in a mole of any chemical substance. • It´s value is 6. 02 x 1023. – One mole of atoms has 6. 02 x 1023 atoms. – One mole of molecules has 6. 02 x 1023 molecules. – One mole of ions has 6. 02 x 1023 ions.

The Mole • Definition: Is the amount of substance (atoms, molecules, ions) in a system. It’s unit is the mol.

Equivalents & Conversions • A mole is a SI unit use in conversions to know: – How many of something are there • There are 6. 02 x 1023 molecules of NH 3 in one mole of NH 3 – Change from grams to moles • There are 46. 1 grams of C 2 H 5 OH (ethanol) in one mole of C 2 H 5 OH • These factors are useful in many different conversions. • To convert we will use the Unit Factor.

Exercise 5 pg 83 • Convert 91. 9 g of Ag 2 Te to unitary formulas

Moles in Solution • There a lot of different ways to express the relation substance – solution. • We use more commonly Molarity. • Molarity: how many moles are there in 1 dm 3 of solution. • NOT in 1 dm 3 of solvent • Remember 1 dm 3 = 1 L = 103 cm 3

For Example • A solution 1 M of Nitric Acid (HNO 3) contains 1 mol of molecules of HNO 3 in 1 L of solution. • A solution 0. 327 M of Ba(NO 3)2 contains 0. 327 mol of Ba(NO 3)2 in 1 dm 3 of solution.

Exercise • What is the molarity of a solution that contains 9. 46 g of Cs. Br, in 2. 50 x 102 cm 3? → 0. 250

More Info… • Based on notes and exercises you most have in your notebook study: – How to prepare a solution? – Empirical formula – Molecular formula – Hydrates