Measuring Matter How do we? Grab a calculator and the handout

Important Stuff: Make-up work? Next two days? When I get back… Quiz Thursday

How many atoms… In H 2 O? – What’s the mass of a molecule of H 2 O? (in amu)

How many atoms… Are in a molecule of Al 2 (SO 4 ) 3 ? What’s it’s mass?

Formula mass: the mass of an ionic or covalent compound, calculated by adding the masses (rounded to the nearest.01) of the atoms together. Unit is amu (atomic mass unit)

The Mole Think of it as a “dozen,” or a “gross,” or a “ream”. Each of those terms represent numbers. A mole of something is a set number of particles of that particular stuff (ions, atoms, molecules)

AVOGADRO’S HYPOTHESIS States that 1 mole of any substance contains 6.02 x molecules (or atoms if a single, non-diatomic element). 1 mole = 6.02 x molecules/atoms/particles The Mole

A mole (mol) of anything is Avogadro’s number: x of that stuff. – A mole of marshmallows = x marshmallows (bury the country 6000 miles deep) – A mole of rice = x grains of rice, enough to cover the earth to a depth of 71 miles.

As far as we’re concerned… A mole of a substance weighs the atomic mass of that substance, expressed in grams (Derived from 12 grams of Carbon-12 having x atoms of carbon in it.) For a compound: a mole is the formula (or molecular) mass in grams/mole. To recap…

How much does one mole weigh? Carbon?

How much does one mole weigh? Carbon? – 12.0 g In other words, 12g of carbon contains x atoms of carbon. Carbon’s molar mass is 12g/mol.

How much does one mole weigh? Zinc ?

How much does one mole weigh? Zinc ? g/mol grams of zinc contains x atoms of zinc

So… Moles contain the same number of particles, even though they weigh different amounts – Hint – think of the weight of a dozen pillows versus a dozen bowling balls. There are 12 of each, but one weighs a whole lot more than the other.

Formula mass for a compound is found by adding up each of the elements atomic masses Ex: NaCl

Formula mass for a compound is found by adding up each of the elements atomic masses Ex: NaCl – Na  amu – Cl  amu

Formula mass for a compound is found by adding up each of the elements atomic masses Ex: NaCl – Na  amu – Cl  amu – = amu

Formula mass for a compound is found by adding up each of the elements atomic masses Ex: H 2 O

Formula mass for a compound is found by adding up each of the elements atomic masses Ex: H 2 O – H  amu – O  amu – 2( ) = amu

Formula mass is the same as molar mass or gram formula mass, but with different units. Instead of amu, the unit is g/mole Ex: NaCl  g/mole Ex: H 2 O  g/mole

Practice - Gram Formula Mass worksheet

Tim & Moby Time…

Picking up with Moles Rev up your calculators

If I know moles and mass… I can go back and forth, easily.

Example 1: 2.00 moles NaCl = ? Grams of NaCl Solving by dimensional analysis (factor label method)…

Example 1: 2.00 moles NaCl = ? Grams of NaCl 2.00 moles NaCl g =117 gNaCl 1 1 mole Solving by dimensional analysis (factor label method)…

Example 1: 2.00 moles NaCl = ? Grams of NaCl 2.00 moles NaCl g =117 gNaCl 1 1 mole Example 2: g H 2 O = ? moles H 2 O Solving by dimensional analysis (factor label method)…

Example 1: 2.00 moles NaCl = ? Grams of NaCl 2.00 moles NaCl g =117 gNaCl 1 1 mole Example 2: g H 2 O = ? moles H 2 O g H 2 O 1 mole g = moles H 2 O Solving by dimensional analysis (factor label method)…

And… I can even tell you how many atoms and molecules are present! I know…boom.

Example 3: 8.76 mole of H 2 O = ? molecules H 2 O

Example 3: 8.76 mole of H 2 O = ? molecules H 2 O 8.76 moles H 2 O 6.02 x molecules = 1 1 mole 5.27 x molecules

Ex 4: 9.75 x atoms of Na = ? moles Na

Ex 4: 9.75 x atoms of Na = ? moles Na 9.75 x atoms Na 1 mole Na x atoms  1620 moles

Practice & Apply Moles and Mass – on the back of the worksheet

Making a Mole of Pencil Marks Procedure: Read the entire procedure and make a table to record collected data. Measure and record the mass of a piece of paper. Place as many pencils marks as you can on your piece of pre-massed paper. Measure and record the mass of the paper with the pencil marks.

Calculations: You MUST show ALL you work. Calculate the mass of the element from the pencil you placed on your piece of paper in two minutes. Calculate the number of moles placed on your paper in two minutes. Calculate the number of atoms you placed on your paper in two minutes. Calculate how many minutes it would take you to place a mole of the element’s atoms on your piece of paper.