Chemical Quantities

• Describe the concept of the mole and its importance to measurement in chemistry.

 • Calculate the mass of compounds in atomic

mass units. • Calculate the molar mass of various substances.

Additional KEY TermsAvogadro’s number

Avogadro (1776-1856)

Any sample of any gas at the same temperature and pressure will contain the same number of particles.

Defined 22.4 L as the molar volume for any gas.

Particles are now counted in moles (n).

The molecular mass of water (H2O) is 18.0 µ ...

One mole of any particle has a mass equal to its total formula mass – IN GRAMS.

The mass of 1 atom of Al = 27.0 µ The mass of 1 mole of Al atoms = 27.0 g

So...the molar mass of water is 18.0 g/mol.

The mass of 1 mole is the molar mass - (g/mol)

What is the molar mass of ammonium dichromate?

Determine the molar mass.

1 mole of (NH4)2Cr2O7 = 2 N + 8 H + 2 Cr + 7 O

= 2(14.0g/mol)+ 8(1.0g/mol)+ 2(52.0g/mol)+ 7(16.0g/mol)

(NH4)2Cr2O7 = 252.0 g/mol

(NH4)2Cr2O7

Mole QuestionsAnd Dimensional Analysis

Rules for using a Dimensional Analysis

1. Start with what you know2. Put ratio units you want to cancel on bottom3. Put ratio units you need on the top4. Multiply across the top, Divide across the bottom

8 slice250 pepperoni

4 pepperoni

1 slice 1 pizza

How many pizzas would 250 pieces of pepperoni make?

= 7.8 Pizzas

What is the mass of 1.20 x 10–5 moles of carbon tetrachloride, CCl4?

CCl4 = 1 C + 4 Cl = 1(12.0 g/mol) + 4(35.5 g/mol) = 154.0 g/mol

or154.0 g1 mole

1.20 x 10-5 mol 1 mol

154.0 g

154.0 g1 mole

1.85 x 10-3 g

Calculating the Number of Particles

We call this - Avogadro's Number

In one mole there is 6.02 x 1023 particles.

6.02 x 1023 pencils is 1 mole of pencils6.02 x 1023 carbon atoms is 1 mole…6.02 x 1023 water molecules is 1 mole…

The term "particle" refers to any individual thing like atoms, formula units, molecules, ions, etc. or6.02 x 10 23 particles 1 mole 6.02 x 10 23 particles

1 mole

How many atoms in 25.0 moles of copper?

25.0 mol Cu1.51 x 10 25 atoms=

How many molecules of water in 1.50 x 10–5 moles?

= 9.03 x 10 18 molecules of water

1.50 x 10–5 mol H2O

6.02 x 10 23 particles

1 mole

6.02 x 10 23 particles

1 mole

How many moles is 5 atoms of zinc?

5 atoms of Zinc is 8.31 x 10–24 moles.

5 atoms Zn= 8.31 x 10-24 moles

6.02 x 10 23 particles

1 mole

The mole allows the conversion between mass and number of particles.

How many molecules of water in a 10.0 g sample of water?

0.556 mol H20=1 mole18.0 g

10.0 g H2O

0.556 mol H2O 6.02 x 10 23 particles

1 mole

= 3.34 x 10 23 molecules H20

Put the two equations together

There are 3.34 x 1023 molecules in 10.0 g of water.

1 mole6.02 x 10 23 particles of H2O10.0 g H2O

18.0 g1 mole

= 3.34 x 10 23 molecules H20

How many atoms in 25.0 g of sodium chloride?

NaCl = 58.5 g/mol

= 5.14 x 10 23 atoms

1 mole6.02 x 10 23 For.U 25.0 g NaCl

58.5 g1 mole 2 atoms

1 For. U

CAN YOU / HAVE YOU?

• Describe the concept of the mole and its importance to measurement in chemistry.

 • Calculate the mass of compounds in atomic

mass units. • Calculate the molar mass of various substances.

Additional KEY TermsAvogadro’s number