Mole-Mass & Mole-Volume Relationships

Section 10.2

What is a Mole?

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What is Avogadro’s number?

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What are representative particles?

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Count-Mole Relationship

Convert number of particles moles

Different definitions for masses• Gram atomic mass (gam)

looking at the mass of individual atoms eg. Fe, Mg• Gram molecular mass (gmm)

Looking at the mass of molecular compounds eg. CO2, N2, C3H8

• Gram formula mass (gfm)Looking at the mass of ionic compounds eg. NaCl, KBr

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To simplify (yay!) we have a term that combines all 3:

Molar mass – the mass (in grams) of one mole of a substance

Because this term is broad, we need to be specific in what we are talking about:

Ex. What is the molar mass of oxygen?

Are we talking about molecular oxygen ( O2 )? or atomic Oxygen (O)? 1 mole Oxygen atoms = 16.00 g O 1 mole O2 molecules = 2 (16.00g) = 32.00g O

We will use (gam) (gmm) or (gfm) instead of molar mass only if we have a situation like this

Mass – Mole Relationship

Mass is an easy way to measure quantity of matter, but in chemical reactions, it is often important to consider the number of atoms of each element present in a sample.

Demo Problem

How many grams are in 9.45 mol of dinitrogen trioxide?Is this compound ionic, molecular, or an acid?

Molecular (you can tell by the prefixes)What is the formula?

N2 O3

List the Knowns & Unknowns in your problem Known: 9.45 moles N2 O3 Molar mass of N2 O3 = ?

1 mol N2O3 = 2(14.01 g N) + 3 (16.00 g O) = 76.02g N2 O3

Solve for the unknown (use dimensional analysis) • 9.45 mol N2 O3 (76.02g N2 O3 /1.00 mol N2 O3) = 718.389 g N2O3• 718 g N2 O3

Practice Problem

How many moles are in 92.2 g of Iron (III) Oxide?

Is this a molecular compound, ionic compound, or acid? Ionic compound with a transition metal cation

What is the formula? Fe2 O3

List the knowns and unknowns in your problem Given mass Fe2 O3 = 92.2 g 1.00 mole Fe2 O3 = 2(55.85g Fe) + 3(16.00gO) = 159.70 g Fe2 O3

Solve for the Unknown 92.2 g Fe2 O3 (1.00 mol Fe2 O3 /159.70 g Fe2 O3 ) = 0.57733 mol Fe2 O3 = 0.577 mol Fe2 O3

Volume – Mole Relationship

• The volumes of one mole of different solids and liquids are not the same– 1 mole glucose molecules = 180.18 g glucose– 1 mole water molecules = 18.02 g water– 1 mole paradichlorobenzene molecules = 147.00 g

paradichlorobenzene

• The volumes of moles of gas are much more predictable if they are under the same conditions

Standard temperature and pressure (STP)

The volume of a gas changes with temperature and pressure – so we need a standard reference

Standard temperature and pressure (STP) ◦ Temperature = 0o C ◦ Standard Pressure = 101.3 kPa = 1

atmosphere(atm)

At STP: 1 mole of any gas occupies a volume of 22.4 L

This is known as the molar volume of a gas and is measured at STP

Recall..

1 mol of any substance contains 6.02 x 1023 representative particles

So…

22.4 L of any gas contains 6.02 x 1023 representative particles of that gas.

Does this mean 22.4 L of all gases at STP should have the same mass? NO. Mass is still measured using molar mass, and 1 mole of each substance has a different mass.

Demo Problem

What is the volume (in Liters) of 0.60 mol SO2 gas at STP?

List the knowns and unknowns 0.60 mol SO2

1 mol SO2 = 22.4 L SO2

volume = ? L

Solve for the unknown

0.60 mol SO2 (22.4 L SO2 )/1 mol SO2

13.44 L SO2 = 13 L SO2

Density of gas

The density of gas is usually measured in grams per Liter (g/L)

If you are given the density of a gas at STP, you can calculate the molar mass of that gas using the conversion factor

1 mol = 22.4 L

Demo Problem

The density of a gaseous compound containing Carbon and Oxygen is 1.964 g/L at STP. Determine the molar mass of the compound.

Density = 1.964 g/L

1 mol (gas at STP) = 22.4 L

Convert g/L to g/mol

1.964 g/1.00L (22.4 L/1.00 mol)

= 43.9936 g/mol = 44.0 g/mol

The mole road map

We can use the mole to convert between particles, mass, and volume of gas at STP.

The mole is the mediator between any of these.

So what is the mole road map?

Mole Road Map

Using the Mole Map..

Find the following..

1.The mass, in grams of 1. 3.32 mol K

2. 2.50 mol iron (II) hydroxide

2.The number of moles in1. 3.70 x 10-1 g TiO2

2. 75.0 g Nitrogen gas

3.What is the volume at STP of these gases? 1. 3.20 x 10-3 mol CO2

Practice Problem

What is the density of krypton gas at STP?

(hint: assume you have one mole of the gas!)