Moles 2

What is a chemical equation

A representation of a chemical reaction using symbols and formulas

What do equations show

Reactants products and their ratios

What do state symbols mean

(s) solid (l) liquid (g) gas (aq) aqueous

What does (aq) mean

Dissolved in water

What does (g) mean

Gas

What does (s) mean

Solid

What does (l) mean

Liquid

What must be balanced in equations

Atoms and charges

Why must equations be balanced

Law of conservation of mass

What does balancing ensure

Equal number of atoms on both sides

What is a coefficient

Number placed before a formula

What do coefficients represent

Mole ratios

Example balanced equation

CH4 + 2O2 → CO2 + 2H2O

What is mole ratio in CH4 combustion

1

Why mole ratio important

Used in calculations

What is stoichiometry

Calculation of quantities in reactions

What is first step in stoichiometry

Write balanced equation

What is second step

Convert given to moles

What is third step

Use mole ratio

What is fourth step

Convert to required unit

What is key idea

Everything goes through moles

What is spectator ion

Ion not involved in reaction

Why remove spectator ions

To write ionic equation

What is ionic equation

Shows only reacting ions

Which ions always spectator

Nitrates ammonium group 1 ions

Which halides insoluble

AgCl AgBr AgI PbCl2 (partially)

Which sulfates insoluble

BaSO4 CaSO4 (slightly)

Example spectator ion Na+

Does not react

Example ionic equation

Ba2+ + SO4 2- → BaSO4

Why ionic equations useful

Show actual reacting species

What does mole ratio tell

Relative amounts reacting

Example ratio CH4 to CO2

1

What does 1

1 mean

How to convert mass to moles

Divide by molar mass

How to convert moles to mass

Multiply by molar mass

Example methane question

50g CH4 gives 137.5g CO2

Steps in methane example

Mass to moles ratio then mass

What is limiting reagent

Reactant that runs out first

What happens when limiting reagent used

Reaction stops

What is excess reagent

Reactant left over

How to identify limiting reagent

Compare mole ratios

What is theoretical yield

Maximum product formed

Why actual yield less

Losses or incomplete reaction

What is percentage yield

(actual ÷ theoretical) × 100

Why yields not 100 percent

Side reactions or loss

What is balanced equation for CaCO3

CaCO3 → CaO + CO2

What is mole ratio CaCO3 to CaO

1

Example CaCO3 problem answer

0.214 g

What is balanced equation for KClO3

2KClO3 → 2KCl + 3O2

What is mole ratio KClO3 to O2

2

Example KClO3 problem answer

3.39 g O2

Why ratios come from coefficients

They represent moles

What must be done before ratio used

Balance equation

What is key exam tip

Never skip balancing step

What factors affect gas volume

Temperature pressure number of moles

What is Avogadro’s law

Equal volumes of gases contain same number of particles at same conditions

What is standard temperature and pressure

298K and 1 atm

What is molar volume of a gas

22.4 L per mole

What does 1 mole of gas occupy

22.4 L

What is formula for moles of gas

moles = volume ÷ 22.4

What is formula for volume of gas

volume = moles × 22.4

What is unit of gas volume

Liters or dm3

Example volume of 0.5 mol gas

11.2 L

Example volume of 2g He

11.2 L

Why divide by molar mass first

To find moles

Why use 22.4 L

Convert moles to volume

What is key idea in gas calculations

Convert to moles first

What is gas volume ratio

Same as mole ratio

Example CH4 + 2O2 → CO2

Volume ratio 1

What is limiting gas

Gas that runs out first

Example gas excess

HCl left over by 40 mL

What is method for gas problems

Moles ratio then volume

What is equation for sodium and water

2Na + 2H2O → 2NaOH + H2

What is mole ratio Na to H2

2

Example hydrogen volume answer

27 L

What is conversion from mL to L

Divide by 1000

What is concentration

Amount of solute per volume

What is unit of concentration

mol/L or M

What is formula for concentration

concentration = moles ÷ volume

What is formula for moles in solution

moles = concentration × volume

What must volume be in

Liters

What is solute

Substance dissolved

What is solvent

Liquid dissolving substance

What is solution

Mixture of solute and solvent

What is aqueous solution

Solution in water

What is 1M solution

1 mole per liter

Example 1M NaOH

40g in 1L

Example 2M NaOH

80g in 1L

Example 0.5M NaOH

20g in 1L

What is first step in concentration problems

Convert volume to liters

Example 600 mL to L

0.6 L

Example concentration 0.20 mol in 600 mL

0.33 M

Example concentration 0.03 mol in 1.5 L

0.02 M

Example concentration from mass

0.25 M

What is molarity

Same as concentration

What is titration

Method to determine concentration using reaction

What equipment used in titration

Burette flask indicator

What happens in titration

Solution added until color change

What is endpoint

Point when indicator changes color

What is titre

Volume used in titration