Chapter 5 A Matter of Concentration. Ionic Phenomena = Things that happen to ions, which can be...

Chapter 5A Matter of Concentration

Ionic Phenomena

= Things that happen to ions, which can be observed

What is matter?

STUFF!http://www.youtube.com/watch?v=tBQcpF_j5Xg

Matter can be found in 3 states:

http://www.youtube.com/watch?v=HAPc6JH85pM

Matter can be categorized 5 ways!

Matter

Element

Compound

Pure substances Mixtures

Homogeneous mixtures

Suspensions

Heterogeneous mixtures

Element

• Substances on the periodic table• Made up of identical atoms

100% copper wire (Cu) Pure gold (Au)

More elements

Chlorine gas (Cl2)

Compound

• A substance which contains different atoms

Water (H2O)

Sugar (C12H22O11)

Salt (NaCl)

Mixtures

Contain two or more different elements or compounds, physically mixed together

Homogenous Mixtures

To the naked eye, looks like one substance (completely uniform)

Salt water – looks clear like pure water

Vinegar is a mixture of acetic acid (CH3COOH) and water (H2O)

Brass – looks like a pure metal, but it’s a mixture of copper and zinc

Solution = Liquid homogenous

mixture

Sterling silver – mixture of silver and copper

Plumber’s solder – mixture of lead and tin

Stainless steel – mixture of iron, carbon, chromium, and nickel

Air!

Heterogeneous MixturesTo the naked eye, it looks like it’s made of two or more substances – an obvious mixture

These substances can be taken apart into their original components

AsphaltDirt

Concrete

The dreaded fruitcake!

SuspensionsBetween homogenous and heterogenous mixtures

– tiny solid bits floating around in liquid

Murky water

Tomato juice – miniscule tomato particles floating in

water

Strawberry milkshake

And now, onto

Solutions

Milk is a suspension

The percentage (1%, 2%, 3.25%) means that it contains that much milk fat, and the rest is water

Most of the milk is made of water

Water = solvent (what the milk fat is dissolved into)Milk fat = solute (particles dissolved into solvent)

Milk in carton = solution (total volume = solvent + solute)

Most of the milk is made of water

Highest percentage = Highest concentration of milk fat

Most of the milk is made of water

The higher the percentage of milk fat (solute), the less water is needed as a solvent

Most of the milk is made of water

In 1L of 1% milk: 10ml milk fat , 990ml waterIn 1L of 2% milk: 20ml milk fat , 980ml water

In 1L of 3.25% milk: 32.5ml milk fat , 967.5ml water

Concentration

Concentration of milk = amount of milk fatamount of milk

Concentration

Concentration of milk = amount of milk fatamount of milk

Concentration equation

Concentration (c) = Solute mass (m)solution volume (V)

C = m V

C g/L m g V L

Making salt water

If you add 1g of NaCl to 1 L of water, you get:

C = 1 g = 1 g/L1 L

1 g/L aqueous solution of NaCl

Making salt water

If you add 10g of NaCl to 1 L of water, you get:

C = 10 g = 10 g/L1 L

10 g/L aqueous solution of NaCl

Making salt water

If you add 10g of NaCl to 500 mL of water, you get:

C = 10 g = 20 g/L0.5 L

20 g/L aqueous solution of NaCl

Remember: 1000ml = 1L

Arrange these solutions from lowest to highest concentration

Solution # grams of sugar

# Litres of solution

Concentration (g/L)

A 3 g 1 LB 5 g 0.5 LC 8 g 4 LD 7 g 3 L

Arrange these solutions from lowest to highest concentration

Solution # grams of sugar

# Litres of solution

Concentration (g/L)

A 3 g 1 L 3 g/LB 5 g 0.5 L 10 g/LC 8 g 4 L 2 g/LD 7 g 3 L 2.3 g/L

Solution C Solution D Solution A Solution B

Which salt solution is most concentrated?

Solution # grams of salt

# Litres of solution

Concentration (g/L)

A 10 g 400 mlB 0.5 kg 1.5 LC 0.2 kg 800 ml

Which salt solution is most concentrated?

Solution # grams of salt

# Litres of solution

Concentration (g/L)

A 10 g 400 ml 25g/LB 0.5 kg 1.5 L 333.3g/LC 0.2 kg 800 ml 250g/L

C = m ÷ V = 10g ÷ 0.4L = 25g/LC = m ÷ V = 0.5kg ÷ 1.5L = 500g ÷ 1.5L = 333.3g/LC = m ÷ V = 0.2kg ÷ 0.8L = 200g ÷ 0.8L = 250g/L

Different ways to say numbers of stuff

12 eggs = 1 dozen eggsA score of years = 20 years

Avogadro’s number = 602, 000, 000, 000, 000, 000, 000, 000

= 6.02 x 1023 molecules = One mole

Mole!Quick lesson on the mole and Avogadro’s

number: http://www.youtube.com/watch?v=TEl4jeETVmg

Molar mass

An element’s atomic mass (in grams) has one mole of that element’s atoms

Atomic mass of Fluorine = 18.998 U Molar mass of Fluorine = 18.998g (round to 19g)

= 1 mole of Fluorine atoms

Symbol for mole = mol

Molar mass

An molecule’s atomic mass (in grams) has one mole of that molecule’s atoms

Atomic mass of water (H20) = (2 x 1.008) + 15.999

= 18.015 U Molar mass of H20 = 18.015 g (round to 18 g)

= 1 mole of water molecules

The Mole equation

Number of moles (n) = mass of solute (m)Molar mass (mm)

n = m mm

n mol m g mm g (per mol)

How many moles of atoms are in 444g of radon (Rn)?

Step 1. Find the atomic mass of Radon

Rn86

Radon222.018

Atomic mass = 222.018 U

Step 2. Make the atomic mass into grams per mole (molar mass) of Rn

Rn86

Radon222.018

Molar mass = 222.018 g 222 g

Step 3. Find out the number of moles using the mole equation

Mass (m) = 444 gMolar mass (mm) = 222.018 g 222 g

mmn = m

222 g/moln = 444 g

n = 2 moles of radon

How many moles are in 591g of gold (Au)?

Step 1. Find the atomic mass of Gold

Au79

Gold196.967

Atomic mass = 196.967 U

2.4

Step 2. Make the atomic mass into grams per mole (molar mass) of Au

Au79

Gold196.967

Molar mass = 196.967 g 197 g

2.4

Step 3. Find out the number of moles using the mole equation

Mass (m) = 571 gMolar mass (mm) = 196.967 g 197 g

mmn = m

197 g/moln = 571 g

n = 3 moles of gold

Steps to find the number of moles of an element/compound

Step 1. Find the atomic mass of the element/compound

Step 2. Make the atomic mass into grams per mole (molar mass)

Step 3. Find out how many moles are in the given weight of the element/compound using the mole equation

These calculations also work with compounds!

How many moles are in 16.3 g of magnesium bromide (MgBr2)?

Step 1. Find the atomic mass of MgBr2

Mg12

Magnesium24.305

Atomic mass = 24.305 + 2(79.904) = 184.113 U

Br35

Bromine79.904

1.2 2.8

Step 2. Make the atomic mass into grams per mole (molar mass) of MgBr2

Mg12

Magnesium24.305

Molar mass = 184.113 g 184.1 g

Br35

Bromine79.904

1.2 2.8

Step 3. Find out the number of moles using the mole equation

Mass (m) = 16.3gMolar mass (mm) = 184.113 g 184.1 g

mmn = m

184.1 g/moln = 16.3 g

n = 0.089 moles of MgBr2

Molar concentration (Molarity)

Molar concentration (C) = # moles of solute (n)volume of solution (V)

C = n V

C mol/L n mol V L

A solution of 800ml contains 2 moles of NaCl. What is the molar

concentration of the solution?

There is only one step: Calculate M!

VC = n = 2 mol = 2.5 mol/L = 2.5 M

0.800L

A chemist wants to prepare a 1.25M aqueous solution of Ca(NO3)2. She has 82g of calcium nitrate. Calculate the maximum

volume that the chemist can prepare.

A chemist wants to prepare a 1.25M aqueous solution of Ca(NO3)2. She has 82g of calcium nitrate. Calculate the maximum

volume that the chemist can prepare.

Molarity = Molar concentration

Compound: Can use to get molar mass

Mass of soluteWhat we’re looking for: Volume (L)

Step 1. Write down what you have, and what you want

We have: C = 1.25 M = 1.25 mol/Lmass of solute = 82 gsolute = Ca(NO3)2

We want:Volume of solution (L) = ?

Step 2. Find the molar mass of Ca(NO3)2

N7

Nitrogen14.007

Molar mass = 40.078 + 2(14) + 6(16) = 164.086 g 164.1 g/mol

O8

Oxygen15.999

3.0 3.5

Ca20

Calcium40.078

1.0

CaN2O6

Step 3. Find out the number of moles using the mole equation

Mass (m) = 82 gMolar mass (mm) = 164.086 g 164.1 g

mmn = m

164.1 g/moln = 82 g

n = 0.5 moles of Ca(NO3)2

Step 4. Plug in values to calculate the volume of the solution

VC = n

Step 4. Plug in values to calculate the volume of the solution

VC = n

V1.25 mol/L = 0.50 mol

Step 4. Plug in values to calculate the volume of the solution

VC = n

V1.25 mol/L = 0.50 mol

cross-multiply

Step 4. Plug in values to calculate the volume of the solution

VC = n

V1.25 mol/L = 0.50 mol

cross-multiply

1.25 mol/L (V) = 0.50 mol

Step 4. Plug in values to calculate the volume of the solution

VC = n

V1.25 mol/L = 0.50 mol

cross-multiply

1.25 mol/L (V) = 0.50 mol1.25 mol/L1.25 mol/L

Step 4. Plug in values to calculate the volume of the solution

VC = n

V1.25 mol/L = 0.50 mol

cross-multiply

1.25 mol/L (V) = 0.50 mol1.25 mol/L1.25 mol/L

V = 0.40 L

How to solve Molarity problems

Step 1. Write down what you have, and what you want

Step 2. Find the molar mass of the element/compound

Step 3. Find out the number of moles using the mole equation

Step 4. Plug values into the molarity equation

What if you need another concentration than what you have?

They have to dilute it themselves

This also saves $$ – chemicals are expensive!

They mostly buy the really concentrated ones

Back to the milk example

In 1L of 1% milk: 10ml milk fat , 990ml waterIn 1L of 2% milk: 20ml milk fat , 980ml water

In 1L of 3.25% milk: 32.5ml milk fat , 967.5ml water

If you really wanted to, you could buy 3.25% milk and add water until it had a concentration of 1%

If only you knew the dilution equation...

Dilution equation

Higher Concentration sol’n (C1) x Its Volume (V1)

Lower Concentration sol’n (C2) x Its Volume (V2)

C1V1 = C2V2

C1, C2 mol/L V1, V2 L

=

sol’n = solution

Using a stock solution of 17.5 mol/L, you want to prepare 500 ml of a 1.00 mol/L acetic acid solution (CH3COOH). What

volume of stock solution will you need?

Using a stock solution of 17.5 mol/L, you want to prepare 500 ml of a 1.00 mol/L acetic acid solution (CH3COOH). What

volume of stock solution will you need?

Higher concentration solution (C1)

Higher concentration sol’n

= stock solution

Lower concentration solution (C2)

What we’re looking for: V1 = Volume of C1

Solute

V2= Volume of C2

Step 1. Write down what you have, and what you want

We have: C1 = 17.5 mol/L

V2 = 500 ml = 0.5 L

C2 = 1.00 mol/L

solute = CH3COOH

We want:V1 = ?

Step 2. Plug values into dilution equation

C1V1 = C2V2

Step 2. Plug values into dilution equation

C1V1 = C2V2

(17.5 mol/L) (V1) = (1.00 mol/L) (0.5 L)

Step 2. Plug values into dilution equation

C1V1 = C2V2

(17.5 mol/L) (V1) = (1.00 mol/L) (0.5 L)

17.5 (V1) = 0.5

Step 2. Plug values into dilution equation

C1V1 = C2V2

(17.5 mol/L) (V1) = (1.00 mol/L) (0.5 L)

17.5 (V1) = 0.517.5 17.5

Step 2. Plug values into dilution equation

C1V1 = C2V2

(17.5 mol/L) (V1) = (1.00 mol/L) (0.5 L)

17.5 (V1) = 0.517.5 17.5

V1 = 0.0286 L = 28.6 mL

Steps to solving a dilution problem

Step 1. Write down what you have, and what you want

Step 2. Plug values into dilution equation

pH scale

Used to test the strength of an acid or base

(Back to the)

Acid: pH less than 7

Neutral: pH exactly 7

Base: pH more than 7

The pH of various substancesSubstance pH (approximate)

Sulphuric acid (H2SO4) 0Hydrochloric acid (HCl), 0.1 M 1.0

Vinegar (CH3COOH) 2.2Soft drinks, wine, beer 3.0

Apples 3.1Black coffee 5.0

Soap 10.0Household ammonia 11.1

Depilatory cream 12.0Sodium hydroxide (NaOH), 0.1 M 13.0

The pH of various substancesSubstance pH (approximate)

Sulphuric acid (H2SO4) 0Hydrochloric acid (HCl), 0.1 M 1.0

Vinegar (CH3COOH) 2.2Soft drinks, wine, beer 3.0

Apples 3.1Black coffee 5.0

Soap 10.0Household ammonia 11.1

Depilatory cream 12.0Sodium hydroxide (NaOH), 0.1 M 13.0

How can HCl be only twice as acidic than vinegar?

The way pH is calculated is not linear

pH Scale – How it works

• The pH scale works by powers of 10.

• That means that an acid with pH 1 has 10 times more H+ ions than pH 2. (10 times stronger acid)

• The left side shows how many times more H+ one pH has compared to another.

What does pH actually mean?What does it measure?

pH = potential of Hydrogen = H+ ion concentration of a solution

(M or mol/L)

H+ ion concentration (M) Exponential notation (M) pH1.0 1 x 100 00.1 1 x 10-1 1

0.01 1 x 10-2 20.001 1 x 10-3 3

0.0001 1 x 10-4 40.00001 1 x 10-5 5

0.000001 1 x 10-6 60.0000001 1 x 10-7 7

0.00000001 1 x 10-8 80.000000001 1 x 10-9 9

0.0000000001 1 x 10-10 100.00000000001 1 x 10-11 11

0.000000000001 1 x 10-12 120.0000000000001 1 x 10-13 13

0.00000000000001 1 x 10-14 14

So if the pH of a solution is 2, it has an H+ concentration of

1 x 10-2 mol/L= 0.01 mol/L

How do chemists find the actual pH of a solution?

Litmus paper is not that accurateIt just tells you if it’s an acid or a base

Acid-base indicators

Different substances change colour at a precise pHUsed together, they can give the approximate pH

of a substance

bromophenol blue

methyl red

universal

resazurin

bromocresol purple

phenolphthalein

Turning point = when the indicator changes colour

Turning Point – Methyl Red

• Let’s see what happens when we use Methyl Red. MR is a liquid. If we put a few drops into each beaker, we’ll see what happens.

pH 0 pH 1 pH 2 pH 3 pH 4 pH 5 pH 6

pH 8 pH 9 pH 10 pH 11 pH 12 pH 13 pH 14

pH 7

Turning Point – Methyl Red

• So what is the turning point of Methyl Red?

pH 0 pH 1 pH 2 pH 3 pH 4 pH 5 pH 6

pH 8 pH 9 pH 10 pH 11 pH 12 pH 13 pH 14

pH 7

Turning Point

Turning Point – phenolphthalein

• Let’s see what happens when we use phenolphthalein If we put a few drops into each beaker, we’ll see what happens.

pH 0 pH 1 pH 2 pH 3 pH 4 pH 5 pH 6

pH 8 pH 9 pH 10 pH 11 pH 12 pH 13 pH 14

pH 7

Turning Point – phenolphthalein

• So what is the turning point of phenolphthalein?

pH 0 pH 1 pH 2 pH 3 pH 4 pH 5 pH 6

pH 8 pH 9 pH 10 pH 11 pH 12 pH 13 pH 14

pH 7Turning Point

pH paper = Universal indicator

Here, the universal indicator paper is dipped in the solution and compared to the colours

What is the pH range of this solution? Indicator Colour change Turning point

Phenol red yellow red 6.4 – 8.2Bromophenol blue yellow violet 3.0 – 4.6

Indigo carmine blue yellow 12.0 – 14.0Bromothymol blue yellow blue 6.0 – 7.6

This solution is yellow in phenol red, violet in bromophenol blue,

blue in indigo carmine and yellow in bromothymol blue

What is the pH range of this solution? Indicator Colour change Turning point

Phenol red yellow red 6.4 – 8.2Bromophenol blue yellow violet 3.0 – 4.6

Indigo carmine blue yellow 12.0 – 14.0Bromothymol blue yellow blue 6.0 – 7.6

This solution is yellow in phenol red (pH < 6.4) violet in bromophenol blue (pH > 4.6)

blue in indigo carmine (pH < 12.0)and yellow in bromothymol blue (pH < 6.0)

pH of solution: 4.6 – 6.0