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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:
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
