1. Pre-Class: Ever drank acid before? P.S. You need a paper towel.
In This Lesson:
Acids and Bases
(Lesson 3 of 4)
Today is Monday, June 8th, 2015
Stuff You Need:
Calculator
Periodic Table
Polyatomic Ion List
Paper Towel
Pre-Class:
Ever drank acid before?
P.S. You need a paper towel.

2. Today’s Agenda Salts Acids and Bases pH and pOH Titrations
The many ways to think of them.
pH and pOH
Titrations
Where is this in my book?
P. 587 and following…

3. By the end of this lesson…
You should be able to define acids and bases using the Arrhenius and Brønsted-Lowry definitions.
You should be able to predict the products of a neutralization reaction.
You should be able to calculate pH, pOH, [H+], and [OH-].
You should be able to perform a titration.

4. Demo – Neutralization Reaction
Vinegar (acetic acid) and Baking Soda (a base) – relates to your homework!

5. Okay, first of all… It’s about time we discuss salt.
Salt in chemistry terms is a very specific thing.
A salt is an ionic compound formed from a neutralization reaction between an acid and a base.
So it’s not just NaCl.
More on neutralization reactions later.

6. Salts Credit to Sam L. May 2015

7. Dissociation Remember that all acids are dissolved in water (aq).
When the acid is dissolved in water, it will break down.
The process of the molecule breaking down is called dissociation.
Strong acids will dissociate completely (or nearly so).
Weak acids will not dissociate much.

8. Naming Acids [REMINDER]
First, cover the (H) and name the anion normally.
Sulfide.
Next, use this key:
Hydrosulfuric acid
Example 2-
H2S
Anion Suffix
Acid Name
-ide
Hydro___ic acid
-ate
___ic acid
-ite
___ous acid

9. Remembering Acid Names
“Ick, I ate it.”
__ic is the acid suffix for stuff otherwise ending in __ate.
“Ite, I oust it.” OR “Riteous”
__ous is the acid suffix for stuff otherwise ending in ___ite.
You’ll have to come up with something for hydro___ic acid. I’m not creative enough.

10. Practice HCl H2SO4 HClO2 Phosphoric acid
Cl- would be chloride, so it’s hydrochloric acid.
H2SO4
SO42- would be sulfate, so it’s sulfuric acid.
HClO2
ClO2- would be chlorite, so it’s chlorous acid.
Phosphoric acid
H3PO4, because “phosphoric” came from “phosphate,” which is PO43-.

11. Properties of Acids pH is lower than 7
Turn methyl orange and blue litmus paper red
Taste sour
React with active metals to produce H2
React with carbonates
Acids neutralize bases

12. Acids’ pH
Acids’ pH values are less than 7:

13. Acids Affect Indicators
Blue litmus paper turns red.
Methyl orange also turns red.

14. Acids Taste Sour Citric acid in citrus fruits.
Malic acid in sour apples.
Lactic acid in sour milk and sore muscles.
Butyric acid in rancid butter.

15. Acids React with Metals
Acids react with metals to form salts and hydrogen gas:
Mg + 2HCl  MgCl2 + H2 (g)
Zn + 2HCl  ZnCl2 + H2 (g)
Mg + H2SO4  MgSO4 + H2 (g)

16. Acids React with Carbonates
Acids react with carbonates, often forming water and carbon dioxide:
2HC2H3O2 + Na2CO3  2NaC2H3O2 + H2O + CO2

17. Acids React with Carbonates
Acid rain’s effect on marble (CaCO3) in Washington Square Park, Manhattan:
George Washington before…
George Washington after…

18. Acids Neutralize Bases
Neutralization reactions are double replacement reactions between an acid and a base.
Specifically Arrhenius acids/bases (more later).
They always produce a salt and water.
HCl + NaOH  NaCl + H2O
H2SO4 + 2NaOH  Na2SO4 + 2H2O
2HNO3 + Mg(OH)2  Mg(NO3)2 + 2H2O
Try underlining the OH and H for water.
Combine the rest to make the salt.

19. Neutralization Reaction Practice
HCl + KOH  ?
HCl + KOH  KCl + H2O
H2SO4 + Ca(OH)2  ?
H2SO4 + Ca(OH)2  CaSO4 + 2H2O
HNO3 + NaOH  ?
HNO3 + NaOH  NaNO3 + H2O
H2CO3 + 2NaOH  ?
H2CO3 + 2NaOH  Na2CO3 + 2H2O

20. Properties of Bases pH is greater than 7
Turn phenolphthalein pink and red litmus paper blue
Taste bitter, feel slippery
Bases neutralize acids

21. Bases’ pH
Bases’ pH values are greater than 7:

22. Bases Affect Indicators
Red litmus paper turns blue.
Phenolphthalein turns pink.

23. Bases Feel Slippery
They dissolve oils and fatty acids on your fingers to make soap, basically.
Get it?

24. Bases Neutralize Acids
Milk of Magnesia is an old-fashioned stomachache cure.
Contains Mg(OH)2 – magnesium hydroxide.
Magnesium hydroxide neutralizes stomach acid, producing water and magnesium chloride (a salt).
2HCl + Mg(OH)2  MgCl2 + 2H2O

25. Acid/Base Definitions
There are three different definitions of acids/bases:
We will talk mainly about two of them:
Arrhenius Acids/Bases
Acids are H+ producers in solution.
Bases are OH- producers in solution.
Brønsted-Lowry Acids/Bases
Acids are proton (H+) donors.
Bases are proton (H+) acceptors.
Lewis Acids/Bases
Acids are electron pair donors.
Bases are electron pair acceptors.

26. Acid/Base Definition Disclaimer
Svante Arrhenius
Svante Arrhenius defined acids and bases in the early 1900s.
It was a major step forward for chemistry, but today it does not explain all the known acids and bases.
However, it remains a good starting point.
Arrhenius also first described activation energy.
Side note: Arrhenius also had a keen interest in eugenics. Whoops.
Meh.

27. Arrhenius Acids H+ + H2O  H3O+
Under the Arrhenius definition of acids, you’ll also see the term H3O+.
When an Arrhenius acid dissolves, it gives off H+ ions (protons).
Many of those protons then join with existing water molecules, creating the hydronium ion (H3O+).
Thus, the presence of hydronium ions is indicative of an Arrhenius acid.
H+ + H2O  H3O+

28. A Field Guide to Arrhenius Acids and Bases
Acids have these formulas:
HX (aq)
HaXbOc (aq)
Bases are ionic compounds and contain either:
OH- (hydroxide)
CO32- (carbonate)
HCO3- (bicarbonate/hydrogen carbonate)
NH3 (ammonia) and others can be bases.
Why? Because NH3 + H2O  NH4+ + OH-

29. Brønsted-Lowry Acids and Bases
Johannes Brønsted
Thomas Martin Lowry
Two scientists independently developed the definition that acids donate protons and bases accept them:

30. Brønsted-Lowry Acids and Bases
There’s something else, though, about acids and bases under this definition. Let’s introduce it with a story:
Suppose, on your birthday, I give you a gift.
A Horse, perhaps?
Don’t look it in the mouth.
I, therefore, am the “gifter” and you are the “giftee.”

31. Brønsted-Lowry Acids and Bases
However, once I’ve given you the Horse, I am all out of gifts.
Also, you could, if you wanted, give the Horse away.
But you probably won’t.
This is just how acids and bases work under the Brønsted-Lowry definition.

32. Brønsted-Lowry Acids and Bases
An acid gives away H+ (protons).
A base accepts H+ (protons).
A conjugate base has already given away H.
A conjugate acid has already received H.
The key is to find the H transfer.
Example next slide…

33. Brønsted-Lowry Acids and Bases
NH3 + H2O  NH4+ + OH-
(the  means the reaction can go either way) H
Base
Acid
Conjugate Acid
Conjugate Base

34. Brønsted-Lowry Acids and Bases
HCl + H2O  H3O+ + Cl- H
Acid
Base
Conjugate Acid
Conjugate Base

35. Quick Vocabulary Words
In the examples we just did, water behaved as an acid in one and a base in the other.
When something can act as an acid or a base, we call it amphoteric.
When we described the different terms in the equation, one might say we were describing the species in the reaction.
Yep, there’s some biology lingo there…
Acidic protons are written in front.
So the hydrogen in C2H3O2- will not be transferred.

36. Quick Summary Arrhenius Acid: Arrhenius Base: Brønsted-Lowry Acid:
Anything that makes H+ in water.
Arrhenius Base:
Anything that makes OH- in water.
Brønsted-Lowry Acid:
Anything that donates H+.
Brønsted-Lowry Base:
Anything that accepts H+.

37. Practice
Conjugate Pairs Worksheet

38. Practice
Close your notebooks but hold the page with a worksheet or something.
Acids and Bases Review Sheet
#1-7 (TO BE DONE INDEPENDENTLY)
Circle any number you’re unsure of. When you try all 7, go back to your notebook for the circled numbers.
We’ll then “grade” it in groups – put an X next to each incorrect answer and give yourself a score.
#8-15 (TO BE DONE INDEPENDENTLY)
Repeat above procedure.
#16-23 (TO BE DONE INDEPENDENTLY)

39. pH pH is the measure of the concentration of an acid or base.
You can also measure concentration with molarity, but it’s tough.
pH is easier.
Thanks to Søren Sørensen for proposing this one in 1909.
Søren Sørensen

40. pH pH stands for “potential Hydrogen” or “power of Hydrogen.”
Basically, it’s a measure of the presence of hydrogen ions (H+), which make solutions acidic.
Don’t forget… [H+] means “concentration of hydrogen ions.”

41. Calculating pH
To calculate pH from the concentration of hydrogen ions [H+], calculate its negative logarithm:
pH = -log [H+]
To calculate [H+] from pH, use this formula:
[H+] = 10-pH
Concentration is usually in the form of molarity (M).

42. Calculating pH Examples
What is [H+] if pH = 9.9?
[H+] = = x M
[H+] in an acid solution is 1.5 x 10-3 M. What is the pH of the solution?
pH = -log [1.5 x 10-3] = 2.82
What is the pH of a solution with hydrogen ion concentration of 4.2 x M? Is it acidic or basic?
pH = -log [4.2 x 10-10] = 9.38
It’s basic.

43. Logarithm FAQ Just an FYI for the math nerds out there:
A logarithm of a number X, unless another base is specified, is the exponent by which 10 has to be raised to produce X.
They’re like backwards-powers.
In other words, log [10] = 1 because 101 = 10.
Or, log [15] = because = 15.

44. Acids, Bases, and pH Anything above 7 is basic.
Anything below 7 is acidic.
Anything at 7 is neutral.
Water (neutral) has an [H+] concentration of 1 x 10-7 M, or M.

45. Practice
pH Practice worksheet
#1, 5, 6, 7, 10

46. pOH – Bizarro World
Less frequently used is pOH, a similar but opposite scale.
<7 = Basic
>7 = Acidic
For the same substance, pH + pOH = 14.

47. pH + pOH = 14

48. Calculating pOH
To calculate pOH from the concentration of hydroxide ions [OH-], calculate its negative logarithm:
pOH = -log [OH-]
To calculate [OH-] from pOH, use this formula:
[OH-] = 10-pOH
Units are M again.

49. Calculating pOH Example
What is [OH-] if pOH = 2.3? Is it acidic or basic?
[OH-] = = 5.01 x 10-3 M
pOH is less than 7, so it’s basic.

50. Practice
pH Practice worksheet
#2-4

51. pH and pOH Summary Calculating pH and pOH:
pH = -log10[H3O+] or -log10[H+]
pOH = -log10[OH-]
Relationship between pH and pOH:
pH + pOH = 14
Finding [H+] or [H3O+] and [OH-]:
[H3O+] or [H+] = 10-pH
[OH-] = 10-pOH

52. pH and pOH Summary Acidic solutions have higher [H+] than [OH-].
Basic solutions have higher [OH-] than [H+].
Neutral solutions have equal [H+] and [OH-].

53. 10-pOH 10-pH pH and pOH Summary pH pOH 14 [H+] [OH-] 1 x 10-14
-log[H+]
10-pOH
-log[OH-]
[H+]
[OH-]
1 x 10-14

54. pH and pOH Summary

55. pH Practice (last one) Multistep pH and pOH Problems worksheet
#1, 2, 5

56. Self-Ionization of Water
Though pure water is considered a non-conductor, there is a slight but measurable conductivity due to self-ionization.
Only about one in 2 billion water molecules does this. + 
H2O
H3O+
OH- +  +

57. Ionization of Water In pure water at 25 °C:
[H3O+] = 1 x 10-7 mol/L
[OH-] = 1 x 10-7 mol/L
Which is why water’s neutral.
The concentration of acid-causing H3O+ and base-causing OH- are equal.
Fun fact: Interestingly, the neutral pH value of 7 changes with different temperatures.
Neutral pH at 100 °C, for example, is 6.14.
At 0 °C, it’s 7.47.

58. Practice
Acids and Bases Review
#24-32

59. Acid/Base Strength
Students frequently confuse pH (or pOH) with acid/base strength.
In reality, pH and pOH concern concentration, which is more about how much than about how strong.
The strength of acids and bases is a product of ionization.
TED: George Zaidan and Charles Morton – The Strengths and Weaknesses of Acids and Bases

60. More About Neutralization Reactions
Chemists frequently use neutralization reactions during the process of titration.
Titration is a way for chemists to determine the concentration of an acid or base solution using the concentration of a known solution.
During titration, the solution whose concentration is known is called the standard solution.

61. Titration Procedure
Let’s imagine that we’ve got an acid with an unknown concentration (molarity).
We’ll add a base indicator to the solution.
It shouldn’t change color because we have an acid in there.

62. Titration Procedure
We’ll then slowly add a base with a known concentration until the indicator changes color.
When the indicator changes, that tells us that the acid can no longer neutralize the base, meaning the neutralization reaction is done.
When the indicator changes color permanently, we’ve reached our endpoint (when we stop titrating).
The endpoint is close to, but not exactly, the equivalence point, which is when the acid and base have neutralized each other.

63. Titration Practice
When solving a titration problem, you need to write the balanced reaction.
Remember, acids + bases form water and a salt.
Step 1: Find the moles (using the molarity) of the known solution.
Step 2: Use a mole ratio to find the number of moles of the unknown solution.
Step 3: Calculate the molarity of the unknown solution using its volume and calculated moles.

64. Titration Problems
Typically, you’ll need to find these things in this order:
Balanced equation.
Concentration of known solution (usually given).
Moles of known solution solute.
Moles of unknown solution solute.
Concentration of unknown solution.
Generally, the problem takes the shape of:
Molarity formula for known.
Mole ratio.
Molarity formula for unknown.

65. Titration Practice Problem
A 25 mL solution of H2SO4 (sulfuric acid) is completely neutralized by 18 mL of 1.0 M NaOH (sodium hydroxide). What is the concentration of the sulfuric acid solution?
Step 1: Find the balanced equation:
H2SO4 + 2NaOH  Na2SO4 + 2H2O

66. H2SO4 + 2NaOH  Na2SO4 + 2H2O
Step 2: Find the moles of the known solution.
Remember, 25 mL of H2SO4 was neutralized by 18 mL of 1.0 M NaOH.
That means there are moles of NaOH present.
Step 3: Use a mole ratio to find moles of unknown solution.
By mole ratio, we would need moles of H2SO4 with which to react.
Step 4: Calculate the molarity of the unknown solution.
If there are moles of H2SO4 in L, that means the molarity of H2SO4 is 0.36 M.

67. Titration Practice Problem 2
If it takes 30 mL of 0.05 M HCl to neutralize 345 mL of NaOH solution, what is the concentration of the sodium hydroxide solution?
Step 1: Find the balanced equation.
HCl + NaOH  NaCl + H2O

68. HCl + NaOH  NaCl + H2O Step 2: Find the moles of the known solution.
0.030 L of 0.05 M HCl = mol HCl
Step 3: Use a mole ratio to find moles of unknown solution.
1 mol HCl reacts with 1 mol NaOH.
Therefore we are neutralizing mol NaOH.
Step 4: Calculate the molarity of the unknown solution.
mol / .345 L = M NaOH

69. Organization
One thing that really helps these problems is to be organized.
You’ll have to find the method that works for you, but I’ll show you the one that works for me.

70. HCl + NaOH  NaCl + H2O KNOWN – HCl 30 mL = 0.03 L 0.05 M
mol HCl
UNKNOWN – NaOH
345 mL = L
? M
mol NaOH
M NaOH

71. Practice Titration Practice Problems Acids and Bases Review Sheet #1
#2-5
Acids and Bases Review Sheet
#33

72. Titration Lab
“My lab is…extra vinegary.”

73. Closure: Titration Joke
Get it?

74. Closure: Titration Boss
You use two burets for a titration.
One measures out the unknown – a sample of HCl. The initial buret reading is 5 mL and the final reading is 19.2 mL.
The other measures out the standard solution – 1.0 M NaOH. The initial buret reading is 2 mL. At endpoint, the final buret reading is 14.8 mL.
What is the concentration of the HCl?

75. Closure: Titration Boss
Equation: HCl + NaOH  NaCl + H2O
HCl volume = 19.2 mL – 5 mL = 14.2 mL
HCl concentration = ? M
NaOH volume = 14.8 mL – 2 mL = 12.8 mL
NaOH concentration = 1.0 M
mol NaOH = mol HCl
mol HCl in L = 0.90 M HCl

76. Closure Why is water neutral on the pH scale?
When water dissociates, it forms an H+ ion, making it acidic, and an OH- ion, making it basic.
The protons and hydroxide ions cancel one another out.