Unit 14: Acids & Bases Chapter 19. Review: Naming an Acid Binary acids (H + nonmetal): hydro...
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Transcript of Unit 14: Acids & Bases Chapter 19. Review: Naming an Acid Binary acids (H + nonmetal): hydro...
Unit 14: Acids & Bases
Chapter 19
Review: Naming an Acid
Binary acids (H + nonmetal): hydro ______ic acid
Ternary acids (H + polyatomic ion): –ate ions: _________ic acid –ite ions: _________ous acid
Name the following acids: HBr H2SO3
H3PO4
Write the formulas for the following acids: Hydrosulfuric acid Nitrous acid Chromic acid
Definition of Bronsted-Lowry Acid
A chemical species that is able to lose or "donate" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)
Acid loses a hydrogen ion
Properties of Acids
Taste sour Corrosive Feel watery Are electrolytes: conduct an electrical current by
forming H+ ions in solution
pH < 7
Review: Naming a Base
Formula is name + “hydroxide”: Metal + OH-
Ammonium + OH-
Name the following bases: NaOH NH3
Ca(OH)2
Write the formulas for the following bases: Magnesium hydroxide Aluminum hydroxide Lithium hydroxide
Definition of Bronsted-Lowry Base
A chemical species that is able to gain or "accept" a hydrogen ion (aka proton because the H+ contains no electrons or neutrons)
Base gains a hydrogen ion
Properties of Bases
Taste bitter Corrosive Feel slippery Are electrolytes: conduct an electrical current by
forming OH- ions in solution
pH > 7
Indicators
Indicators: organic substances that change colors in an acid or a base (sometimes paper, sometimes liquids)
Acids turn… Litmus paper – red Phenolphthalein – clear Universal indicator – red/orange
Bases turn… Litmus paper – blue Phenolphthalein – pink Universal indicator – blue
Household Items& the pH Scale
pH and pOH Scale
Measured on a numeric scale from 0-14 This scale number indicates ion concentration of a solution
It is much easier to work numbers 0-14 than with than the actual range of 1 to 10–14 (0.00000000000001)
In an acidic solution, [H+] > [OH-] In a basic solution, [H+] < [OH-] pH + pOH = 14
pH pOH
Stands for “power of hydrogen”
Stands for “power of hydroxide”
Shows the [H+] in a solution
Shows the [OH-] in a solution
pH = -log[H+] pOH = -log[OH-]
pH and pOH Scale
[H+] and [OH-] are inverses: the exponents always add up to -14 Ex: If [H+] = 1.0x10-3M, then [OH-] = 1.0x10-11M
pH and pOH Calculations
Notice the relationship between concentration and the pH / pOH value: Toothpaste has a hydrogen ion concentration of
10–10M, so its pH is 10.
pH = -log[10-10] = 10 Pure water, which is neutral, has a pH of 7. That
means its hydrogen ion concentration is 10–7M.
7 = -log[H+] ; [H+] = 10-7
pH & pOH Practice
1. In a NaOH solution the pH = 11. What is the [H+] of the solution?
2. If a substance’s pH = 3, what is the pOH?
3. Find the pH and pOH of a 0.1M HNO3 solution.
n If the [H+] = 1x10-4M, what is the [OH-]? What is the pH and pOH?
11 = -log[H+] ; [H+] = 10-11 M
3 + pOH = 14 ; pOH = 11
pH = -log[0.1] = 1
1 + pOH = 14 ; pOH = 13
1x10-4 + [OH-] = 1x10-14 ; [OH-] = 1x10-10
pH = -log[1x10-4] = 4 & pOH = -log[1x10-10] = 10
(once you get pH, you can just subtract from 14 to get pOH)
Strength of Acids and Bases
Determined by how much they ionize (dissociate) in water
Strong – ionize 100% in water Weak – only partially ionize in water
a) Complete dissociation - all HCl compounds have separated into H+ and Cl- ions
b) Partial dissociation - some HNO2 compounds have separated into H+ and NO2
- ions, while some remain together
Strength of Acids and Bases
The terms weak and strong are used to compare the strengths of acids and bases
The terms dilute and concentrated are used to compare the concentration of solutions
They do not mean the same thing!
The combination of strength and concentration ultimately determines the behavior of the acid or base.
Strength of Acids and Bases
Strong Acids: Only HNO3, HI, HBr, HCl, H2SO4, HClO4
Remember: NO, I Brought Claude SOme ClOthes All other acids are weak, and remain in equilibrium
Ex: HNO2 ↔ H+ + NO2-
Strong Bases: Group I or II metals
Ex: NaOH, Mg(OH)2…etc.
All other bases are weak, and remain in equilibrium Ex: NH3 + H2O ↔ NH4
+ + OH-
Conjugate Acids & Bases
Conjugate acids are formed when a base accepts a proton (H+)
Conjugate bases are formed when an acid donates a proton (H+)
Conjugate Strength
Strong Acid = weak conjugate base Strong Base = weak conjugate acid
Weak Acid = strong conjugate base Weak Base = strong conjugate acid
Example:HCl + NH3 → Cl- + NH4
+
(strong acid) (weak base) (weak conjugate base) (strong conjugate acid)
Conjugate Practice
Label the acid (A), base (B), conjugate acid (CA) & conjugate base (CB).
1. NH3 + HNO3 → NH4+ + NO3
-
2. CH3OH + NH2- → CH3O- + NH3
3. OH- + H3O+ → H2O + H2O
4. NH2- + H2O → NH3 + OH-
B A CA CB
A B CB CA
B A CA CB
B A CA CB
Neutralization
Neutralization: the reaction of an acid and a base; products are salt and water Example: consuming antacid products, which
are basic, neutralizes stomach acid
Neutralization
Example: sodium hydroxide (base) and hydrochloric acid (acid) react to form sodium chloride (salt) and water.
Neutralization Practice
Neutralizations are double displacement reactions!Practice predicting products (always a salt and water):
Example #1__Ca(OH)2 + __H3PO4 → ?
Example #2
__Fe(OH)2 + __HBr → ?
__Ca(OH)2 + __H3PO4 → __Ca3(PO4)2 + __H2O3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O
__Fe(OH)2 + __HBr → __FeBr2 + __H2O
Fe(OH)2 + 2HBr → FeBr2 + 2H2O
Titration
1. An indicator (phenolphthalein) is added to the standardized acid (acid of known concentration).
2. The unknown base is added until the solution is neutralized and reaches the equivalence point (where [H+] is equal to [OH-]).
3. Adding one more drop of base changes the color of the solution to pink. This is called the endpoint.
* The equivalence point is not necessarily the midpoint, or the point where pH = 7
Titration – determining the concentration of a base by using an acid whose concentration is known.
Titration Calculations
MaVa(#H+) = MbVb(OH-) M = concentration (molarity) V = volume (L or mL) (#H+ or OH-) = number of ions
Example: It took 75mL of NaOH to neutralize 50mL of 2M HCl. What is the concentration of the NaOH?
MaVa(#H+) = MbVb(#OH-)
(2M)(50mL)(1) = (x)(75mL)(1)
x = 1.33M NaOH
Titration Practice
Practice: It took 20mL of Ca(OH)2 to neutralize 25mL of 0.05M HCl. What is the concentration of the base?
MaVa(#H+) = MbVb(#OH-)
(0.05M)(25mL)(1) = (x)(20mL)(2)
x = 0.031 M
Definition of Arrhenius’ Acids & Bases
Acids/bases are determined by what type of ions they produced Arrhenius Acids produce H+ ions in solution
Monoprotic acids – have 1 ionizable hydrogen Diprotic acids – have 2 ionizable hydrogens Triprotic acids – have 3 ionizable hydrogens
Arrhenius Bases produce OH- in solution
Produces H+ ions in solution
Produces OH- ions in solution