Acids & Bases Acids and Bases are found in many everyday items, like foods, cleaners, and medicines. Weak acids are strong bases; strong acids are weak.

Acids & Bases Acids and Bases are found in many everyday items, like foods, cleaners, and medicines. Weak acids are strong bases; strong acids are weak bases.

General Properties ACIDS BASES sour taste bitter taste pH below 7
pH above 7 react with metals to form H2 gas slippery feel vinegar, milk, soda, apples, citrus fruits ammonia, lye, antacid, baking soda ChemASAP

HCl + H2O  H3O+ + Cl– – + Definitions
In aqueous solution… Acids form hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– H Cl O – + acid

NH3 + H2O  NH4+ + OH- – + Definitions Bases form hydroxide ions (OH-)
In aqueous solution… Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- H N O – + base

Types of Acids/Bases Arrhenius Acids/Bases
• Acids release H+ into water • Bases release OH- into water Ex: Acid: HCl (aq) H+ (aq) + Cl- (aq) Base: NaOH (aq) Na+ (aq) + OH- (aq) Monoprotic = acid that contain 1 proton (H+) Ex.) HBr Diprotic = acids that contain 2 protons (2H+) Ex.) H2SO4

Bronsted-Lowry Acids/Bases
• Acid = Proton H+ Donor • Base = Proton H+ Acceptor Ex: NH3 + H2O  NH4+ + OH- NH3 - base HOH - acid NH4+ - conjugate acid (formed when base gains H+) – usually positively charged OH- - conjugate base (formed when acid loses an H+) – usually negatively charged

Proton-Transfer Reactions—Direction and Strength
The extent to which a proton-transfer reaction takes place depends on the strength of the acids and bases involved in the reaction. Weak acids/bases do not ionize completely, so they tend to re-form in aqueous solution. Therefore, the reactions those compounds undergo with water are reversible. When a strong acid or base reacts with water in aqueous solution, a non-reversible (single-direction) reaction occurs. Example: the strong acid HCl ionizes completely in water due to its high polarity once it is broken apart, it does not reform, hence the single-sided arrow pointing to the right. The reason HCl (and all other strong acids) do not re-form is because the conj. bases they make are very weak and have trouble re-gaining the proton from the conj. acid. Therefore, when a strong acid (or base) breaks up, it does not re-form again, so we say it “ionizes/dissociates completely.” HCl H2O Cl H3O+

Two important rules about proton-transfer reactions can be made:
The stronger an acid is, the weaker its conj. base will be; the stronger a base is, the weaker its conj. acid will be Proton-transfer reactions tend to favor the production of the weaker acid/base

Ionization of Water When compounds dissociate/ionize in an aqueous solution, they produce ions - hydronium (H3O+) and hydroxide (OH-) These ion concentrations can be expressed more easily as [H3O+] = 1.0 x 10-7 M and [OH-] = 1.0 x 10-7 M. The brackets indicate “concentration of” in Molarity (M).

Kw = [H3O+][OH-] = 1.0  10-14 H2O + H2O H3O+ + OH-
Ionization of Water H2O + H2O H3O+ + OH- Kw = [H3O+][OH-] = 1.0  10-14

pH of Common Products

: measures acidity/basicity
pH scale : measures acidity/basicity ACID BASE 10x 100x 10x 10x NEUTRAL Each step on pH scale represents a factor of 10. pH 5 vs. pH (10X more acidic) pH 3 vs. pH (100X different) pH 8 vs. pH (100,000X different)

Ionization of Water Find the hydroxide ion concentration of 3.0  10-2 M HCl. [H3O+][OH-] = 1.0  10-14 [3.0  10-2][OH-] = 1.0  10-14 [OH-] = 3.3  M Acidic or basic? Acidic

The pH Scale pH – of a sol’n is the negative of the common logarithm of the hydronium ion concentration [H3O+]. pOH - of a sol’n is the negative of the common logarithm of the hydroxide ion concentration [OH-].

pouvoir hydrogène (Fr.)
pH Scale 14 7 INCREASING ACIDITY INCREASING BASICITY NEUTRAL pH = -log[H3O+] pouvoir hydrogène (Fr.) “hydrogen power”

pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14
pH Scale pH = -log[H3O+] pOH = -log[OH-] pH + pOH = 14

pH Scale What is the pH of 0.050 M HNO3? pH = -log[H3O+]
Acidic or basic? Acidic

pH Scale What is the molarity of HBr in a solution that has a pOH of 9.6? pH + pOH = 14 pH = 14 pH = 4.4 pH = -log[H3O+] [H3O+] = 10-pH [H3O+] = [H3O+] = 4.0  10-5 M HBr Acidic

The pH Scale Basic pH and pOH calculations: pH = -log[H3O+]
pOH = -log[OH-] pH = 14 – pOH pOH = 14 – pH Calculating pH from [H3O+] Determine concentration of [H3O+] using Kw formula. Determine pH using logarithm formula. Calculating pOH from [OH-] Determine concentration of [OH-] using Kw formula. Determine pOH using logarithm formula.

Example pH (pOH) calculations
If you had a sol’n with the concentration of M [H3O+], what is the sol’ns pH? What is the sol’ns pOH? 1. Given: [H3O+] = M Unknown: pH = ?? pH = -log [H3O+] = -log[0.025M] = 1.6 pOH = 14 – pH = = 12.4

B. What is the pH of M HNO3? Is it acidic or basic? pH = -log[H3O+] pH = -log[0.050] = 1.3 It is acidic because 1.3  7.

C. What is the pH of a M HCl sol’n? Given: Identity Concentration: [0.100 M] Unknown: pH = ???? 2. [H3O+] = M pH = -log[0.100 M] = 1.00

D. What is the pH of a 1.5 M sol’n of KOH? 1. Given: Identity Concentration: [1.5 M] Unknown: pH = ???? 2. [OH-] = 1.5 M [H3O+] = 1.0 x M2/[OH-] = 1.0 x M2/[1.5 M] = 6.7 x 10-15M pH = -log[H3O+] = -log[6.7 x 10-15M] = 14.17 Check : Answer does indicate that KOH forms a sol’n pH  7, which is basic.

E. Determine the hydronium concentration and the hydroxide concentration of an aqueous sol’n that has a pH of 5.6. 1. Given: pH = 5.6 Unknown: [H3O+] = ???? [OH-] = ???? 2. [H3O+] = 10-pH = = 2.5 x 10-6 M [OH-] = 1.0 x M2/[H3O+] = 1.0 x M2/[2.6 x 10-6] = 3.8 x 10-9 M Check: The pH is acidic, therefore it should be found that the [H3O+]  [OH-]. Yes it is.

F. What is the molarity of HBr in a solution that has a pOH of 9.6? 1. Given: pOH = 9.6 Unknown: pH = ???? [H3O+] = ???? 2. pH + pOH = 14 pH = 14 – 9.6 = 4.4 [H3O+] = 10-pH = = 4.0 x 10-5 M

The Three Acid/Base Theories
Arrhenius Bronsted-Lowry Lewis

A Comparison b/w acid-base theories
Type Acid Base Arrhenius H+ or H3O+ producer OH- producer Bronsted-Lowry Proton donor (H+) Proton acceptor (H+) Lewis Electron-pair acceptor Electron-pair donor

HCl + H2O  H3O+ + Cl– – + B. Definitions
Arrhenius - In aqueous solution… Acids form hydronium ions (H3O+) HCl + H2O  H3O+ + Cl– H Cl O – + acid

NH3 + H2O  NH4+ + OH- – + B. Definitions
Arrhenius - In aqueous solution… Bases form hydroxide ions (OH-) NH3 + H2O  NH4+ + OH- H N O – + base

HCl + H2O  Cl– + H3O+ B. Definitions acid conjugate base base
Brønsted-Lowry Acids are proton (H+) donors. Bases are proton (H+) acceptors. HCl + H2O  Cl– + H3O+ acid conjugate base base conjugate acid

B. Definitions H2O + HNO3  H3O+ + NO3– B A CA CB

Amphoteric - can be an acid or a base.
B. Definitions NH3 + H2O  NH4+ + OH- B A CA CB Amphoteric - can be an acid or a base.

Polyprotic - an acid with more than one H+
B. Definitions Give the conjugate base for each of the following: HF H3PO4 H3O+ F - H2PO4- H2O Polyprotic - an acid with more than one H+

Br - HSO4- CO32- HBr H2SO4 HCO3- B. Definitions
Give the conjugate acid for each of the following: Br - HSO4- CO32- HBr H2SO4 HCO3-

Range and Color Changes of Some Common Acid-Base Indicators
pH Scale 1 2 3 4 5 6 7 8 9 10 11 12 13 14 Indicators Methyl orange red – yellow Methyl red red yellow Bromothymol blue yellow blue Neutral red red yellow From F. Brescia et al., Chemistry: A Modern Introduction, W. B. Saunders Co., 1978. Adapted from R. Bates, Determination of pH, Theory and Practice, John Wiley & Sons, Inc., New York, 1964. Phenolphthalein colorless red colorless beyond 13.0

Common pH Indicators Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 520

Edible Acid-Base Indicators
COLOR CHANGES AS A FUNCTION OF pH INDICATOR pH RED APPLE SKIN BEETS BLUEBERRIES RED CABBAGE CHERRIES GRAPE JUICE RED ONION YELLOW ONION PEACH SKIN PEAR SKIN PLUM SKIN RADISH SKIN RHUBARB SKIN TOMATO TURNIP SKIN * Source: Volume 62, Number 4, April 1985 pg 285 (Not sure of magazine title) *YELLOW at pH 12 and above

Phenolphthalein Indicator
Colorless = Acidic pH Pink = Basic pH

Acid-Base Neutralization
1+ 1- + + Hydronium ion Hydroxide ion H3O+ OH- Water H2O Water H2O Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 584

Acid-Base Neutralization
1+ 1- + + H3O+ OH- H2O H2O Hydronium ion Hydroxide ion Water Water Dorin, Demmin, Gabel, Chemistry The Study of Matter 3rd Edition, page 584

Titration Acids and bases sometimes react in a 1:1 mole ratio.
HCL(aq) + NaOH(aq)→ NaCl(aq) + H2O(l) When sulfuric acid and sodium hydroxide react…the ratio is 1:2. H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l) This acid - base mole ratio from the balanced equation is a conversion factor used when neutralizing an acid or a base

Titration – using mole ratios…
How many moles of sulfuric acid would you require to neutralize 0.50 mol of sodium hydroxide? STEP 1: Write the balanced equation for the rxn to find acid:base mol ratio H2SO4(aq) + 2NaOH(aq) → Na2SO4(aq) + 2H2O(l) STEP 2: Use the mole ratio to calculate the necessary number of moles of H2SO4 0.50 mol NaOH x 1 mol H2SO4 = 0.25 mol H2SO4 2 mol NaOH

Titration – Your Turn  How many moles of sodium hydroxide are required to neutralize 0.20 mol of nitric acid? STEP 1: NaOH + HNO3 → NaNO3 + H2O STEP 2: 0.20 mol HNO3 x 1 mol NaOH 1 mol HNO3 ANSWER: 0.20 mol NaOH needed How many moles of potassium hydroxide are needed to neutralize 1.56 mol of phosphoric acid?

Acid-Base Titration

1: 30 mL of 0. 10M NaOH neutralized 25. 0mL of hydrochloric acid
1: 30 mL of 0.10M NaOH neutralized 25.0mL of hydrochloric acid. Determine the concentration of the acid Write the balanced chemical equation for the reaction Extract the relevant information from the question: NaOH V = 30mL , M = 0.10M HCl V = 25.0mL, M = ? Calculate moles NaOH n(NaOH) = M x V = From the balanced chemical equation find the mole ratio NaOH:HCl Find moles HCl Calculate concentration of HCl using the formula: M=n÷V

2. What volume of 0. 75M H2SO4 is required to neutralize 25. 0 mL of 0
2. What volume of 0.75M H2SO4 is required to neutralize 25.0 mL of 0.427M KOH? Write the balanced chemical equation for the reaction Extract the relevant information from the question: KOH V = 25.0mL , M = 0.427M HCl V = ?mL, M= 0.75M Calculate moles KOH n(KOH) = M x V = From the balanced chemical equation find the mole ratio KOH: H2SO4 Find moles H2SO4 Calculate volume of H2SO4 using the formula: V=n÷M

3. 50. 0 mL of an unknown solution of Ca(OH)2 are titrated with 0
mL of an unknown solution of Ca(OH)2 are titrated with 0.15M HCl. Find the molarity of the Ca(OH)2 solution if 83 mL of acid are required to reach the equivalence point. Write the balanced chemical equation for the reaction Extract the relevant information from the question: Ca(OH)2 V = 50.0mL , M = ?M HCl V = 83 mL, M= 0.15M Calculate moles HCl n(HCl) = M x V = From the balanced chemical equation find the mole ratio Ca(OH)2 : HCl Find moles Ca(OH)2 Calculate molarity of Ca(OH)2 using the formula: M=n÷V

Titration Curve

Titration – Virtual Lab

Acids & Bases Acids and Bases are found in many everyday items, like foods, cleaners, and medicines. Weak acids are strong bases; strong acids are weak.

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Acids & Bases Acids and Bases are found in many everyday items, like foods, cleaners, and medicines. Weak acids are strong bases; strong acids are weak.

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