Solutions Unit

Honors Chemistry

Naming Acids Review: A. Binary – H +one anion Prefix “hydro”+ anion name +“ic”acid

Ex) HCl hydrochloric acid

Ex) H3P hydrophosphoric acid

B. Tertiary – H + polyatomic anion no Prefix “hydro”

(oxo) end “ate” = “ic” acidend “ite” = “ous” acid

Ex) H2SO4 sulfuric acid

Ex) H2SO3 sulfurous acid

Properties of Acids and Bases:

Taste Touch Reactions with Metals

Electrical Conductivity

Acid sour

looks like water, burns, stings

Yes-produces

H2 gas

electrolyte in solution

Base(alkali)

bitter

looks like water, feels

slippery

No Reaction

electrolyte in solution

Indicators: Turn 1 color in an acid and another color in a base.

A. Litmus Paper: Blue and RedAn aciD turns blue litmus paper reDA Base turns red litmus paper Blue.

B. Phenolphthalein: colorless in an acid and pink in a base

C. pH paper: range of colors from acidic to basic

D. pH meter: measures the concentration of H+ in solution

• Neutralization: A reaction between an acid and base. When an acid and base neutralize, water and a salt (ionic solid) form.

Acid + Base → Salt + Water

Ex) HCl + NaOH → NaCl + HOH

Reactions

Arrhenius Definition (1884):A. An acid dissociates in water to produce more

hydrogen ions, H+.HCl H+1 + Cl-1

B. A base dissociates in water to produce more hydroxide ions, OH-.

NaOH Na+1 + OH-1

C. Problems with Definition:• Restricts acids and bases to water solutions.• Oversimplifies what happens when acids

dissolve in water.• Does not include certain compounds that have

characteristic properties of acids & bases. Ex) NH3 (ammonia) doesn’t fit

Bronsted-Lowry Definition (1923):A. An acid is a substance that can donate hydrogen ions.

Ex) HCl → H+ + Cl-

– Hydrogen ion is the equivalent of a proton.– Acids are often called proton donors.– Monoprotic (HCl), diprotic (H2SO4) , triprotic (H3PO4)

B. A base is a substance that can accept hydrogen ions. Ex) NH3 + H+ → NH4

+

– Bases are often called proton acceptors.C. Advantages of Bronsted-Lowry Definition

•Acids and bases are defined independently of how they behave in water.

•Focuses solely on hydrogen ions.

Hydronium Ion:

Hydronium Ion – H3O+ This is a complex ion that forms in water.

H+1 + H2O H3O+1

To more accurately portray the Bronsted-Lowry, the hydronium ion is used instead of the hydrogen ion.

STRONG Acid/Base versus WEAK Acid/Base

Strength refers to the % of molecules that form IONS.

A strong acid or base will completely ionize (>95% as ions). This is represented by a single () arrow.

HNO3 + H2O H3O+ + NO3-

A weak acid or base will partially ionize (<5% as ions). This is represented by a double (↔) arrow.

HOCl + H2O ↔ H3O+ + ClO-

HF < HCl < HBr < HIincreasing strength

7 Strong AcidsHNO3 H2SO4 HClO3

HClO4 HCl HBrHI

8 Strong BasesLiOH NaOH KOHRbOH CsOH Ca(OH)2

Sr(OH)2 Ba(OH)2

Strength vs. Concentration

• Strength refers to the percent of molecules that form ions

• Concentration refers to the amount of solute dissolved in a solvent. Usually expressed in molarity.

Ionization of Acids & Bases

• H2SO4 2 H+ + SO4-2

– Sulfuric acid

• H3PO3 – Phosphorous acid

• Ca(OH)2 – Calcium hydroxide

3 H+ + PO3-3

Ca+2 + 2 OH-1

Conjugate Acid-Base Pairs: A pair of compounds that differ by only one hydrogen ion

A. Acid donates a proton to become a conjugate base.

B. Base accepts proton to become a conjugate acid.

• A strong acid will have a weak conjugate base.

• A strong base will have a weak conjugate acid.

Acid (A), Base (B), Conjugate Acid (CA), Conjugate Base (CB)

NH3 + H2O ↔ NH4+ + OH-

HCl + H2O ↔ Cl- + H3O+

• Base and Conjugate Acid are a Conjugate Pair.

• Acid and Conjugate Base are a Conjugate Pair.

B

B

A

A

CA CB

CB CA

1. H2O + H2O ↔ H3O+ + OH− B A CA CB

2. H2SO4 + OH− ↔ HSO4− + H2O

A B CB CA

3. HSO4− + H2O ↔ SO4

−2 + H3O+ A B CB CA

4. OH− + H3O+ ↔ H2O + H2O B A CA CB

AciDonates & Bases accept

The Self-ionization of Water & pH1. Water is amphoteric, it acts as both an acid and a base in the

same reaction.

Ex) H2O(l) + H2O(l) ↔ H3O+(aq) + OH-

(aq)

Keq = equilibrium constant = [H3O+] [OH-]Because reactants and products are at equilibrium, liquid water is

not included in the equilibrium expression

@ 25C, [H3O+] = 1 x 10-7 M and [OH-] = 1 x 10-7 M Kw = ion product constant or equilibrium constant for water

Kw = [H3O+] [OH-] = 1 x 10-14 M2

1.0 x 10-14 M2 = [1.0 x 10-7 M] [1.0x10-7 M]

1.0 x 10-14 = [H3O+] [OH-]

Acids: [H3O+] > 1 x 10-7 MBases: [OH-] > 1 x 10-7 M

Using Kw in calculations: If the concentration of H3O+ in the blood is 4.0 x 10-8 M, what is the concentration of OH ions in the blood? Is blood acidic, basic or neutral?

Kw = [H3O+] [OH-]1.0 x 10-14 M2 = [4.0 x 10-8 M] [OH-]

2.5 x 10-7 M = [OH-] slightly basic

The pH scale (1909): the power of Hydrogen

A. Measure of H3O+ in solution.

B. pH = -log[H3O+]

C. Range of pH: 0-14

pH < 7: acid

pH > 7: base

pH = 7: neutralD. pOH = -log[OH-]

E. pH + pOH = 14

H+

OH

-

pH [H3O+] [OH-]

14 1x10-14 1x100

13 1x10-13 1x10-1

12 1x10-12 1x10-2

11 1x10-11 1x10-3

10 1x10-10 1x10-4

9 1x10-9 1x10-5

8 1x10-8 1x10-6

7 1x10-7 1x10-7

6 1x10-6 1x10-8

5 1x10-5 1x10-9

4 1x10-4 1x10-10

3 1x10-3 1x10-11

2 1x10-2 1x10-12

1 1x10-1 1x10-131

14

Significant Digits Rule

• The number of digits AFTER THE DECIMAL POINT in your answer should be equal to the number of significant digits in your original number

• Ex -log[8.7x10-4M] –Calc Answer = 3.0604807474 –Sig Fig pH = 3.06

Concentration• Percent concentration by mass (mass %

– (solute/solution) x 100% = % Concentration• Molarity (M)

– Moles of solute/Liters of solution = mol/L• Molality (m)

– Moles of solute/mass of solvent = mol/kg• ppm and ppb

– Used for very dilute solutions• Dilution – a process in which more solvent is

added to a solution– How is this solution different?

• Volume, color, molarity– How is it the same?

• Same mass of solute, same moles of solute

– In Dilution ONLY – M1V1 = M2V2

Dissolution Process• Ionic Compounds

NaCl(s) Na+1(aq) + Cl-1(aq)

– For dissolution to occur, must overcome solute attractions and solvent attractions.

– Dissociation Reaction: the separation of IONS when an ionic compound dissolves (ions already present)

– Try calcium chloride

hexahydrated for Na+1; most cations have 4-9 H2O molecules

6 is most common

Solvation: process of solvent moleculessurrounding solute

Hydration: solvation with water

nonelectrolyte

electrolyte

Dissolving NaCl in water

V. Solution StoichiometryA. Many reactants are introduced to a reaction chamber

as a solution.B. The most common solution concentration is molarity.

molarity = mol/liter

C. Examples1. Excess lead(II) carbonate reacts with 27.5 mL of 3.00M nitric

acid. Calculate the mass of lead(II) nitrate formed

PbCO3 + 2HNO3 Pb(NO3)2 + H2CO3

2. Calculate the volume, in mL, of a 0.324 molar solution of sulfuric acid required to react completely with 2.792 g of sodium carbonate according to the equation below.

H2SO4 + Na2CO3 Na2SO4 + CO2 + H2O

Energy Changes• Heat of solution = Hsoln

• Endothermic– Solute particles separating in solid– Solvent particles moving apart to allow solute to enter

liquid– Energy absorbed

• Exothermic– Solute particles separating in solid– Solvent particles attracted to solvating solute particles– Energy released