Week 2 - Acids and bases

Week 2

Amphoteric

can accept and donate protons

How to identify acids vs bases vs conjugate acids vs conjugate bases

Ex) HNO3 + NH3 → NH4^+ + NO3^-

1. pair similar looking molecules together

• HNO3 and NO3^-, NH3 and NH4^+

2. look on the products side. in the pairs, whichever reactant that matches to that product became MORE negative is the acid (donated a proton), and whichever became MORE positive is the base (accepted the proton).

• Acid: HNO3

• base: NH3

3. Conjugate bases and acids are flipped: NO3^- is the conjugate base (opposite of the NH3 group) and NH4^+ is the conjugate acids (opposite of the HNO3 group)

pH of acids, neutral, and bases

Acid: pH<7 and H^+>10^-7

natural pH=7

bases (alkaline): pH>7 and H^+<10^-7

Acids vs bases

acids - donate a proton (accepts an electron pair)

bases - accept a proton (donates an electron pair)

Types of acids

1. Hydrohalic acids: HF, HCl, HBr, HI

2. oxoacids: central element is surrounded by oxygens

3. Carboxylic acids: COOH group

Types of bases

1. First and second column of the periodic table AND an OH group

2. When a nitrogen has 3 bonds and a lone pair

Bronsted-lowry vs Arrhenius vs Lewis definition acid and bases definition

Bronsted-lowry

• acids: donates H^+

• bases: accepts H^+

Arrhenius

• acids: donates H^+

• bases: Donates OH^-

Lewis

• acids: accepts electron pair, + charged

• bases: donates electron pair, - charged, has a lone pair

How to write conjugate acids vs bases

How to write conjugate acids: add an H, add a + 1 charge (if there are multiple hydrogens, add one more H just to the last hydrogen in the formula)

How to write conjugate bases: Remove an H, add - 1 charge

conjugate bases do NOT have H in front (bc they are not acids)

Relation of H3O+ and OH^- in solutions (concentration vs acid, base, neutral)

Image

How to find pH vs pOH

-log(H+) = pH

-log(OH^-) = pOH

also, p(OH)+p(H) = 14

pH + pOH = ?

14

(H^+)(OH^-) = ?

1 times 10^-14 (at 25 degrees celsius)

H^+ and OH^- relationship

Inversely proportional

List the chemical formula and names of strong acids

Image

Strong acids and bases (definition not list)

we assume they completely ionize, and equilibrium to far to the right

Weak acids and bases (definition not list)

We assume they do NOT completely ionize, and equilibrium to far to the left

List strong bases

image (assume the box means also strong bases, for now)

Trick for memorizing strong vs weak acids and bases?

Just memorize all the strong acids and bases, the rest are weak

When something refers to “concentration", what does it mean?

10^-pH or 10^-pOH

Bond enthalpy (length) and acid strength relationship (periodic table)

As you go DOWN the periodic table, strength of acids INCREASES

Anion and acid strength relationship

the MORE you stabilize the anion, the STRONGER the acid (make it stay as an anion)

How to determine strength of oxoacids?

1. Different central atoms but same oxidation number

• more electronegative element in the middle → stronger oxoacid (bc electronegativity of central atom stabilizes the negative charge that happens bc of dissociation. it spends more time dissociated)

2. Same central atoms but different oxidation number

• greater oxidation number surrounding central atom → stronger oxoacid

  • greater number of oxygens → more resonance structures → stronger acids

oxidation number - greater number of oxygens around central atom (generally)

How to determine strength of carboxylic acids?

1. More stable conjugate base (anion) → stronger carboxylic acid

• situations that stabilize anion:

  • electronegative atoms in R group

  • aromaticity in R group (alternating single and double bonds)

What is the difference between carboxylic acids and alcohols?

Alcohols have an -OH group and are effectively neutral (NOT ACIDIC)

carboxylic acids have a -COOH group and are acidic

How to rank carboxylic acid strength?

1. Look for most electronegative atom next to COOH

2. the more electronegative atom next to COOH is the stronger carboxylic acid

Ka

ion predict constant (same as Kc) prod/reactants, except you don’t have to deal with superscripts

[H+][A^-]/[HA]

HA: acid

H+: proton

A^-: conjugate base of acid

Relationship between Ka and acid strength and pH

Larger Ka, stronger acid, lower pH

Kb

base ionization constant (same as Kc) prod/reactants, except you don’t have to deal with superscripts

Relationship between Kb and base strength and pH

Larger Kb, stronger base, higher pH.