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14. Acids and bases

Acids and bases

acid

base

sour

bitter

donates H⁺ (proton)

accepts H⁺ (proton)

There are no rows in this table

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K_a and K_w

K for acids

⁠

K_a: tells you the strength of the acid

strong: dissociates completely (~100%)

K_a is infinite (division by ~0)

weak: dissociates partially

K_a is small

amphoteric: can be an acid or a base (e.g. water)

⁠

pure water: when [H₃O⁺] = [OH⁻]

find concentration of pure water

⁠

autoionization: when one water reacts with another water

change value of K by changing temperature

K_w differs at different temperatures

pH and pOH

⁠

for an acid

⁠

0 to 14

7: pure

< 7: acid

> 7: base

⁠

for an acid

0 to 14

7: pure

< 7: base

> 7: acid

opposite for a base

pH + pOH = 14

example: what is the pH of an acid with concentration 0.001 M?

⁠

Titrations

titration: experiment to determine the concentration of an unknown acid or base

⁠

known acid/base goes into the burette

unknown acid/base goes into the flask

stopcock

perpendicular: closed

parallel: open

indicator

changes color at specific pH

located in flask with unknown

⁠

pH based on the amount of known substance

equivalence point: where molarities of acids and bases are equal

⁠

a: acid

b: base

acid

base

equivalence point

strong

weak

strong

> 7

strong

weak

< 7

weak

depends

There are no rows in this table

⁠

K_b

⁠

K_b: tells you the strength of the base

strong: dissociates completely (~100%)

K_a is infinite (division by ~0)

weak: dissociates partially

K_a is small

⁠

half-equivalence point (halfway to the equivalence point):

⁠

pH for acids and bases

strong

acid:

⁠

base:

⁠

weak

get the concentration of [H₃O⁺] or [OH⁻] from K_a or K_b

⁠

find pH using formula

example (acid):

⁠

H⁺

F⁻

initial

1.00 M

0.00 M

change

- x

+ x

equilibrium

1.00 - x

0 + x

There are no rows in this table

⁠

find concentration of H⁺

⁠

x will be very small so due to significant figures you can use x^2/1 instead of x^2/(1-x)

⁠

simpler way

⁠

percent dissociation:

⁠

example: add NaF to

⁠

; what happens to pH

add to the right → shifts left

pH goes up because fewer H⁺ so more basic

Polyprotic acids

polyprotic acid: acid with more than one H in the formula

many + proton + acid

example: H₃PO₄

⁠

as you go through the steps it becomes harder to remove H

strong acids: HCl, HBr, HI, H₂SO₄ (polyprotic), HClO₄, HNO₃

H₂SO₄

K_a_1: infinite

K_a_2: weak

Structures of acids and bases

an acid is stronger if:

it has more oxygen

it has a higher electronegativity

pulls electrons away from the H which makes the H fall off

base: opposite of acids (stronger if fewer oxygens, lower electronegativity)

because

⁠

conjugate acid/base

pH for acids and bases

Polyprotic acids

Structures of acids and bases

Gallery

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