acids and bases things I still don't know

Question 1

basic buffer composition

Answer 1

weak base+its conjugate acid

Question 2

acidic buffer composition

Answer 2

weak acid+its conjugate base

Question 3

basic buffer with NH3 as its weak base

Answer 3

NH3+H2O<->NH4+ + OH-
if you add acid, the ammonia reacts w it moving eq right, if we add base, it reacts with ammonium to bring concentrations back to what they were, shifting equilibrium left

Question 4

henderson-hasselbach

Answer 4

-pH=-pKa+log ([A-]/[HA]
shows that pH=pKa at the half equivalence point (when the concentrations of the weak acid and its conjugate base are the same)

Question 5

2 ways to make a buffer

Answer 5

1. titrate a weak acid and its conjugate base (a strong base), stop when [HA]=[A-]
2. add a weak acid and a salt containing its conjugate base (strong base) to water

Question 6

first step in most questions

Answer 6

dissociation in water of the weak acid (ignore the strong base!)

Question 7

finding ph at equivalence point

Answer 7

1. at equivilance point, only the conjugate of the original weak acid/base is present. Find it’s conraction:
   - find total volume: add up volume of the weak acid and salt solutions added
   - find mols of the conjugate acid/base: same as the moles of the og weak acid/base
2. set up an ice table using this concentration of the conjugate base (dissociation of the conjugate acid/base in water, because that’s what it’s doing), and 0 for the other 2 (or 10^-7 for H+ ig)
3. use K (given) to find pH

Question 8

why is the conjugate of the original weak acid/base the only thing affecting pH at the equivilance point?

Answer 8

At the equivilance point, the [H+]=[OH-], so the acid and base neutralize each other.

Question 9

rule about polyprotic acids

Answer 9

usually, their conjugate is amphoprotic

Question 10

strong/weak acid/base K values:

Answer 10

strong: K>1, weak K<1, usually less than 10^-2 (smaller K means weaker acid because the ion [] is lower)

Question 11

conjugate pairs

Answer 11

strong-very weak
weak-weak
very weak-strong

Question 12

4 rules (with 14)

Answer 12

Ka x Kb=10^-14
[H+] x [OH-]=10^-14
pKa+pKb=14
pH+pOH=14

Question 13

when is the pH of a salt not 7, and steps to find pH of the salt

Answer 13

when either of the ions in the salt is the conjugate of a weak acid base (ex. NH4Cl, NH4 is the conjugate of a weak base so the solution will be acidic)
steps:
write out dissociation in water of NH4+ (the ion that is the conjugate of the weak acid/base)
concentration of NH4+ is the same as the concentration of the original salt, all else is 0 or 10^-7
find Ka of NH4+, using this find pH (solve for x)

Question 14

on which side does equilibrium lie for conjugate acid-base pairs?

Answer 14

equilibrium lies in the direction of the weaker conjugate

Question 15

acid and metal oxide products

Answer 15

a salt and water

Question 16

acid and metal hydroxide products

Answer 16

a salt and water

Question 17

acid and metal hydrogencarbonates products

Answer 17

salt, co2, water

Question 18

acid and carbonate products

Answer 18

salt, co2, water

Question 19

pH indicator equation to show colour change

Answer 19

(red) HIn + H2O <-> In- + H3O+ (blue)

Question 20

for a salt made up of the conjugates of of weak base and strong acid, is it acidic or basic?

Answer 20

acidic