Chapter 11 Flashcards
Bronsted-lowry Acid and bases
Acids: are proton (H+) donors
Bases: are proton (H+) acceptors.
Conjugate Acids and bases
When a bronsted-Lowry acid donates an H+, the remaining structure is called the conjugate base of the acid, and the same with bases they are left with conjugate acids. The difference between an acid and a conjugate acid is that the acid has an extra H+ and for bases and conjugate bases, the bases have a missing H+
*pg231
Strong and weak acids
Strong acids are ones that completely ionize in water. and weak acids do not go to completion and there is leftover of that acid that is undissociated.
*pg232
How do we determine strength of acids
It depends on how much the products are favoured over the reactants. It follows The generic equilibrium expression format. denoted as K_a, which is known as the acid-ionization (or acid dissociation) constant.
If K_a > 1, then products are favoured and the acid is strong
If K_a < 1 then the reactants are favoured and the acid is weak.
The larger the K_a the stronger the acid.
Common strong acids
Hydroiodic Acid (HI) Hydrobromic acid (HBr) Hydrochloric Acid (HCl) Perchloric acid (HClO4) Sulfiric Acid (H2SO4) Nitric Acid (HNO3) --they have very very high K_a values. Anything not on this list is a weak acid. *pg233
Base equilibrium constant
Same form, K_b. Known as base-ionization (or base dissociation) constant. The larger the K_b value, the stronger the base
*pg234
Common strong bases
Group I hydroxides (For example, NaOH) Group I oxides (ex: Li2O) Some group II hydroxides (Ba(OH)2, Sr(OH)2, Ca(OH)2) Metal Amides (For example, NaNH2) *pg234
Weak bases
include ammonia (NH3) and amines, as well as the conjugate bases of many weak acids. *pg234
properties/strengths of conjugate acid and base
- -The conjugate base of a strong acid has no basic properties in water.
- -The conjugate acid of a strong base has no acidic properties in water
- -The conjugate base of a weak acid is a weak base, the weaker the acid, the more the reverse reaction is favoured, and the stronger is conjugate base.
- -The conjugate acid of a weak base is a weak acid. (the weaker the base the stronger the conjugate acid)
- pg235
Polyprotic
Acids that have more than one proton to donate.
*pg236
amphoteric substances
A substance that can act as both either acid or a base. The conjugate base of a weak polyprotic acid is always amphoteric, bc it can either donate or accept another proton. A great example is water.
*pg236
Auto-ionization (or self-ionization) of water.
Water reacts with itself one molecule acting as the acid, while the other as the base. the equil expression is:
K_w = [H3O+] [OH-] = 1.0e14. (@25ºC)
–In this case each of thsoe conc will be 1e7.
–K_w is constant at a given temp, regardless of the H3O+
This can vary with temperature, it inc as the temp inc
If an acid is added the conc of H3O+ inc and equil is disturbed, same with base that inc the conc of OH- ions. But in either case the product of [H3O+] amd [OH-] will remain eqial to K_w
*pg236/237
pH / pOH
measures the concentration of H+ (or H3O+) ions in a solution. pH = -log [H+] ; pOH = -log[OH-] [H+] = 10^-pH ; [OH-] = 10^-pOH pH + pOH = 14 (@25ºC) Low pH means a high [H+] -- pH > 7 : basic solution -- pH = 7 : neutral solution -- pH < 7 : acidic solution if [H+] = y x 10^-n (n is a whole number) then the pH will be bw (n-1) and n *pg237/238
pK_a and pK_b
p is equal to the -log of that something:
pK_a = -log K_a
pK_b = -log K_b
pK_a + pK_b = 14
The lower the pK_a value, the stronger the acid (opposite of K_a), same with pK_b
*pg238
K_aK_b
acid base conjugate pair
K_aK_b = K_w = 1e-14
pH calculations for strong acids
Strong acids dissociate completely, so the hydrogen ion concentration will be the same as the concentration of the acid. So you can calculate the pH directly from the molarity of the solution. For example, a 0.01 M solution of HCl will have [H+] = 0.01 M and pH = 2.
*pg240
pH calculations for weak acids
weak acids come to equil with their dissociated ions. for a weak acid at equil, the concentrayion of undissociated acid will be much greater than the concentration of H ions. To get the pH of a weak acid solution, you need to use the equil expression. You need to use ICE boxes.
If the K < 10e-4, you can assume that the x added or subtracted from a number is negligible.
*pg241
Neutralization reaction
when an acid and base are combines, they will react in a neutralization reaction. This type of reaction takes place when you want to neutralize an acid or base (for example taking medicine when you have excess acid build up in your stomach. If there is equal amounts of strong acid and strong base reacting, you will end up with a pH neutral, but if its a weak base and weak acid there won’t be neutral pH. But if a weak acid/base is reacted with a strong base/acid you will have complete neutralization.
all neutralizations have the same exo “heat of neutralization” so the heat released from these reactions is the same for all
All neutralization reactions go to completion
*pg242/243
Formula to figure out how much base to add to an acidic solution (or vice versa) to neutralize
a x [A] x V_a = b x [B] x V_b
- -a is the number of acidic hydrogens per formula
- b is a constant that tells us how many H+ ions the base can accept
- V is for volume
Salt and the 2 possibilties
an ionic compound, consisting of a cation and an anion. In water, the salt dissociated ions, and depending on how they react with water, the solution can either be acidic, basic or pH neutral. there are 2 possibilities for both the cation and an anion.
Cation:
1) Doesn’t react with water, (ex: group 1 cations, and larger group 2 cations)
2) Stronger acid than water (EX: NH4+, Be 2+, Cu 2+, Zn 2+, Al 3+, Cr 3+, Fe 3+)
Anion:
1) Doesn’t react with water (EX: conj base of a strong acid)
2) Stronger base than water (Ex: conj base of a weak acid)
whether the salt solution will be acidic, basic, or neutral is dependent on which combination of possibilities applies. (4 possible)
*pg244
Hydrolysis of water
The reaction of a substance – such as salt – with water.
*pg244
Buffer
A solution that resists changing pH when a small amount of acid or base is added. The buffering capacity comes from the presence of a weak acid and its conjugate base (or a weak base and its
conj acid) in roughly equal concentrations.
Can be made from a weak acid and a salt of its conj base (ex: HCN and NaCN)
*pg246
Henderson-Hasselbach Equation (for acid)
Used to calculate the new pH of a buffer solution
pH = pK_a + log ( [conj base] / [weak acid] )
switch pH to pOH and pK_a to pK_b for bases.
*pg247
Alkaline buffer solution
made of a weak base and its salt
pg248
Indicator
is a weak acid that undergoes a colour change when its converted to its conjugate base. if colour #1 of the indicator is a reactant and colour #2 is a product, then if equil shifts to the reactants we’ll see colour 1 and if products then colour 2. The indicator changes colour within a fairly short pH range, about 2 units. Some indicators have more than 2 colours (polyprotic indicators)
*pg248/249
Acid-base titration
An experimental technique used to determine the identity of an unknown weak acid (or weak base) by determining its pK_a (or pK_b). Can also be used to determine the concentration of any acid or base solution. The procedure consists of adding a strong/base of known identity and conc (the titrant) to a solution containing the unkown base/acid. always has to be an acid with a base or vice versa never the same. As the titrant is added in small amounrs, the pH of a solution is recorded.
*pg250
Titration curve
When we plot the date points of pH value (y axis) vs the volume of titrant added (x axis).
*pg250
Buffering region ( or buffering domain) in titration curve
The region where the pH changes very gradually.
*pg250
Acid-base equivalence point in titration curve
a point during the drastic pH change at which just enough base is added to completely neutralize the acid. the equivalence points for these conditions:
- -For a weak acid (titrated with a strong base) : pH > 7
- -For a weak base (titrated with a strong acid) : pH < 7
- For a strong acid (titrated with a strong base) or strong base (with strong acid) : pH =7
- pg251
Half-equivalence point in titration curves.
when half of the acid/base is neutralized. The pH at this point is equal to the pK_a
*pg251
Titration curves of polyprotic acids
They have more than one equivalence point, the number of the points will equal to the number of ionizable H the acid can donate.
*pg253
