Buffers
What two components make up a buffer system? Additionally, define what a buffer is supposed to do.
Weak acid and its conjugate base or weak base and its conjugate acid.
A buffer is supposed to resist changes of pH.
What is the name of the point in a titration where the amount of acid equals the amount of base?
Equivalence Point
This term describes a salt solution that does not affect the pH of water.
Neutral salts
These are formed from neutralization from a strong acid and a strong base.
Define what a Lewis acid is & provide an example.
A Lewis acid is an electron acceptor. Examples: Metal cations (Cu2+, Fe2+, Fe3+, etc.), BF3, AlF3 (these have incomplete octets so they can accept more electrons), Molecules that have multiple bonds between two atoms of different electronegativities (ex:.CO2, SO2).
Provide the rate law equations for 0th, 1st, and 2nd order reactions.
0th: rate = k
1st: rate = k [A]
2nd: rate = k [A][B]
OR rate = k [A]2
Name the equation used to calculate the pH of a buffer solution.
Henderson Hasselbach.
How can you determine the pKa of a weak acid from its titration curve?
We can use the Henderson Hasselbach equation.
pH=pKa+log([HA]/[A−])
At the half-equivalence point, [A−]=[HA][A−]=[HA], so log(1)= 0.
log(1)=0, therefore pH=pKa.
Which ion will form a basic solution when dissolved in water?
A. Br-
B. NO3-
C. HSO4-
D. SO32-
D.
SO32- is is the conjugate base of H2SO3 (which is a weak acid). When dissolved in H2O, the SO32- can react with water to produce OH- ions, therefore it will be basic.
Which would have a higher Kb: NH4OH or C5H5N? State which is the stronger base.
NH4OH would have a higher Kb due to having more hydroxide ions than C5H5N.
The rate law for the following reaction is listed below:
aA + bB --> cC + dD
Rate= k[A]2[B]
At certain concentrations of A & B, the reaction has an initial rate of 0.220 M/s. Calculate the new initial rate when the concentration of A is doubled and the concentration of B is tripled.
2.64 M/s
Calculate the pH of a buffer formed when 10.0 mL of 0.10 M LiOH is added to 50.0 mL of 0.1 M HF. Ka = 6.8×10−4
2.57
In a titration of 25 mL of 0.1 M HCl with 0.1 M NaOH, what is the pH at the equivalence point?
7
Write the acid dissociation equations for H2CO3, H2SO4, H3A
H2CO3
H2CO3(aq) ⇌ HCO3− (aq)+ H+ (aq)
HCO3− (aq) ⇌ CO32− (aq)+ H+ (aq) HCO3−(aq) ⇌ CO32−(aq) + H+(aq)
H2SO4
H2SO4 (aq)→ HSO4− (aq) + H+(aq)
HSO4− (aq) ⇌ SO42− (aq)+ H+ (aq)
H3A
H3A (aq) ⇌ H2A− (aq)+ H+ (aq)
H2A− (aq) ⇌ HA2− (aq)+ H+ (aq)
HA2− (aq) ⇌ A3− (aq)+ H+ (aq)
Arrange the following acids from strongest to weakest based on the given Ka values: HCN (6.2 * 10-10), HCl (1.3 * 106), CH3COOH (1.8 * 10-5),
HCl > CH3COOH > HCN
Consider the following reaction
2HBr (g) --> H2 (g) + Br2 (g)
In the first 25 seconds of this reaction, the concentration of HBr drops from 0.600 M to 0.512 M. Calculate the average rate of the reaction during this time interval.
0.00176 M/s
Calculate the pH of a buffer solution that is 0.250 M in HCN and 0.170 M in KCN. For HCN; pKa = 9.31
9.14
Suppose that 25.00 mL of a 0.300 M solution of the strong acid HC104 is titrated with a 0.225 M solution of NaOH. Determine the pH at the following points:
a. before NaOH is added
b. after 25.00 mL of NaOH solution is added
c. at the equivalence point
d. after 40.00 mL of NaOH solution is added
a. 0.523
b. 0.824
c. 7.0
d. 12.363
Find the percent ionization of a 0.500 M HC2H3O2 solution at 25°C. (Ka = 1.8 x 10-5)
0.60%
A 0.100 M solution of HCN (hydrocyanic acid) has a dissociation constant Ka= 4.9×10−10. Calculate the following:
[H3O+] at equilibrium
pH
pOH
1. 7.0×10−6 M
2. 5.15
3. 8.85
Initial rate data have been determined at a certain temperature for the gaseous reaction:
2NO + 2 H2 --> N2 + 2 H2O
[NO]0 [H2]0 Initial Rate (M/s)
0.10 0.20 0.0150
0.10 0.30 0.0225
0.20 0.20 0.0600
The numerical value and units of the rate constant are
7.5 M-2 s-1
Which of the following would be the best buffer at the indicated pH?
A. 0.0500 M HClO (Ka = 2.9 × 10−8) and 0.0500 M NaClO at about pH = 5.10
B. 0.200 M HClO (Ka = 2.9 × 10−8) and 0.200 M NaClO at about pH = 5.10
C. 0.0500 M C6H5CO2H (Ka = 6.5 × 10−5) and 0.0500 M C6H5CO2K at about pH = 5.10
D. 0.200 M C6H5CO2H (Ka = 6.5 × 10−5) and 0.200 M C6H5CO2K at about pH = 5.10
D. 0.200 M C6H5CO2H (Ka = 6.5 × 10−5) and 0.200 M C6H5CO2K at about pH = 5.10
Calculate the pH at the half-equivalence point in the titration of 50.0 mL 0.10 M acetic acid (Ka = 1.8 × 10⁻⁵) with 0.10 M NaOH.
4.74
Identify each salt as acidic, basic, or neutral:
LiClO4
CN3CH2NH3NO3
Ca(OCl)2
LiClO4 --> neutral
CN3CH2NH3NO3 --> acidic
Ca(OCl)2 --> basic
This is the equilibrium constant (Ka) for the conjugate acid of a weak base, whose base dissociation constant (Kb) is 9.2×10−8 . What is the value of Ka?
Ka= 1.09×10−7
For a given reaction, the rate constant is 3.83 x 10-3 s-1. What concentration of reactant will remain after 142 sec for an initial concentration of 0.500 M?
0.291 M.