Midterm 2 (CH 17-19) Flashcards
When a chemical system is at equilibrium:
Which of the following has an effect on the magnitude of the equilibrium constant?
A)Removing products as they are formed
B)Adding more of a reactant
C)Adding a Catalyst
D)Increasing the pressure, in a gas-gas reaction
E)Change in temperature
E)Change in temperature
Which of the following is a strong acid?
A)H2CO3
B)H2SO3
C)H2SO4
D)H3PO3
E)CH3COOH
C)H2SO4
Strong acids include the hydrohalic acids (HCl, HBr, HI) and oxoacids in which the number of oxygen atoms exceeds ionizable protons by two or more
Which of the following acids has the lowest pH?
0.1 M HBO, pKa = 2.43
0.1 M HA, pKa = 4.55
0.1 M HMO, pKa = 8.23
0.1 M HST, pKa = 11.89
pure water
HBO (lowest pKA = strongest acid = highest Ka)
What is the pH of a 0.20 M HCl solution?
B) 0.70
pH=-log(H3O+)
pH= -log (.2) because HCl fully dissociates in aqueous environments and therefore [H3O+] = .2
What is the pH of a 0.0035 M KOH solution?
E)11.54
pOH=-log[OH-] pH + pOH = 14
pOH=-log[.0035]= 2.46
14-2.46=pH
pH=11.54
What is the [OH−] for a solution at 25°C that has [H3O+] = 2.35 × 10−3 M?
C)4.26 x 10^-12
[H3O+] x [OH-] = 1x10^-14
[OH-]= (1x10^-14)/(2.35x10^-3)
What is the [H3O+] for a solution at 25°C that has pOH = 5.640?
C)4.37x10^-9
pH+pOH=14
14-5.640=8.36
10^-pH = [H3O+]
10^-8.36=[H3O+]
Butyric acid is responsible for the odor in rancid butter. A solution of 0.25 M butyric acid has a pH of 2.71. What is the Ka for the acid?
D)1.5x10^-5
CH3CH2CH2COOH = butyric acid
What is the value of Kb for the cyanide anion, CN−? Ka(HCN) = 6.2 × 10−10
B)1.6 × 10−5
Kw=Ka x Kb Kw=1x10^-14
(1x10^-14)/(6.2x10^-10) = 1.6x10^-5
Which of the following aqueous liquids is the most acidic?
A solution is prepared by adding 0.10 mol of sodium fluoride, NaF, to 1.00 L of water. Which statement about the solution is correct?
A) The solution is basic
NaF + H2O -> Na+ F- Solution will be basic as there are no acidic ions to balance the basicity.
A solution is prepared by adding 0.10 mol of iron(III) nitrate, Fe(NO3)3, to 1.00 L of water. Which statement about the solution is correct?
C)The solution is acidic
Which of the following is considered a Lewis acid?
Lewis acid = lone pair acceptor. Must have an atom that has an empty orbital to accept electrons.
B)BCl3 Boron has empty p orbitals and can accept the lone pairs
Which one of the following is a Lewis acid but not a Brønsted-Lowry acid?
A)Fe3+
Lewis Acid is a lone pair acceptor whereas Brønsted-Lowry acid donates a proton in aqueous solution and must have a proton in the formula. Fe3+ is a Lewis Acid but doesn’t have a proton to donate and therefore is not a Brønsted-Lowry Acid
Which of the following aqueous mixtures would be a buffer system?
D)H3PO4, H2PO4−
Buffer system consists of an acid and its conjugate base
Which of the following has the highest buffer capacity?
0.50 M H2PO4−/0.50 M HPO42−
-Buffer capacity is best at 1:1 ratio of acid and conjugate base
-0.5M + 0.5M
A solution is prepared by adding 500 mL of 0.3 M NaClO to 500 mL of 0.4 M HClO. What is the pH of this solution?
What is the pH of a buffer that consists of 0.45 M CH3COOH and 0.35 M CH3COONa?
Ka = 1.8 × 10−5
What is the pH of a buffer that consists of 0.20 M NaH2PO4 and 0.40 M Na2HPO4?
For NaH2PO4, Ka = 6.2 × 10−8
pH=7.51
You need to use KH2PO4 and K2HPO4 to prepare a buffer with a pH of 7.45. Which of the following ratios of [base]/[acid] is required? For phosphoric acid, (H3PO4), Ka2 = 6.2 × 10−8.
At the equivalence point in an acid-base titration:
The moles of acid = moles of base
ensure that it is in stoichiometric ratio
When a strong acid is titrated with a strong base, the pH at the equivalence point:
is equal to 7.0
When a weak acid is titrated with a strong base, the pH at the equivalence point:
is >7.0
When a strong acid is titrated with a weak base, the pH at the equivalence point
is < 7.0
Describe the titration curve of a weak acid and weak base
Equivalence point depends on relative concentrations of each.
Describe the titration curve of a polyprotic acid
Multiple equivalence associated with the different Ka values for each acidic proton
The indicator propyl red has Ka = 3.3 × 10−6. What would be the approximate pH range over which it would change color?
pH of an indicator = +/- pKa
pKa=-log(3.3x10^-6)= 5.48
pH= 4.5-6.5
A 50.0-mL sample of 0.50 M HCl is titrated with 0.50 M NaOH. What is the pH of the solution after 28.0 mL of NaOH have been added to the acid?
Write the ion product expression for calcium phosphate, Ca3(PO4)2.
The solubility of silver chromate is 0.0287 g/1.0 L of solution. What is the Ksp for Ag2CrO4?
