Polyprotic Acids/bases
What is the predominant species of carbonic acid (H2CO3) at a pH of 6.5? (Ka1 = 4.5 x 10-7 , Ka2 = 4.7 x 10-11)
HCO3-
What is the pH at the equivalence point of a strong acid and strong base titration?
7.00
What is the volume of 0.100 M NaOH needed to reach the last equivalence point when titrated with 20.0 mL of 0.100 M phosphoric acid (H3PO4)
Eq 3 = 60.0 mL NaOH
EDTA forms _______ complexes with any metal regardless of charge
1:1
In a titration, 20.46 mL of sodium hydroxide solution is required to titrate a 0.1082 g sample of potassium hydrogen phthalate (KHP, molar mass 204.22). What is the molarity of the sodium hydroxide given the following balance reaction
NaOH + KHP 🡪 NaKP + H2O
What is the pH of 1.00 M Carbonate (CO32-) solution at 25 0C ? (ignore activities) Ka1 = 4.5 x 10-7; Ka2 =4.7 x 10-11
12.16
Consider the titration of 100.0 mL of 0.100 M Hydrochloric acid with 0.100 M sodium hydroxide. What is the pH when 99.0 mL of sodium hydroxide have been added?
3.299
Citric acid is a triprotic acid abbreviated H3A. A 0.125 M sample of citric acid is titrated with 0.250 M LiOH. What is the pH halfway to equivalence point 1, halfway to equivalence point 2, and halfway to equivalence point 3? (Ka1 = 7.1 x 10-4, Ka2 = 1.7 x 10-5, Ka3 = 6.4 x 10-6)
Halfway to eq. 1, pH = 3.15
Halfway to eq. 2, pH = 4.77
Halfway to eq. 3, pH = 5.19
The _______ form of EDTA is the only species that binds to metal to form metal-EDTA chelate
Y4- (the basic form)
Predominant at high pH
When a sample of impure salt (0.4500g) was dissolved in water and treated with an excess of silver nitrate, 0.8402 g of silver chloride was precipitated. Calculate the percentage KCl in the original sample.
AgNO3 + KCl → AgCl + KNO3
what is 97.1%
Calculate the pH of the resultant buffer if 7.00 g of Na2CO3 (105.99 g/mol) and 5.00 g of NaHCO3 (84.01 g/mol) are dissolved in 1000.0 mL of solution. Ka1 and Ka2 for H2CO3 are 4.5 x 10-7 and 4.7 x 10-11
pH = 10.374
What volume of NaOH must be added to reach the equivalence point for the titration of 0.100 M NaOH and 50.0 mL of 0.0500 M HCN (HCN is a weak acid)?
25.0 mL NaOH
Citric acid is a triprotic acid abbreviated H3A. A 0.125 M sample of citric acid is titrated with 0.250 M LiOH. What is the pH at equivalence point 1 and equivalence point 2 (Ka1 = 7.1 x 10-4, Ka2 = 1.7 x 10-5, Ka3 = 6.4 x 10-6)
@ eq. 1 = 3.96
@ eq. 2 = 4.98
Calculate the conditional formation constant (K'f) for an EDTA titration with Li+ at pH 12. (logKf = 2.95 , alphaY4- = 0.98)
K'f = Kf x alphaY4-
K'f = (102.95) x (0.98) = 870
A 0.411 g sample of powdered copper mixed with an inert, soluble additive was fully consumed by 23.4 mL of 0.602 M nitric acid, producing copper(II) nitrate, water and nitric oxide (NO) gas. What was the percent copper (by mass) in the sample?
3 Cu + 8 HNO3 → 3 Cu(NO3)2 + 2 NO + 4 H2O
What is 81.7% copper
What is the pH at the first equivalence point of the amino acid alanine? pKa1 = 2.34 and pKa2 = 9.69
pH = 6.015
Consider the titration of 10.0 mL of 0.100 M HF (pKa 3.19) with 0.100 M sodium hydroxide. What is the pH of the solution at the equivalence point?
pH = 7.944
Consider the titration of 10.0 mL of 0.100 M weak acid H2A (pKa1 1.92, pKa2 6.27) with 0.100 M NaOH. What is the pH when 20.0 mL of NaOH has been added?
pH = 9.60
Consider the titration of 25.0 mL of 0.0255 M Cd(NO3)2 with 0.0120 M EDTA in a solution buffered at pH 9.00. (log Kf = 16.50 for the Cd2+-EDTA complex) a. Calculate pCd2+ at two of the volumes below. (12 points)
ď‚· At the equivalence point
what is pCd = 8.66
The legal definition of intoxication is most states is a BAL (blood alcohol level) of 0.08% alcohol by mass or higher. “Alcohol” has the chemical formula C2H5OH.
In a given case, 35.48 mL of 0.05182 M K2Cr2O7 is required to titrate a 50.02 g sample of blood. What is the % of C2H5OH in this person’s blood?
16 H+ + C2H5OH+ 2 Cr2O7-2 🡪 4Cr+3 + 11 H2O + 2 CO2
What is 0.0847%