Help me with these 10 chemistry problems, please show work. 1) Which one of the
ID: 1057263 • Letter: H
Question
Help me with these 10 chemistry problems, please show work.
1) Which one of the following pairs cannot be mixed together to form a buffer solution?
A) RbOH, HBr
B) KOH, HF
C) NH3, NH4Cl
D) H3PO4, KH2PO4
E) NaC2H3O2, HCl (C2H3O2- = acetate)
2) What change will be caused by addition of a small amount of HCl to a solution containing fluoride ions and hydrogen fluoride?
A) The concentration of fluoride ions will increase as will the concentration of hydronium ions.
B) The concentration of hydronium ions will increase significantly.
C) The concentration of fluoride ion will decrease and the concentration of hydrogen fluoride will increase.
D) The fluoride ions will precipitate out of solution as its acid salt.
E) The concentration of hydrogen fluoride will decrease and the concentration of fluoride ions will increase.
3) The pH of a solution prepared by mixing 50.0 mL of 0.125 M NaOH and 40.0 mL of 0.125 M HNO 3 is ________.
A) 13.29
B) 8.11
C) 7.00
D) 11.00
E) 12.14
4) The concentration of fluoride ions in a saturated solution of barium fluoride is ________ M. The solubility product constant of BaF2 is 1.7 × 10-6.
A) 3.8 × 10-4
B) 1.4 × 10-4
C) 3.0 × 10-3
D) 7.5 × 10-3
E) 1.5 × 10-2
5) The solubility of lead (II) chloride (PbCl2) is 1.6 × 10-2 M. What is the Ksp of PbCl2?
A) 3.1 × 10-7
B) 1.6 × 10-5
C) 1.6 × 10-2
D) 5.0 × 10-4
E) 4.1 × 10-6
6) A 25.0 mL sample of 0.723 M HClO4 is titrated with a 0.27 M KOH solution. The H3O+ concentration after the addition of 80.0 mL of KOH is ________ M.
A) 0.7
B) 4 × 10-2
C) 0.4
D) 3 × 10-13
E) 1 × 10-7
7) The Ka of benzoic acid is 6.30 × 10-5. The pH of a buffer prepared by combining 50.0 mL of 1.00 M potassium benzoate and 50.0 mL of 1.00 M benzoic acid is ________.
A) 0.851
B) 4.201
C) 1.705
D) 3.406
E) 2.383
8) Ka for HX is 7.5 × 10-12. What is the pH of a 0.15 M aqueous solution of NaX?
A) 7.97
B) 1.96 C
C) 12.10
D) 8.04
E) 6.00
9) 50 mL of 0.100 M HF is titrated to the equivalence point with 0.100 M KOH. The Ka of HF is 6.8 x 10-4 . What is the pH of the solution at the equivalence point.
A) 6.07
B) 7.93
C) 7.00
D) Coffee
10) 50 mL of 0.100 M HF is titrated with 55 mL of 0.100 M KOH. What is the pH of the solution. Ka of HF = 6.8 x 10-4.
A) 11.68
B) 2.32
C) 7.00
D) Coffee
Explanation / Answer
1) Which one of the following pairs cannot be mixed together to form a buffer solution?
A) RbOH, HBr --> strong acid/base, wont form buffer
B) KOH, HF --> they could form buffer if correct amounts are used
C) NH3, NH4Cl --> they could form buffer if correct amounts are used
D) H3PO4, KH2PO4 --> they could form buffer if correct amounts are used
E) NaC2H3O2, HCl (C2H3O2- = acetate) --> they could form buffer if correct amounts are used
2) What change will be caused by addition of a small amount of HCl to a solution containing fluoride ions and hydrogen fluoride?
A) The concentration of fluoride ions will increase as will the concentration of hydronium ions.
B) The concentration of hydronium ions will increase significantly.
C) The concentration of fluoride ion will decrease and the concentration of hydrogen fluoride will increase. TRUE
D) The fluoride ions will precipitate out of solution as its acid salt.
E) The concentration of hydrogen fluoride will decrease and the concentration of fluoride ions will increase
3) The pH of a solution prepared by mixing 50.0 mL of 0.125 M NaOH and 40.0 mL of 0.125 M HNO 3 is ________.
mmol of acid = MV = 40*0.125 = 5
mmol of base = MV = 50*0.125 = 6.25
mmol of base left = 6.25-5 = 1.25
[OH-] = mmol of OH- / total V = 1.25 / (50+40) =
pOH = -log(0.013888) = 1.857360
pH = 14- pOH = 14-1.857360 = 12.14 answer is E
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