I would really appreciate it if someone showed me how to solve each of these pro
ID: 869982 • Letter: I
Question
I would really appreciate it if someone showed me how to solve each of these problems instead of just giving the answers. I bolded the correct answer. Thank you
1. How many milliliters of a 5.0 x 10^-2 stock solution would you need to add to a final volume of 10 liters to obtain a solution with a pH of 3.60?
a. 50 mL
b. 34 mL
c. 13 mL
2. A 0.25 M solution of a hypothetical weak acid, HX has a pH of 3.42. What is the Ka value for this acid?
a. 8.8 x 10^ -6
b. 1.6 x 10^ -7
c. 5.8 x 10^ -7
3. What is the pH of a 0.30 M solution of magnesium hypochlorite(Mg(ClO)2)? For HClO Ka= 3.0 x10^ -8
a. 9.06
b. 3.06
c. 10.65
4. The pH= 2.84 for a 0.35 M pyridine hydrochoride, C5H5NHCl, solution. Based on this information, determine the Kb value of pyridine (C5H5N)
a. 9.4 x10^-8
b. 1.7x 10^ -9
c. 5.3 x 10^ -7
5. If you wanted to prepare a buffer composed of hypochlorous acid (HClO0 and potassium hypochlorite (KClO), how may moles of KClO would be added to 2 liters of a 1.0 M HClO solution to get a buffer with a final pH of 7.70? For HClO, Ka= 3.0 x 10^-8
a. 3.0 mol KClO
b. 1.2 mol KClO
c. 2.2 mol KClO
6. The pH of a solution by mixing 300 mL of 0.050 M HClO4 and 40.0 mL of 0.10 M Ba(OH)2 is?
a. 1.69
b. 1.77
c. 1.85
7. A 150 mL sample of 0.20 M HF solution is titrated with a strong base. What is the pH after adding 40 mL of 0.80 M NaOH? For HF, Ka= 6.8 x 10^-4
a. 13.11
b. 12.02
c. 10.37
8. A solution of Pb(NO3)2 is mixed with a solution of NaCl. A precipitate forms and analysis of the supernatant reveals the following concentrations of ions.
[Pb^2+] = 0.0062 M [NO3-]= 0.25 M [Na+]= 0.40 M [Cl-]= 0.054 M
Based on these data, what is the Ksp value for PbCl2(s)?
a. 7.2 x 10^-6
b. 5.6 x 10^-8
c. 1.8 x10^ -5
9. At an elevated temperature, Ksp= 7.5x 10^ -5 for Ca(OH)2. What is the pH of a saturated solution of a calcium hydroxide?
a. 13.06
b. 9.51
c. 12.73
Explanation / Answer
1)
V1 =
M1 = 5.0 x 10^-2
V2 = 3.60 L
M2 = ?
get M2 with pH = 3.6
[H+] = 10^-ph = 10^-3.6 = 0.0002512
M2 = 0.0002512
M1*V1 = M2*V2
5*10^-2 * V1 = 0.0002512*10
V1 = 0.05 liters or 50 ml
2)A 0.25 M solution of a hypothetical weak acid, HX has a pH of 3.42. What is the Ka value for this acid?
M1 = 0.25 M HX
ph = 3.42
[H+] = 10^-3.42 = 0.00038
Ka = [H+][X-] / [HX]
[H+] = [X-] = 0.00038
[HX] = 0.25 -0.00038 = 0.2496
Ka = [H+][X-] / [HX] = (0.00038*0.00038) / (0.2496) = 5.78*10^-7
3) What is the pH of a 0.30 M solution of magnesium hypochlorite(Mg(ClO)2)? For HClO Ka= 3.0 x10^ -8
Kb = Kw/Ka = (10^-14)/(3*10^-8) = 3.33*10^-7
Assume all MgClO2 are in solution, then 0.30 mol will give 2*0.3 mol of ClO-
0.6 M of ClO-
ClO- + H2O <--> HClO + OH-
Kb = [OH-][HClO] / [ClO-]
[OH-] = [HClO] = x
[ClO-] = 0.6
Solve for x
3.33*10^-7 = x*x / (0.6)
x^2 = 3.33*10^-7 * 0.6 = 1.99*10^-7
x = sqrt ( 1.99*10^-7 ) = 0.000446 OH-
pOH = -log(Oh-) = -log(0.000446) = 3.35
pH = 14- pOH = 14-3.35 = 10.65
4) The pH= 2.84 for a 0.35 M pyridine hydrochoride, C5H5NHCl, solution. Based on this information, determine the Kb value of pyridine (C5H5N)
Pyridine Kb value is actually a reported value in books, this is a constant and will not change (if temperature is not changed)
PLEASE Consider posting all other questions in another set of Q&A