100ml of each sol is mixed. Which is a buffer?
1. 1.0 M NH4Cl and 1.0 M KOH
2. 1.0 M NH3 and 0.60 M KOH
3. 1.0 M NH3 and 1.0 M HCl
4. 0.10 M NH4Cl and 0.40 M HCl
5. 1.0 M NH3 and 0.40M HCL
All answers to the General Chemistry II Buffers/Titrations/Solubility Test
1.C
2. Answer: A buffer consists of a weak acid
and its conjugate base in roughly equal
amounts. If acid is added to the solution, it
is consumed by the conjugate base. If base
is added to the solution, it is consumed by
the weak acid. If the amounts are such that
the ratio of conjugate base/weak acid
concentrations doesn’t change much, then
the pH doesn’t change much. Dilution
does not affect the pH because this
concentration ratio doesn’t change upon
dilution.
3.B
4.B
5.C
6.A
7.A
8.D
9.A
10.D
11.B
12.C
13.C
14.B
15.D
16.E
17.D
18.C
19.C
20. 9.43
21.D
22. 3.08
23. 3.61
24.B
25.C
26.A
27.A
28.C
29.A
30.D
31.D
32.D
33.A
34.C
35.A
36. 2.74
37. 3.16
38. 9.03
39. 9.55
40.A
41. 9.07g
42.D
43.B
44.D
45.B
46.D
47.B
48.D
49.C
50.B
51.B
52.B
53.D
54.A
55.A
56.B
57.B
58.D
59.B
60.A
61.B
62.D
63.E
64.A
65.B
66.C
67. PbCl
2(s)→ Pb2+(aq) + 2Cl–(aq)Ksp = [Pb2+] [Cl–]2
68.B
69.D
70.D
71.B
72.D
73.C
74.C
75.A
76.E
77.D
78.B
79.D
80.C
81.A
82.D
83.D
84.C
85.E
86.A
87.C
88.C
89.D
90.E
Also I have the whole PDF of answers for proof if you don't believe me!
Then is it 3? 1.0 M NH3 and 1.0 M HCl
Stop
A buffer is EITHER
1. a weak acid + a salt of the acid or
2. a weak base + a salt of the base
Examples:
acetic acid + sodium acetate or a mixture of
acetic acid + NaOH. becausre the reaction give you a weak acid and its salt.The reaction is HC2H3O2 + NaOH ==> NaC2H3O2 + H2O so if you use an excess of the acetic acid the result is that you produced the NaC2H3O2 which is the salt and you had an excess of the acid resent and that is an example of 1 above.
An example of #2 is NH3(aq) + NH4Cl or you can make one by using and excess of aqueous NH3 and adding HCl. That provides NH4Cl (the salt) and you have an excess of aq NH3.
For those problems above, e.g., #5. you will need to write the equation, calculate the moles of each initially and see if you have an excess of the base left over to go with the salt that is formed. Let me know if you need further assistance.
@ Adeline. WOW!
There isn't anything wrong with having the answers to problems BUT let me caution you and others that having all of the answers is not the answer. The answers don't help on an exam (a REAL exam I mean). Answers are useful as a check to see if the solution by the student is the same or at least close to that provided by the "cheat sheet". To understand this stuff you need to learn to work these problems on your own and not depend upon some outside oracle to help. When you're out in the cold cruel world you're on your own. If you're the chief engineer of a nuclear plant and it starts to run away and melt down, what oracle will you use? Do you have a cheat sheet for that? AND how fast can you get it? Think about that. Having said all of that note that I'm not against having answers. Used correctly they can help.
@ John, is 3 a weak base and its salt? Let's see.
NH3 + HCl --> NH4Cl
You have 100 x 1.0 M NH3 = 100 millimoles NH3 initially.
You have 100 x 1.0 M HCl = 100 millimoles HCl initially.
How much NH3 is left? 100 - 100 = 0
How much HCL is left? 100 - 100 = 0
How much NH4Cl is formed. 100.
So do you have a weak base and a salt? I see the salt but don't see a weak base. I don't think C will do it.