1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in...
-
Upload
roderick-malone -
Category
Documents
-
view
212 -
download
0
Transcript of 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in...
![Page 1: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/1.jpg)
1
Acids and Bases
23-3-2011
![Page 2: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/2.jpg)
2
Definition of Acids
Arrhenius acid: A substance that releases H+ in water ( e.g. HCl)
H+ + H2O H3O+ Hydronium Ion
Acid: A substance which increases [H+] when dissolved in water.
Base: A substance which increases [OH-] when dissolved in water.
![Page 3: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/3.jpg)
3
Arrhenius Acids
- Strong acids completely ionize in water to release H+ (H3O+) and an anion;
Strong Acids:HClO4 H2SO4 HI HBr HCl HNO3
HI + H2O H3O+ + I- or HI H+ + I- (100%)
![Page 4: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/4.jpg)
4
Arrhenius Acids
- Weak acids only partially ionize in water;
Weak Acids:
HC2H3O2 HF H3PO4 HCN H2S HNO2 NH4+
HC2H3O2 H+ + C2H3O2-
C CHH
HO
OH
![Page 5: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/5.jpg)
5
Brønsted-Lowry Acids and Bases
The Arrhenius definition does not apply when water is not the solvent; so, a broader definition (Brønsted-Lowry) was generated.
Acid: A proton donor
Base: A proton acceptor
Example:
HCl(aq) H+(aq) + Cl-
H+(aq) + :NH3(aq) NH4
+(aq)
![Page 6: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/6.jpg)
6
Conjugate Acids and Bases:
• From the Latin word conjugare, meaning “to join together.”
• Reactions between acids and bases always yield their conjugate bases and acids.
![Page 7: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/7.jpg)
7
Examples: HF + HCO3- H2CO3 + F-
HF = Acid F- = Conjugate Base
HCO3- = Base H2CO3 = Conjugate Acid
CH3NH2 + HI CH3NH3+ + I-
Which is conjugate acid & which is conjugate base?
I- = conjugate base CH3NH3+ = conjugate
acid
![Page 8: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/8.jpg)
8
Strong Acids
You will recall that the six strong acids are HCl, HBr, HI, HNO3, H2SO4, and HClO4.
These are, by definition, strong electrolytes and exist totally as ions in aqueous solution.
For the monoprotic strong acids,
[H3O+] = [acid].
![Page 9: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/9.jpg)
9
Strong Bases
Strong bases are the soluble hydroxides, which are the alkali metal and heavier alkaline earth metal hydroxides (Ca2+, Sr2+, and Ba2+).
Again, these substances dissociate completely in aqueous solution.
![Page 10: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/10.jpg)
10
Autoionization of Water
H2O(l) + H2O(l) H3O+(aq) + OH−(aq)
Autoionization is the self-ionization of a neutral
molecule into positive and negative ions.
What is the equilibrium-constant expression for this equilibrium?
![Page 11: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/11.jpg)
11
At 25°C, Kw = 1.0 10−14 and [H+] = [OH-] = 10-7
Kw is also called ion-product of water as well as autoprotolysis of water
Kc = [H3O+] [OH-]
Kc is given the special symbol, Kw
The expression is…. 2 H2O H3O+ + OH-
K = [H3O+][OH-]/[H2O]2
![Page 12: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/12.jpg)
12
pH Scale
In most cases, the hydrogen ion concentration is very small which makes it difficult to practically express a meaningful concept for such a small value. Currently, the pH scale is used to better have an appreciation of the value of the hydrogen ion concentration where:
pH = - log [H+]pH + pOH = 14
![Page 13: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/13.jpg)
13
In the case of pure water at 25oC , the pH is 7 and
the solution is said to be neutral.
![Page 14: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/14.jpg)
14
What is the concentration of OH- ions in a HCl solution whose hydrogen ion concentration is 0.013 M?
Kw = [H+][OH-] = 1.0 x 10-14
[H+] = 0.013 M
[OH-] =Kw
[H+]
1 x 10-14
0.013= = 7.7 x 10-13 M
![Page 15: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/15.jpg)
15
The OH- ion concentration of a blood sample is 2.5 x 10-7 M. What is the pH of the blood?
pH + pOH = 14.00
pOH = -log [OH-] = -log (2.5 x 10-7)
= 6.60
pH = 14.00 – pOH = 14.00 – 6.60 = 7.40
![Page 16: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/16.jpg)
16
What is the pH of a 2 x 10-3 M HNO3 solution?
HNO3 is a strong acid – 100% dissociation.
HNO3 (aq) + H2O (l) H3O+ (aq) + NO3- (aq)
pH = -log [H+] = -log [H3O+] = -log(0.002) = 2.7
Start
End
0.002 M
0.002 M 0.002 M0.0 M
0.0 M 0.0 M
![Page 17: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/17.jpg)
17
More detailed manipulation:
Find the pH of a 0.1 M HCl solution.
SolutionHCl is a strong acid that completely
dissociates in water, therefore we haveHCl H+ + Cl-
H2O H+ + OH-
[H+]Solution = [H+]from HCl +[H+]from water
![Page 18: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/18.jpg)
18
However, [H+]from water = 10-7 in absence of a common ion, therefore it will be much less in presence of HCl and can thus be neglected as compared to 0.1 (0.1>>[H+]from water)
Always neglect [H+]from water when [H+]from
ACID is larger than 10-6M
[H+]solution = [H+]HCl = 0.1pH = -log 0.1 = 1
![Page 19: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/19.jpg)
19
Calculate the pH of the solution that is 0.04 M Ca(OH)2 in water.
[OH-] = [OH-]Ca(OH)2 + [OH-]water
Always neglect [OH-]water when [OH-]base is larger than 10-6M
[OH-]Ca(OH)2 = 0.08 M
[H+] = 10-14/0.08 = 1.2x10-12 M, Therefore:
[OH-] = [OH-]Ca(OH)2 = 0.08 MpOH = 1.097pH = 14 – 1.097 = 12.9
![Page 20: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/20.jpg)
20
What is the pH of a 1.8 x 10-2 M Ba(OH)2 solution?
Ba(OH)2 is a strong base – 100% dissociation.
Ba(OH)2 (s) Ba2+ (aq) + 2OH- (aq)
Start
End
0.018 M
0.018 M 0.036 M0.0 M
0.0 M 0.0 M
pH = 14.00 – pOH = 14.00 + log(0.036) = 12.6
![Page 21: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/21.jpg)
21
The pH of rain water in northeastern United States on a particular day was 4.82. Find [H+].
pH = -log [H+]
[H+] = 10-pH
[H+] = 10-4.8
[H+] = 1.5*10-5 M
![Page 22: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/22.jpg)
22
Acid - Base Strengths
- Two factors influence acid strength:
1) Bond Polarity - The more polar the bond, the stronger the acid.- HCl (∆EN = 0.9) > > H2S (∆EN = 0.4)
2) Bond Strength - The weaker the bond, the stronger the acid.- HI >> HF. HI bond is weaker than that of HF bond.- Bond strength is the larger of the two factors.
![Page 23: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/23.jpg)
23
![Page 24: 1 Acids and Bases 23-3-2011. 2 Definition of Acids Arrhenius acid: A substance that releases H + in water ( e.g. HCl) H + + H 2 O H 3 O + Hydronium.](https://reader036.fdocuments.us/reader036/viewer/2022081603/56649f015503460f94c1701c/html5/thumbnails/24.jpg)
24
Strength of Oxyacids