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Acids produce H+ ions in waterH2O
HCl(g) H+(aq) + Cl−(aq)
they are electrolyteshave a sour taste turn litmus redneutralize bases
Some acids like sulfuric and phosphoric release more than 1 H+ in water; other like acetic acid (vinegar) release far less than 1 H+ per molecule
Bases produce OH− ions in waterare electrolytesfeel soapy and slipperyneutralize acids
NaOH sodium hydroxideKOH potassium hydroxide
sodium and potassium hydroxide release 1 OH- /molecule
other bases such as ammonium hydroxide (NH4OH) release far fewer OH-
fewer
Strong acids completely ionize (100%) in aqueous solutions.HCl(g) + H2O(l) H3O+(aq) + Cl−(aq)
Amount of acid added
Weak acids dissociate only slightly in water to form a solution of mostly molecules and a few ions.
H2CO3(aq) + H2O(l) H3O+(aq) + HCO3−(aq)
NH3(g) + H2O(l) NH4+(aq) + OH−(aq) Windex weak base
H2CO3 + OH- HCO3- + H2O CO3
= + H3O+ Baking Soda weak base
NaOH Na+ + OH- Drano strong base
Water reacts with itself in the following manner:
H+ is transferred from one H2O molecule to another ;one water molecule acts as an acid, while another acts as a base
H2O + H2O H3O+ + OH−
.. .. .. ..H:O: + H:O: H:O:H+ + :O:H−
.. .. .. ..H H H
water water hydronium hydroxideion(+) ion(-)
The concentration of
H3O+ = OH- = 10-7 mols/L
pHThe pH of a solution is used to indicate
the acidity of a solution;it has values that usually range
from 0 to 14;the solution is acidic when the
values are less than 7;the solution is neutral with
a pH of 7;the solution is basic when the
values are greater than 7
How is the numerical value of pH determined?
pH = - log[H3O+ concentration]; pOH = -log [OH- concentration]
when the H3O+ concentration is
expressed in mols/L
pH + pOH = 14
What is the log of 4*108?
log[4]+log[108]
log[4] = 0.6
log[108] = 8
log[4*108] = 8.6
What is the log of 4*10-8?
log[10-8] = -8
log[4*10-8] = -7.4
pH = 7.4
Reactions of acids and bases
Acid + Base = Salt + Water
Mg(OH)2 + HCl (gastric juice) = MgCl2 + H2O
Mg(OH)2 + 2HCl (gastric juice) = MgCl2 + 2 H2O
CaCO3 + HCl = CaCl2 + H2CO3 = CaCl2 + H2O + CO2
CaCO3 + 2HCl = CaCl2 + 2H2CO3 = CaCl2 + 2H2O + 2CO2+ burp
O H - ( e q u i v a l e n t s )
0 .0 0 0 .0 2 0 .0 4 0 .0 6 0 .0 8 0 .1 0 0 .1 2
pH
0
1
2
3
4
5
6
7
How does the pH vary if we add NaOH (0.1 mol/L) dropwise to a solution of HCl (0.1 mol/L)?
HCl + NaOH = H2O + NaCl
pH of resulting solution
buffered in this region
0.001 M H+
0.1
0.01
Moles of NaOH added
How does the pH vary is we add NaOH (0.1 mol/L) dropwise to a solution of the weak
acid acetic acid (0.1 mol/L)?
OH - (equivalents)
0.00 0.02 0.04 0.06 0.08 0.10
pH
2
3
4
5
6
7
8
9
HOAc + NaOH = H2O + NaOAc
pH of resulting solution
buffered in this entire region
Moles of NaOH added
• The most important weak acid in blood is NaHCO3-
• H2CO3 is a very weak acid; however both hydrogens can be removed in the presence of strong base; the pH of a solution of NaHCO3 is very close to physiological pH; in the presence of an acid the HCO3- ion tends to pick up the proton, thus buffering the solution and preventing the solution to become too acidic.
• H+ + HCO3- H2CO3 CO2 + H2O
In the presence of a base, the HCO3- ion can
lose its proton as H+ and thus neutralize the strong base; thus the HCO3
- ion can buffer the solution in both directions
HCO3- + OH- CO3
-2 + H2O
The pH in living systems is very important. For example the pH of blood is kept at 7.4 and must be maintained within ±0.5 pH units. How is this done?
At a pH of 7.4, most CO2 is in the form of HCO3-
HCO3- can react with either acid or base
HCO3- + H3O+ H2CO3 CO2 + H2O
HCO3- + OH- H2O + CO3-2
In this manner, HCO3-
stabilizes the pH and does not allow it to become too acidic or to basic; it acts as a buffer
What is the H+ concentration in blood? pH = -log[H+]
[H+] = 10-7.4
10-7.4 = 100.6*10-8
100.6 = 4
10-7.4= 4*10-8 mols/L
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