Title: The pH Scale
1The pH Scale
- is used to indicate the acidity (H3O) of a
solution - has values between 0 and 14
2pH lt 7.0 (0-6)
pH 7.0
pH gt 7.0 (8-14)
3pH H3O
?
Example For a solution with H3O 1 x 10-4
pH -log 1 x 10-4 pH - -4.0 pH
4.0
4Significant Figures in pH
- When expressing log values, the number of decimal
- places in the pH is equal to the number of
significant - figures in the coefficient of H3O.
- H3O 1 x 10-4 pH 4.0
- H3O 8.0 x 10-6 pH 5.10
- H3O 2.4 x 10-8 pH 7.62
5Calculating pH
- Find the pH of a solution with a H3O of 1.0 x
10-3 - STEP 1 Press (-) log key
- - log
- STEP 2 Enter H3O
- Enter 1 x 10-3 by pressing 1 (EXP) (/-) 3
- The EXP key gives an exponent of 10
and - change sign (/- key or key)
- - log (1x10-3) 3
- STEP 3 Adjust figures after decimal point to
equal the - significant figures in the
coefficient. - 3 3.00 Two significant figures in
1.0 x 10-3
6Learning Check
- What is the pH of coffee if the H3O is 1 x
10-5 M? - pH -log 1 x 10-5 5.0
- Acidic or neutral or basic?
-
7Learning Check
- A. The H3O of tomato juice is 2 x 10-4 M.
- What is the pH of the solution?
- pH - log 2 x 10-4 3.69897
- SF 2 gt 1 decimal place in 3.7
8- B. The OH- of a solution is 1.0 x 10-3 M.
- What is the pH of the solution?
- Remember pH is hydrogen ion concentration
- Use the Kw (1.0 x 10-14) OH- x H3O
- to obtain H3O 1.0 x 10 -11
- pH - log 1.0 x 10 -11 11.00
9Learning Check
- Identify each solution as
- 1) acidic 2) basic 3) neutral
- A. ___ HCl with a pH 1.5
- B. ___ pancreatic fluid H3O 1 x 10-8 M
- C. ___ Sprite soft drink pH 3.0
- D. ___ pH 7.0
- E. ___ OH- 3 x 10-10 M
- F. ___ H3O 5 x 10-12
10(No Transcript)
11Reactions of Acids and Bases
HCl (aq) Mg(OH)2 (s) ? ?
12Neutralization Reactions
- an acid and a base react to produce a salt and
water. - acid base salt water
-
- HCl NaOH NaCl H2O
-
- 2HCl Ca(OH)2 CaCl2 2H2O
13Neutralization Reactions
- Write the balanced equation for the
neutralization of - magnesium hydroxide and nitric acid.
- STEP 1 Write the acid and base.
- Mg(OH)2 HNO3
- STEP 2 Balance H in acid with OH- in base.
- Mg(OH)2 2HNO3
- STEP 3 Balance with H2O.
- Mg(OH)2 2HNO3 salt 2H2O
- STEP 4 Write the salt from remaining ions.
- Mg(OH)2 2HNO3
Mg(NO3)2 2H2O
14Balance neutralization reactions
- A. HCl (aq) Al(OH)3(aq) AlCl3(aq)
H2O(l) - B. Ba(OH)2(aq) H3PO4(aq) Ba3(PO4)2(s)
H2O(l)
15Learning Check
- Write the neutralization reactions between
stomach acid, - HCl, and the compounds in Mylanta.
- Mylanta Al(OH)3 and Mg(OH)2
- HCl(aq) Al(OH)3(s)
- HCl(aq) Mg(OH)2(s)
16Buffers
17Buffers
- resist changes in pH from the addition of acid
or base. - in the body, absorb H3O or OH- from foods and
cellular processes to maintain pH. - are important in the proper functioning of cells
and blood. - in blood maintain a pH close to 7.4. A change in
the pH of the blood affects the uptake of oxygen
and cellular processes.
18H2CO3 / HCO3- Buffers in the Blood
- arterial blood pH 7.35-7.45
- if changes to pHlt6.8 or pHgt8.0
- cells cannot function properly, may die
- Buffer system in blood
- CO2(g) H2O H2CO3 H3O
HCO3-
H2O
19What happens? CO2(g) H2O(l) H2CO3(aq)
H3O(aq) HCO3-(aq)
H2O
If excess acid enters blood, reaction proceeds
from here to left, produces H2O and H2CO3.
Excess base (OH-) reacts with H2CO3
H2CO3 OH- ? H2O HCO3-
20In bloodcarbonic acid (H2CO3) linked to CO2
CO2(g) H2O(l) H2CO3(aq) H3O(aq)
HCO3-(aq)
- Acidosis CO2 increases, H2CO3 increases, H3O
increases gt lower pH (acidic) - CO2 increase due to
- respiratory causes failure to breath due to
lung disease (emphysema, pneumonia, asthma) - H increase due to
- metabolic causes renal diseases (hepatitis,
cirrhosis), increased acid production in diabetes
21- Alkalosis
- CO2 decreases (lower partial pressure), H2CO3
forms CO2 and H2O, decreasing H3O gt Higher pH
(basic) - CO2 decrease due to respiratory causes
hyperventilation, reactions to drugs - H decrease due to metabolic causes vomiting,
ingestion of excess alkali