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The pH Scale

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The pH Scale is used to indicate the acidity ([H3O+]) of a solution has values between 0 and 14 * * pH 7.0 (8-14) pH [H3O+] * ? – PowerPoint PPT presentation

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Title: The pH Scale


1
The pH Scale
  • is used to indicate the acidity (H3O) of a
    solution
  • has values between 0 and 14

2
pH lt 7.0 (0-6)
pH 7.0
pH gt 7.0 (8-14)
3
pH H3O
?
Example For a solution with H3O 1 x 10-4
pH -log 1 x 10-4 pH - -4.0 pH
4.0
4
Significant 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

5
Calculating 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

6
Learning 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?

7
Learning 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

9
Learning 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)
11
Reactions of Acids and Bases
HCl (aq) Mg(OH)2 (s) ? ?
12
Neutralization 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

13
Neutralization 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

14
Balance 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)

15
Learning 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)

16
Buffers
17
Buffers
  • 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.

18
H2CO3 / 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
19
What 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-
20
In 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
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