chemphys unit 6b: electrolytes
TRANSCRIPT
Chemistry
Periodic table
Chemical reaction
Matter
Atoms
Chemical bonding
Electrolytes
Hydrocarbons
Organic chemistry
PreQuiz (2)
1. What is the ionization constant of water?a) Keq; b) [H2O]; c) Kw
2. The pH value indicatesa) the strength of an acid/base; b) the reactivity of acids/bases; c) the concentration of a solution
3. The pH value of human blood isa) 6.85-6.95; b) 7.35-7.45; c) 7.75-7.85
4. Define “buffer”:a) neutralization of an equilibrium reaction; b) solution which donates H+ ions; c) resists changes in pH when small amounts of acid or base is added
5. The buffer system of the blood is thea) carbonate buffer; b) chloride buffer; c) phosphate buffer
6. When the pH of the blood is low, the patient suffers froma) acidosis; b) alkalosis; c) diabetis
7. Excessive vomiting may causea) acidosis; b) alkalosis; c) diabetis
8. Salt is the product of a(n)a) acid/base reaction; b) hydrolysis reaction; c) equilibrium reaction
9. The salt used for X-ray analysis isa) KI; b) NHCO3; c) BaSO4
Learning activities (2)
• Electrolytes– Define common terms
• pH, buffer, salts– Explain properties of salts and buffer
solutions– Explain the concept of pH– Discuss the use of acids and bases in body– Describe the buffering system in the body– Describe the process of titration
Ionization of water
• Pure water at 25 °C– Only tiny amount of water ionizes
(1 out of 10 million molecules dissociates)
– [H+] = 10-7 mol/L = 10-7 M– [OH-] = 10-7 mol/L = 10-7 M– Kw = 10-7 x 10-7 = 10-14 M
𝐾 𝑒𝑞=¿¿ 𝐾 𝑒𝑞×[𝐻 2𝑂 ]=¿¿
“Ion product of water”
When [OH-] increases, [H+] decreases: basic
When [H+] increases, [OH-] decreases: acidic
Sackheim’s Chemistry: Chapter 12
Concentration: in moles per liter (M)
pH
• Indicates the exact strength of an acid or base = pH
– pH < 7 = acidic– pH = 7 = neutral– pH > 7 = basic
• Based on hydrogen ion concentration in a solution (maths)
• Examples– Lemon: [H]+ = 10-2
pH = -log[10-2] = 2 (acidic)
– Pure water: [H]+ = 10-7 pH = -log[10-7] = 7 (neutral)
– Soap: [H]+ = 10-10 pH = -log[10-10] = 10 (basic)
𝑝𝐻=− 𝑙𝑜𝑔¿ ¿
Log is exponent!
Sackheim’s Chemistry: Chapter 12
pH in body
• pH values of body fluids– Gastric juice: strongly acidic– Blood: weakly basic– Bile: weakly basic– Urine: weakly acidic/basic– Saliva: weakly acidic/basic
• Acid/base balance– Monitored by: lungs, kidneys, buffers– Minor changes have big consequences
• Acidosis: pH too low (< 7.35)• Alkalosis: pH too high (> 7.45)
Sackheim’s Chemistry: Chapter 12,30
Bicarbonate buffer
• Buffer solution– Resists changes in pH when small amounts of acid or base is added– Consists of weak acid + salt of weak acid (conjugated base)– In blood (pH = 7.35-7.45), carbonate buffer: H2CO3 + NaHCO3
Reduce number of free hydrogen Resists pH drop
Sackheim’s Chemistry: Chapter 12,30
Na+ buffers: blood plasma
K+ buffers: blood cells
Phosphate buffer
• Buffer solution– Resists changes in pH when small amounts of acid or base is added– Consists of weak acid + conjugated base– Intracellular, phosphate buffer: H2PO4
- + HPO42-
– Both excess acid (H+) and base (OH-) react with buffer system• pH remains constant
Sackheim’s Chemistry: Chapter 12,30
Acidosis
• pH too low (< 7.35): more common than alkalosis
• Acidosis: [HCO3-] ↓ or CO2 ↑
– Mechanism: • Loss or decreased production of HCO3
- → decreased buffer for acid: drop in pH
• Building up of CO2 → increase of H+: drop in pH
– Causes: • Diarrhea, renal failure, diabetic ketoacidosis• Pulmonary disease (asthma, pneumonia), Hypoventilation, adverse effects of
drugs, neurological problem– Compensation:
• Saving HCO3- → increased buffer for acid: increase in pH
• Hyperventilation → loss of CO2 → loss of H+: increase in pH• BUT compensation NEVER leads to a complete recovery to normal pH!
Sackheim’s Chemistry: Chapter 12,30
Alkalosis
• pH too high (> 7.45): less common than acidosis
• Alkalosis: [HCO3-] ↑ or CO2 ↓
– Mechanism: • Building up of HCO3
- → increased buffer for acids: increase in pH
• Loss of CO2 → loss of H+: increase in pH
– Causes: • Prolonged vomiting, adverse effects of drugs • Hyperventilation
– Compensation: • Decreased production of HCO3
- → decreased buffer for acid: drop in pH
• Hypoventilation → increase of CO2 → increase of H+: drop in pH
Sackheim’s Chemistry: Chapter 12,30
pH indicators
• Indicate the pH of fluids– pH indicator
• Substance changes color with pH change
– pH indicator paper• Color indicates pH values
– pH meter• Digital representation of pH
Indicator Low pH High pH
Litmus Red Blue
Phenolphtalein Colorless Pink
Methyl orange Red Yellow
Sackheim’s Chemistry: Chapter 12
Titration
• Acid-base titration– Buret
• Base (or acid) of known concentration– Flask
• Acid (or base) of unknown concentration• Indicator
• Base is added to acid until indicator changes color– Concentration of acid can be determined
Sackheim’s Chemistry: Chapter 12
Salt (1)
• Formed by reaction of acid with base (neutralization)• Common in daily live
– Table salt– Iron supplements– Photographs– Batteries
Sodium chloride
Silver bromide
Iron sulphate
Ammonium chloride
Sackheim’s Chemistry: Chapter 12
Salty taste
Salt (2)
• Acid reacts with base (alkali) to form water and salt:
• Dissociation of salts: no common ion (like H+ for acids and OH- for bases)
Sackheim’s Chemistry: Chapter 12
Hydrolysis of salts
• Reaction with water = Hydrolysis– Reverse of neutralization reaction
– Positive ion of salt (Na+) derived from base (NaOH)– Negative ion of salt (SO4
-) derived from acid (H2SO4)– Strong relationship between acids/bases and salts
Salt Water Acid Baseequilibrium
Sackheim’s Chemistry: Chapter 12
Medical use of salts
Salt Use
CaCO3, NaHCO3 Antacids
Na2SO4, MgCO3 Cathartics
NH4Cl Diuretic
NH4Cl, KI Expectorants
AgNO3 Germicide (Killing microbes)
BaSO4 X-ray work
CaCl2 Decrease of blood clotting time
FeSO4 Against anemia
NaF, SnF2 Reduction of caries
NaCl Saline solution
Sackheim’s Chemistry: Chapter 12
Summary
Electrolytes
Acids(sour)
Strong (pH = 1-3)Completely ionized
Weak (pH = 3-6)Partially ionized
Bases(bitter)
Weak (pH = 8-11)Partially ionized
Strong (pH = 11-14)
Completely ionized
NeutralizationSalts
(salty)
PostQuiz (2)
1. What is the ionization constant of water?a) Keq; b) [H2O]; c) Kw
2. The pH value indicatesa) the strength of an acid/base; b) the reactivity of acids/bases; c) the concentration of a solution
3. The pH value of human blood isa) 6.85-6.95; b) 7.35-7.45; c) 7.75-7.85
4. Define “buffer”:a) neutralization of an equilibrium reaction; b) solution which donates H+ ions; c) resists changes in pH when small amounts of acid or base is added
5. The buffer system of the blood is thea) carbonate buffer; b) chloride buffer; c) phosphate buffer
6. When the pH of the blood is low, the patient suffers froma) acidosis; b) alkalosis; c) diabetis
7. Excessive vomiting may causea) acidosis; b) alkalosis; c) diabetis
8. Salt is the product of a(n)a) acid/base reaction; b) hydrolysis reaction; c) equilibrium reaction
9. The salt used for X-ray analysis isa) KI; b) NHCO3; c) BaSO4