ChemPhys UNIT 6b: Electrolytes

Chemistry & Physics

UNIT 6B: ELECTROLYTES

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

Convenient chemistry

Salts

SOLUBILITY

HYDROLYSIS

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

The End