NSC1951 Lecture 18 Acids

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NSC1951 Lecture 18 Acids Bases
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Objectives

• Properties of acids and bases
• The pH scale
• Distinguish between strong and weak acids and
  list the clinical uses of these acids
• Distinguish between strong and weak bases and
  list the clinical uses of these acids
• Understand neutralisation and the clinical
  applications of neutralisation

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1. PROPERTIES OF ACIDS BASES

• Acids
• Produce hydrogen ions (H) in H2O
• Taste sour Marieb, Fig 15.1
• Turn blue litmus (vegetable dye) ? red
• Act as electrolytes in solution
• Neutralise solutions containing hydroxide ions
  (OH -)
• React with several metals releasing H2(g) ?
  corrosion
• React with carbonates releasing CO2(g)
• Destroy body tissue

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• Bases
• Produce or cause an increase in hydroxide ions
  (OH-) in H2O
• Taste bitter Marieb, Fig 15.1
• Turn red litmus ? blue
• Act as electrolytes in solution
• Neutralise solutions containing hydrogen ions (H
  )
• Have a slippery, soapy feel
• Destroy body tissue/ dissolve fatty (lipid)
  material

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2. THE pH SCALE

• Ion Product of Water
• Pure H2O at 25C
• Some molecules ionise
• H2O ? H OH-
• H 1 x 10-7 M OH-

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• ? Ion Product of H2O
• H x OH- 1 x 10-7 x 1 x
  10-7
• Add exponents
• 1 x 10-14

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• Acidic solution
• H gt OH-
• Neutral solution
• H OH-
• Basic solution
• H lt OH-

Timberlake, Fig 9.3
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• pH describes H OH-
• Indicates if a fluid is
• 0 Acidic H 100 OH- 10-14
• 7 Neutral H 10-7 OH- 10-7
• 14 Basic H 10-14 OH- 100

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On the pH scale, values below 7 are acidic, a
value of 7 is neutral, and values above 7 are
basic.
Marieb, 2.12
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3. STRENGTHS OF ACIDS
Marieb, Fig 26.11

• Strong Acids (very few)
• Eg
• HCl Hydrochloric Acid
• Stomach acid
• HNO3 Nitric Acid
• May be used to cauterise warts
• Drugs, explosives, fertilisers, dyes
• H2SO4 Sulphuric Acid
• ? conc. to treat stomach hypoacidity
• Fertilisers, dyes, glues

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• Strong acids are
• Strong electrolytes
• 100 ionisation ? good conductors
• Severe burns to body tissue
• Stomach lining protected against HCl by mucus

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• Dissociation in Water Strong acids
• Polar covalent molecules ? ions
• Eg.
• HCl(l) H(aq) Cl-(aq)
•  
• HNO3(l) H (aq) NO3- (aq)
•  
• H2SO4(l) 2H (aq) SO42-
  (aq)

H2O
H2O
H2O
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• Dissociation in water Weak acids (cont)
• CH3COOH (l) H (aq) CH3COO- (aq)
• H2CO3 (l) H (aq)
  HCO3-(aq)
• H3PO4 (l) H (aq) H2PO4- (aq)

H2O
H2O
H2O
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Marieb, Fig 26.11
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4. STRENGTHS OF BASES

• Strong Bases
• Eg
• NaOH Sodium Hydroxide
• Removes grease drains, ovens
• Mg(OH)2 Magnesium hydroxide
• Antacid Laxative
• Al(OH)3 Aluminium hydroxide
• Antacid
• Absorbs toxins, gases,
• Causes constipation

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• Strong bases are
• Strong electrolytes
• 100 dissociation in water ? good conductors
• Severe damage to skin eyes
• (Group 1A elements)

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• Dissociation in Water Strong bases
• Metal hydroxides ? ions
• Eg.
• NaOH(s) Na(aq) OH-(aq)
•  
• Mg(OH)2(s) Mg 2 (aq) OH-
  (aq)
•  
• Al(OH)3(s) Al 3(aq)
  OH- (aq)

H2O
H2O
H2O
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• Weak bases are
• Weak electrolytes
• Do not contain OH but react with H2O ? small
  numbers of OH
• Reaction with Water Weak bases
• NH3(g) H2O NH4 (aq) OH (aq)
• HCO3 (aq) H2O H2CO3 (aq) OH-(aq)

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5. ACID-BASE NEUTRALISATION

• Neutralisation Reaction
• Acid Base ? Salt Water
• HCl NaOH ? NaCl H2O
• H OH ? H2O
• Neutralise each other
• Must be equal concentrations

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• Antacids clinical applications (Check for side
  effects!!)
• Neutralise excess stomach acid
• Raise stomach pH gt 4
• Pepsin inactive
• Assist with ulcer treatment
• ? solubility in H2O but still produce high of
  ions

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• Eg
• Mg(OH) 2 Milk of Magnesia in Mylanta
• 2HCl Mg(OH) 2 ? MgCl 2 2H2O
• Al(OH) 3 In Mylanta
• 3HCl Al(OH) 3 ? AlCl 3 3H2O

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• CaCO 3
• 2HCl CaCO 3 ? CaCl 2 H2O CO 2 (g)
• Also a Ca 2 supplement
• Long term overuse ? Ca 2 levels
• ? risk kidney stones (renal calculi)

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• NaHCO 3 Baking Soda
• Not recommended!!
• HCl NaHCO 3 ? NaCl H2O CO2
  (g)
• Elderly tend to OD
• ? Stomach can explode

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Key Concepts
Acids and Bases
Acid
Base
Ionization in water
undergo
produce
produce
Neutralization
gives
H ions
OH- ions
to form
OH-
H
100
Small
Salt

100
Small
product
Water
H x OH-
Strong acid
Weak acid
Strong base
Weak base
is
pH
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REFERENCES
Cree Rischmiller, 2001 Ch. 8 pp
205-216 Marieb, 2004 Ch. 2 pp 41-43, Ch.
16 p556 Ch. 27 p1049
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Review questions

1. List the properties of acids bases.
2. Discuss the pH scale
   Define the ion product of water
   indicate how this is determines the pH scale.
   
   Use the pH scale to determine if a given
   solution is acidic, neutral or basic.
3. Distinguish between strong acids weak acids
   List clinical uses of these acids write
   equations for their dissociation in water

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Review questions (cont)

• Distinguish between strong weak bases List
  clinical uses of these bases write equations
  for their dissociation in water.
• Complete simple equations for the neutralisation
  reaction of an acid a base Discuss clinical
  applications of acid-base neutralisation.