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Introduction to Chemical Concepts

EXPRESSIONS OF SOLUTES:

  • MOLARITY (M):
    • by definition, 1 mole per liter.
    • Solvent is added and brought up to 1 L
  • MOLALITY (m):
    • by definition, 1 mole per kg of solvent
    • for example, an aqueous solution with water, 1 kg of H20 is approximately 1 L
    • 1mole is added to 1 kg of solvent
  • NORMALITY (N):
    • by definition, one equivalent per liter
    • What is an equivalent?
      • Molecular weight divided by the number of replaceable protons. For example, HCl there is one replaceable proton and therefore normality = molarity
      • In contrast, H2SO4 or H3PO4 have two and three replaceable protons, respectively. In the case of H2SO4, a 1 N solution would be equal to a 0.5 M solution.
    • The advantage of normality is in titration, 1 equivalent of acid will completely normalize one equivalent of base.
  • EQUILAVENTS (Eq):
    • Electrolyte concentrations are expressed in milliequivalents (mEq)
    • For single elements, an equivalent is the molecular weight divided by the absolute value of the oxidative state.
      • Na+1: 23 gm = 1 Eq and 23 mg = 1 mEq
      • Cl-1: 35.5 gm = 1 Eq and 35.5 mg= 1 mEq
      • Ca+2: 20.0 gm = 1 Eq and 20 mg = 1 mEq
    • For compounds, equivalents are calculated as the molecular weight divided by the absolute value of the highest oxidative state
      • NaCl: 58.5 gm = 1 Eq NaCl
      • CaCl2: 55.5 gm = 1 Eq CaCl2
      • AlCl3: 44 gm = 1 Eq AlCl2
    • Equivalent weights do not always remain the same since they result from the net electron change
  • PERCENT COMPOSITION SOLUTIONS
    • weight/weight (w/w)
      • gm of solute per gm of solvent
      • Example:
        • 10% (w/w) NaOH: 10 gm of NaOH and 90 gm H20
    • weight/volume (w/v)
      • Example:
        • 10% (w/v) NaOH: 10 gm of NaOH dissolved in a small amount of solvent then brought up to 100 mL
    • volume/volume (v/v)
      • Example:
        • 30% Ethanol: 30 mL of 100% Ethanol and 70 mL H20
  • CLINICAL EXAMPLES
    • mg % = mg/dL = mg/100 mL
  • TRACE METALS
    • ppm (parts per million): mg / L
    • ppb (parts per billion) µg / L