Physical Properties of Solution PHM 312

What is the definition of a solution?

A chemically and physically homogeneous mixture of two or more substances.

What does "homogeneous" mean in the context of a solution?

The mixture is uniform; all parts are identical. When subjected to routine chemical and physical analysis, the parts test the same.

In a solution, what is the solute and what is the solvent?

The solute is the substance dissolved in another substance, known as the solvent. There is no distinction between components—the solvent is the "major component."

What is the primary solvent used in pharmaceutical solutions?

Water (aqueous). In some cases, the solvent is water + ethanol (elixirs, tinctures, etc.).

What is the solvent and main component of syrups?

Syrups contain large amounts of sucrose (> approximately 80%).

What are the specific requirements for parenteral and ophthalmic solutions?

They must be sterile and isotonic.

What is a dispersed system?

A heterogeneous (not continuous) system where you can distinguish between various components.

What is a suspension (as a dispersed system)?

A system of solids + liquids, where the solids are poorly soluble in the liquid.

What is an emulsion (as a dispersed system)?

A system of liquids + liquids, where the liquids are immiscible.

What is required for the physical stability of suspensions and emulsions?

Intervention of a third substance: a suspending agent for suspensions; an emulsifier for emulsions.

What are the characteristics of oral solutions (elixirs, syrups)?

Taken by mouth; inactives are added for flavor, viscosity, and other purposes; water is the usual solvent.

What are the characteristics of topical solutions?

Application to skin or mucous membranes; can be aqueous or alcoholic.

What are the characteristics of otic (aural) solutions?

For the ear; usually not aqueous; solvents include glycerin, propylene glycol, and polyethylene glycol.

What are the characteristics of ophthalmic solutions?

For use in the eye; inactives for viscosity, tonicity, preservation, and other purposes; free of particulates; isotonic; sterile.

What are the characteristics of parenteral solutions?

For injection IV, IM, or SQ; few if any inactives; rigid standards for sterility; free of particulates; free of pyrogens.

What are the advantages of liquid solutions?

Faster onset of activity, good for children and the elderly, flexible dosing, and can be given by any route of administration.

What are the disadvantages of liquid solutions?

Bulkiness, less stable than solid dosage forms (shelf-life), and more pronounced taste.

What are the different ways concentration can be expressed?

Percent solution (%), Ratio strength, Molarity, Milliequivalents/unit volume (Normality), Mole fraction, Molarity, and Osmolarity.

What happens to electrolytes when dissolved in water?

They dissociate completely ("strong") or partially ("weak") into ions.

What happens to salts of a weak electrolyte when they dissolve?

They completely ionize.

What happens to nonelectrolytes when dissolved in water?

They do not dissociate into ions. (Note: Nonelectrolytes may hydrolyze, e.g., sucrose, but this is not the same as dissociation and does not occur easily).

What are examples of strong electrolyte salts?

KBr, NaCl, NH₄Cl, KNO₃, CaCl₂, Na Benzoate, penicillin VK, Ephedrine sulfate, Tetracycline HCl.

What are examples of strong acids and bases?

HCl, HNO₃, NaOH, KOH.

Do weak electrolytes completely dissociate?

No, they do not completely dissociate; their dissociation depends on pH and pKa.

What are examples of weak acids?

Acetic acid, benzoic acid, aspirin, ampicillin, phenobarbital.

What are examples of weak bases?

NH₃, atropine, nicotine, codeine.

Although most drugs are acids or bases, in what form are they generally used?

They are generally used in the salt form, which are strong electrolytes.

What is the Henderson-Hasselbalch equation used for?

It allows you to predict the degree of ionization as a function of pH and pKa.

What is the Henderson-Hasselbalch equation for weak acids?

pH = pKa + log ([A⁻]/[HA]).

What is the Henderson-Hasselbalch equation for weak bases?

pH = pKa + log ([B]/[BH⁺]).

What is the definition of pH and pKa?

pH = -log [H⁺]; pKa = -log [Ka].

Why is the Henderson-Hasselbalch equation important in pharmacy?

Most medications are weak electrolytes, and the pH of a solution can affect drug activity by altering drug stability, drug solubility, and drug partitioning.

How does pH affect drug stability?

Drug degradation can occur as a function of pH.

How does pH affect drug solubility?

Ionization increases solubility.

How does pH affect drug partitioning?

The unionized form of the drug has better partitioning and permeates biological membranes better.

What is important to control in pharmaceutical applications to manage pH?

It is important to use buffers to control the pH of a solution.

What is Molarity (M, c, C, [ ]) and is it temperature-dependent?

Moles (gram molecular weight) of solute in 1 L of solution, also millimoles/mL (mM). It is temperature-dependent.

What is Normality (N) and is it temperature-dependent?

Equivalents (gram equivalent weights) of solute in 1 L of solution, also mEq/mL. It is temperature-dependent.

What is Molality (m) and is it temperature-dependent?

Moles of solute in 1000 g of solvent. It is temperature-independent.

What is Mole fraction (X)?

The ratio of the moles of one constituent (e.g., the solute n₂) of a solution to the total moles of all constituents (solute and solvent n₂ + n₁). X₁ = n₁/(n₁+n₂), X₂ = n₂/(n₁+n₂), and X₁ + X₂ = 1.

How is Mole percent calculated?

Moles of one constituent in 100 moles of the solution; obtained by multiplying mole fraction by 100 (X₂ × 100).

What is Percent by weight (% w/w) and is it temperature-dependent?

Grams of solute in 100 g of solution. It is temperature-independent.

What is Percent by volume (% v/v) and is it temperature-dependent?

Milliliters of solute in 100 mL of solution. It is temperature-dependent.

What is Percent weight in volume (% w/v) and is it temperature-dependent?

Grams of solute in 100 mL of solution. It is temperature-dependent.

What is Milligrams per deciliter (mg/dL) and is it temperature-dependent?

Milligrams of solute in 100 mL of solution. It is temperature-dependent.

What is Osmolality (mOsmol/kg) and is it temperature-dependent?

The mass of solute that, when dissolved in 1 kg of water, will exert an osmotic pressure equal to that exerted by a gram molecular weight of an ideal unionized substance dissolved in 1 kg of water. It is temperature-independent.

What is Osmolarity (mOsmol/L) and is it temperature-dependent?

The mass of solute that, when dissolved in 1 L of solution, will exert an osmotic pressure equal to that exerted by a gram molecular weight of an ideal unionized substance dissolved in 1 L of solution. It is temperature-dependent.

What did Avogadro state regarding gases?

Equal volumes of different gases (at the same T, P) contain the same number of molecules.

What is Avogadro's number?

6.0225 x 10²³.

What are the units for Molecular Weight (MW)?

Grams/mol or mg/mmol.

What happens to strong electrolytes in solution regarding ionization?

They undergo extensive ionization (e.g., CaCl₂ → Ca²⁺ + 2Cl⁻).

What are osmoles?

Osmoles reflect the total number of ions formed in solution.

What is the formula for osmoles?

osmoles = moles × i (where i represents the van't Hoff factor).

How many osmoles are generated by 1 mole of KCl?

2 osmoles (KCl → K⁺ + Cl⁻).

How many osmoles are generated by 1 mole of NaCl?

2 osmoles (NaCl → Na⁺ + Cl⁻).

How many osmoles are generated by 1 mole of MgCl₂?

3 osmoles (MgCl₂ → 1Mg²⁺ + 2Cl⁻).

For nonelectrolytes (no ionization), what is the van't Hoff factor (i) and osmoles formula?

i = 1 and osmoles = moles.

For weak electrolytes, what is the formula for the van't Hoff factor (i)?

i = 1 + α(ν - 1), where α is the degree of dissociation and ν is the theoretical number of ions generated per molecule.

What is the van't Hoff factor (i) for acetic acid assuming 2% dissociation (α = 0.02, ν = 2)?

i = 1 + 0.02(2 - 1) = 1.02.

What does electroneutrality mean in an electrolyte solution?

It maintains an equal number of positive (+) and negative (-) charges.

In the example CaCl₂ → Ca²⁺ + 2Cl⁻, how many equivalents per mole are generated?

2 equivalents/mole (1 mol of CaCl₂ generates two (+) and two (-) charges).

What is the formula for Equivalent Weight (EqWt)?

EqWt = MW / (# eq/mole).

What are the units for equivalent weight?

g/Eq OR mg/mEq.

How many equivalents are generated by 1 mole of KCl?

1 equivalent (KCl → K⁺ + Cl⁻).

How many equivalents are generated by 1 mole of NaCl?

1 equivalent (NaCl → Na⁺ + Cl⁻).

How many equivalents are generated by 1 mole of MgCl₂?

2 equivalents (MgCl₂ → Mg²⁺ + 2Cl⁻).

Calculate the number of millimoles contained in 5.55 g CaCl₂ (MW = 111).

5.55 g = 5550 mg. 5550 mg × (1 mmol / 111 mg) = 50 mmol.

Calculate the number of milliosmoles contained in 5.55 g CaCl₂ (MW = 111).

mOsmol = mmol × i = 50 mmol × 3 = 150 mOsmol.

Calculate the number of milliequivalents contained in 5.55 g CaCl₂ (MW = 111).

mEq = mmol × mEq/mmol = 50 mmol × 2 = 100 mEq.