Concentrations & Pharmaceutical Calculations

• Why is knowledge of concentrations vital within pharmacy?

  It is essential for effective therapy.
• What are the two key concentrations in pharmacy?

  Drug concentration in formulation and body.
• What units are used to express concentration?

  Percentages, fractions, and ratios.
• How can grams per litre be expressed?

  As a ratio or fraction.
• What is an example of percentage strength?

  Vodka is 40% alcohol.
• What does parts per million represent?

  A ratio or fraction.
• How is concentration defined in pharmacy?

  Strength of component x in component y.
• What does m/m stand for in concentrations?

  Mass by mass.
• What is the formula for mass by volume (m/v)?

  Mass of x in volume of y.
• What does v/v stand for in concentrations?

  Volume by volume.
• What is the relationship between mass and weight in pharmacy?

  Mass and weight are used interchangeably.
• What are the units of mass in pharmacy?

  Grams, kilograms, etc.
• What is the true unit of weight?

  Newtons (N).
• How is concentration expressed in a powder mix?

  Mass by mass (m/m or w/w).
• How is concentration expressed in a solution?

  Mass by volume (m/v) or volume by volume (v/v).
• What is the formula for expressing ratios in pharmacy?

  Any units as long as they are stated.
• What does a percentage express?

  Parts per 100 parts.
• How is a 20 g/L solution expressed as a percentage strength?

  2% w/v.
• How would you express 5 mg of drug in a 100 mg tablet as a fraction?

  5/100.
• How would you express 5 mg of drug in a 100 mg tablet as a ratio?

  5:100.
• How would you express 5 mg of drug in a 100 mg tablet as a percentage?

  5%.
• What is the significance of moles in concentration?

  They deal with particle numbers rather than masses.
• What is the mass corresponding to one mole of an element?

  6.022 x 10²³ particles.
• What is the molecular weight (MW) of an element?

  The mass corresponding to 6.022 x 10²³ particles.
• How is the mass of one mole expressed?

  In grams.
• How is molarity defined?

  Moles of substance per litre of solution.
• What is the formula for calculating molarity?

  mol = mass/mr.
• What is molality defined as?

  Moles of solute per kilogram of solvent.
• How do you calculate molality?

  Mass present (per kg) = molality.
• How do you calculate molarity for aspirin dissolved in water?

  0.22 mol/L.
• How do you calculate molality for citric acid monohydrate?

  0.12 mol/kg.
• Why is molarity preferred in pharmaceutical practice?

  Volumes are affected by temperature, masses are not.
• How do you adjust a formula for different volumes?

  Proportionally scale the ingredients.
• How do you prepare a double strength chloroform water?

  1 in 20 dilution of concentrated chloroform water.
• What does a percentage strength of 5% w/w mean?

  5 g in 100 g.
• How is the mass of drug calculated in a solution?

  Using the formula b' = (a' / a) x b.
• How much volume should be administered for 250 mg of amoxicillin?

  5 mL.
• How much drug is in 70 mL of a 30% w/v solution?

  21 g.
• How much drug is in 1 L of a 30% w/v solution?

  300 g.
• How is a 1 in 500 potassium permanganate solution prepared?

  1 g drug in 500 mL product.