Volumetric analysis

• Solution


  A homogeneous mixture of a solute and a solvent
• Concentration


  The amount of solute dissolved in a given volume of the solution
• Molarity


  The number of moles of solute in 1 litre of solution
• Ways to express concentration of solutions


  • mol/L (molarity)
  • g/L
  • % (w/v) g/100cm3
  • % (v/v)cm3/100cm
  • % (w/w)g/100g
  • Parts per Million (ppm)
  • this is calculated by multiplying the concentration in g/l by 1000
• Everyday use of % v/v is in alcoholic beverages
• Calculating molarity from concentration in grams per litre and vice versa


  1. Divide concentration in g/L by molar mass to get molarity

  2. Multiply molarity by molar mass to get concentration in g/L
• Calculating number of moles from molarity and volume

  Multiply molarity by volume in litres

  
• Calculating the effect of dilution on concentration

  Use the formula: Vc x Mc = Vd x Md
• Colour intensity can be used as an indicator of concentration
• Primary standard

  A substance that can be directly weighed and used to make a standard solution
• Standard solution

  A solution whose concentration is accurately known
• Requirements for a primary standard

  • Available in a pure and stable solid state
  • Soluble in water
  • High molecular mass
  • Anhydrous (no water of crystallisation)

  
• Examples of primary standards

  • Na2CO3
  • NaCl
• Examples of non-primary standards

  • HCl (gas)
  • I2 (sublimes)
  • H2SO4 (absorbs moisture)
  • NaOH (absorbs CO2 and moisture)
  • KMnO4 (reduced by sunlight)
• Pipette

  • Used to accurately measure a known volume of liquids/solutions
  • Procedure for cleaning, filling and transferring solutions using a pipette
• Calculating Md

  1. 15 × 2

  2. 250

  3. = Md

  4. 0.12 M = Md
• Primary Standard

  A substance that can be directly weighed and used to make a standard solution. It must: be available in a pure and stable solid state, be soluble in water, have a high molecular mass, and be anhydrous (no water of crystallisation)
• Primary Standards

  • Na2CO3
  • NaCl
• Not Primary Standards

  • HCl (it is a gas)
  • I2 (it sublimes)
  • H2SO4 (it absorbs moisture from air)
  • NaOH (it absorbs CO2 and moisture from air)
  • KMnO4 (it is reduced by sunlight)
• Pipette

  • Used to accurately measure a known volume of liquids/solutions
  • Procedure for cleaning, filling and transferring solutions using a pipette
• Burette

  • Used to accurately measure the volume of liquid/solution added
  • Procedure for cleaning and filling a burette
• Conical Flask

  • A specially shaped flask that allows swirling without spilling the contents
  • Procedure for cleaning the conical flask
• Acid/Base Titration to standardise HCl using Na2CO3

  1. Acid: HCl (strong acid)

  2. Base: Na2CO3 (weak base)

  3. Indicator: Methyl Orange (SAWBMO), Colour change: Yellow to Red

  4. Equation: 2HCl + Na2CO3 → NaCl + H2O + CO2

  5. Ratio: 2 HCl : 1 Na2CO3
• Sample calculation for standardising HCl using Na2CO3
• Acid/Base Titration to determine concentration of ethanoic acid in vinegar

  1. Acid: CH3COOH (weak acid)

  2. Base: NaOH (strong base)

  3. Indicator: Phenolphthalein (WASBPH), Colour change: Pink to Colourless

  4. Equation: CH3COOH + NaOH → CH3COONa + H2O

  5. Ratio: 1 CH3COOH : 1 NaOH

  
• Notes on determining concentration of ethanoic acid in vinegar

  
• Sample calculation for determining concentration of ethanoic acid in vinegar

  
• Acid/Base Titration to determine amount of water of crystallisation in washing soda

  1. Acid: HCl (strong acid)

  2. Base: Na2CO3 (weak base)

  3. Indicator: Methyl Orange (SAWBMO), Colour change: Yellow to Red

  4. Equation: 2HCl + Na2CO3 → NaCl + H2O + CO2

  5. Ratio: 2 HCl : 1 Na2CO3

  
• Notes on determining amount of water of crystallisation in washing soda

  
• Sample calculation for determining amount of water of crystallisation in washing soda

  
• Acidic solutions have pH values less than 7.
• Basic (alkaline) solutions have pH values greater than 7.
• Neutral solutions have pH values equal to 7.