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Brief review of important concepts for quantitative analysis

Brief review of important concepts for quantitative analysis. CHM 235 – Dr. Skrabal. Some important units of quantification Units for expressing concentrations in solids and liquids Concentration-dilution formula. Fundamental SI units. Remember the correct abbreviations!.

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Brief review of important concepts for quantitative analysis

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  1. Brief review of important concepts for quantitative analysis CHM 235 – Dr. Skrabal • Some important units of quantification • Units for expressing concentrations in solids and liquids • Concentration-dilution formula

  2. Fundamental SI units Remember the correct abbreviations!

  3. Some other SI and non-SI units

  4. Some common prefixes for exponential notation Remember the correct abbreviations!

  5. Commonly used equalities 103 mg = 1 g milli = thousandth 1 mg = 10-3 g 106μg = 1 g micro = millionth 1 μg = 10-6 g 109 ng = 1 g nano = billionth 1 ng = 10-9 g 1012 pg = 1 g pico = trillionth 1 pg = 10-12 g

  6. Concentration scales • Molarity (M) = • Molality (m) = • Molarity is a temperature-dependent scale because volume (and density) change with temperature. • Molality is a temperature-independent scale because the mass of a kilogram does not vary with temperature.

  7. Concentration scales (cont.) • Formality (F) = • Formality is sometimes used to express the concentration of substances, such as electrolytes, acids, and bases, that turn into different species in solution. • For example: • 0.1 M NaCl gives 0.1 M Na+ and 0.1 M Cl- in solution • 0.5 M HCl gives 0.5 M H+ and 0.5 M Cl- in solution Based on D.Harvey (2000) Modern Analytical Chemistry

  8. Concentration scales (cont.) Weight / weight (w/w) basis % (w/w) = ppt (w/w) = ppm (w/w) = ppb (w/w) = ppt (w/w) =  percent  ppt = parts per thousand  ppt = parts per million  ppt = parts per billion  ppt = parts per trillion This scale is useful for solids or solutions.

  9. Concentration scales (cont.) Weight / volume (w/v) basis % (w/v) = ppt (w/v) = ppm (w/v) = ppb (w/v) = ppt (w/v) =  percent  ppt = parts per thousand  ppt = parts per million  ppt = parts per billion  ppt = parts per trillion

  10. Concentration scales (cont.) Volume / volume (v/v) basis % (v/v) = ppt (v/v) = ppm (v/v) = ppb (v/v) = ppt (v/v) =  percent  ppt = parts per thousand  ppt = parts per million  ppt = parts per billion  ppt = parts per trillion

  11. Concentration examples • Concentrated HCl • Alcoholic beverage • Color indicator for titrations

  12. Concentration example: %(w:v) What is the concentration, on a %(w:v) basis, of V in a solution that contains 281.5 mg/L of V?

  13. Concentration scales (cont.) • Parts per million, billion, trillion are very often used to denote concentrations of aqueous solutions: Note: ppt = parts per trillion

  14. Concentration scales (cont.) It will be very useful to memorize: • 1 part per million (ppm) = 1 mg / L • 1 part per billion (ppb) = 1 μg / L • 1 part per trillion (ppt) = 1 ng / L

  15. Concentration examples Conversion of molarity to ppm Solution of 0.02500 M K2SO4

  16. Concentration examples What is concentration (in ppm) of K+ in this solution? Solution of 0.02500 M K2SO4

  17. Concentration-dilution formulaA very versatile formula that you absolutely must know how to use • C1 V1 = C2 V2 where C = conc.; V = volume • M1 V1 = M2 V2 where M = molarity • Cconc Vconc = Cdil Vdil where “conc” refers to the more concentrated solution and “dil” refers to the more dilute solution

  18. Concentration-dilution formula example Problem: You have available 12.0 M HCl (conc. HCl) and wish to prepare 0.500 L of 0.750 M HCl for use in an experiment. How do you prepare such a solution? Cconc Vconc = Cdil Vdil Write down what you know and what you don’t know:

  19. Concentration-dilution formula example Problem: You have available 12.0 M HCl (conc. HCl) and wish to prepare 0.500 L of 0.750 M HCl for use in an experiment. How do you prepare such a solution? Cconc Vconc = Cdil Vdil Cconc = 12.0 mol L-1 Cdil = 0.750 mol L-1 Vconc = ? Vdil = 0.500 L Vconc = (Cdil)(Vdil) / Cconc Vconc = (0.750 mol L-1) (0.500 L) / 12.0 mol L-1 Vconc = 3.12 x 10-2 L = 31.2 mL

  20. Concentration-dilution formula example Great! So how do you prepare this solution of 0.750 M HCl? • Use a pipet or graduated cylinder to measure exactly 31.2 mL of 12.0 M • Transfer the 31.2 mL of 12.0 M HCl to a 500.0 mL volumetric flask • Gradually add deionized water to the volumetric flask and swirl to mix the solution • As the solution gets close to the 500.0 mL graduation on the flask, use a dropper or squeeze bottle to add water to the mark • Put the stopper on the flask and invert ~20 times to mix

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