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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 (= 0.1 F NaCl) gives 0.1 M Na+ and 0.1 M Cl- in solution • 0.5 M HCl (= 0.5 F HCl) gives 0.5 M H+ and 0.5 M Cl- in solution

  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 vanadium in a solution that contains 281.5 mg/L of vanadium?

  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 is important 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. Note that you can use any units you want for conc. and vol. as long as they are the same on both sides of the equation.

  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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