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

Fundamental SI units Remember the correct abbreviations! Mass kilogram (kg) Volume liter (L) Distance meter (m) Temperature kelvin (K) Time second (s) Current ampere (A) Amount of substance mole (mol) Luminous intensity candela (cd)

Some other SI and non-SI units Length angstrom (Å) Force newton (N) Pressure pascal (Pa), atmosphere (atm) Energy, work, heat joule (J) Power watt (W) Electric charge coulomb (C) Electric potential volt (V) Electric resistance ohm () Electric capacitance farad (F) Temperature degree Celsius (°C) degree Fahrenheit (°F)

Some common prefixes for exponential notation 1012 tera (T) 109 giga (G) 106 mega (M) 103 kilo (k) 10-1 deci (d) 10-2 centi (c) 10-3 milli (m) 10-6 micro (μ) 10-9 nano (n) 10-12 pico (p) 10-15 femto (f) 10-18 atto (a) Remember the correct abbreviations!

Commonly used equalities 103 mg = 1 g milli = thousandth 1 mg = 10-3 g 106 μg = 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

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.

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

Concentration scales (cont.) Weight / weight (w/w) basis % (w/w) = ppt (w/w) = ppm (w/w) = ppb (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.

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

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

Concentration examples Concentrated HCl Alcoholic beverage Color indicator for titrations

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?

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

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

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

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

Concentration-dilution formula A 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.

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:

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

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