7MolarityThe most common unit of solution concentration is molarity (M)The molarity of a solution is defined as the number of moles of solute per one liter of solution.Note that the unit of volume for molarity is liters, not milliliters or some other unit.Also note that one liter of solution contains both the solute and the solvent.Molarity, therefore, is a ratio between moles of solute and liters of solution.To prepare laboratory solutions, usually a given volume and molarity are required.To determine molarity, the formula weight or molar mass of the solute is needed.
15Simple dilutionSimple diluttion - A unit volume of liquid material of interest is combine with an appropriate volume of a solvent liquid to archieve the desired concentrationDilution factor – the total number of unit volume in which material will be dissolvedDiluted material must be thoroughly mixed to achieve the true dilution1:10 dilution
161:10 dilution (verbalize as 1 to 10) = 1 unit volume of diluent (material to be diluted) + 9 unit volumes of the solventHence, 1+9=101:300 = 1 unit volume of diluent volumes of solvent medium
17Sometimes, solution are expressed in term of ‘X’, an indicator of relative solute concentration. Eg. Buffer – made up to 20X stock solution.1X buffer = 1 unit volume of buffer + 19 volumes of water
18Mixing parts or volumes Not to confused with simple dilutionInstruction:Add 1 part glacial acetic acid with 3 parts waterMix 1 volume of glacial acetic acid with 3 volume waterMake up a 1:3 acetic ethanol solution(just add accordingly)But, if the instruction to make a 1:3 dilution of acetic acid in ethanol = 1 unit acetic acid with 2 unit volumes of ethanol
20V1C1 = V2C2V= volume;C=concentration (In what ever units you are working)Eg: Suppose you have 3 ml of stock solution of 100 mg/ml ampicilin and you want to make 200 ul of solution having 25 mg/ml. What is the volume of the stock to use?
22StoichiometryRefers to quantities of reactants and products in a balanced chemical reaction.aA + bB cC + dDi.e. a moles of A react with b moles of B to give c moles of C and d moles of D.a,b,c,d are stoichiometric quantitiesPaul Ashall, 2008
23TutorialHow would you prepare 400 ml of a 0.24 M NaCl solution (MW=58.44 g/mole)?How would you prepare 750 ml of a 0.35 M Na2PO4(MW=141.96)?How would you prepare 225 ml of a 0.15 M citric acid solution (MW=453.6)?What volume of stock 0.24 NaCl is needed to prepare 75 ml of 0.1 M NaClWhat volume of stock 0.35 M Na2PO4 is needed to prepare 150 ml of 0.2 M Na2PO4 ?
24What volume of stock 0.15 M citric acid is needed to prepare 230 ml of 2.5x10-3M citric acid. How much (ml) 3x10-3 M Na2PO4can be prepared from 20 ml of 0.2 M Na2PO4If you have 35 ml of 0.1 M NaCl, is it enough to prepare 200 ml of 0.06 M NaCl?
25For each of the following, indicate the mass (g) of reagent needed to prepare 125 ml of the indicated percent solutionA protocol calls for using a working concentration of 1.5X10-4M boric acid. To save shelf space, you decide to make up a 20X stock solution. What will be the molarity of that stock solution?ReagentMolecular weightPercent solution needed (125 ml)Mass of reagent (g)NaCl58.4410%Na2PO4141.964.5%Citric Acid453.62.5%