5Solutions Types of solutions we are dealing with today: solid to liquidliquid to liquid
6Solution PreparationWhen you are required to make a solution of accurate concentration, a volumetric flask is used.We never make solutions of accurate concentration in:BeakersGraduated cylindersErlenmeyer flasks
7Solution Preparation from Solids Determine the mass of the solid needed by using:Molar mass of the solidTotal volume desiredFinal concentration desiredCalculation:Mass, g = [ ], mol/L x MW, g/mol x Vol, LRemember the tolerances on your glassware!
8Solution Preparation from Solids Make the solution:Weigh out the appropriate mass of solid.Place a small volume of distilled water in the volumetric flask.Add the solid to the volumetric flask.Add some more distilled water to the flask, stopper, and invert several times.Add distilled water to the calibration line (fill to volume) using a medicine dropper, stopper, and invert several times.
9Solution Preparation from Liquids Determine the volume of stock solution needed by using:Concentration of stock solution (M1)Desired concentration of diluted solution (M2)Desired volume of diluted solution (V2)Calculation:M1V1 = M2V2Remember the tolerances of your glassware!
10Solution Preparation from Liquids Make the solution:Obtain the appropriate volume of stock solution using a graduated cylinder. (Always add a few mL extra.)Place a small volume of distilled water in a volumetric flask.Use the appropriate pipet to transfer the correct volume of stock solution from the graduated cylinder to the volumetric flask.Add some more distilled water to the flask, stopper, and invert several times.Add distilled water to the calibration line (fill to volume) using a medicine dropper, stopper, and invert several times.
11Electrolytes Strong Electrolytes 100% dissociation and high conductivityNaCl(s) Na+(aq) + Cl-(aq)Weak Electrolytespartial dissociation and partial conductivityCH3COOH(aq) CH3COO-(aq) + H+(aq)Non Electrolytesno dissociation and no conductivityC12H22O11(s) C12H22O11(aq)
12ConductivityThe ability of an aqueous solution to conduct electricity is dependent on the presence of ions in solution.Conductivity or K has units of S/cm, mS/cm, or S/cm.We measure conductivity so we can make a comparison regarding relative numbers of ions present in solution.
13ConductivityThe extent to which a solution conducts electricity is dependent on the proportional amount of ions present in solution.Which of the following will have a higher conductivity?NaCl vs. CaCl2 Why?NaCl vs. C6H5COOH Why?
14Procedure Conductivity Standard Conductivity, S/cm Distilled Water Soak your conductivity probe in distilled water for 30 minutes before starting your experiment. Why?CalibrationConductivity StandardConductivity, S/cmDistilled Water0.0M KCl578.0M KCl1202.6M KCl2949.6M KCl5560.0M KCl8426.9
15ProcedureAny glassware that will be containing non-electrolytes or weak electrolytes need to be rinsed thoroughly with distilled water prior to use!!!Make up your three known solutions.Measure the conductivity of your known solutions, distilled water, tap water, and three unknowns.The unknowns are already at the required concentration. No dilution is necessary!
16Safety Concerns Reagents: Eye Contact: Skin Contact: Inhalation: Acetic Acid (3%)KClNaClSucroseEye Contact:Irritation, redness, pain, and possible damageSkin Contact:Irritation. May cause sensitization and / or allergic reaction. Absorption may cause symptoms similar to ingestionInhalation:Irritation and coughingIngestion:Gastrointestinal irritation, nausea, vomiting, diarrhea, prostration, dehydration and congestion of internal organs, and violent inflammatory reactions in the gastrointestinal tract
17WasteAll neutral solutions can go down the drain with plenty of water when you are finished. Solutions with a pH above 8 or below 6 need to go in the acid / base waste container in the fume hood.
18Next Week - Skill Evaluations Read through pages 281 – 300.Remember to bring your goggles and lab manual.