3 Concentration = # of moles volume (L) V = 1000 mL V = 1000 mL n = 8 moles[ ] = 32 molarV = 1000 mLV = 1000 mLV = 5000 mLn = 2 molesn = 4 molesn = 20 molesConcentration = 2 molar[ ] = 4 molar[ ] = 4 molar
4 Making Molar Solutions …from liquids(More accurately, from stock solutions)
5 Concentration…a measure of solute-to-solvent ratio concentrated vs dilute“lots of solute” “not much solute”“watery”Concentration of a solution describes the quantity of a solute that is contained in a particular quantity of solvent or solutionKnowing the concentration of solutes is important in controlling the stoichiometry of reactant for reactions that occur in solutionA concentrated solution contains a large amount of solute in a given amount of solution. A 10 mol/L solution would be called concentrated.A dilute solution contains a small amount of solute in a given amount of solution. A 0.01 mol/L solution would be called dilute.Add water to dilute a solution; boil water off to concentrate it.
6 Making a Dilute Solution removesamplemoles ofsoluteinitial solutionsame number ofmoles of solutein a larger volumemixMaking a Dilute Solutiondiluted solutionTimberlake, Chemistry 7th Edition, page 344
7 Concentration “The amount of solute in a solution” A. mass % = mass of solutemass of sol’nB. parts per million (ppm) also, ppb and ppt– commonly used for minerals orcontaminants in water suppliesC. molarity (M) = moles of soluteL of sol’n– used most often in this class% by mass – medicated creams% by volume – rubbing alcoholmolLMMOLARITY - Most common unit of concentrationMost useful for calculations involving the stoichiometry of reactions in solutionMolarity of a solution is the number of moles of solute present in exactly 1 L of solution:moles of solutemolarity = liters of solutionUnits of molarity — moles per liter of solution (mol/L),abbreviated as MRelationship among volume, molarity, and moles is expressed asVL M Mol/L = L (mol) = moles(L)There are several different ways to quantitatively describe the concentration of a solution, which is the amount of solute in a given quantity of solution.1. Molarity– Useful way to describe solution concentrations for reactions that are carried out in solution or for titrations– Molarity is the number of moles of solute divided by the olume of the solutionMolarity = moles of solute = mol/Lliter of solution– Volume of a solution depends on its density, which is a function of temperature2. Molality– Concentration of a solution can also be described by its molality (m), the number of moles of solute per kilogram of solvent– Molality = moles of solutekilogram solvent– Depends on the masses of the solute and solvent, which are independent of temperature– Used in determining how colligative properties vary with solute concentrations3. Mole fraction– Used to describe gas concentrations and to determine the vapor pressures of mixtures of similar liquids– Mole fraction () = moles of componenttotal moles in the solution– Depends on only the masses of the solute and solvent and is temperature independent4. Mass percentage (%)– The ratio of the mass of the solute to the total mass of the solution– Result can be expressed as mass percentage, parts per million (ppm), or parts per billion (ppb)mass percentage = mass of solute 100%mass of solutionparts per million (ppm) = mass of solute 106parts per billion (ppb) = mass of solute 109– Parts per million (ppm) and parts per billion (ppb) are used to describe concentrations of highly dilute solutions, and these measurements correspond to milligrams (mg) and micrograms (g) of solute per kilogram of solution, respectively– Mass percentage and parts per million or billion can express the concentrations of substances even if their molecular mass is unknown because these are simply different ways of expressing the ratios of the mass of a solute to the mass of the solutionM =molLD. molality (m) = moles of solutekg of solvent
8 A part per million may be hard to comprehend or visualize. Want to see how much it is?It’s a credit card lying in the middle of a football field.A step in a journey of 568 miles.Or one minute in two years.Taking that further, a part per trillion is a million times smaller than that credit card on the football field, for example, or 6 feet out of a journey of six round trips to the sun (Editor's note: 95 million miles one way to the sun).Want to see what taking in a milligram perkilogram of your body weight amounts to?It’s the equivalent of 726 people,each weighing 150 pounds,sharing a chocolate bar (~50 grams).
9 ppm 1 inch in 16 milesppb 1 inch in 16,000 milesppt 1 sec = 32,000 years
11 Glassware – Precision and Cost beaker vs. volumetric flaskWhen filled to 1000 mL line, how much liquid is present?beaker5% of 1000 mL =volumetric flask50 mL1000 mL mLRange:950 mL – 1050 mLRange:mL– mLimprecise; cheapprecise; expensive
12 Markings on Glassware Beaker 500 mL + 5% Range = 500 mL + 25 mL Graduated Cylinder1000 mL mLRange = mL + 5 mL475 – 525 mLVolumetric Flask500 mL mLRange = – mLTC 20oC “to contain at a temperature of 20 oC”22TD “to deliver”Ts“time in seconds”
14 How to mix solid chemicals Lets mix chemicals for the upcoming soap lab.We will need 1000 mL of 3 M NaOH per class.How much sodium hydroxide will I need, for five classes, for this lab?M =molL3 M =? mol1 L? = 3 mol NaOH/classx 5 classes15 mol NaOHHow much will this weigh?1 23g/mol + 16g/mol g/molMMNaOH = 40g/molTo prepare a solution that contains a specified concentration of a substance, it is necessary to dissolve the desired number of moles of solute in enough solvent to give the desired final volume of solution.Solute occupies space in the solution so the volume of the solvent that is needed is less than the desired volume of solution.To prepare a particular volume of a solution that contains a specified concentration of a solute, calculate the number of moles of solute in the desired volume of solution and then covert the number of moles of solute to the corresponding mass of solute needed.40.0 g NaOHX g NaOH = mol NaOH=600 g NaOH1 mol NaOHFOR EACH CLASS:To mix this, add 120 g NaOH into 1L volumetric flask with~750 mL cold H2O.Mix, allow to return to room temperature – bring volume to 1 L.
15 How to mix a Standard Solution Wash bottleVolume marker(calibration mark)Weighedamountof soluteUse a VOLUMETRIC FLASK to make a standard solution of known concentrationStep 1> add the weighed amount of solute in the volumetric flaskStep 2> add distilled water (about half of final volume)Step 3> cap volumetric flask, and shake to dissolve solute completelyStep 4> add distilled water to volume marker (calibration mark)The solution process may be exothermic (release heat). This may cause the liquid to show a larger volume than is real. Allow the solution to return to ambient (room) temperature and check volume again.Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 480
16 How to mix a Standard Solution An aqueous solution consists of at least two components, the solvent (water) and the solute (the stuff dissolved in the water). Usually one wants to keep track of the amount of the solute dissolved in the solution. We call this the concentrations. One could do by keeping track of the concentration by determining the mass of each component, but it is usually easier to measure liquids by volume instead of mass. To do this measure called molarity is commonly used. Molarity (M) is defined as the number of moles of solute (n) divided by the volume (V) of the solution in liters.It is important to note that the molarity is defined as moles of solute per liter of solution, not moles of solute per liter of solvent. This is because when you add a substance, perhaps a salt, to some volume of water, the volume of the resulting solution will be different than the original volume in some unpredictable way. To get around this problem chemists commonly make up their solutions in volumetric flasks. These are flasks that have a long neck with an etched line indicating the volume. The solute (perhaps a salt) is added to the flask first and then water is added until the solution reaches the mark. The flasks have very good calibration so volumes are commonly known to at least four significant figures.
17 Process of Making a Standard Solution from Liquids Solutions can be made using liquids or solids (or gases).To make a 5% solution v/v (volume to volume)This means to add 5 mL of solute in 95 mL of solvent. The total is 5 mL / 100 mL or 5%.For the diagram add 25 mL of liquid solute and add water to bring volume to 500 mL (about 475 mL water).SAFETY NOTE: Always add acid concentrate to water…never add water to concentrated acid.If you’ve seen what happens when water or ice crystals hit hot oil…a similar phenomenon occurs when water is added to concentrated acid.The addition of water to concentrated dissipates a large amount of heat. This heat rapidly boils the acid and causes it to spatter.If however, you start with a large volume of water and slowly add acid, the same amount of heat is generated.This time, the large volume of water is capable of absorbing the heat. The solution will not splatter.Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 483
19 Reading a pipette 4.48 - 4.50 mL 4.86 - 4.87 mL 5.00 mL Identify each volume to two decimal places(values tell you how much you have expelled)mLmL5.00 mL
20 MConc.VConc. = MDiluteVDilute Dilution of SolutionsSolution GuideFormulaWeightSpecific GravityMolarityReagentPercentTo Prepare 1Liter of one molarSolutionAcetic Acid Glacial (CH3COOH)60.051.0517.4599.8%57.3 mLAmmonium Hydroxide (NH4OH)35.050.9014.5356.6%69.0 mLFormic Acid (HCOOH)46.031.2023.690.5%42.5 mLHydrochloric Acid (HCl)36.461.1912.137.2%82.5 mLHydrofluoric Acid (HF)20.01.1828.949.0%34.5 mLNitric Acid (HNO3)63.011.4215.970.0%63.0 mLPerchloric Acid 60% (HClO4)100.471.549.160.0%110 mLPerchloric Acid 70% (HClO4)1.6711.770.5%85.5 mLPhosphoric Acid (H3PO4)97.11.7014.885.5%67.5 mLPotassium Hydroxide (KOH)Sodium Hydroxide (NaOH)40.019.445.0%Sulfuric Acid (H2SO4)98.081.8418.050.5%51.5 mLThis chart quickly shows you the amount of concentrated acid needed to make 1 liter of a 1 M solution. If you need a 5 M solution, add 5x the amount of acid in the same volume.MConc.VConc. = MDiluteVDilute
21 **Safety Tip: When diluting, add acid or base to water.** Acids (and sometimes bases) arepurchased in concentrated form (“concentrate”) and are easilydiluted to any desired concentration.Dilutions of Solutions **Safety Tip: When diluting, add acid or base to water.**C = concentrateD = diluteDilution Equation:Concentrated H3PO4 is 14.8 M. What volume of concentrateis required to make L of M H3PO4?VC = L = 845 mL
22 How would you mix the above solution? 1. Measure out L of concentrated H3PO4 .2. In separate container, obtain ~20 L of cold H2O.3. In fume hood, slowly pour [H3PO4] into cold H2O.4. Add enough H2O until L of solution is obtained.Be sure to wear your safety glasses!
23 You have 75 mL of conc. HF (28.9 M); you need 15.0 L of 0.100 M HF. Do you have enough to do the experiment?MCVC = MDVD28.9 M (0.075 L) = M (15.0 L)Yes;we’re OK.mol HAVE>1.50 mol NEED
24 What do you call a tooth in a glass of water? - A one molar solution. One mole, in solution.What do you call a tooth in a glass of water? - A one molar solution.
25 DilutionPreparation of a desired solution by adding water to a concentrate.Moles of solute remain the same.
26 DilutionWhat volume of 15.8M HNO3 is required to make 250 mL of a 6.0M solution?GIVEN:M1 = 15.8MV1 = ?M2 = 6.0MV2 = 250 mLWORK:M1 V1 = M2 V2(15.8M) V1 = (6.0M)(250mL)V1 = 95 mL of 15.8M HNO3
27 Preparing Solutions How to prepare 500 mL of 1.54 M NaCl solution mass 45.0 g of NaCladd water until total volume is 500 mL500 mLvolumetricflask500 mLmark45.0 g NaClsolute
28 Preparing Solutions 500 mL of 1.54M NaCl molalitymolarity1.54m NaCl in kg of water500 mL of 1.54M NaClmass 45.0 g of NaCladd kg of watermass 45.0 g of NaCladd water until total volume is 500 mL500 mL water500 mLvolumetricflask45.0 g NaCl500 mLmark
29 Preparing Solutions measure 95 mL of 15.8M HNO3 250 mL of 6.0M HNO3 by dilutionmeasure 95 mL of 15.8M HNO395 mL of 15.8M HNO3combine with water until total volume is 250 mL250 mL markSafety: “Do as you oughtta, add the acid to the watta!”water for safety
30 Solution Preparation Lab Turn in one paper per team.Complete the following steps:A) Show the necessary calculations.B) Write out directions for preparing the solution.C) Prepare the solution.For each of the following solutions:1) mL of 0.50M NaCl2) 0.25m NaCl in mL of water3) mL of 3.0M HCl from 12.1M concentrate.