1 Solutions Chemistry I2 – Chapters 7 & 8

2 Some Definitions A solution is a homogeneous mixture of 2 or more substances. One constituent is usually regarded as the SOLVENT and the others as SOLUTES.

3 Parts of a Solution SOLUTE – the part of a solution that is being dissolved (usually the lesser amount) SOLVENT – the part of a solution that dissolves the solute (usually the greater amount) Solute + Solvent = Solution SoluteSolventExample solid Metal alloys solidliquidKool aid liquid Alcoholic drinks gasliquidPepsi gas air

4 Definitions Solutions can be classified as saturated or unsaturated. A saturated solution contains the maximum quantity of solute that dissolves at that temperature. An unsaturated solution contains less than the maximum amount of solute that can dissolve at a particular temperature

5 Definitions SUPERSATURATED SOLUTIONS contain more solute than is possible to be dissolved Supersaturated solutions are unstable. The supersaturation is only temporary, and usually accomplished in one of two ways: 1.Warm the solvent so that it will dissolve more, then cool the solution 2.Evaporate some of the solvent carefully so that the solute does not solidify and come out of solution.

6 Miscibility Miscible: compounds that dissolve readily in each other in any proportion. Ex: water and alcohol. Immiscible: Liquids that do not readily dissolve in each other Ex: oil and water

7 Solubility Solubility is relative, most substances will dissolve by extremely small amounts. Soluble: the solute will dissolve in a particular solvent greater than 1 g / 100 mL Insoluble: the solute will dissolve only 0.1 g / 100 mL, or not dissolve in the solvent

8 IONIC COMPOUNDS Compounds in Aqueous Solution Many reactions involve ionic compounds, especially reactions in water — aqueous solutions. KMnO 4 in water K + (aq) + MnO 4 - (aq)

9 How do we know ions are present in aqueous solutions? The solutions _______________ __________ They are called ELECTROLYTES HCl, MgCl 2, and NaCl are strong electrolytes. They dissociate completely (or nearly so) into ions. Aqueous Solutions

10 Aqueous Solutions Some compounds dissolve in water but do not conduct electricity. They are called nonelectrolytes. Examples include: sugarethanol ethylene glycol Examples include: sugarethanol ethylene glycol

11 Concentration of Solute The amount of solute in a solution is given by its concentration The amount of solute in a solution is given by its concentration. Molarity (M) = moles solute liters of solution

L of water was used to make 1.0 L of solution. Notice the water left over.

13 PROBLEM: Dissolve 5.00 g of NiCl 2 6 H 2 O in enough water to make 250 mL of solution. Calculate the Molarity. Step 1: Calculate moles of NiCl 2 6H 2 O Step 2: Calculate Molarity NiCl 2 6 H 2 O [NiCl 2 6 H 2 O ] = M

14 Step 1: Change mL to L. 250 mL * 1L/1000mL = L Step 2: Calculate. Moles = ( mol/L) (0.250 L) = moles Step 3: Convert moles to grams. ( mol)(90.00 g/mol) = 1.13 g USING MOLARITY moles = MV What mass of oxalic acid, H 2 C 2 O 4, is required to make 250. mL of a M solution?

15 Practice For homework: Pg 242 # 1-6, 9 Pg 268 # 19 & 20 (Read pg )

16 Solutions (continued) Day 2 Mrs. Kay

17 Learning Check How many grams of NaOH are required to prepare 400. mL of 3.0 M NaOH solution? 1)12 g 2)48 g 3) 300 g

18 An IDEAL SOLUTION is one where the properties depend only on the concentration of solute. Need conc. units to tell us the number of solute particles per solvent particle. The unit “molarity” does not do this! Concentration Units

19 Two Other Concentration Units grams solute grams solution MOLALITY, m % by mass = % by mass m of solution= mol solute kilograms solvent

20 Calculating Concentrations Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate molality and % by mass of ethylene glycol.

21 Calculating Concentrations Calculate molality Dissolve 62.1 g (1.00 mol) of ethylene glycol in 250. g of H 2 O. Calculate m & % of ethylene glycol (by mass). Calculate weight %

22 Learning Check A solution contains 15 g Na 2 CO 3 and 235 g of H 2 O? What is the mass % of the solution? 1) 15% Na 2 CO 3 2) 6.4% Na 2 CO 3 3) 6.0% Na 2 CO 3

23 Using mass % How many grams of NaCl are needed to prepare 250 g of a 10.0% (by mass) NaCl solution?

24 Try this molality problem 25.0 g of NaCl is dissolved in mL of water. Find the molality (m) of the resulting solution. m = mol solute / kg solvent 25 g NaCl 1 mol NaCl 58.5 g NaCl = mol NaCl Since the density of water is 1 g/mL, 5000 mL = 5000 g, which is 5 kg mol NaCl 5 kg water = molal salt water

25 Preparing Solutions Weigh out a solid solute and dissolve in a given quantity of solvent.Weigh out a solid solute and dissolve in a given quantity of solvent. Dilute a concentrated solution to give one that is less concentrated.Dilute a concentrated solution to give one that is less concentrated.

26 Practice for homework: Read pg Do Pg 261 #5-8 (%m/m) Do Pg 268 # (molarity)

27 Changing Concentration: Our calculations for this unit are based on solutions being carefully made with known concentrations. Two ways to have a known concentration: 1.Dissolving a measured mass of pure solute in a certain volume of solution. (We practiced this as molarity questions) 2.Diluting a solution of known concentration to the new concentration you’re trying to achieve.

28 Diluting a Standard solution: Use the formula: C 1 v 1 = C 2 v 2 You will be given 3 of the 4 variables and need to solve for the unknown. C 1 = the original concentrated solution v 1 = the amount of original concentrated solution used. C 2 = the new diluted concentration of solution v 2 = the new volume of diluted solution

29 Practice: I have 2.0 L of 0.10 M of sulfuric acid. This usually sold as an 18 M concentrated solution. How much of the concentrated solution do I need to make my new solution? YOU KNOW: C 1 =18 M; C 2 =0.10 M; v 2 = 2.0 L So, v 1 = C 2 v 2 C 1 v 1 = (0.10 M)(2.0 L) (18 M) v 1 = L or 11 mL

30 More Practice: Page 273 # Finish the Handout called “Molarity Review ” # 5-9

31 CHEM 11A Solution Stoichiometry You can solve for amounts of product made or reactants needed even though they are stated as mol/L rather than g or moles. You need to use the basics that you learned in stoichiometry from grade 11 chemistry and apply it to what you’ve learned about solutions Let’s work through an example

32 How many grams of Ca(NO 3 ) 2 can be prepared by reacting 75 mL of 2.6 mol/L HNO 3 with an excess of Ca(OH) 2 ? 2 HNO 3(l) + Ca(OH) 2(s)  Ca(NO 3 ) 2(aq) + 2H 2 O (l) What are you given? V HNO 3 = 0.075L and M=2.6 mol/L Find the moles of HNO 3 used: 2.6 mol/L x L = mol 3.Use stoichiometry to find the ratio of acid moles to calcium nitrate mol (acid) x 1 mol (calcium nitrate) = mol 2 mol (acid)

33 2 HNO 3 + Ca(OH) 2  Ca(NO 3 ) 2 + 2H 2 O mol calcium nitrate needs to be converted to mass mol Ca(NO 3 ) 2 X g = g mol Ca(NO 3 ) 2 So, we will make g of calcium nitrate during this reaction.

34 Practice: Handout # 56-60