PowerPoint Presentation by R. Schultz Chemistry 20 Chapter 5 - Solutions PowerPoint Presentation by R. Schultz robert.schultz@ei.educ.ab.ca

5.1 Classifying Solutions Solutions are homogeneous mixtures solvent: part of solution present in greatest quantity – e.g. water in an aqueous solution solute: the substance dissolved in the solvent – e.g. salt in a saltwater solution types of solutions: not just solid in liquid, but gas in gas, gas in liquid, liquid in liquid, ……. (chart page 167) Do questions 1, 2 page 168

5.1 Classifying Solutions aqueous solutions will be our main focus Dissolving processes: a solute bonds break (endothermic) b solvent intermolecular bonds break (endothermic) c new solute/solvent bonds form (exothermic) ionic molecular Ec > Ea + Eb (exothermic); Ec< Ea + Eb (endothermic)

5.1 Classifying Solutions discuss question 4, page 170 discuss cold packs:

5.1 Classifying Solutions Electrolytes: substances that conduct electricity when dissolved in water (ionics and strong acids) Non-Electrolytes: don’t (moleculars) Theory: dissolved ionic compounds dissociate; the compound breaks apart to release free cations and anions Dissociation equations: NaOH(s) Na+(aq) + OH¯(aq) K2SO4(s) 2 K+(aq) + SO42ˉ(aq)

5.1 Classifying Solutions The dissociation equation shows what happens when ionics dissolve in water starts with the pure ionic compound in (s) state and produces (aq) ions Ionics with low solubility remain in (s) state Acids – molecular compounds that ionize to form H+(aq) and an anion in water. Ionization equation: HCl(g) H+(aq) + Clˉ(aq)

5.1 Classifying Solutions Difference between ionization and dissociation (and equations)?: Do worksheet BLM 5.1.3B ionization: acids – ions not initially present; they form in the presence of water starting compound in pure state or (aq) dissociation: ionics – ions already present in crystal lattice; they just separate starting compound in (s) state Discuss questions 3, 4, 6, page 175

5.2 Solubility solubility:  the ability to be dissolved saturated solution supersaturated solution:  the ability to be dissolved  often expressed in g (solute) per 100 mL solution  solution of maximum concentration under a given set of conditions  solution of > maximum concentration under a given set of conditions

5.2 Solubility Gas solubilities low in general, but very important in some cases e.g. O2 in H2O In a saturated solution dissolving never really stops; dynamic equilibrium exists between dissolving and crystallizing processes dissolving  undissolved solute dissolved solute crystallizing

5.2 Solubility dynamic equilibrium: 2 opposing processes, occurring at same rate so that no net change is observed experimental evidence: in a mixture of a saturated solution with some undissolved solute, the size of the crystals will increase over time, even though the mass of crystals remains unchanged

5.2 Solubility Example 11a, page 179 NaCl(s) Na+(aq) + Clˉ(aq) Example 11c, page 179 (NH4)2CO3(s)  2 NH4+(aq) + CO32-(aq) Try 11b, 11d, page 179 Note the difference in equations for saturated & unsaturated

As pressure of a gas  solubility of that gas  Solubility Generalizations: Solubility of Effect of Temperature Effect of Pressure Solids in liquids As temp  solubility  No appreciable effect Liquids in liquids Gases in liquids As temp  solubility  As pressure of a gas  solubility of that gas 

5.2 Solubility Question 7, page 183 – discuss Do questions 2a, 3c, 4, 5, 6

5.2 Solubility Do Lab 5.B.1 – handout to help with report

5.2 Solubility Solubility Chart 2009-10 Data Booklet H+, NH4+ H+, Na+ K+, NH4+ only K+, NH4+ K+, NH4+

5.3 Concentration of Solutions Concentration of solution: quantity of solute per quantity of solution (it’s always solution, not solvent) Can use terms “concentrated” or “dilute”, but most often using numbers Expressions of Concentration: % by mass: commercial hydrogen peroxide is 3

5.3 Concentration of Solutions For very small concentrations: parts per million, ppm, and parts per billion, ppb Used for toxic environmental pollutants

5.3 Concentration of Solutions Examples: Practice Problem 2, page 186 Practice Problem 6a, page 188 Do worksheet BLM 5.3.2, #1 – 4, and 6

5.3 Concentration of Solutions moles – because we are doing the course in different order from the text we need to deal with moles now recall from Science 10: a mole (mol) is a gigantic # of particles (6.02 x 1023) atoms and molecules are so small that gigantic #’s are needed to make them have a measurable mass Green Pea Analogy, Moles Song you don’t need to know this # by memory

5.4 Preparing and Diluting Solutions October 23 each year from 6:02 am to 6:02 pm is International Mole Day since date and time is 6:02 10 23 National Chemistry Week in USA is week in which Mole Day falls Could you write a moles song, a moles poem, dress up as a mole – I challenge you /

5.4 Preparing and Diluting Solutions 1 mol of moles placed head to tail would cover a distance of 11 million light years! They would have a mass of approximately 90% of the Moon

5.3 Concentration of Solutions molar mass: mass of 1 mol of a substance Examples: Molar Mass of sodium 22.99 Molar Mass of nitrogen Molar Mass of (NH4)2CO3 nitrogen is N2 2 x 14.01 = 28.02 you will need to calculate molar masses often as part of other calculations in every further chapter in this chapter you need to show this working in further chapters no

5.3 Concentration of Solutions Calculating # of moles of a substance example: calculate # moles in 3.50 g Na3PO4 formula method unit cancelling method mass of sample (g) number of moles (mol) molar mass need mol; have g and to get mol, do g since g = g x = mol

5.3 Concentration of Solutions calculating mass of a substance from # of moles example: calculate mass of 1.75 mol of Ca(NO3)2 formula method unit cancelling method m n M need g; have mol and to get g do mol x Do worksheet BLM 3.0.2

5.3 Concentration of Solutions Back to concentrations – molar concentration don’t memorize this formula – get it upside down and you’re sunk molar concentration units (mol/L) – that tells you everything you need molar concentration (mol/L) # moles solute (mol) volume of solution (L)

5.3 Concentration of Solutions Example: Practice Problem 12a, page 191 Do worksheet, BLM 5.3.3 a, b, e

5.3 Concentration of Solutions Molar concentration of ions Solving these always requires a dissociation or ionization equation Example: calculate the molar concentration of each ion in 0.125 mol/L Fe2(SO4)3 1 Fe2(SO4)3(s) 2 Fe3+(aq) + 3 SO42(aq) you will use this ratio often in Chapters 5, 7, and 8 (get used to it here) “[ a ]” stands for molar concentration of a

5.3 Concentration of Solutions Example: Calculate the molar concentration of Ca3(PO4)2 required to produce a solution with [Ca2+]=0.425 mol/L 1 Ca3(PO4)2(aq) 3 Ca2+(aq) + 2 PO3-(aq) Do worksheet BLM 5.3.5A – answers on my website

5.3 Concentration of Solutions Molar concentration of ions in solution (continued) Example: Practice Problem 17, page 193 1 Na2CO3(s) 2 Na+(aq) + 1 CO32-(aq) Do worksheet BLM 5.3.5 2, 5, 6 this looks like final answer, but need concentration of Na+, not solute

5.3 Concentration of Solutions Calculating mass from concentration and volume Example: Practice Problem 23a, page 194 unit cancellation is better

5.3 Concentration of Solutions Calculating volume from mass and concentration Example: Practice Problem 27b, page 195 Do worksheet BLM 5.3.6 first side only

5.4 Preparing and Diluting Solutions standard solution: carefully made solution with known concentration you’ll learn, in the lab, how to prepare a standard solution by 2 methods Method 1: Preparation from solid – calculation already done (slide 27)

5.4 Preparing and Diluting Solutions Method 2: Preparation by Dilution This is done for 2 possible reasons: calculated mass of solute is too small to be weighed out you may already have a more concentrated solution available and can prepare your by diluting the other

5.4 Preparing and Diluting Solutions Dilution calculation: since in dilution, moles of solute can’t change, ni = nf the dilution equation!

5.4 Preparing and Diluting Solutions Example: Practice Problem 31a, page 198 biggest problem students have with these is misidentifying the variables I encourage you to list them: ci = 1.25 mol/L vi = ? cf = 1.00 mol/L vf = 50 mL formulas with all multiplication are easy to rearrange  do this 1st units don’t have to “match”; as long as both v’s and both c’s have same units Do worksheet BLM 5.4.1 all

5.4 Preparing and Diluting Solutions Investigation 5.D – Solution Preparation and Dilution, page 200

5.4 Preparing and Diluting Solutions Chapter Review Calculation Review: worksheet BLM 5.3.7

5.4 Preparing and Diluting Solutions