1 Chapter 8 Aqueous solutions

2 Parts of Solutions l Solution- homogeneous mixture.Components are uniformly distributed throughout mixture l Solute- what gets dissolved. l Solvent- what does the dissolving. l Soluble- Can be dissolved. l Miscible- liquids dissolve in each other. l Immiscible-substances that do not mix with each other. Eg. Oil and water

3 Solutions l Solubility- refers to amount of substance needed to make a saturated solution at a specific temperature measured in moles per litre or grams per litre. l Soluble if more than 0.1 mole of substance dissolved in 1.0 L in solution.

4 Saturated solution l Is a solution that holds as much solute as it can at a given temperature. l The rate at which solid solute dissolves can be increased by: a) Temperature b) Stirring c) Surface area

5 Supersaturated Solution l Solution that occurs when more solute is dissolved than it would normally hold at a given temperature.

6 Molarity l Concentration – describes the amount of components in a solution. l Molarity – measure of concentration of solution in moles of solute per Litre l Molarity = moles of solute/litres of solution l Units of molarity = M l [ ] = concentration

7 calculations l Example 1 – Calculate the molarity of a solution containing mol of HCl in 335 mL of solution? l Calculate the molarity of a solution that contains 13.5g of sodium sulfate in 850 mL of solution? l Calculate the number of grams of solute in 150mL of 0.30M NaOH solution? l Do worksheet #1-5–hand in quality work.

8 Dilution calculations l Concentrated solution- a solution with a relatively high concentration of a particular substance. l eg 6.0 M CuSO4- dark blue (concentrated) l 0.1 M CuSO4 – light blue ( dilute) l Stock solution– contains very high concentration. 12M HCl is stock solution. Used to make dilutions.

9 Dilute Solution l Moles of concentrated solution = moles of dilute solution. l The moles and grams do not change Only volume changes. McVc = MdVd c=concentrated d=dilute l The volume of dilute solution is higher than concentrated because more water is added.

10 Dilution Calculations.

11 Dilution Calculations l 250mL of 0.16 M Ca(NO 3 ) 2 solution is diluted to 8.0L. Find the new concentration of the solution.

12 Dilution Calculations l Eg. 2 A student has 450mL of a 0.40M NaCl solution. How much water is needed to make it a 0.10M solution? Dilution Calculations

13 Mixing same solution l 0.300M KOH at 150mL is mixed with 0.150M KOH at 250mL. What is the resulting molarity?

14 Preparing Solutions l Standard solution – a solution with a known concentration.

15 How to prepare solution 1. Find mass of solid required. 2. Weigh the solid into a 100 mL beaker. 3. Dissolve the solid in 50mL of distilled water. 4. Transfer the solution from beaker to volumetric flask and make it upto the mark with more distilled water. Use dropper. Dilution Calculations

16 Making solutions l How would you make 250.0mL of 0.350M CaCl 2 solution?

17 Volumetric Flask l Making solutions read page 319

18 Aqueous solutions l Dissolved in water. l Water is a good solvent because the molecules are polar. l The oxygen atoms have a partial negative charge. l The hydrogen atoms have a partial positive charge. l The angle is 105ºC.

19 Hydration l The process of breaking the ions of salts apart. l Ions have charges and attract the opposite charges on the water molecules.

20 Hydration H H O H H O H H O H H O H H O H H O H H O H H O H H O

21 Ionization

22 Solubility l How much of a substance will dissolve in a given amount of water. l Usually g/100 mL l Varies greatly, but if they do dissolve the ions are separated, l and they can move around. l Water can also dissolve non-ionic compounds if they have polar bonds.

23 Electrolytes l Electricity is moving charges. l The ions that are dissolved can move. l Solutions of ionic compounds can conduct electricity. l Electrolytes. l Solutions are classified three ways.

24 Types of solutions l Strong electrolytes- completely dissociate (fall apart into ions). l Many ions- Conduct well. l Weak electrolytes- Partially fall apart into ions. l Few ions -Conduct electricity slightly. l Non-electrolytes- Don’t fall apart. l No ions- Don’t conduct.

25 Types of solutions l Acids- form H + ions when dissolved. l Strong acids fall apart completely. l many ions l H 2 SO 4 HNO 3 HCl HBr HI HClO 4 l Weak acids- don’ dissociate completely. l Bases - form OH - ions when dissolved. l Strong bases- many ions. l KOH NaOH

26 Measuring Solutions l Concentration- how much is dissolved. l Molarity = Moles of solute Liters of solution l abbreviated M l 1 M = 1 mol solute / 1 liter solution l Calculate the molarity of a solution with 34.6 g of NaCl dissolved in 125 mL of solution.

27 Molarity l How many grams of HCl would be required to make 50.0 mL of a 2.7 M solution? l What would the concentration be if you used 27g of CaCl 2 to make 500. mL of solution? l What is the concentration of each ion?

28 Molarity l Calculate the concentration of a solution made by dissolving 45.6 g of Fe 2 (SO 4 ) 3 to 475 mL. l What is the concentration of each ion?

29 Making solutions l Describe how to make mL of a 1.0 M K 2 Cr 2 O 4 solution. l Describe how to make 250. mL of an 2.0 M copper (II) sulfate dihydrate solution.

30 Dilution l Adding more solvent to a known solution. l The moles of solute stay the same. l moles = M x L l M 1 V 1 = M 2 V 2 l moles = moles l Stock solution is a solution of known concentration used to make more dilute solutions

31 Dilution l What volume of a 1.7 M solutions is needed to make 250 mL of a 0.50 M solution? l 18.5 mL of 2.3 M HCl is added to 250 mL of water. What is the concentration of the solution? l 18.5 mL of 2.3 M HCl is diluted to 250 mL with water. What is the concentration of the solution?

32 Dilution l You have a 4.0 M stock solution. Describe how to make 1.0L of a.75 M solution. l 25 mL 0.67 M of H 2 SO 4 is added to 35 mL of 0.40 M CaCl 2. What mass CaSO 4 Is formed?

33 Types of Reactions  Precipitation reactions l When aqueous solutions of ionic compounds are poured together a solid forms. l A solid that forms from mixed solutions is a precipitate l If you’re not a part of the solution, your part of the precipitate

34 Precipitation reactions NaOH(aq) + FeCl 3 (aq)   NaCl(aq) + Fe(OH) 3 (s) l is really Na + (aq)+OH - (aq) + Fe +3 + Cl - (aq)   Na + (aq) + Cl - (aq) + Fe(OH) 3 (s) l So all that really happens is OH - (aq) + Fe +3  Fe(OH) 3 (s) l Double replacement reaction

35 Precipitation reaction l We can predict the products l Can only be certain by experimenting l The anion and cation switch partners AgNO 3 (aq) + KCl(aq)  Zn(NO 3 ) 2 (aq) + BaCr 2 O 7 (aq)  CdCl 2 (aq) + Na 2 S(aq) 

36 Precipitations Reactions l Only happen if one of the products is insoluble l Otherwise all the ions stay in solution- nothing has happened. l Need to memorize the rules for solubility (pg 145)

37 Solubility Rules  All nitrates are soluble  Alkali metals ions and NH 4 + ions are soluble  Halides are soluble except Ag +, Pb +2, and Hg 2 +2  Most sulfates are soluble, except Pb +2, Ba +2, Hg +2,and Ca +2

38 Solubility Rules  Most hydroxides are slightly soluble (insoluble) except NaOH and KOH  Sulfides, carbonates, chromates, and phosphates are insoluble  Lower number rules supersede so Na 2 S is soluble

39 Three Types of Equations l Molecular Equation- written as whole formulas, not the ions. K 2 CrO 4 (aq) + Ba(NO 3 ) 2 (aq)  l Complete Ionic equation show dissolved electrolytes as the ions. 2K + + CrO Ba NO 3 -  BaCrO 4 (s) + 2K NO 3 - l Spectator ions are those that don’t react.

40 Three Type of Equations l Net Ionic equations show only those ions that react, not the spectator ions Ba +2 + CrO 4 -2  BaCrO 4 (s) l Write the three types of equations for the reactions when these solutions are mixed. l iron (III) sulfate and potassium sulfide Lead (II) nitrate and sulfuric acid.

41 Stoichiometry of Precipitation l Exactly the same, except you may have to figure out what the pieces are. l What mass of solid is formed when mL of M Barium chloride is mixed with mL of M sodium hydroxide? l What volume of M HCl is needed to precipitate the silver from 50.ml of M silver nitrate solution ?

42 Types of Reactions  Acid-Base l For our purposes an acid is a proton donor. l a base is a proton acceptor usually OH - l What is the net ionic equation for the reaction of HCl(aq) and KOH(aq)? Acid + Base  salt + water H + + OH -  H 2 O

43 Acid - Base Reactions l Often called a neutralization reaction Because the acid neutralizes the base. l Often titrate to determine concentrations. l Solution of known concentration (titrant), l is added to the unknown (analyte), l until the equivalence point is reached where enough titrant has been added to neutralize it.

44 Titration l Where the indicator changes color is the endpoint. l Not always at the equivalence point. l A mL sample of aqueous Ca(OH) 2 requires mL of M Nitric acid for neutralization. What is [Ca(OH) 2 ]? l # of H + x M A x V A = # of OH - x M B x V B