Announcements. Please come to the front of the classroom and pick up a Solution Problems worksheet before class starts!

Transcription

1 Announcements Please come to the front of the classroom and pick up a Solution Problems worksheet before class starts!

2 Announcements 1. Mid-term grades will be posted soon (just used scaled exam 1 score so you have a gauge). 2. Electronic Homework due Monday, 10/15 (Type I) and Wednesday, 10/17 (Type II) by 7:00pm 3. Lab tomorrow! (Nuts and Bolts)

3 Mixing Acids and Bases Sodium hydroxide and hydrochloric acid NaOH(aq) + HCl(aq) NaCl + H 2 O What happens when the two solutions are mixed together? No solid formed! So does that mean that no reaction occurred?

4 Mixing Acids and Bases Molecular equation: NaOH(aq) + HCl(aq) NaCl(aq) + H 2 O(l) Complete ionic equation: Na + (aq) + OH - (aq) + H + (aq) + Cl - (aq) Na + (aq) + Cl - (aq) + H 2 O(l) Net ionic equation: OH - (aq) + H + (aq) H 2 O(l)

5 What makes a chemical reaction? Bonds in reactants have to be broken Atoms rearrange Bonds form to make products So since we can write a net ionic equation, a chemical reaction has occurred

6 A Microscopic Look

7 Conductivity and ions Will the resulting solution conduct electricity? Yes. The resulting solution contains ions which conduct electricity. Na + and Cl - are spectator ions since they did not participate in reaction (just floating around; only present to balance charge)

8 Acids and Bases reactants: Ba(OH) 2 (aq) and H 2 SO 4 (aq) What will be the products of this reaction? BaSO 4 and H 2 O Would there be a precipitate in this reaction? Yes, BaSO 4 (rule #4) Solubility Rules Most nitrate salts are soluble. Most salts of sodium, potassium, and ammonium cations are soluble. Most chloride salts are soluble. Exceptions: Ag + and Pb 2+. Most sulfate salts are soluble. Exceptions: Ca 2+, Ba 2+, and Pb 2+. Most hydroxide salts are only slightly soluble. Soluble ones are: Na +, K +, and Ca 2+. Most sulfide, carbonate, and phosphate salts are only slightly soluble.

9 Clicker #1 Will the resulting solution conduct electricity? A) No. There is no precipitate formed and a solid is required to conduct electricity. B) No. The resulting solution is pure water which does not conduct electricity. C) Yes. The resulting solution is pure water which conducts electricity. D) Yes. The resulting solution contains ions which conduct electricity.

10 A Microscopic Look

11 Molecular equation: Ba(OH) 2 (aq) + H 2 SO 4 (aq) BaSO 4 (s) + 2H 2 O(l) Complete ionic equation: Ba 2+ (aq) + 2OH - (aq) + 2H + (aq) + SO 4 2- (aq) BaSO 4 (s) + 2H 2 O(l) Net ionic equation: Ba 2+ (aq) + 2OH - (aq) + 2H + (aq) + SO 4 2- (aq) BaSO 4 (s) + 2H 2 O(l)

12 Concentration and Molarity What does concentration tell us? Quantity per volume (ratio!) Density: mass of substance per volume of solid or liquid (or solution) Molarity: number of moles of species per volume of aqueous solution

13 Concentration and Molarity Think about what concentration means before getting lost in the math Solutions are always homogeneous! DEMO: three flasks of red aqueous solution

14 Clicker #2 Which of the three solutions is the most concentrated? A) Solution #1 B) Solution #2 C) Solution #3 D) The concentrations are the same.

15 Concentration and Molarity Which liquid is the most concentrated (has the most food coloring per volume)? They are all the same! While the volumes are different, the RATIO of food coloring per volume is still the same

16 Concentration and Molarity How could we change the concentration then? Add more food coloring higher concentration Remove water by evaporation higher concentration Add more water lower concentration

17 Concentration and Molarity Start with 12 particles in 6.0L water 12/6.0 6/3.0L 2/1.0 2/6.0 = 2 = 2 = 2 = 1/3

18 Molarity Concentration of solution molarity Molarity = (moles of solute) / (liters of solution) has units of moles per liter (moles/l) Solute is whatever is being dissolved into solution

19 Clicker #3 You add ml of water to ml of a 2.00 M sugar solution. How many of the following will change? I. total volume of the solution II. moles of solute in the solution III. mass of solute in the solution IV. concentration of the solution V. number of solute molecules in the solution A) 1 B) 2 C) 3 D) E) 4 5

20 Solution Problem #1 You have 1.00 mol of sugar in ml of solution. Calculate the concentration in units of molarity.

21 Solution Problem #2 You have a 2.50 M sugar solution. Calculate the number of moles of sugar in ml of this solution.

22 Solution Problem #3 You have a 10.0 M sugar solution. What volume of this solution do you need to have 2.00 mol of sugar?

23 Clicker #4 If 200. ml is removed from the original 10.0 M solution, what is the concentration of the remaining (original) solution? A) M B) 1.00 M C) 2.00 M D) 8.00 M E) 10.0 M

24 Solution Problem #4 You add ml of water to ml of a 4.00 M sugar solution. Calculate the concentration of the new solution in units of molarity. (Assume the volumes are additive.)

25 Clicker #5 Do you predict that the concentration of the 4.00 M sugar solution will increase, decrease, or stay the same? A) increase B) decrease C) stay the same

26 Solution Problem #5 Consider separate solutions of NaOH and KCl made by dissolving equal masses of each solute in equal volumes of solution. Which solution has the greater concentration?

27 Clicker #6 Without using a calculator, which solution has the greater concentration? MM of NaOH = g/mol MM of KCl = g/mol A) NaOH B) KCl

28 Solution Problem #6 Consider separate solutions of NaOH and KCl made by dissolving g of each solute in ml of solution. Calculate the concentration of each solution.

29 Solution Problem #7 We have a M solution of NaOH. You need 75.0 ml of a 0.35 M solution. How do you make such a solution?

30 Solution Problem #8 You prepare 525 ml of a 0.50 M solution of HI in an Erlenmeyer flask. You forget to seal the flask and don t realize this until you find it three days later. Checking its molarity, you now find it to be a 0.82 M solution. How much water evaporated?

31 Solution Problem #9 Answer the following questions for 60.0 ml of 2.00 M calcium chloride solution. a) How many moles of calcium chloride are in solution? How many moles of chloride ions are in this same solution? b) You add 40.0 ml of water to the solution. How many moles of calcium chloride are in the new solution? c) What is the molarity of the new solution?

32 Solution Problem #10 I mix 220 ml of 1.5 M HCl solution with 405 ml of 0.42 M HCl solution. Indicate the volume and molarity of the final solution.