CHEM 200/202. Professor Jing Gu Office: EIS-210. All s are to be sent to:

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1 CHEM 200/202 Professor Jing Gu Office: EIS-210 All s are to be sent to: My office hours will be held in GMCS-212 on Monday from 9 am to 11 am or by appointment.

2 FALL 2018 ROOM ASSIGNMENTS EXAMS 1 3 GMCS-333 AL-201 Lab TA: Section: Lab TA: Section: Chem Chem Chem Tranvo Chem Schroeder Chem Chem Chem Chem Chem Johnson Chem Chem Chem Chem Chem Xu Chem Chem ENS-280 SHW-012 Lab TA: Section: Lab TA: Section: Trammel Chem Chem Chem Younan Chem Chem Chem Sun Zhu Chem Chem Lin Chem Chem Chem Chem Bowles Chem Chem Chem Chem Yazdani Chem Chem Li Chem Chem

3 ANNOUNCEMENTS Chapter 2 homework due 9/14/18 Lab report Volumetric Equipment and Pre-Lab assignment and report: Qualitative Analysis is due on 9/17/18 Quiz 1 due 9/20/18. Homework 3 and 4 due 9/21/18. Exam 1 is on 9/22/18 at 2-4 pm.

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5 PRACTICE PROBLEM How many grams are in molecules of dinitrogen pentoxide? a) 317g b) 37g c) g d)37 kg e)36.8 g

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7 QUESTION What is the total concentration of ions in a 0.10 M iron(iii) sulfate solution? Answers A B C D E 0.10 M 0.20 M 0.30 M 0.40 M 0.50 M Fe2(SO4)3 2Fe 3+ +3SO M 2(0.10 M) + 3(0.10 M) = 0.50 M

8 CALCULATE THE MOLARITY OF EACH OF THE FOLLOWING SOLUTIONS: mol of sucrose in 34.5 ml of water. practice together) 327 g of silver nitrate in L of water.(do it by yourself) 45.7 ml of ethanol (CH 3 CH 2 OH, density g/ml) in 612 ml of water.(do it by yourself)

9 CALCULATE THE FOLLOWING DILUTIONS You wish to make a 125 ml solution of lithium sulfate with a concentration of 28.0 mm. You have a stock solution with a concentration of lithium sulfate that is 1.87 M. What volumes of water and stock Li 2 SO 4 do you need?(practice together) You have ml of a 3.94 mol/l stock potassium phosphate solution. You take ml of the stock solution and mix that with 1.45 L of water. What is the concentration of the diluted solution you prepared?(do it by yourself)

10 OTHER UNITS OF CONCENTRATION Concentrations are used to express the amount of a solute in a solution, this can be done in more ways than just mol/l. Mass percent Volume percent Mass-volume percent Parts per million and parts per billion

11 PERCENTAGES The expression of concentration as a percentage is very similar to how percentage grades are expressed. The key is to use the proper units for each calculation. Mass percent (w/w%) Volum percent (v/v%) Mass-volume percent (w/v%)

12 MASS PERCENT CALCULATIONS What is the mass percentage of oxygen in potassium phosphate?( Do it together) A sulfuric acid solution has contains 32% H2SO4 by mass. If the density of the solution is 1.28 g/ml, what is the molar concentration of the acid? (practice by yourself)

13 VOLUME PERCENTAGE CALCULATIONS You wish to make a 425 ml aqueous solution with a 10.00% hydrogen peroxide concentration by volume. Pure hydrogen peroxide has a density of g/ml. What mass of hydrogen peroxide do you need? Sculpin beer has a 7.0% alcohol content by volume. What is the molar concentration of ethanol in this beer? (Ethanol: g/mol, g/ml)

14 PARTS PER MILLION Concentrations are occasionally expressed in terms of parts per million (ppm) or parts per billion (ppb), typically when the concentrations are very small. The calculations are similar to those for w/w% and v/v%.

15 PPB CALCULATIONS The lead content of the tap water in Flint Michigan was found to be as high as 27 ppb. The EPA limit is 15 ppb, though levels above 5 ppb are a cause for concern. How many atoms of lead were in a 250. ml volume of Flint tap water at its worst? What was the molar concentration of lead in Flint s tap water at its worst?

16 LECTURE OBJECTIVES Chapter 3.4 Express and calculate concentrations in a variety of units (e.g. w/w%, v/v%, ppm, ppb). Chapter Balance chemical reactions. Express aqueous ionic reactions in various manners. Identify spectator ions in aqueous ionic reactions. Identify precipitates in aqueous ionic reactions.

17 BALANCING CHEMICAL EQUATIONS It is crucial to have properly balanced reactions when trying to interpret chemical reactions. The balanced reaction shows us how much of each reagent is required and how much of each product is formed. Methane (CH4) undergoes a combustion reaction with oxygen (O2), producing carbon dioxide (CO2) and water (H2O).

18 BALANCE THE REACTIONS BELOW _N2(g) + _H2(g) _NH3(g) _Pb(s) + _H2O(l) +_O2(g) _Pb(OH)2(s)

19 IONIC REACTIONS Many chemical reactions which take place in aqueous solutions involve ionic compounds. These ionic reactions can be depicted in various forms depending on how we wish to focus our attention. The various forms include: The molecular equation The complete ionic equation The net ionic equation

20 IONIC EQUATIONS Sample reaction: lead nitrate reacting with potassium iodide. The molecular equation Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) The reaction depicts the molecular reactants and products, but does not show the ions present in solution.

21 IONIC EQUATIONS Pb(NO 3 ) 2(aq) + 2KI (aq) PbI 2(s) + 2KNO 3(aq) Dissociation of ionic compounds: Pb(NO 3 ) 2(aq) Pb 2+ (aq) + 2NO 3 (aq) KI (aq) K + (aq) + I (aq) KNO 3(aq) K + (aq) + NO 3 (aq) PbI 2(s) PbI 2(s) (There are no ions, lead iodide is insoluble in water.) Complete ionic equation: Pb 2+ (aq) + 2NO 3 (aq) + 2K + (aq) + 2I (aq) PbI 2(s) + 2K + (aq) + 2NO 3 (aq)

22 IONIC EQUATIONS The net ionic equation is a simplification of the complete ionic equation. The net ionic equation removes all the spectator ions. Pb 2+ (aq) + 2NO3 (aq) + 2K + (aq) + 2I (aq) PbI2(s) + 2K + (aq) + 2NO3 (aq) Net ionic equation: Pb 2+ (aq) + 2I (aq) PbI2(s)

23 REACTION CLASSIFICATIONS There are three principle aqueous chemical reactions that we will focus on in this course: Precipitations reactions Acid-base reactions Redox reactions (oxidation-reductions)

24 PRECIPITATION REACTIONS Precipitation reactions occur when pairs of insoluble ions (e.g. Ag + and Cl ) are both present in solution at the same time. A mixture of aqueous solutions may result in more than one precipitate being formed, if more than one insoluble pair is present. Knowledge of the common soluble and insoluble ions is required to predict precipitations (solubility rules).

25 Soluble SOLUBILITY RULES 1. All common compounds of Group 1A(1) ions (Li +, Na +, K +...) and ammonium ions (NH4 + ) 2. All common nitrates (NO3 - ), acetates (CH3CO2 - ) and most perchlorates (ClO4 - ) 3. All common chlorides (Cl - ), bromides (Br - ) and iodides (I - ); except those of Ag +, Pb 2+, Cu + and Hg2 2+. All common fluorides (F - ) are soluble; except for Pb 2+ & Group2A(2) 4. All common sulfates (SO4 2- ); except Ca 2+, Sr 2+, Ba 2+, Ag + & Pb 2+

26 SOLUBILITY RULES Insoluble 1) All common metal hydroxides are insoluble; except those of Group 1A(1) and the larger members of Group 2A(2) - beginning with Ca 2+. 2) All common carbonates (CO3 2- ) and phosphates (PO4 3- ) are insoluble; except those from Group 1A(1) and ammonium (NH4 + ). 3) All common sulfides (S 2- ) are insoluble; except those of Groups 1A(1), 2(A)2 and NH4 +.

27 PREDICTING PRECIPITATION 1. Note the ions present in the reactants. 2. Consider the possible cation-anion combinations. 3. Decide wether any of the ion combinations is insoluble.

28 QUESTION Predict the identity of the precipitate formed when solutions of Na2CO3 and CaCl2 are mixed. Answers A B C D E Na2CO3 CaCl2 CaCO3 NaCl No ppt forms

29 PREDICTING PRECIPITATION For the following aqueous reactions, does a precipitate form? Write the net ionic equation for the reaction, if applicable. Potassium nitrate + Silver(I) acetate Sodium iodide + Copper(I) nitrate