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

Transcription

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 ANNOUNCEMENTS The add/drop day is today 9/10 The first real labs will be Sep10/11(must have protective clothing) Pre-Assignment: Volumetric Experiment due 9/10 at 8:00 am(owl lab) Chemistry and Math review are due on 9/10/18 Chapter 1 HW due 9/10/18 at 11:55 pm( you need to have a 85% or higher in the generation chemistry review to unlock the assignment)

3 PRACTICE PROBLEMS Which one of the following is most likely to be an ionic compound? (a) HNF2 (b) H2CO (c) N2H4 (d) ZnSO4 (e) CH3Cl Answer : D

4 PRACTICE PROBLEMS Which of the following ions does Not have a -1 charge? (a)oxide (b)fluoride (c)hydroxide (d)nitrate (e)acetate Answer: A

5 WRITE MOLECULAR FORMULAS Rubidium Bromide Magnesium Selenide Sodium Oxide Calcium Chloride Hydrogen Fluoride Gallium Phosphide Aluminum Bromide Ammonium Sulfate

6 NAME EACH IONIC COMPOUND Ca(H2PO4)2 FeSO4 CaCO3 MgO NaNO2 KI

7 CHAPTER 3 COMPOSITION OF SUBSTANCES & SOLUTIONS

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12 QUESTION Which of the following ionic compounds has the greatest total number of atoms? g of HgCl g of K2SO mg of LiF

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14 CONCENTRATED & DILUTE SOLUTIONS Concentrated solutions have more solute per unit volume than dilute solutions. Concentrated solutions can be made dilute by adding more solvent. Dilute solutions can be made more concentrated by adding more solute, or by removing (selectively) more solvent.

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16 QUESTION Which one of the following solutions is the most dilute? A: M HCl solution B: 0.50 L of solution containing 0.40 moles of HCl 0.40 mol 0.50 L = 0.80 M > 0.50 M C: 75 ml of solution containing 0.40 moles of HCl 0.40 mol L = 5.3 M > 0.50 M

17 Each of the following salts are soluble in water. Which will produce the largest number of ions, per mole, of dissolved solute? Answers QUESTION A B Aluminum chloride Sodium chloride AlCl3 NaCl : 4 moles of ions : 2 moles of ions C Ammonium nitrate NH4NO3 : 2 moles of ions D Sodium sulfate Na2SO4 : 3 moles of ions E Calcium nitrate Ca(NO3)2 : 3 moles of ions

18 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

19 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)

20 LECTURE OBJECTIVES Chapter Calculate solution concentrations using molarity. Perform dilution calculations. Express and calculate concentrations in a variety of units (e.g. w/w%, v/v%, ppm, ppb).

21 DILUTIONS CALCULATIONS Solutions often need to be diluted to obtain the desired concentration, from a higher concentration stock solution. Calculations for dilutions require us to determine the total number of moles involved in the dilution. M 1 V 1 = # of moles = M 2 V 2

22 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)

23 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

24 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%)

25 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)

26 VOLUME PERCENTAGE CALCULATIONS 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)

27 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%.

28 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?