Introduction to Chemistry Connections

Transcription

1 I N T R O D U C T I O N Introduction to Chemistry Connections Introduction As a student attempting to successfully complete senior level chemistry, you will find this exciting 50-part series extremely effective. It will help you develop the major concepts in Therm o c h e m i s t ry, Electro c h e m i s t ry, Chemical Equilibrium and Acid-Base Chemistry. In addition, you will discover that this series connects science, technology and society to the themes of matter, change, energ y, systems, equilibrium and diversity. Your presenters will be senior high school chemistry teachers, fellow students, college and university professors, or professionals in technologies with strong chemistry connections. They will work with you to p rovide instruction by illustrating chemistry concepts in the form of demonstrations, laboratory experiments, technological applications and examinations of the impact of science and technology on society. Prerequisite Knowledge To achieve the objectives in this series of programs, you should already have an understanding of the basic chemical principles taught in an introductory high school chemistry course. These prerequisite chemistry topics should include the following: Classifying matter, elements and the Periodic Table Atomic theories and chemical bonding theory Classifying compounds and chemical nomenclature Writing, balancing and classifying chemical reaction equations Classifying solutions, and the concentration and solubility of solutions Kinetic Molecular Theory and the behavior of solids, liquids and gases Mole calculations and stoichiometry calculations for chemical re a c t i o n s S.I. (Système International d'unités) unit conversions, scientific notation and significant digits What s in This Course This course consists of the following materials and activities: A series of 50 video programs Three Activity Guides to help you work through the video materials Introduction to Chemistry Connections 1

2 I N T R O D U C T I O N Introduction to Chemistry Connections Working Through the Materials In general, you will read the Program Synopsis, Prerequisite Knowledge, and Learner Expectations sections for the assigned video program. Then you will watch the video and do the activities listed in the Unit for that program to help you work with and remember the concepts. This will help you gain the maximum benefit from this series and lead to success in writing examinations. You should supplement the questions and problems explained in the programs with reading and practice exercises on related topics found in senior level textbooks. As you work through the materials, you ll use the following study aids: Prerequisite Knowledge Learner Expectations Additional Information Video Pause Point Icons Prerequisite Knowledge This section lists the knowledge you should have before you view the video and work through the material in your resources. Learner Expectations This section lists the things you should be able to do after you have viewed the video and worked through the associated materials. Additional Information Additional Information sections provide material which reviews specific ideas or problems from the video or is supplementary to the video program, and will aid in your understanding of concepts. Additional Information may contain definitions, examples, solutions to problems, or discussions of concepts. Not every program will have an Additional Information section. Video Pause Point Icons In some of the video programs, the icon to the left will be displayed in the lower part of your television screen to indicate a pause point. When you see this icon, check the unit to see what activities you should do before you continue the program. In some programs, some pause points will refer to material in the Additional Information section. 2 Introduction to Chemistry Connections

3 I N T R O D U C T I O N Introduction to Chemistry Connections Suggestions for Classroom Learners Your teacher will assign all or part of the C h e m i s t ry Connections m a t e r i a l to you. The programs and activities may be used to: Supplement classroom instruction by either viewing a program in its entirety (with appropriate pauses) or by viewing selected segments appropriate to your lesson. Assist you in working independently or in an individualized mode. Enable you to "catch up" if you have been absent from classes. Review for examination preparation. Follow your teacher s instructions for using the materials. General Guidelines Significant Digits and Manipulation of Data The rules of significant digits used throughout this series are those commonly adhered to in scientific fields or studies. These rules address the apparent inconsistencies that may arise from time to time when you do a series of calculations. The rule you should follow is to do all calculations with the calculator running. Then round the final answer to the same number of significant digits contained in the quantity (given or measured) with the fewest number of significant digits. When you write intermediate results, or print them in graphics, round the results to the appropriate number of significant digits. But remember, don t carry an intermediate result forward, and don t use it when you verify calculations. Instead, use the running calculator quantity. Introduction to Chemistry Connections 3

4 Program Synopsis In Program 45, the presenters: Show that the control of ph in swimming pools and hot tubs provides an example of a stoichiometric acid-base calculation. Discuss the various types of ph curves generated using a ph probe and a computer interface, make comparisons of the different curves, and obtain information from the curves. Use STS links as examples of neutralization reactions. Prerequisite Knowledge To achieve the objectives of this course, you should have an understanding of the basic chemical principles taught in an introductory chemistry course as specified in the Introduction to this course. To achieve the objectives of this program, you should also be familiar with the following specific concepts and skills from an introductory chemistry course(s) or from preceding programs: Polyprotic acids and anions of polyprotic acids The five-step method for writing Brønsted-Lowry equations ph and poh calculations and conversions Solution and gravimetric stoiciometry Acid-base titration Graphing SI unit conversion and significant digits Learner Expectations After you view this program and complete the activities, you should be able to: Write and interpret chemical reaction equations illustrating the Brønsted-Lowry definitions of acids and bases and neutralization. P e rf o rm calculations related to quantitative reactions between acids and bases, including excess reagents in strong acid-strong base combinations. Use a ph meter and laboratory glassware related to titrations. Equilibrium, Acids and Bases in Chemical Changes 47

5 Draw and interpret titration curve graphs, using data from titration experiments involving acids and bases in various combinations, including: a strong acid with a strong base a strong acid with a weak base a weak acid with a strong base a strong acid with a polybasic species a strong base with a polyprotic acid. Demonstrate an understanding of the value of the role of precise observations and careful experimentation in learning about the chemistry of acids and bases. Watch the video program now. Additional Information Pause Point 1 05:56 The problem posed by the lifeguard at the swimming pool and the solution for the problem are shown below. Question What quantity of sodium carbonate would have to be added to a swimming pool containing 1.70 x 10 6 L of water to raise the ph from 6.80 to 7.50? Solution CO 3 2 (aq) + H 3 O + (aq) HCO 3 (aq) + H 2 O (l) HCO 3 (aq) + H 3 O + (aq) H 2 CO 3(aq) + H 2 O (l) CO 3 2 (aq) + 2H 3 O + (aq) H 2 CO 3(aq) + 2H 2 O (l) [H 3 O + (aq) ] of pool water at a ph of 6.80 = 1.6 x 10-7 mol/l mol of H 3 O + (aq) in 1.70 x 10 6 L of pool water at a ph of 6.80 = (1.6 x 10-7 mol/l)(1.70 x 10 6 L) = 2.7 x 10-1 mol 48 Equilibrium, Acids and Bases in Chemical Changes

6 [H 3 O + (aq) ] of pool water at a ph of 7.50 = 3.2 x 10-8 mol/l mol of H 3 O + (aq) in 1.70 x 10 6 L of pool water at a ph of 7.50 = (3.2 x 10-8 mol/l)(1.70 x 10 6 L) = 5.4 x 10-2 mol Required decrease in mol of H 3 O + (aq) = (2.7 x 10 _ 1 mol) - (5.4 x 10 _ 2 mol) = 2.2 x 10 _ 1 mol mol of CO 3 2 _ (aq) required = 1 2 x 2.2 x 10_ 1 mol = 1.1 x 10 _ 1 mol Mass of Na 2 CO 3(s) required = (1.1 x 10 _ 1 mol) x ( g/mol) = 11 g Challenge Question Pause Point 2 11:10 Calculate the ph of the solution after 15.0 ml of base have been added. Solution Adding 15.0 ml of 0.10 mol/l HaOH (aq) to 20.0 ml of 0.10 mol/l HCI (aq) Initial amount of: H 3 O + (aq) (mol) Initial amount of: OH (aq) (mol) Volume of NaOH (aq) (ml) Reagent in Excess (mol) Equilibrium Concentration [H 3 O + (aq) ] (mol/l) Equilibrium Concentration [OH (aq) ] (mol/l) ph 2.0 x x x 10-4 of HCl (aq) 5.0x1 0-4 m o l L 7.0 x = 1.4 x 10-2 Equilibrium, Acids and Bases in Chemical Changes 49

7 Natural Buffers The water quality scientist refers to natural buffers found in water which tend to protect the surface water from large changes in ph when acids or bases are added. The proper mix of solutes ensure that a solution will not experience a significant change in ph even if small amounts of a strong acid or a strong base are added. Such mixtures of solutes are called buffers. The water quality scientist refers to the buffering action of the natural substances found in local surface water (H 3 O + (aq), CO 3 2 (aq), OH (aq), other anions, A (aq), and H+ (aq)). The scientist uses the phrase, the buffer's capacity, which is determined by the actual concentration of these natural components. The amount of the natural buffer substances in water (measured in moles per liter) determines how much acid or base the water can safely absorb (the buffer's capacity). Titration Curve Data The following data was obtained by titrating a base with continuous addition of acid. Use this data to construct a titration curve which plots ph vs. volume of acid added. After you complete your graph, identify the equivalence point and write the net ionic equation for the neutralization. What volume of acid is required to reach the equivalence point? Volume of acid ph added(ml) Equilibrium, Acids and Bases in Chemical Changes

8 A Mystery ph Curve Pause Point 3 26:49 Helen has been titrating an unknown acid and base. Kathy tells Helen the unknown acid was phosphoric acid and the unknown base was sodium hydroxide. The reaction equations are shown below. The reaction completed at the first equivalence point was: H 3 PO 4(aq) + OH (aq) H 2 PO 4 (aq) + H 2 O (l) The reaction completed at the second equivalence point was: H 2 PO 4 (aq) + OH (aq) HPO 42 (aq) + H 2 O (l) The net equation for the titration can be determined by adding these two reaction equations: H 3 PO 4(aq) + OH (aq) H 2 PO 4 (aq) + H 2 O (l) H 2 PO 4 (aq) + OH (aq) H 2 PO 4 (aq) + H 2 O (l) net equation: H 3 PO 4(aq) + 2OH (aq) H 2 PO 4 (aq) + 2H 2 O (l) Helen asks why the third proton in H 3 PO 4(aq) does not produce a third 2 equivalence point. Kathy explains that the acid, HPO 4 (aq), is a weak acid. Its reaction with OH (aq) is not quantitative. Equilibrium, Acids and Bases in Chemical Changes 51