Unit 4 REVIEW. Understanding Concepts H 3

Transcription

1 REVIEW Understanding Concepts 1. Describe the physical and chemical properties of water. (4.1) 2. Briefly explain each of the following properties of water: (a) the bonding in a water molecule (b) the polarity of a water molecule (c) why water is such a good solvent (d) why water exists as a liquid most of the time (Figure 1) (e) why bodies of water are able to moderate extremes in climates (f) why most oils float on the surface of water (4.1) Figure 1 Water is found in the liquid state most of the time. 3. Water is known as the universal solvent. What implication does this property have on drinking water? (4.1) 4. (a) What two metal ions are most responsible for the hardness of water? (b) Why is ground water hard in some areas, but not in other areas? (4.2) 5. Describe how hard water can reduce the efficiency of appliances that are used to heat water. (4.2) 6. List the three categories of contaminants in water. Give at least two examples of each contaminant. (4.3) 7. A sample of water contains 1.55 ppm of dissolved nitrate. Calculate the mass of nitrate in a 1.0-L sample of this water. (4.3) 8. A diagnostic test for a certain pollutant is applied to a sample of drinking water (Figure 2). Will a negative test result prove that the ion is not present? Explain. (4.4) Figure 2 The formation of coloured precipitates is a diagnostic test for certain ions in water. Measuring the mass of a precipitate provides the concentration of one of these ions in a water sample. 9. Distinguish between qualitative analysis and quantitative analysis. (4.4) 10. The Great Lakes Action Plan identifies 42 Areas of Concern. (a) What is an Area of Concern? (b) What is a Remedial Action Plan? (c) Summarize, in your own words, the seven objectives of a RAP. (4.6) 11. Describe three properties of acids and three properties of bases. (4.7) 12. (a) What is the evidence of a strong acid and a weak acid? (b) Explain the terms strong acid and weak acid using the Arrhenius definition of an acid. (4.7) 13. Classify each of the following solutions as an acid or a base: (a) lye, NaOH (s) (b) vinegar, HC 2 H 3 O 2(aq) (c) milk of magnesia, Mg(OH) 2(s) (d) slaked lime, Ca(OH) 2(s) (e) window-cleaning solution, NH 3(aq) (4.7) 14. A 0.1-mol/L solution of nitric acid, HNO 3(aq), has a ph of about 1. A 0.1-mol/L solution of acetic acid, HC 2 H 3 O 2(aq), has a ph of about 3. (a) How can you explain this difference in ph? (b) Which solution requires greater caution when being used? Why? (c) Write the ionization reaction equation for each acid. (4.7) Chemistry in the Environment 363

2 15. Swimming pools should have a ph of between 7.2 and 7.6 to maintain the correct level of chlorine in the water and to prevent algal growth (Figure 3). (a) Is pool water acidic, basic, or neutral? Justify your answer. (b) A homeowner tests the water in a pool and determines that the ph is 7.9. What could the homeowner add to the water to adjust the ph? Explain. (4.7) 18. (a) What type of solution forms when soluble metal oxides react with water? (b) What type of solution forms when nonmetal oxides react with water? (4.10) 19. Baking soda, NaHCO 3(s), is a unique chemical substance because it reacts with both strong acids and strong bases. Write a balanced chemical equation for the reaction between baking soda and hydrochloric acid. (4.11) 20. Three trials in a titration analysis produce the following volumes of a standard base solution delivered from the burette (Table 1). From a quality control perspective, is a fourth trial necessary? Why or why not? (4.12) Table 1 Volume of Standard Base Used during Titration Trial Volume of base solution ml ml ml Figure 3 The ph of a swimming pool must be carefully maintained. 16. Drinking water standards in Canada specify that the ph should range from 6.5 to 8.5. (a) What household products, if carelessly discarded, might cause the ph of a freshwater source to decrease? List three products. (b) What household products, if carelessly discarded, might cause the ph of a freshwater source to increase? List three products. (4.8) 17. A strong acid solution has a ph of 4.0. The acid solution is mixed with water to make a large volume of solution. (a) How will the concentration of hydrogen ions be affected? (b) How will the ph change? (c) How does dilution affect the ph of a basic solution? (4.9) 21. Just as litmus paper is a chemical indicator, a lake trout is a biological indicator that can be used to indicate the level of acidity of lake water. Explain this statement. (4.13) 22. (a) Name two pollutants that are major contributors to acid precipitation. (b) Identify the sources of each pollutant. (4.13) 23. Use the kinetic molecular theory to explain each of the following behaviours of gases: (a) The boiling point of a liquid decreases as the altitude increases. (b) The volume of a gas in a container can be decreased by increasing the external pressure on the container. (c) Gases are more easily compressed than solids or liquids. (d) Hot-air balloons are partially inflated with cold air. As the air is heated, the balloon expands and rises. (4.14) 364

3 24. Explain how CFCs reduce the number of ozone molecules, resulting in more ultraviolet light reaching the surface of Earth. Use balanced chemical equations in your explanation. (4.15) 25. What is smog, and how does it form (Figure 4)? (4.16) Complete the Analysis in the following lab report: Question Which of the solutions (labelled A, B, C, and D) contain potassium hydroxide, sugar, sodium chloride, and sulfuric acid? Observations Table 2 Results for Litmus and Electrical Conductivity Unidentified Red Blue solution litmus litmus Conductivity A stays red blue to red high B stays red stays blue none C red to blue stays blue high D stays red stays blue high Figure 4 Smog contributes to bad air days. 26. Do you think it is important to test for air quality accurately, on a regular basis? Why or why not? (4.16, 4.17) Applying Inquiry Skills 27. A wastewater technician wants to determine the concentration of lead(ii) ions in a sample of wastewater. (a) Suggest an appropriate chemical to add to the wastewater sample to precipitate the lead(ii) ions from solution as lead(ii) sulfate. (b) The technician adds the chemical you suggested in (a) to a volume of the sample, and a precipitate forms. The precipitate is filtered, and the mass of the precipitate is determined. This mass is then used to calculate the concentration of lead(ii) ions in the original wastewater sample. Critique the accuracy of the results obtained. (4.4) 28. A forensic scientist needs to identify four colourless solutions that have been collected at a crime scene. Each solution is tested with red and blue litmus paper. Then it is tested for electrical conductivity. (Note that the four solutions are at the same concentration and temperature.) Analysis Using the Evidence in Table 2, answer the Question. (4.7) 29. Design an experiment to test the Prediction that diluting a solution of a strong acid by a factor of 10 will change the ph by one. Provide a list of Materials and a Procedure that you could follow to carry out your Experimental Design. (4.7) 30. Each of the elements sodium, Na (s), barium, Ba (s), and sulfur, S (s), has the potential to react with oxygen to form a soluble oxide in water. The oxide may produce either an acidic or basic solution when dissolved in water. (a) Design an experiment to produce the oxide of each of these elements and to test the nature of the solution. (b) Write a complete chemical equation to show the formation of the oxide of each element. (c) Write a complete chemical equation to show the formation of the product when each oxide in (b) dissolves in water. (d) Predict whether each solution will be acidic or basic. (4.10, 4.11) 31. A student is asked to determine the concentration of hydrochloric acid so that the solution can be used as a standard for other class experiments. Samples of a standard sodium carbonate solution are titrated with the hydrochloric acid of unknown concentration. Chemistry in the Environment 365

4 Methyl orange indicator is used to show the endpoint. Complete the Observations and Analysis in the following lab report: Question What is the molar concentration of hydrochloric acid? Observations (a) Copy and complete Table 3. Table 3 Titration of 10.0 ml of mol/L Na 2 CO 3(aq) with HCl (aq) Trial Final burette ml ml ml ml reading (ml) Initial burette 0.30 ml ml 5.90 ml ml reading (ml) Figure 5 Lives depend on the accuracy of drinking water tests. Volume of HCl (aq) added (ml) Analysis (b) Calculate the molar concentration of hydrochloric acid. (4.11) Making Connections 32. (a) If pure water were tested with classroom electrical conductivity apparatus, would the light bulb glow? (b) Can you be electrocuted if you are standing in pure water? Explain. (Hint: Pure water contains no dissolved substances.) (4.1, 4.2) 33. Propose a solution to reduce the pollution of ground water. Choose one source of contamination, and suggest ways to minimize or eliminate it. (4.2, 4.3) 34. Why are very precise equipment and technologies needed to test drinking water samples (Figure 5)? (4.2, 4.4) 35. The transportation of hazardous wastes from the Nova Scotia tar ponds to a disposal site just outside Sarnia, Ontario, is a contentious issue. Find out whether your community has a hazardous waste disposal depot. What are the skills and qualifications of people who work at these depots? What types of substances do they handle? Do you agree or disagree that Figure 6 Is it safe to transport hazardous wastes over long distances on busy highways? hazardous wastes from Nova Scotia should be trucked to southwestern Ontario (Figure 6)? Why or why not? (4.8) 36. The maximum quantity of oxygen that dissolves in water is 14.7 ppm at 0 C and 8.7 ppm at 25 C. (a) What temperature do you think active game fish prefer? Explain your answer. (b) If you were trying to catch a fish, where would you cast your lure? Why? (4.14) 366

5 37. In movies, acids are often portrayed as dangerous, with the ability to burn or eat through anything. In one movie, for example, an aluminum boat is quickly eaten away by acidic lake water. Is this portrayal accurate? Justify your answer with personal experiences, examples, and explanations. Which acids are the most dangerous? (4.7) 38. Laboratory safety rules require students to wear eye protection and be extremely careful when handling acids, such as hydrochloric acid and sulfuric acid. In contrast, boric acid, H 3 BO 3(aq), is sold in pharmacies as a soothing eyewash (Figure 7). Explain why boric acid is relatively harmless, while hydrochloric acid and sulfuric acid are very corrosive. (4.7) 40. Will the information you have learned in this unit affect your attitude toward the materials that you pour down the sink at home or at school? Explain your answer. (4.8) Extension 41. Reverse osmosis is a water-treatment process that is widely used to produce many brands of bottled water and to purify seawater. Outdoor supply stores sell reverse osmosis kits for purifying water on wilderness trips. Research reverse osmosis to answer the following questions: (a) How is pure drinking water obtained from seawater using reverse osmosis? (b) Is reverse osmosis commercially viable? (c) Research a water-treatment plant that uses reverse osmosis to purify seawater. Present your findings to your class in a report. 42. When travelling in the wilderness, people are often advised to take chlorine or iodine tablets to put in their drinking water. Research the purpose of these tablets and how they are used. Prepare a leaflet to be included inside the packets of chlorine or iodine tablets. Figure 7 Boric acid is recommended for soothing sore eyes. 39. Gardeners know that coniferous trees like acidic soil. Acid precipitation adversely affects coniferous trees, however. Explain. (4.13) 43. Many chemical substances that are potentially toxic or harmful to the environment have maximum allowable concentrations set by government regulations. Research these regulations. (a) If a chemical is dangerous, should the MAC be zero? Explain. (b) Is a zero MAC possible? Can it be measured? (c) If a nonzero limit is set, how is this limit determined? Chemistry in the Environment 367