Solutions and Concentrations PDF

1.4 Solutions and Concentrations Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attach...

1.4 Solutions and Concentrations Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. Figure A1.13: Most household cleaners are sold in solution form. As a consumer, you use many products that are sold in the form of solute dissolved in a solvent—a solution. Beverages, medicines, household cleaners, and hair-care products are all examples of commercial solutions people use on a regular basis. In each case, manufacturers make sure that the ratio of solute to solvent is safe and appropriate for the application. Changing this ratio can dramatically change the properties of the solution. Y ID ? O D U A concentrated solution of acetic acid would hurt you if you drank it. Yet, most people commonly use vinegar—a 5% solution of acetic acid—as an ingredient in their cooking. To keep consumers safe, there are regulations about the proper labelling of products. The ratio of solute to solvent is often noted on the product’s label. 5% Acetic Acid 34 Unit A: Chemical Change  In some cases, the solute that may be part of the product The concept of concentration is something you encounter Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. is an unintended ingredient. Polychlorinated biphenyls every day. Whether you are buying juice or cleaning products (PCBs) are pollutants that can be present in water. They or looking at government guidelines for water quality, you may also be found in fish living in water polluted with are dealing with concentrations. Understanding concentration PCBs. The maximum concentration allowed by Canada’s will help you answer questions like the following: health guidelines regarding the level of PCBs in fish that How much of the solute is in the product you are are harvested to be eaten is 2 parts per million (ppm). This buying? guideline is to ensure that the fish you eat will not harm you. What are the safe or acceptable limits for certain chemicals in food or drinking water? Are there safety concerns associated with products that have higher solute concentrations? Can you save money by buying concentrated solutions and diluting them yourself? These are a few of the questions you will be exploring in this lesson and the next. Not only will you find that understanding concentration gives you a greater knowledge of the information listed on the products you buy, but it will also give you a better understanding of how to interpret and analyze this information. Figure A1.14: Canada has strict guidelines regarding the levels of PCBs Practice present in fish sold for human consumption. All of these examples relate to the amounts of a certain One of the “hidden costs” included in the price of most substance present in a solution. Whether it is the amount consumer products is shipping—the cost of transporting the goods from the factory or warehouse to the store. of PCB in fish or the amount of acetic acid in vinegar, If the consumer product is in the form of an aqueous the ratio of solute to solution is described as a solution’s solution, it is frequently shipped in a concentrated form concentration. A solution with more solute in it than a to reduce the mass of the product. Every litre of water solution of the same volume is said to be more concentrated. that does not have to be shipped reduces the load by A solution containing a large amount of solute per given 1 kg, helping keep transportation costs low. volume is called a concentrated solution. A solution containing a small amount of solute per given volume is 25. Soft drinks served at many restaurants are called a dilute solution. dispensed from a “fountain.” In this process, the concentrated form of the soft drink is taken concentration: the ratio of the quantity of from a pressurized canister and mixed with solute to the quantity of solution carbonated water. Explain the advantage of using a concentrated solution: a solution concentrated form of soft drink stored in a canister. containing a high ratio of solute to solution 26. A fertilizer for flowers is sold as a dry, granular dilute solution: a solution containing a low powder that must be mixed with water by the ratio of solute to solution gardener before applying it to the flowering plants. a. Determine whether the dry, granular powder is the solute or the solvent of the liquid fertilizer Concentrated Solutions and Dilute Solutions solution. b. A 0.500-kg package of this dry powder is capable of making 189 L of liquid fertilizer solution. By approximately what factor would the shipping costs increase if the fertilizer was sold to consumers as a ready-to-use liquid? c. List some disadvantages of selling a dry powder that requires the gardener to mix the liquid A concentrated solution A dilute solution has a low fertilizer solution. has a high ratio of solute ratio of solute to solution. to solution. Chapter 1: Aqueous Solutions 35  Observing the Effects of Reduced Concentrations Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. In the next investigation, “Repeated Dilutions,” you will have an opportunity to observe the effects of concentration on a chemical reaction. Although the observations of this investigation focus on colour changes, the solution has its concentration reduced as measured by the number of moles per litre. The meaning of this unit will be explored fully in Lesson 1.5. For this investigation, you only need to know that a solution with a concentration of 4.00 mol/L has twice the concentration as a solution with 2.00 mol/L. Investigation Repeated Dilutions Purpose You will observe the effects of concentration on a step 4: Repeat step 3 by halving the volume of the solution chemical reaction. in beaker 2 and creating a new solution in beaker 3. Repeat this process by using the solution in beaker 3 Science Skills to create a more dilute solution in beaker 4 and so on until you have eight beakers with successively more Performing and Recording dilute concentrations. Each beaker will end up with a Analyzing and Interpreting solution that is half the concentration of the previous beaker. All of the beakers will have 50 mL of solution Materials except for the last beaker, which will have 100 mL. 100-mL graduated cylinder step 5: Carefully add two drops of phenolphthalein 9, 100-mL beakers solution to beakers 1 through 8 and to the beaker distilled water with the distilled water. Observe the effect of the phenolphthalein solution in a bottle with an eyedropper phenolphathalein on the solution in each beaker. 100 mL of 1.00-mol/L sodium hydroxide solution Stir the liquid using a clean stirring rod, rinsing it off NaOH(aq) between each beaker. masking tape Analysis felt-tipped pen 1. Copy and complete the following table. stirring rod Concentration of NaOH(aq) Beaker Relative to Beaker 1 Use gloves, safety glasses, 1 100 and a lab apron for this activity. 2 50 Procedure 3 step 1: Measure 50 mL of distilled water using the 4 graduated cylinder, and pour it into a beaker. Label the beaker “Distilled Water.” 5 step 2: Measure 100 mL of sodium hydroxide solution using the graduated cylinder. Pour this solution 6 into another beaker. Label the beaker “1.” 7 step 3: Pour 50 mL of the solution in beaker 1 into the graduated cylinder. Carefully add 50 mL of water 8 so the graduated cylinder now has 100 mL of solution. Pour this diluted solution into another 2. Identify the manipulated variable and the responding beaker, labelling it as beaker “2.” Note that the variable. solution in beaker 2 has only half the 3. State the process that you used to create the solutions in concentration of beaker 1 because the amount of beakers 2 through 8. solvent has been doubled. In other words, the concentration in beaker 2 is 50% of the concentration in beaker 1. 36 Unit A: Chemical Change Qualitative Properties of Solutions Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. You know the difference between concentrated juice and dilute juice because you can taste the difference. You should also see a difference in the colour and consistency. You can get a lot of information about a substance simply by observing its physical properties, like colour, taste, and odour. These are the qualitative properties of a solution. Figure A1.16: The solution on the left has a higher concentration than the solution on the right. 4. How many times did you dilute the sodium hydroxide solution before you reached a point where the diluted qualitative property of a solution: a basic attribute of a solution you can observe with one or more of the five senses solution no longer reacted with the phenolphthalein? Is it possible to dilute the solution to the point where it will have no sodium hydroxide left? Qualitative properties include a description of a solution’s 5. Imagine that the fluid you were diluting was sewage colour taste transparency instead of sodium hydroxide. You repeated this colour intensity odour experiment and produced eight beakers of sewage in decreasing concentrations. a. Would you feel comfortable drinking from beaker 8? Never taste or inhale any Give a reason for your answer. solution prepared in a laboratory. b. List some substances that might affect the quality of the water. c. Use the Internet or other resources to obtain a Because the solute provides each solution with a new copy of the drinking water standards for your local set of properties, qualitative tests can be used to detect the area or the Guidelines for Canadian Drinking Water presence and, in some cases, identify the solute present in a Quality to determine what kinds of tests solution. Often, the difference in the qualitative observations are performed on drinking water to ensure between concentrated and dilute solutions is directly related its safety. Are tests for the substances to the number of particles of solute dissolved within the you listed in question 5.b. included in the solution. As shown in the “Repeated Dilutions” investigation, standards? the greater the number of particles in the solution, the greater the specific effect. The beaker that had the lowest concentration of sodium hydroxide had the fewest particles to react with the drops of phenolphthalein to produce a colour change. A highly concentrated solution had a deeper colour because it contained more solute particles (sodium hydroxide) to react with the phenolphthalein. Qualitative Characteristics of Solutions A concentrated solution has A dilute solution has fewer many dissolved particles, dissolved particles, resulting resulting in a higher conductivity in a weaker conductivity and and in a more intense colour, a less intense colour, taste, Figure A1.15: Sewage must be processed thoroughly before returning to taste, and scent. and scent. the environment. Chapter 1: Aqueous Solutions 37  It is not always easy, however, to use qualitative Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. properties to compare the concentrations of solutions. This is Practice especially the case for colourless solutions. How could you determine which of the following solutions had the higher 27. Many fertilizers sold to gardeners have a concentration? non-staining dye to the ingredients. This dye has no beneficial effects on the plants, but it serves many purposes for the gardeners. a. Suppose two gardeners each read the instructions on two bags of identical fertilizer and worked independently to prepare their solutions. Each gardener produced a solution of liquid fertilizer in identical 20-L pails. Although both solutions were blue, one has a much more intense blue colour than the other. Identify which pail has the more concentrated solution and suggest what these two gardeners should do next. b. Many liquid fertilizers can be dispensed by a hose. Why is the presence of the dye in the fertilizer regarded by some gardeners as a Figure A1.17: Sometimes it is difficult to tell which solution has a higher useful safeguard? concentration just by looking. As you explored earlier, one method to accomplish this task would be to compare how the two different solutions conduct electricity. It is possible to place two electrodes into a solution and measure how easily an electrical current can pass through the solution from one electrode to another. Solutions with higher concentrations are more effective than dilute solutions at passing the current through the solution. Y ID ? O D U All chemical reactions involve collisions between atoms, ions, and molecules. This idea is explained by the collision-reaction theory. This theory states that a chemical reaction collision-reaction theory: a theory stating that chemical will occur if the reactions involve the collision particles collide with and rearrangement of particles a certain minimum energy and if they collide with a certain orientation. The rearrangement of particles that occurs after the collision is the chemical reaction. Example of Collision Theory Figure A1.18: A conductivity meter provides numerical data for I–(g) + CH3Br(g) Æ CH3I(g) + Br –(g) comparing solutions. This reaction only occurs if the iodide ion, I–(g), collides Another method to determine the relative concentrations with enough energy, travelling from the direction shown. of two solutions is to look at chemical characteristics, such as how readily each solution reacts. 38 Unit A: Chemical Change Concentration Affects the Speed of Chemical Reactions Science 20 © 2006 Alberta Education (www.education.gov.ab.ca). Third-party copyright credits are listed on the attached copyright credit page. A solution having a greater concentration of solute to solution reacts faster than a more dilute solution. This occurs for the Reactions of Concentrated following reasons: Versus Dilute Solutions A chemical reaction is a result of collisions between particles. A concentrated solution has more particles of solute available for possible collisions than a dilute solution. The probability of collisions increases as the number Reactions with concentrated Reactions with dilute of solute particles within a system increases. solutions occur more quickly solutions occur at a slower because you have a greater rate because collisions are number of collisions. a little less probable. 1.4 Summary Concentration is a description of the amount of solute dissolved within a solvent to form a solution. A concentrated solution has more solute particles dissolved in the solution than a dilute solution. The amount of solute in a solution can affect the qualitative characteristics of that solution, such as the intensity of colour and reactivity with other substances. Concentrated solutions and dilute solutions have similar physical characteristics; but due to the number of particles in a concentrated solution, there tends to be an increased intensity of physical and chemical properties. These properties include greater colour intensity and an increased Figure A1.19: Using only one of the five senses, it is very difficult to determine rate of chemical reactions. which solution is more concentrated. 1.4 Questions Knowledge 1. Define the following terms. a. concentration b. concentrated solution c. dilute solution d. qualitative properties e. collision-reaction theory 2. Describe how the qualitative characteristics of concentrated solutions compare with those of dilute solutions. 3. Explain why a chemical reaction appears to occur faster using a more concentrated solution versus a dilute solution. Applying Concepts 4. A person accidentally swallows a poisonous compound. You immediately call the local poison control centre. They tell you that the person should drink at least three glasses of water and then go to the hospital. State a reason for the advice given. 5. State two situations when dilute solutions are used and two situations when concentrated solutions are used. 6. Explain why you must be much more aware of safety procedures when working with concentrated solutions than with dilute solutions. 7. Suggest appropriate safety procedures for shipping concentrated solutions by rail cars. Chapter 1: Aqueous Solutions 39 Photo Credits and Acknowledgements All photographs, illustrations, and text contained in this book have been created by or for Alberta Education, unless noted herein or elsewhere in this Science 20 textbook. 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