M ATTER - S OLUTIONS Chemistry 2012. Q UESTION ? What is a solution? How is a solution made? Is it a...

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Transcript of M ATTER - S OLUTIONS Chemistry 2012. Q UESTION ? What is a solution? How is a solution made? Is it a...

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  • M ATTER - S OLUTIONS Chemistry 2012
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  • Q UESTION ? What is a solution? How is a solution made? Is it a mixture or a compound? How can we tell the difference?
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  • E NGAGE In a large test tube or jar, mix 10 mL of sodium silicate (sometimes called water- glass solution) and 40 mL of water. Carefully drop solid-colored crystal compounds of cobalt, copper, nickel, iron, and/or manganese in different locations inside the jar. a) Is there evidence of a change immediately? In several minutes? In several hours? In several days? b) Is the phenomenon you see the result of a physical or a chemical change? Explain your answer.
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  • I NVESTIGATE - P ART 1 Prepare a data table in your Journal There should be 4 columns and 8 rows. One column for what was done another for what is observed, and the 4 th for physical or chemical change. Record your observations. Label each interaction as being a physical or a chemical change. What are some examples of chemical and physical changes you encounter in your everyday life?
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  • D ATA T ABLE 1 ReactionsPredictionObservationsChemical/Physical 1. Add lemon juice to chocolate milk- 2. Add vinegar to baking soda 3. Add salt to water- 4. Add phenolphthalein to KOH- 5. Add sodium carbonate to sodium hydrogen sulfate- 6. Add copper sulfate to water 7. Add ammonia to copper sulfate- 8. Add vinegar to marble chips or chalk-
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  • M AKE A NOTHER C HART In your Journal, make a chart. Use an entire page, leaving room to record observations. Observations: color change and/or formations of precipitate (sometimes observed as a cloudy solution).
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  • L AB A CTIVITY Now it is time to mix the solutions. After mixing the pairs of solutions, make note on your chart of any changes you observe. Complete your data table with your observations. Do not use more than two drops and do not allow the tips of the pipettes to touch the chemicals. If a precipitate forms, record its color in the table in your log by using the notation Ppt (color). If no precipitate forms, record Sol (for solution) in the table. Notice that the symbol (aq) has been added to the solutions to indicate that the chemical is dissolved in water (aqueous solution). The symbol (s) has been added to identify the solid precipitate.
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  • B ACKGROUND I NFORMATION There are thousands upon thousands of reactions that occur in the world, and most of them take place in water (aqueous) solutions. When certain cations and anions are combined, water-insoluble ionic compounds may form. (Cations are positively charged ions and anions are negatively charged ions.) When these ions are in separate aqueous solutions and then brought together, an insoluble solid, or precipitate forms. The precipitate is an ionic compound (often called a salt) that forms because certain ions attract each other so strongly that they are removed from the water solution as the product of a chemical reaction. A double-replacement reaction is one type of precipitation reaction where a precipitate forms when one of the products is insoluble. Look at the example of the reaction between solutions of zinc nitrate and sodium carbonate that you observed in the activity: Zinc nitrate (aq) + sodium carbonate (aq) sodium nitrate (aq) + zinc carbonate (s) Zn(NO 3 ) 2(aq) + Na 2 CO 3(aq) 2NaNO 3(aq) + ZnCO 3(s) Note that (aq) means a compound is in aqueous solution, and (s) means that a solid has formed (the precipitate).
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  • S IMPLE R ULES FOR S OLUBILITY OF C OMPOUNDS IN W ATER 1. Most nitrate (NO 3 1 ), acetate (CH 3 COO 1 ), and perchlorate (ClO 4 1 ) compounds are soluble. 2. Group 1A metal (Li +1, Na +1, and K +1 ) and ammonium (NH 4 +1 ) compounds are soluble. 3. Most chloride (Cl 1 ), bromide (Br 1 ), and iodide (I 1 ) compounds are soluble. The most notable exceptions are when these anions are combined with Cu +1, Ag +1, Pb 2+, Hg 2+, and Hg 2 2+. 4. Most sulfate (SO 4 2 ) compounds are soluble, except when they are combined with Ba 2+, Hg 2 2+, Sr 2+, and Pb 2+. Ca 2+ compounds are slightly soluble. 5. Carbonate (CO 3 2 ) and phosphate (PO 4 3 ) compounds are only slightly soluble. 6. Most hydroxide (OH ) compounds are insoluble except when combined with group 1A cations. Ca(OH) 2 is slightly soluble. An ionic compound is said to be soluble if a large amount of it dissolves in water. How much is a large amount? Typically, this means a solution with a concentration of at least 0.1 mol/L (mole per liter) at room temperature. An insoluble ionic compound is defined as one that will not dissolve in water, typically producing an aqueous solution of less than 0.001 mol/L at room temperature. A slightly soluble compound falls somewhere between these two boundaries, usually forming a precipitate in water.
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  • A NALYSIS 1. How can mixing two clear solutions produce a solid material? What is happening at the molecular level? Provide a specific example in your discussion. 2. What experimental data do you have that shows how a pigment can form from a precipitation reaction? 3. Predict the products when the following aqueous solutions are combined; a) copper sulfate plus sodium hydroxide b) potassium iodide plus iron (III) bromide 4. Use the solubility rules to determine which of the following are insoluble in water: a) lithium acetate b) ammonium chloride c) silver bromide
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  • I NVESTIGATE P ART 3- D EMONSTRATION Your teacher will show you a solution of sodium acetate in a 250-mL flask. Observe the solution carefully. Your teacher will then add one crystal of sodium acetate to the flask. a) Record your observations in your Active Chemistry log. b) What happens? Record your observations in your log. c) Was this a chemical or physical change?
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  • E XPLAIN Q UESTION ? Imagine a situation where two colorless solutions are mixed together. There is no color change, no precipitate is formed, and no gas is released. However, heat is released as the solutions are mixed. Even though dissolving is a physical process, it very often results in a change in temperature, which can be either positive or negative, depending on the solute and solvent. Is this an example of a chemical or physical change? Explain your choice.
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  • E XPLAIN -C HEM T ALK Read the Chem Talk on pp. 436-437 and answer the following questions: 1. What is a physical change? Provide two examples. What does it mean when substances undergo physical change? 2. Is making a solution a chemical or physical change? Explain your answer. 3. Explain the meaning of a solution, a solute, and a solvent. 4. How do you describe the concentration of a solution? 5. Explain the difference between an unsaturated solution, a saturated solution, and a supersaturated solution. 6. Did you have difficulty at the beginning of this activity in telling the difference between physical and chemical changes? What about solutions?
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  • I NVESTIGATE P ART 4 What are the factors that affect how a solution is formed? How would you test the factors?
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  • D ATA T ABLE StationFactor being testedObservations Copy the data table and use it to perform the investigation.
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  • I NVESTIGATE - S TATION 1 1. Pour 200 mL hot water into one beaker and 200 mL ice water into another beaker. Add a tea bag to each. a) Record your results. b) Describe the relationship between temperature and the rate of solution.
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  • I NVESTIGATE - S TATION 2 2. Prepare two beakers, each containing equal amounts (about 200 mL) of room temperature water. Obtain two sugar cubes. Crush one and leave the other whole. Simultaneously add the crushed cube to one beaker and the whole cube to the other beaker. a) Record your observations. What factor was being studied? b) Describe the relationship between that factor and the rate of reaction.
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  • I NVESTIGATE - S TATION 3 3. Prepare two large test tubes, each containing equal amounts (about 10 mL) of room temperature water. Add a scoop of table salt to each test tube. Using a stopper, place the stopper in only one test tube and shake the solution for 1 minute. a. Compare the two test tubes. Describe your observation. b. What factor are you testing? Explain how it affects your solutions.
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  • E XPLAIN - A NALYSIS 1. What is happening at Station 1? What is causing the difference to occur? 2 What is happening at Station 2? What is causing the difference to occur? 3. What is happening at Station 3? What is causing the difference to occur? Write a page summarizing the factors affecting the formation of a solution.
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  • E VALUATE - T HE D IAPER D ILEMMA Obtain a sample of diaper material. Determine its mass and record. Place the material from the disposable diaper into a large beaker. Predict how much liquid the diaper material will be able to hold. Record your prediction in your Journal.
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  • D IAPER E XPLAIN : P OLYMER Sodium Polyacrylate- Sodium polyacrylate is a polymer. It is made up of many (poly) repeating units of a smaller group of elements (the monomer called acrylate). The polymer is used in disposable diapers Unique property-can absorb more that 800 times its own mass in distilled water
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  • E LABORATE -L AB R EPORT -R OUGH D RAFT Problem: Which brand is th