Golf Ball Lab What is the minimum amount of salt needed to make a golf ball float?

Determine the minimum amount of salt needed to make a golf ball float in 100 mL water. Weigh out 50.0 g of NaCl Add 5 g additions of salt to the water, dissolve, check to see if ball floats. Continue with this method of successive additions until ball floats. Re-weigh remaining salt and subtract this amount from 50.0 g to determine the amount of salt needed. Finally, repeat…begin 5 g less salt and add 1 g increments to narrow range. Trial Salt (g) Total Float /Sink 1 5.0 g Sink 2 10.0 g 3 15.0 g 4 20.0 g 5 25.0 g Float http://www.foodsubs.com/Salt.html (Comparison of salts.)

Theorize, but Verify …We must trust in nothing but facts. These are presented to us by nature and cannot deceive. We ought in every instance to submit our reasoning to the test of experiment. It is especially necessary to guard against the extravagances of imagination which incline to step beyond the bounds of truth. Antoine Laurent Lavoisier, 1743 - 1794 Graphic: http://images.google.com/imgres?imgurl=http://historyofscience.free.fr/images-Lavoisier/lavoisier_seul.jpg&imgrefurl=http://historyofscience.free.fr/Lavoisier-Friends/a_tab2_lavoisier_alone.html&h=689&w=400&sz=40&tbnid=QYfa5Ida5AwJ:&tbnh=137&tbnw=79&hl=en&start=36&prev=/images%3Fq%3DLavoisier%26start%3D20%26svnum%3D10%26hl%3Den%26lr%3D%26sa%3DN Unlike the Greeks, Lavoisier believed in experimental evidence to prove a point -- not just logic and reasoning. Jaffe, New World of Chemistry, 1955, page 1

Theory Guides, Laboratory Decides! Density of water = 1.0 g/mL Need to determine density of a golf ball. mass =______ g (electronic balance) volume = ______ mL (water displacement method) or formula? Density of golf ball cannot be made to decrease. Therefore, you need to increase the density of the water by dissolving salt into the water. Limiting Factor: accurate determination of volume of golf ball Solubility Curve of salt in water. Water has a limit to how much salt can be dissolved. Saturation – point at which the solution is full and cannot hold anymore solute.

Packing of NaCl Ions Electron Microscope Photograph of NaCl Sodium chloride is a cubic-shaped crystalline solid that has a melting point of 808oC. Electron Microscope Photograph of NaCl

Dissolving of Salt in Water Cl- ions Na+ Water molecules When sodium chloride crystals are dissolved in water, the polar water molecules exert attracting forces which weaken the ionic bonds. The process of solution occurs the ions of sodium and chloride become hydrated. NaCl(s) + H2O  Na+(aq) + Cl-(aq)

Dissolving of NaCl - - - O + + + + Cl- Na+ hydrated ions H Timberlake, Chemistry 7th Edition, page 287

Interstitial Spaces and Particle Size (holes in water where substances dissolve) 100 mL Parking at school if you arrive at 7:00 AM = _____ Easy Parking at school if you arrive at 7:45 AM = _____ Hard More available spaces if you arrive early. Salt dissolves quicker when you begin because there are more available spaces to 'park'. Analogy: Compact car is easier to park than SUV. Theory: Crush salt to make particles smaller (increase surface area) …it will dissolve more rapidly. STIR

100 mL of water = 100 g density of water= 1.00 g/mL You determine the density of golf ball to be 1.18 g/mL Add 19 g salt to 100 g water = 119 g salt + water Volume remains100 mL (saltwater) Density = Mass volume 119 g 100 mL or Density (saltwater) = 1.19 g/mL If golf ball doesn’t float, add 2 g additions of salt until it floats. Add 3.0 mL water,stir…float Add 3.0 mL water,stir…float Add 3.0 mL water,stir…sink

Goals and Objectives: a Goals and Objectives: a.  Given materials and problem, formulate and test a hypothesis to determine if a golf ball can float in salt water. b.  Collect accurate data and compare own data to other class data.  Evaluate own results. Investigation Procedure: a.  Design an experiment to accurately determine how dense salt water must be in order for a golf ball to float.  Use metric units.  Be sure to control as many variables as possible. b.  Write down the procedure that you and your partner(s) are going to use prior to lab day.  Record any researched facts that may be useful in knowing before conducting your experiment. c.  Carefully run your experiment, make observations and record your measurements in a data table.  Use grams and milliliters in your measurements.  Include a calculation  column in your data table. d.  Critique your own procedure, discuss and compare your process with another group, then modify your own steps as needed. e.  Repeat your experiment to check for accuracy, if time allows.

Discussion Questions for Understanding: a.  How did you determine the density of your golf ball? b.  Why does a golf ball normally sink to the bottom of a pond at the golf course? c.  What variables were difficult or impossible for you to control during this experiment?      How much salt can be dissolved in 100 mL of water?  (saturated)           effect of temperature on solubility      Surface area of salt may affect rate of dissolving (may need to crush salt finely) d.  What variables may have changed as time went on that could have affected the outcome of your results? e.  Did you improve the accuracy of your results after conferring with another group? f.  Describe your sources of error.  (Human error and faulty equipment are unacceptable answers)

Materials: electronic balance Materials:      electronic balance      100 mL & 500 mL graduated cylinder          mortar / pestle     glass stirring rod      golf ball     salt (Kosher, iodized table salt, table salt)          250 mL beaker  Extension: a.  Research the manufacturing of golf balls to determine why they sink in pond water. b.  Research to determine which body of salt water in the world would float a golf ball the highest. Lab Report :  (10 - 12 point font two page maximum length)       Background / problem      Hypothesis (if...then)       Procedure (protocol)        Data (table, graph)        Analysis          Conclusions / Future directions (limitations)              Sample calculations - appendix Do not use references to yourself or others in your writing of a lab report (except for citing past research). OR Poster (25 words or less) A picture is worth 1000 words!

of solubility on temperature Solubility vs. Temperature for Solids 140 KI KCl NaNO3 KNO3 HCl NH4Cl NH3 KClO3 SO2 130 120 gases solids 110 Solubility Table 100 90 80 shows the dependence of solubility on temperature 70 Solubility (grams of solute/100 g H2O) 60 50 “Solubility Curves for Selected Solutes”   Description: This slide is a graph of solubility curves for 10 solutes. It shows the number of grams of solute that will dissolve in 100 grams of water over a temperature range of 0cC to 10 cC. Basic Concepts The maximum amount of solute that will dissolve at a given temperature in 100 grams of water is given by the solubility curve for that substance. When the temperature of a saturated solution decreases, a precipitate forms. Most solids become more soluble in water as temperature increases, whereas gases become less soluble as temperature increases. Teaching Suggestions Use this slide to teach students how to use solubility curves to determine the solubilities of various substances at different temperatures. Direct their attention to the dashed lines; these can be used to find the solubility of KClO3 at 50 cC (about 21 g per 100 g of H2O). Make sure students understand that a point on a solubility curve represents the maximum quantity of a particular solute that can be dissolved in a specified quantity of solvent or solution at a particular temperature. Point out that the solubility curve for a particular solute does not depend on whether other solutes also are present in the solution (unless there is a common-ion effect; this subject usually is covered at a later stage in a chemistry course). Questions Determine the solubilities (in water) of the following substance at the indicated temperatures: NH3 at 50 oC; KCl at 90 oC; and NaNO3 at 0 oC. Which of the substances shown on the graph is most soluble in water at 20 oC? Which is lease soluble at that temperature? For which substance is the solubility lease affected by changes in temperature? Why do you think solubilities are only shown between 0 oC and 100 oC? In a flask, you heat a mixture of 120 grams of KClO3 and 300 grams of water until all of the KClO3 has just been dissolved. At what temperature does this occur? You then allow the flask to cool. When you examine it later, the temperature is 64 oC and you notice a white powder in the solution. What has happened? What is the mass of the white powder? Compare the solubility curves for the gases HCl, NH3, and SO2) with the solubility curves for the solid solutes. What generalizations(s) can you make about the relationship between solubility and temperature? According to an article in an engineering journal, there is a salt whose solubility in water increases as the water temperature increases from 0 oC to 65 oC. The salt’s solubility then decreases at temperatures above 65 oC, the article states. In your opinion, is such a salt likely to exist? Explain your answer. What could you do to verify the claims of the article? 40 30 NaCl 20 10 0 10 20 30 40 50 60 70 80 90 100 LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517

Teacher Notes Some golf balls will NOT float in a saturated solution of salt water. Their mass is too great. The maximum density of salt water is ~1.36 g/mL. The solution is saturated. The limiting factor is determining an accurate volume for the golf ball. My students use a 250 mL graduated cylinder. Anything smaller and the golf ball won’t fit. Each line is 5 mL (students often think it goes by 10 mL increments).