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Objectives

Objectives. 1. Determine the Molality of a saltwater solution necessary to “flink” a golf ball. 2. Determine the maximum amount of salt that can be dissolved in mL of water. Density of pure water = 1.0 g/mL. Need to determine density of a golf ball. mass =______ g (electronic balance)

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Objectives

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  1. Objectives 1. Determine the Molality of a saltwater solution necessary to “flink” a golf ball. 2. Determine the maximum amount of salt that can be dissolved in mL of water. Density of pure 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.

  2. Na+ ions Water molecules Cl- ions Dissolving of Salt in Water NaCl(s) + H2O  Na+(aq) + Cl-(aq)

  3. Interstitial spaces (holes in water where substances dissolve) 100 mL Interstitial Spaces and Particle Size Parking at school if you arrive at 6:45 AM = _____ Easy Parking at school if you arrive at 7:25 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

  4. Mass volume Density = density of water= 1.00 g/mL 100 mL of water = 100 g You determine the density of golf ball. Add 19 g salt to 100 g water = 119 g salt + water Volume remains100 mL (saltwater) 119 g 100 mL or Density (saltwater) = 1.19 g/mL If golf ball doesn’t float, add 2 mL additions of salt until it floats. Add 2.0 mL water,stir…float Add 2.0 mL water,stir…float Add 2.0 mL water,stir…sink

  5. 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.  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.

  6. Materials:     electronic balance      graduated cylinder          mortar / pestle     glass stirring rod     golf ball     salt (Kosher, iodized table salt, table salt)          250 mL beaker  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?d.     How much salt can be dissolved in 100 mL of water?  (saturated) e.  What variables may have changed as time went on that could have affected the outcome of your results?f.  What is the Molality (Moles of Solute/kg of Solvent) of the Salt Water solution necessary to “flink” the golf ball? g.  Could a small piece of solid aluminum (Density =2.70 g/mL) float in saltwater, explain why or why not?

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