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

Trial Salt (g) Total Float /Sink

1 5.0 g 5.0 g Sink

2 5.0 g 10.0 g Sink

3 5.0 g 15.0 g Sink

4 5.0 g 20.0 g Sink

5 5.0 g 25.0 g Float

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 determinethe amount of salt needed.

Finally, repeat…begin 5 g less salt and add 1 g increments to narrow range.

Theorize, but Verify

Jaffe, New World of Chemistry, 1955, page 1

…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

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 MicroscopePhotograph of NaCl

Dissolving of Salt in Water

NaCl(s) + H2O Na+(aq) + Cl-(aq)

Cl-

ions

Na+

ions Water molecules

Dissolving of NaCl

Timberlake, Chemistry 7th Edition, page 287

HH

O

Na+

+

-- + -+

+

-

Cl-

+ -

+

hydrated ions

100 mL

Interstitial Spaces and Particle Size

Interstitial spaces(holes in water where substances dissolve)

Parking at school if you arrive at 7:00 AM = _____

Parking at school if you arrive at 7:45 AM = _____

More available spaces if you arrive early. Salt dissolves quicker when youbegin because there are more available spaces to 'park'.

Analogy: Compact car is easier to park than SUV.

STIR

Easy

Hard

Theory: Crush salt to make particles smaller (increase surface area)…it will dissolve more rapidly.

100 mL of water = 100 g

Add 3.0 mL water,stir…float

You determine the density of golf ball to be 1.18 g/mL

density of water= 1.00 g/mL

Add 19 g salt to 100 g water = 119 g salt + water

Volume remains100 mL (saltwater)

Density = Massvolume

119 g100 mLor

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…floatAdd 3.0 mL water,stir…sink

mL 100salt gx

mL 6 mL 100

g 119

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      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).

ORPoster (25 words or less) A picture is worth 1000 words!

Solubility Table

LeMay Jr, Beall, Robblee, Brower, Chemistry Connections to Our Changing World , 1996, page 517

0 10 20 30 40 50 60 70 80 90 100

Solubility vs. Temperature for Solids

Sol

ubili

ty (

gram

s of

sol

ute/

100

g H

2O)

20

10

30

40

50

60

70

80

90

110

120

130

140

100

NaCl

KI

KCl

NaNO3

KNO3

HCl NH4Cl

NH3

KClO3

SO2

shows the dependence

of solubility on temperature

gases

solids

Teacher NotesSome 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).