Illustrated Guide to Home Chemistry Experiments

Chapter 13 Laboratory: Chemical Equilibrium and Le Chatelier’s Principle 241

8.ntinue heating the beaker to drive off all remaining Co

water. When you have evaporated all of the remaining

water, remove the heat and allow the beaker to cool to

room temperature.

9. Weigh the beaker and record the mass of the beaker
   plus sodium chloride to 0.01 g on line D of Table 13-2.
   Subtract the empty mass of the beaker from the mass of
   the beaker plus sodium chloride, and record the mass of
   sodium chloride on line E of Table 13-2.
   Calculate the solubility of sodium chloride in g/L and
   enter that value on line F of Table 13-2.
   The gram molecular mass of sodium chloride is 58.442
   g/mol. Use that value to calculate the molar solubility
   of sodium chloride and enter that value on line G of
   Table 13-2.
   The Ksp of sodium chloride is the product of the activities
   (concentrations) of the sodium ion and the chloride ion:
   Ksp = [Na+] · [Cl–]. Those concentrations are the same,
   and are equal to the concentration of sodium chloride, so
   we can simplify the equation to: Ksp = [NaCl]^2. Therefore,
   the solubility product constant of sodium chloride equals
   the square root of the molar solubility of sodium chloride.
   Calculate that value and enter it on line H of Table 13-2.


10. If you have not already done so, put on your splash
    goggles, gloves, and protective clothing.


11. Weigh a clean, dry, empty 250 mL beaker and record its
    mass to 0.01 g on line A of Table 13-2.


12. Add about 125 mL of room temperature distilled or
    deionized water and about 50 g of sodium chloride
    to the 250 mL beaker. Allow the salt to dissolve for at
    least 15 minutes, stirring periodically, to ensure that the
    solution is saturated. Record the temperature of the
    solution on line B of Table 13-2.


13. Carefully decant 100.00 mL of the saturated sodium
    chloride solution into the 100 mL volumetric flask,
    making sure that none of the undissolved sodium
    chloride is transferred to the volumetric flask. Fill the
    flask to the index line, using a dropper or disposable
    pipette to add the last mL or so, and record the
    volume on line C of Table 13-2. (If you’ve calibrated the
    volumetric flask, as described in Chapter 5, record the
    actual volume that the flask contains rather than the
    nominal 100.00 mL volume.)


14. Discard the remaining sodium chloride solution
    and undissolved sodium chloride and rinse the beaker
    thoroughly, first with tap water and then with distilled
    water.


15. Pour the contents of the 100 mL volumetric flask into
    the 250 mL beaker. Do a quantitative transfer, rinsing
    the volumetric flask several times with a few mL of
    distilled water and adding the rinse water to the beaker
    to make sure all of the sodium chloride is transferred to
    the beaker.


16. Place a stirring rod in the beaker to prevent boil-over,
    and heat the beaker until the solution comes to a gentle
    boil. Continue heating the beaker gently until nearly all
    of the water has evaporated. When most of the water
    has vaporized, remove the stirring rod from the beaker,
    and use a few mL of distilled water to rinse any sodium
    chloride into the beaker.

10.

11.

12.

13.

POCEDURER
This lab session is in two parts. In Part I, we’ll determine
the solubility product constant for sodium chloride
gravimetrically, by evaporating a known volume of a saturated
sodium chloride solution and determining the mass of the dry
solid remaining. In Part II, we’ll determine the solubility product
constant for potassium hydrogen tartrate titrimetrically
(volumetrically) by titrating a known volume of saturated
potassium hydrogen tartrate solution with sodium hydroxide
titrant of known molarity.

TABLE 13-2: Determine a solubility product constant,

Part I—observed and calculated data

Item Data

A. Mass of empty beaker _________._____ g

B. Temperature of solution _________._____ °C

C. Volume of sodium saturated

sodium chloride solution_________._____ mL

D. Mass of beaker + sodium

chloride _________._____ g

E. Mass of sodium chloride (D – A)_________._____ g

F. Mass solubility of sodium

chloride ([1000/C] · E) _________._____ g/L

G. Molar solubility of sodium

chloride (F/58.442 g/mol)_________._____ mol/L

H. Ksp of sodium chloride (square

root of G) _________._____

PRTI:A ETERd mINE THE kSp of UdSo I m
CHLoRIdE GRAvImETRICALLy