Ch 15 Review Sheet Answers 13-16

13. You measure 36.2 mL of 0.259 M solution of KOH and pour it into an Erlenmeyer flask.  You add a drop of phenolphthalein.  It turns magenta color.  You titrate HCl into the solution until the magenta turns colorless and discover the volume of acid in the buret goes from 3.14 to 33.67.  What is the molarity of the HCl solution?

1) KOH + HCl = KCl + H₂O                           2) mol = M x L

                                                                                                = 0.259 mol/L x 0.0362 L

                                                                                                = 0.009375 mol KOH

3) 9.38 x 10^-3 mol KOH│1 mol HCl    = 9.38 mol HCl

                                                  │ 1 mol KOH

            4) M = mol/Liters         M= 9.38 x 10^-3 mol / 0.03053 L = 0.307 mol/L

14. If a NaCl crystal with a mass of 3.45 x 10^-7 g is dropped into a 100 mL of distilled water, what is the concentration of the solution in ppm?

1 mL of H₂0 = 1 g of H₂0

_grams of solute_ x  10⁶ = ppm            ___3.45 x 10^─7___ x  10⁶   = 3 x 10^─3 ppm

grams of solution                                   (3.45 x 10^─7 + 100)                                                     

15.  List three ways of making a solute dissolve faster.

increase the surface area by grinding

stir

increase temperature of solids

decrease the temperature of gases

16. Kool-Aid mixture is added to water and stirred.  Which is the solute?  Which is the solvent?

solute (Kool-aide)                    solvent (water).