Hydrolysis of Salts

Document Sample
Hydrolysis of Salts Powered By Docstoc
					                                                             Salt Hydrolysis
Introduction
A salt formed in the neutralization reaction between a strong acid and a strong base will dissolve in water to give a solution that has a
pH of 7. Salts formed from reactions of other types of acids and bases can give solutions having pH's different from 7. The salt of a
strong acid and a weak base yields an acidic solution in water. The salt of a weak acid and a strong base gives a basic solution. The
process of a salt reacting with the water it is dissolving is called hydrolysis.
     In salt hydrolysis, the ions of the dissolved salt from the weak specie reacts with water to produce either hydronium ions, forming
an acidic solution, or hydroxide ions, forming a basic solution.
          For example, NaNO2 dissociates as follows: , NaNO2  Na+1 + NO2-1 The NO2-1 being weak will react with water as follows:
     -1
NO2 + HOH  HNO2 + OH-1 The excess hydroxide ion makes the solution basic.
          ZnCl2 dissociates as follows: ZnCl2  Zn+2 + 2 Cl-1 . Zn2+ being weak will react with water as follows:
    +2
 Zn + 2 HOH  Zn(OH)2 + 2 H+1 The excess hydrogen (hydronium) ion makes the solution acidic.
Objective: To determine the pH of aqueous solutions of salts you will prepare and to explain the results in terms of hydrolysis.

Materials                                        distilled water                                 potassium chloride
safety goggles                                    sodium chloride,                               aluminum chloride
7 small or medium test tubes                      sodium acetate,                                copper(II) sulfate
1 test tube rack                                  ammonium chloride,                             sodium bicarbonate,
 spatula                                         sodium carbonate,                               sodium phosphate,
 glass stirring rod                              ammonium chloride                               pH test paper (pH 1 to 14)
10-mL graduated cylinder                         aluminum sulfate
                                                 lead(II) nitrate

Procedure
1. Connect the pH Sensor to LabQuest and choose New from the File menu. If you have an older sensor that does not auto-ID,
manually set up the sensor by plugging the pH Probe into a DIN adapter and plug it into Channel 1 of the LabQuest interface. Press
the Power Button to turn on LabQuest. Touch: Sensor/Sensor Setup. Wait for sensor screen. Select Channel 1. Scroll down and select
pH. Click OK. If screen shows Red box with CH 1:and some numbers between 1-14 , continue. If not ask teacher for help
2. Use a utility clamp to secure the pH Sensor to a ring stand.
3. Place small quantities (tip of a spatula) of one of the salts into a 50ml beaker. Add 10 mL distilled water and dissolve the sample.
4. Determine the pH of your solution by:
         a. Use a wash bottle to rinse the electrode. Catch the waste in a 250ml beaker.
         b. Place the beaker with your salt solution so the liquid completely covers the bottom of your pH probe.
         c. When the pH reading stabilizes, record the pH value displayed on the Meter screen.
         d. Rinse solution from the pH probe
5. Repeat until you have tested all salts
6. When done, place the pH Sensor in its container.
7. Discard all solutions in the sink and clean your work area.

Observations
    Complete the data table below. Add rows to allow all salts to be entered. The first salt is done for you

                                                  pH of Salts
Formula         pH       Acidic/Basic/       Parent           Strength         Parent           Strength
                         Neutral             acid             of acid          Base             of Base
NaCl            7        Neutral             HCl              Strong           NaOH             strong

Questions
1. For each salt, write a balanced equation to show how it ionizes in solution.

				
DOCUMENT INFO