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.