Obtaining of neutral, acidic and basic salts and their interaction with acids, alkalis and other salts.

4.1. Pour about 10 ml of KOH solution in the beaker and add 1 – 2 drops of phenolphthalein. Notice the colour of the solution. Then gradually add small quantities of hydrochloric acid solution from the burette. After each portion is added, stir the solution and continue to add acid until the solution becomes colourless. Why has the solution become colourless? Write down equation of the reactions. What property is the most characteristic for bases? Why do all the bases have common properties?

4.2. Pour some solution of barium hydroxide to the test tube and pass the carbon dioxide from the gas-generating device through the solution. What can you observe? Write down equation of the reactions.

Continue passing carbon dioxide СО₂ through the precipitate of obtained neutral salt until it dissolves completely. Why does the precipitate dissolve? Write down equation of the reactions. What salts are called acidic? How can they be obtained?

Add the solution of barium hydroxide Ва(ОН)₂ base to the obtained solution of acidic salt Ba(HCO₃)₂. Give equation of the reactions. What properties do acidic salts have? How do they dissociate into ions?

4.3. Add drop by drop the solution of base to 4 – 5 ml of cobalt neutral salt cocl₂. Observe the formation of precipitate of basic cobalt salt Co(OH)Cl.

Divide the obtained precipitate into two test tubes. Continue to add the solution of base to the first one until pink colour of cobalt hydroxide Со(ОН)₂ appears and add the solution of acid to the second. Write down equation of the reactions.

4.4. Place 2 – 3 ml of such 1 M solutions in three test tubes: copper sulphate in the first one, nickel sulphate in the second one and iron (III) chloride in the third. Add 2 - 3 ml of KOH solution to each test tube. What can you observe? What proves the proceeding of reactions? Give the equations of the reactions in molecular and ionic form. Derive a general conclusion on methods of base forming.

4.5. Pour 5 ml of concentrated solution of Na₂SiO₃ salt to the test tube and add 2 – 2.5 ml of hydrochloric acid. Stir the liquid thoroughly with the glass rod and observe the forming of jellies of silica acid н₂sio₃. Write down equation of the reactions.

4.6. Add 2 – 3 drops of barium chloride solution to the sodium sulphate solution. Write down your observations. Explain why those salts react one with the other.

Carry out some more double replacement reactions. For this purpose, prepare two beakers, each with 10 ml of sodium silicate na₂sio₃ solution. Add 2 – 3 crystals of iron (iii) chloride and nickel (ii) chloride to each solution. Observe the growth of the semi-transparent precipitates of corresponding silicates. Write down equation of the reactions.

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