Hydrogen index. Hydrolysis of salts.

 

Operation purpose: Determination of response of the environment by means of the indicator. Study of different cases of hydrolysis.

Instruments and reagents: solutions CH₃COOH, HCl, AlCl₃, NH₄OH, Na₂CO₃, CH₃COONa, test tubes, the universal indicator, фенолфталейн.

Experience 1. Determination and comparing рН solutions of the strong and feeble electrolytes.

Operation course: рН it is possible not only to determine response of the environment of solution of this electrolyte by value of a hydrogen index, but also to compare force of appropriate acids and the bases.

Enter 2-3 drops of 0,1 N of CH₃COOH solution in a test tube. By means of the universal indicator, using these tables 2 or a color scale of the indicator, evaluate value рН solution. For this purpose a glass stick a small amount of researched solution transfer to a strip of the universal indicator paper. (After use the stick needs to be rinsed in a glass with the distilled water and to wipe filter paper.)

Table 2. Color of the universal indicator (solution or paper)

рН	Colour	рН	Colour
1...3	Red	8	Cyan
4,5	Orange	9,10	Blue
6	Yellow	11...13	Violet
7	Green

 

Compare the found value to value рН 0,1 N of the HCl solution, defined by a similar method. Draw an output on force of acetic acid. Write the equation of its dissociation. Knowing рН solution and the initial concentration of acid, calculate a level of dissociation of CH₃COOH.       

Similar method study 0,1 N NH₄OH solution. Carry out comparison from 0,1 N NaOH solution. Draw an output on force of hydroxide of ammonium. Write the equation of its dissociation. Knowing рН solution and the initial concentration, calculate a level of dissociation of NH₄OH.       

Experience 2. Interaction of the connections strengthening hydrolysis of each other

If to solution of the salt which is hydrolyzing on a cation to add solution of the salt which is hydrolyzing on anion, that, according to Le-Shatelye's principle, equilibrium of hydrolysis of salts will displace towards its gain. If formation of precipitates and separation of gases is thus possible, joint hydrolysis proceeds up to the end.

Enter 2-3 drops of 0,1 N of solution of chloride of AlCl₃ aluminum in a cell of a dropwise pad and by means of the universal indicator evaluate value рН solution. Write the equation of hydrolysis of this salt. Draw an output, response of interaction of this salt belongs to what type of hydrolysis with water.

In other cell enter 2-3 drops of 0,1 N of solution of a carbonate of Na₂CO₃ sodium and by means of the universal indicator evaluate value рН. Write the equation of hydrolysis of this salt. Draw an output, response of interaction of this salt belongs to what type of hydrolysis with water.

In a cell with AlCl₃ solution add 2-3 drops of Na₂CO₃ solution, and in a cell with Na₂CO₃ solution add 2-3 drops of AlCl₃ solution. Watch precipitate separation. Write the equation of response of interaction of solutions of these salts. Draw an output on offset of position of equilibrium of hydrolysis.

 

Laboratory work 8

Complex connections

Operation purpose: Receiving and research of properties of complex connections. Establishment distinction between simple and complex ions.

Instruments and reagents: test tubes, pipettes, solutions FeCl₃, KCNS, 25% ammonia solution, K₃[Fe(CN)₆], (NH₄)₂SO₄∙Fe₂(SO₄)₃

Experience 1. Distinction between double and complex salt.

Pour in a test tube of 10-12 drops of FeCl₃ solution and add on drops solution of thiocyanate of KCNS potassium. Watch appearance of blood-red coloration owing to formation of thiocyanate of Fe(CNS)₃ iron. This response allows to find in solution Fe³⁺ iron ions.

In one test tube pour 10-12 drops of K₃[Fe(CN)₆], and in another – 10-12 drops of solution iron-ammonium alum (NH₄)₂SO₄∙Fe₂(SO₄)₃. In both test tubes on drops add KCNS solution. Watch color of solutions in test tubes. Based on it to make the inference what of the taken salts is double and what – complex.

Experience 2. Education and corrupting of complex ions.

Receiving an ammoniac complex of copper.

a) Pour in a test tube of 10-12 drops of solution of sulfate of copper (II) and add on drops 25%-y ammonia solution. Watch original formation of a precipitate hydroxosulfate of copper and its subsequent dilution a lot of ammonia with formation of the colored solution of complex salt.

b) To the received solution add a small amount of solution of hydrochloric acid. Watch change of a painting of solution. (The coordination number of Cu²⁺ is 4).

Receiving an ammoniac complex of silver.

a) Pour in a test tube 1-2 ml of solution of silver nitrate and as much solution of chloride of sodium. The received precipitate dissolve, having received solution of complex salt of silver. For this purpose add some drops of the concentrated solution of ammonia.

b) The received solution of complex salt of silver pour in two test tubes. In one test tube add solution of chloride of sodium, in another – solution of iodide of potassium. Watch absence of a precipitate in the first test tube and its existence in the second. (The coordination number of Ag⁺ is 2, PR (AgCl) = 1.10^-10, PR (AgI) = 1.10^-16, K[Ag(NH₃)₂]⁺ = 9,3.10^-8).

Receiving gidroksokompleks of zinc.

a) Pour in a test tube 2-3 ml of solution of sulfate of zinc and add on drops sodium hydroxide solution before precipitate appearance. To solution with a precipitate add excess of alkali before full dilution of a precipitate as a result of formation of solution of complex salt.

b) To the received solution add 3-4 drops of solution of sulfuric acid. Watch precipitate appearance in the form of solution blush. (The coordination number of Zn²⁺ is 4).

Receiving a rodanidny complex of iron.

In the first test tube pour 2-3 ml of solution of chloride of iron (Ш), and in the second – as much potassium solution K₃[Fe(CN)₆]. In each test tube add some drops of solution of thiocyanate of potassium. Watch change of color of solution only in the first test tube. Based on experience draw an output on what of two complexes of iron (Ш) is steadier – tsianid or rodanid?

Receiving an ammoniac complex of nickel.

Pour in a test tube 1 ml of solution of sulfate of nickel and add on drops the concentrated solution of ammonia. Watch a precipitate of sulfate of nickel and its subsequent dilution owing to formation of solution of complex salt.

To the received solution add the equal volume of saturated solution of bromide of potassium and watch formation of a precipitate Br₂[Ni(NH₃)₆]²⁺. Then to a precipitate add solution of hydrochloric acid. Mark dilution of a precipitate and change of color of solution. Based on results of experience draw an output on what compound of ammonia - [NH₄]⁺ or [Ni(NH₃)₆]²⁺ is steadier in these conditions.

Experience 3. Influence of concentration of solution on a complex formation.

Pour in a test tube of 10^-12 drops of CoCl₂ solution, add on drops saturated KCNS solution. Watch change of color of solution.

To the received solution on drops add the distilled water and watch behind color change. (The coordination number of Со²⁺ is equal 4).

 

Laboratory work 9