-LW Examination "The law of mass action and homo- and heterogeneous systems"

To need to explore and organize training material in accordance with the questions below.

The process of hydrolysis.

1. Constant and degree of hydrolysis.

2. The output of the calculation formulas and constants, degree of hydrolysis of salts (hydrolysis of the cation).

3. Conclusion of formulas and calculating the concentration of hydrogen ions and hydroxide ions (for cation hydrolysis).

4. The dependence of hydrolysis constants from dissociation (ionization) of acids and bases, temperature, dilution of the solution.

5. The use of hydrolysis for the determination and separation of ions.

The process of complexation.

6. Complex compounds, their General characteristics.

7. Nomenclature, types of complex compounds.

8. Properties of coordination compounds: stability, solubility, optical properties, volatility.

9. Stepwise dissociation of complex compounds. Stability of complex compounds.

10. The equilibrium constant of the complexation reaction. The constants of stability and instability.

11. The use of chelation for the opening, separation, masking ions. Chelation.

13. The calculation of the concentrations of the products of dissociation and disintegration of complex compounds.

A heterogeneous system.

14. The equilibrium between solution and solid phase (sediment).

15. Quantitative characteristics of the conditions of dissolution or deposition. Short, medium, well-soluble substances.

16. The solubility product (PR). Limitations in the application of rule of solubility product.

17. The product of the activity of the ions.

18. Calculation of solubility product of solubility and Vice versa.

19. Applying PR in practice qualitative analysis.

20. Deposition. Factors completeness of precipitation: the amount and nature of the precipitant, ionic strength, pH of the solution.

21. Salt effect.

22. Cases of the influence of excess of the precipitant.

23. Fractionated (fractional) deposition.

24. Dissolution of sparingly soluble precipitates.

25. Effect on the solubility of sparingly soluble precipitation ionic strength of the solution.

26. Effect on the solubility of sparingly soluble ions in precipitation of the same name.

27. Effect on the solubility of sparingly soluble precipitation of the hydrogen ion concentration.

28.Effect on the solubility of sparingly soluble precipitation-complexation processes.

29.Effect on the solubility of sparingly soluble precipitation of redox processes.

30. The transformation of sparingly soluble compounds.

A useful property of potassium permanganate solution is its intense purple colour, which to serve as an indicator for most titrations. The surface of the permanganate solution rather than the bottom of the meniscus can be used to measure titrant volumes.

Sodium oxalate is widely used to standardise permanganate solution. In acidic solutions the oxalate ion is converted to the undissociated acid:

Na₂C₂O₄ + H₂SO₄ = H₂C₂O₄ + Na₂SO₄

Thus, its reaction with the permanganate ion can be described as

2KMnO₄ + 5H₂C₂O₄ + 3H₂SO₄ = K₂SO₄ + 2MnSO₄ + 10CO₂ + 8H₂O

The reaction between permanganate ion and oxalic acid is complex and proceeds slowly even at elevated temperature unless manganese(II) is present as a catalyst. Thus, when the first few millilitres of the standard permanganate are added to a hot solution of oxalic acid, several seconds are required before the colour of the permanganate ion disappears. Solution of sodium oxalate are titrated at 60 C to 90 C. After the added permanganate is completely consumed (as indicated by the disappearance of colour), the solution is heated to about 60 C and titrated to a pink colour that persists for about 30 seconds.

1. Calculate a primary standard sample (mOxT) for preparation 100 ml of solution:

m_OxT = N V meq 1000 _Ox. M.m. Na₂C₂0₄ = 126,06 g; mass of borax equivalent meq_Ox = M/2.

2. Weight sodium oxalate sample on hand balance with 0,1 g accuracy and put powder into weighting bottle. Weight weighting bottle with sodium oxalate on analytical balance.

3. Transfer the sodium oxalate into volumetric flask and weight empty weighting bottle on analytical balance. Calculate the sodium oxalate sample weight m_OxP.

4. Dissolve sodium oxalate in 40-50 ml of 1 M H₂SO₄ and establish exact volume of solution with 1 M H₂SO₄.

5. Calculate precision normal concentration of prepared solution of sodium oxalate: N_Ox = m _OxP 1000/V meq _Ox.

6. Calculate the correction factor for prepared 0,1 N sodium oxalate solution: CF_Ox =m _OxP/m_OxT.

1. Load a burette with potassium permanganate solution.

2. To conical flask pour in 10 ml aliquot of standard sodium oxalate solution (V_Ox).

3. Heat solution to 80°C to 90°C, and titrate with potassium permanganate solution. The pink colour imported by one addition should be permitted to disappear below any father titrant is introduced.

4. Reheat if the temperature drops below 60°C. Take the first persistent (≈ 30 s) pink colour as the end point. Read the burette mark.

5. Repeat titration also two times. Calculate the approximate value of used potassium permanganate solution (V_PP).

6. Calculate the exact concentration of the potassium permanganate solution accordance to equivalents law (N_Ox⋅V_Ox = N_PP⋅V_PP): N_PP = N_Ox⋅V_Ox/V_pp.

III. Quantitative determination of hydrogen peroxide

2KMnO₄ + 5H₂O₂ + 3H₂SO₄ = 2MnSO₄ + K₂SO₄ + 5O₂ + 3H₂O

1. Load a burette with 0,1 N potassium permanganate solution.

2. To conical flask pour in 10 ml aliquot of sample (V_S).

3. Add 10 ml of 2 N H₂SO₄ solution and titrate with 0,1 N potassium permanganate solution to pink colour appearance. Read the burette mark (V_T).

4. Repeat titration also two times. Calculate the median volumes of used potassium permanganate solution.

5. Calculate hydrogen peroxide percentage in sample:

xH₂O₂ = V_T N_T meq _H2O2/Vs⋅100%

M.m. H₂O₂ = 34,00

IV. Quantitative determination of sodium nitrite

5NaNO₂ + 2KMnO₄ + 3H₂SO₄ = 5NaNO₃ + 2MnSO₄ + K₂SO₄ + 3H₂O

1. Load a burette with determined problem!

2. To conical flask pour in 10 ml aliquot of 0,1 N potassium permanganate solution (V_T) and 10 ml of 2 N H₂SO₄ solution.

3. Titrate the standard solution with problem sample solution to pink colour appearance. Read the burette mark (V_S).

4. Repeat titration also two times. Calculate the median volumes of used sample solution.

5. Calculate sodium nitrite percentage in sample: x_NaNO2 = V_T N_T meq _NaNO2/ Vs⋅100%

M.m. _NaNO2 = 69,00

12-LW. Determination of Iron (II) content in More’s salt

More’s salt is a double salt - iron (II) ammonium sulfate hexahydrate  (Fe(NH₄)₂(SO₄)₂·6H₂O) included ions of Fe (II). The last one may reacts with potassium permanganate in acidic medium:

10 Fe(NH₄)₂(SO₄)₂·6H₂O + 2 KMnO₄ + 8 H₂SO₄ = 5 Fe₂(SO₄)₃ + 2 MnSO₄ + 10 (NH₄)₂SO₄ + K₂SO₄ + 68 H₂O

This reaction isn’t heating, because ion Fe (II) may oxidizes by air oxygen transformed to Fe (III) with rising of temperature.

 Procedure. Add 20 mL of More’s salt solution (according to your variant of task) with unknown concentration used measuring pipet to 250-300 mL Erlenmeyer flask. Acidify this solution adding 20 mL of 2 N H₂SO₄ using graduated cylinder. Add near 40 mL of DW. BE CAREFUL, DON’T HEAT SOLUTION!

Using a buret, slowly add the KMnO₄ solution to hot solution in flack. Reaction (9) will occur. KMnO₄ acts as its own in

dicator. The slightly pink color of the dilute solution MnO₄^- indicates the end of the reaction. This color must safe during at least 1 min. The procedure of titration repeats two times or more as described above.

Results of experiment present in the form of table 17:

where N (Fe²⁺) = 0,XXXX g-eq/L.