Turkestan - 2014

Silver nitrate with ions AsО₃^3- forms yellow precipitate Ag₃AsО₃ which is dissolved in HNO₃ and NH₄OH.

AsО₂^– + 3Ag⁺ + H₂O A Ag₃AsО₃¯ + 2H⁺;

Ag₃AsО₃ + 6NH₄OH 3 [Ag(NH₃)₂]⁺ + AsО₃^3– + 6H₂O.

The РО₄^3-, J ^- Br ^- ions interfere with the exposure of ions of As^III.

Reaction performance. To 2-3 drops of an investigated solution add 1-2 drop of 0,1 mol/L AgNO₃ solution. If there are Аs (III) yellow precipitate Ag₃AsО₃ forms.

Iodine in a neutral or basic medium becomes colourless by arsenit ions (forms arsenat ions):

AsО₂^– + I₂ + 2H₂O H H₂AsО₄^– + 2I^- + 2H ⁺.

Reaction is carry out in the presence of NaHCO₃.

The other reducers interfere with the exposure of ions of As^III.

Reaction performance. To 2-3 drops of a acidic investigated solution add a some crystals of NaHCO₃, and after its dissolution – one drop of a solution of iodine. If at a solution there are arsenit-ions iodine becomes colourless.

Sodium sulphide Na₂S (pharmacopeia’s reaction) in the acidic medium reacts with arsenits with formation of a yellow precipitate, insoluble in concentrated hydrochloric acid, but soluble in ammonia solution:

AsО₃^3- + 6H⁺ ®As³⁺ + 3H₂O;

2As³⁺ + 3S^2- ®As₂S₃¯.

Reaction performance. To 4-5 drops of an investigated solution add 3-4 drops of 2 mol/L chloric acid solution and a solution of Sodium sulphide. If there are As (ІІІ) ions, the yellow precipitate forms.

Sodium hypophosphite NaH₂PO₂ (pharmacopeia’s reaction) (reaction Bugo and Tille) in the acidic medium reductes compounds of As (III) and As (V) to elementary Arsene which is formed black-brown precipitate:

4H₃AsО₃ + 3H₂PO₂^- ® 4As¯ + 3H₂PO₄^- + 6H₂O.

Reaction performance. To 5-7 drops of an investigated solution add 5-7 drops of Sodium hypophosphite solution. If there are As (III) or As (V) ions, a black-brown precipitate forms.

Characteristic reactions of ions AsО₄^3–

Silver nitrate with ions AsО₄^3– forms a chocolate precipitate:

AsО₄^3– + 3Ag⁺ ®Ag₃AsО₄¯.

All ions which form with Ag⁺ ions precipitate interfere with the exposure of ions of As^V.

Reaction performance. To 2-3 drops of an investigated solution add 4-5 drops of Silver nitrate solution. If there are arsenat-ions, the precipitate of chocolate colour is formed.

Ammonium molybdat (NH₄)₂MoО₄. Arsenitic acid and its salts at presence nitric acid and ammonium nitrate by h

 

Turkestan - 2014

 

Guidelines for conducting practical classes compiled on the basis of a model curriculum for chemistry developed for the specialty «General Medicine» and «Dentistry" and approved by the Department of Education, Science and human resources of the Ministry of Health of Kazakhstan (Astana, 2007, protocol number 11).

 

Guidelines for conducting practical classes discussed at a meeting of the department of laboratory disciplines.

Minutes № ______, "____" _____________ 2014 y.

 

Head of the Department, Ph.D., Associate Professor _____________ A.K.Mamyrbekova

 

 

Guidelines for conducting practical classes discussed at a meeting of the Committee of Education and Evaluation

Minutes № ______, "____" _____________ 2014 y.

 

Chairman of the committee, the teacher ___________ A.I.Kushkarova

 

 

Methodical recommendations on practical training agreed by the Committee on educational programs

Minutes № ______, "____" _____________ 2014 y.

 

Committee Chairman PhD, Senior Lecturer _________ B.U.Bayzakova

 

Theme number 1: Chemical equivalent. Value solutions in the life of organisms. Modes of expression of the solutions.

 

Session Purpose: Expand the general idea of ​​the solution was added and dissolved, to consider ways of expressing the concentration of solutions, to study the thermodynamics and mechanism of formation of solutions, modern physico-chemical theory of solutions, solubility and its dependence on various factors, the phenomenon of osmosis, the laws of van't Hoff and Raul.

 

The main questions of the theme:

 

1. Simple stoichiometric calculations. Mol, the molar mass, equivalent, equivalent weight.

2. What is the solution? Classification of solutions.

3. Explain the following concepts: solvent, solute solubility.

4. The effect of different factors on the solubility of (temperature, pressure, nature of the substance).

5. What is called concentration?

6. Methods of expressing concentration of solutions: the mass fraction, the mole fraction, molar, normal (equivalent), molal concentration, titer.

7. Equivalent factor and equivalence.

 

Methods of teaching and learning: effective formative feedback on the development of competencies, training in small groups SGL, task-based learning Task BL.

 

Literature

 

1. Lenski A.S.Introduction to bioinorganic and biophysical chemistry.- М.: VW, 1989.- 256 page.

2.Glinka N.L.. General chemistry.Edited by V.A. Rabinovich.- L.: Chemistry,1988.- 704 с.

3.Glinka N.L.. exercises and works in chemistry.Edited by A.Rabinovich and X.MRubin.- Chemistry 1985.- 264 page.

4Vasileva Z.G., Granovskaya А.А., Taperova А.А. Laboratorial works in inorganic chemistry.- Chemistry, 1986. - 288 page.

5.Lectures and synopsis.

6.Ahmetov N.B. Genaerally and inorganic chemistry. М.: VW, 1981. – 679 page.