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Methodical guidance for laboratory work №6

SEMEY STATE MEDICAL ACADEMY

Methodical recommendation for the laboratory lesson

Specialty:0501301General medicine

Discipline: chemistry

Chair:of chemistry and technology of medicine

Higher base medical education, course– 1

Topic №6: Electrode potential. Oxidation-reduction electrode. Potentiometry in medical practice

Semey 2007

Approved

on the chair meeting from “_____”____________2007.

Protocol № ____

Head of the chair of chemistry and technology of medicine,

prof. __________ Gavrilenko I.V

1.Topic №6:Electrode potential. Oxidation-reduction electrode. Potentiometry in medical practice

2.Aim: to study the reason of the origin electrode potential. The particularities oxidation-reduction potential, application of potentiometry in medical practice

3.Objectives of teaching: to teach to calculate value of electrode potential and EMF of element; teach to define potentiometric definition of pH in the solutions and concentrations of hydrochloric acid by potentiometric titration method.

4. Basic questions:

1. Electrode potential. Mechanisms of electrode potential appearance. Nernst’s formula.

2. Electrodes classification: definition, comparison, oxidation-reduction

3.Oxidation-reduction electrode potentials, mechanisms of appearance and its biological significance.

4.Biopotential. Membrane and diffusion potentials and their biological significance. Biocurrent.

5. Galvanic cells and their EMF: bio metallic and concentration chains.

6.Potentiometry. Potentiometric definition of pH. Potentiometric titration.

Methods of teaching:

The determining initial level knowledge’s of student on chemistry. The conversation and questioning on topic of the lesson. Fulfilling the laboratory work and protection of the report.

Methodical guidance for laboratory work №6

Experiment №1.Potentiometric definition of concentration of hydrochloric acid

The purpose of the work: to get acquainted with technique of potentiometric titration strong acid by strong base on pH-metre.

Define molar concentration of the solution of the hydrochloric acid. Draw the graph on result experimental.

Movement of the work:

1. To get acquainted with description and rule of the application laboratory pH-metre (on passport of the instrument).

2. To turn off network instrument pH-metre for 30 minutes for heating by tumbler "is included".

3. Fill in glass for titration 20.00 ml solution of the hydrochloric acid with unknown concentration.

4. Sink in investigation solution indicator glass electrode and electrode of the comparison (chlorine-silver), beforehand washed by distilled water and drained by filter paper.

5. The glass electrode must be on height not less 1,5-2 refer to from bottom of the glass.

6. The anchor of the magnetic mixer place in glass. Attention to not to split glass electrode a distance between anchor of the magnetic mixer and electrode must be not less 1.

7. Take off initial evidence of pH solution of the hydrochloric acid with unknown concentration.

8. Conduct titration of investigation solution of 0,1 N alkali solution. Flow the solution an alkali on 2 ml and after determination of the balance to take off the evidences of pH. After each flowed alkali solution in glass to mix. The results of titration write in table 1.

Table 1. Results of first titration

Volume of flowed solution (ml)

рН

9. On base got data, approximately define the position of leap pH i.e. approximately define the point of equivalence P.E. Write the approximate volume an alkali in point of equivalence.

10. Conduct repeated titration for exact determining of leap pH.

Beforehand once again wash the glass electrode and electrode of the comparison by distilled water and drain the filter paper. In washed by distilled water glass once again to contribute 20,00 ml solution of the hydrochloric acid with unknown concentration. Under the repeated titration in approximate point of equivalence (before and after), solution of sodium hydroxide to flow on 0,5 ml and remove the evidences pН. After each flowing of alkali solution in glass to mix.

The results of repeated titration writes in table 2.

Table 1. Results of repeated titration

№№ measurements	Volume of flowed alkali solution, V мл	рН	ΔV мл	Δ рН	ΔрН/ ΔV
1.
2.
N

11. Having finished titration, to turn off the instrument pH-metre by tumbler "is included" and to cut off the instrument from electric network. The electrodes to wash distilled water and place in glass with distilled water.

12. On result two repeated titration to draw the graph:

1 - a curve of titration in coordinate pH-volume of titrate (the integral curve of titration),

2 - a curve of titration in coordinate ΔрН/ΔV-volume of titrate (the differential curve of titration).

6.Literature:

1. J. M. Sehgal. Modern Chemistry, class XI, Delhi, 1989 - 15 items.

2. Jean B. Umland & John M. Bellama, General Chemistry. Houston. USA. 1996 - 1 item.

3. Darrel D. Ebbing, General Chemistry, Wayne University, USA. 1990 - 3 items.

4. Karen C. Timberlake, Chemistry - An Introduction to General. Organic and Biochemistry, Los Angeles, USA, 1991-1 item.

7. Control:

Problem and exercises:

№1. Calculate the potential of the cupper electrode dipped in the solution of its salt with, concentration 0.01 mole/1 by е⁰_С_u= +0,34 V.

№2. How change of the potential of the zinc electrode if 1 M of ZnSO₄solution dilute in 10 times.

№3. Write the schemes copper-lead of galvanic cells by standard conditions if е⁰_С_u = +0,34 В. е⁰_Р_b= -0,13 В.

№4. Calculate the potential of the hydrogen electrode dipped in the distilled water by 25 grade.

№5. Calculate the EMF of the copper-zinc galvanic element by 18 grade, if concentration of copper ions 0.1 mole/l, concentration of zinc ions 0.001 mole/l, standard potential of copper +0.34 V, standard potential of zinc -0.76 V.

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