Experiment 2. Oxidation and reducing power of nitrous acid and Nitrites

A) Put 3-5 drops of KMnO₄ solution into the test-tube, acidify it by 2-3 drops of H₂SO₄ and add 5-7 drops of solution or 1-2 granules of NaNO₂. What properties does Sodium Nitrite show in this reaction? Write the reaction.

B) Fill the test-tube with 3-5 drops of NaNO₂, acidify it by 2-3 drops of H₂SO₄ solution and then add 3-4 drops of KI solution. Why does the color of solution change? Draw the reaction and determine the properties of NaNO₂ in this case.

Experiment 3. Oxidizing properties of nitric acid

Fill the test-tube with 3-5 drops of concentrated HNO₃, add piece of Copper. Make sure of gassing presence. Dilute the mixture by 20-30 drops of distilled water. How does the color of the gas change? Write the equation of oxidation-reduction reaction of cooper and concentrated and diluted HNO₃ interaction.

Experiment 4. Low soluble Phosphate formation

A) Add 1-2 drops of Potassium or ammonia thiocyanate solution to 3-4 drops of FeCl₃. The solution is colored in red. Draw the reaction equation.

Add some drops of Sodium or ammonia hydroPhosphate up to red color disappearance of Iron thiocyanate (III) and FePO₄ precipitation formation. Draw the equation of the reaction.

B) Put 4-5 drops of Na₃PO₄, Na₂HPO₄, NaH₂PO₄ solutions into three test tubes and adds the same volume of CaCl₂. Note the order of precipitation formation and draw the equation of the reactions.

Experiment 5. Representative reaction to phosphoric acid ions.

Add 5-6 drops of H₃PO₄ solution or its salt to 5-6 drops of molybdenum solution. Heat the mixture on water bath. The yellow precipitation of mixture (NH₄)₃H₄[P(Mo₂O₇)₆] is formed. Draw the equation of the reaction.

Chapter # 14. Chemistry of main biometals

Vocabulary

English	Українська назва	English	Українська назва
Macronutrient (macroelement)	Макроелемент	Heavy metal	Важкий метал
Micronutrient (microelement)	Мікроелемент	Pollutant	Забруднювач

Sourses:

1. Introduction in General, Organic and Biochemistry, 7^th Edition, by Morris Hein, Leo R. Best, Scott Pattison and Susan Arena, Brooks/Cole Publishing Co., 2001. (Chapter 10.3, pp. 299-302);

2. http://www.chemsoc.org/viselements/pages/Visual Elements The Alkali Metals.html

3. http://www.chemsoc.org/viselements/pages/Visual Elements The Alkali-Earth Metals.html

3. http://www.chemsoc.org/viselements/pages/Visual Elements Group 13.html

4. http://www.hrw.com/science/mc/index/htm

1. The Alkali Metals

The elements of Group 1, the Alkali metals, are:

Symbol	Electron configuration
Lithium Li Sodium Na Potassium K Rubidium Rb Cesium Cs Francium Fr	[He]2s1 [Ne]3s1 [Ar]4s1 [Kr]5s1 [Xe]6s1 [Rn]7s1

In each element the valency electron configuration is ns¹, where n is the period number. The last element, Francium, is radioactive and will not be considered here.

Appearance

All the Group 1A elements are silvery-colored metals. They are soft, and can be easily cut with a knife to expose a shiny surface, which dulls on oxidation.

General Reactivity

These elements are highly reactive metals. The reactivity increases on descending the Group from Lithium to Cesium. There is a closer similarity between the elements of this sub-Group than in any other Group of the Periodic Table.

Occurrence and Extraction

These elements are too reactive to be found free in nature. Sodium occurs mainly as NaCl (salt) in seawater and dried-up seabeds. Potassium is more widely distributed in minerals such as sylvite, KCl, but is also extracted from seawater. The alkali metals are so reactive that they cannot be displaced by another element, so are isolated by electrolysis of their molten salts.

Physical Properties

The alkali metals differ from other metals in several ways. They are soft, with low melting and boiling temperatures. They have low densities - Li, Na and K are less dense than water. They show relatively weak metallic bonding, as only one electron is available from each atom.

Alkali metals color flames. When the element is placed in a flame the heat provides sufficient energy to promote the outermost electron to a higher energy level. On returning to ground level, energy is emitted and this energy has a wavelength in the visible region: Li - red; Na - yellow; K - lilac; Rb - red; Cs - blue.

The ionic radii of the alkali metals are all much smaller than the corresponding atomic radii. This is because the atom contains one electron in an s-level relatively far from the nucleus in a new quantum shell, and when it is removed to form the ion the remaining electrons are in levels closer to the nucleus. In addition, the increased effective nuclear charge attracts the electrons towards the nucleus and decreases the size of the ion.

Chemical Properties

The alkali metals are strong reducing agents. The standard electrode potentials all lie between -2,7V and -3,0V, indicating a strong tendency to form cations in solution. They can reduce Oxygen, Chlorine, Ammonia and Hydrogen. The reaction with Oxygen tarnishes the metals in air, so they are stored under oil. They cannot be stored under water because they react with it to produce Hydrogen and alkali hydroxides:

2M + 2H₂O = 2MOH + H₂.

This reaction illustrates the increasing reactivity on descending the Group. Li reacts steadily with water, with effervescence; Sodium reacts more violently and can burn with an orange flame; K ignites on contact with water and burns with a lilac flame; Cs sinks in water, and the rapid generation of Hydrogen gas under water produces a shock wave that can shatter a glass container. Na dissolves in liquid Ammonia to give a deep blue solution of Sodium cations and solvated electrons. This solution is used as a reducing agent.

At higher concentrations the color of the solution changes to bronze and it conducts electricity like a metal.

The chemistry of Li shows some anomalies, as the cation Li⁺ is so small it polarizes anions and so introduces a covalent character to its compounds. Li has a diagonal relationship with Magnesium.

Oxides

The Alkali metals form ionic solid oxides of composition M₂O when burnt in air. However, Na also forms the peroxide Na₂O₂ as the main product, and K forms the superoxide KO₂, also as the main product:

4Li + O₂ 2Li₂O;

2Na + O₂ Na₂O₂;

K + O₂ KO₂.

Hydroxides

Alkali metal hydroxides are white ionic crystalline solids of formula MOH, and are soluble in water. They are all deliquescent except LiOH. The aqueous solutions are all strongly alkaline (hence the name of this Group) and therefore dangerous to handle. They neutralize acids to form salts, eg: NaOH + HCl= NaCl + H₂O.

Halides

Alkali metal halides are white ionic crystalline solids. They are all soluble in water except LiF.

Oxidation States

Alkali metals have oxidation states of 0 and +1. All the common compounds are based on the M⁺ ion. This is because the first ionization energy of these elements is low, and the second ionization energy is much higher. The outermost electron is well shielded from the attraction of the nucleus by filled inner electron levels and so is relatively easy to remove. The next electron is much more difficult to remove as it is part of a full level and is also closer to the nucleus.