Experiment 6. Dilution of concentrated Sulfuric acid

Carefully add 2-3 drops of concentrated H₂SO₄ to 3-4 drops of distilled water (but not conversely). Pay attention to the heating of the mixture in test-tube. Why is it necessary to add concentrated H₂SO₄ into water and is it wrong to add water into the acid?

Experiment 7. Oxidizing properties of H₂SO₄

A) Put Zinc granule into test-tube and add 15-20 drops of dilute sulfuric acid. What gas is released? Write the reaction.

B) Put Zinc granule into test-tube and add 7-8 drops of concentrated sulfuric acid. Heat the mixture in water bath. Detect the presence of Hydrogen Sulfide by odor (carefully direct gas by the movement of palm). Write the reaction. What is the ion-oxidizing agent in first reaction and what is in the second one?

Experiment 8. Qualitative reaction of SO₄^2- ion

Fill test-tube with 8-9 drops of Potassium or Sodium Sulfate solution and add 5-6 drops of BaCl₂. Test the solubility of received precipitate in HNO₃ or HCl, as well as in NaOH and KOH. Write the reactions of precipitate formation.

Experiment 9. Instability of thiosulfuric acid

Dissolve some grains of Potassium Thiosulfate (Na₂S₂O₃) in 15-20 drops of distilled water and add 8-10 drops of Sulfuric acid. Observe turbidity of solution in 5-10 min. What is the reason? Write the reaction.

Chapter # 13. Nitrogen, phosphorus

Vocabulary

English	Українська назва	English	Українська назва
Laughing gas	Веселящий газ	Сaliche	чілійська селітра
Ammophos	Амофос	Nitre, saltpetre, saltpeter, niter	Селітра (як добриво)
Diammophos	Дифмофос

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 Group 15.html

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

1. General characteristics

The elements of Group 5A (or the main sub-group of V group) are:

Symbol	Electron configuration
Nitrogen N	[He]2s22p3
Phosphorus P	[Ne]3s23p3
Arsenic As	[Ar]3d104s24p3
Antimony Sb	[Kr]4d105s25p3
Bismuth Bi	[Xe]4f145d106s2 6p3

The most important members of this sub-group are Nitrogen and Phosphorus. The other elements will mostly not be considered here.

Appearance

The appearance of the Group 5A elements varies widely. Nitrogen is a colorless, odorless gas; Phosphorus exists in white, red and black solid forms (allotropic modifications); Arsenic is found in yellow and gray solid forms; Antimony is found in a metallic or amorphous gray form; and finally Bismuth is a white, crystalline, brittle metal. These appearances reflect the changing nature of the elements as the sub-Group is descended, from non-metal to metal.

General Reactivity

The elements of Group 5A show a marked trend towards metallic character on descending the Group. This trend is reflected both in their structures and in their chemical properties, as for example in the oxides, which become increasingly basic.

Occurrence

Nitrogen is found in the atmosphere, and makes up 78% of the air by volume. Phosphorus is not found free in nature, but occurs in several minerals and ores such as Phosphate rock (see Appendix 12). The other elements are all found in the elemental form in the Earth crust, but more frequently as minerals.

Physical Properties

The physical properties of this Group vary widely as Nitrogen is a gas, and the other elements are solids of increasingly metallic character.

Nitrogen exists as the diatomic molecule N₂. It is a colorless, odorless gas, which condenses to a colorless liquid at -196⁰C. The strength of the bond and the short bond length provide evidence for the bond between the N atoms being a triple bond: N N.

Phosphorus has at least two allotropes, red and white one. White phosphorus is a solid composed of covalent tetrahedral P₄ molecules, and red phosphorus is an amorphous solid, which has an extended covalent structure.

The covalent radii of the atoms increase on descending the sub-Group. However, the N atom is anomalously small and so it can multiple-bond to other N, C and O atoms.

Chemical Properties

Both Nitrogen and phosphorus exist in oxidation states +3 and +5 in their compounds. Nitrogen is very unreactive. The only element to react with Nitrogen at room temperature is Lithium, to form the nitride Li₃N. Magnesium also reacts directly, but only when ignited. Some microorganisms, however, have developed a mechanism for reacting directly with Nitrogen gas and building it into protein - this is called Nitrogen fixation, and is an important early step in the food chain.

Phosphorus is more reactive than Nitrogen. It reacts with metals to form phosphides, with Sulfur to form Sulfides, with halogens to form halides, and ignites in air to form oxides. It also reacts with both alkalis and concentrated nitric acid.