By means of chemical equations express the following chemical reactions: 

(a) [Cr(H₂O)₆]Cl₃ dissolved in water, is mixed with an excess of sodium hydroxide solution. A clear green solution is formed. The colour of the solution changes to yellow when an aqueous hydrogen peroxide solution is added. 

(b) If an aqueous solution of a violet manganese compound is mixed with a hydrogen peroxide solution, the resulting solution is decolourised and a gas is released from it. 

An amount of 20 g of cooper (II) oxide was treated with a stoichiometric amount of a warm 20% sulphuric acid solution to produce a solution of copper (II) sulphate. 

How many grams of crystalline copper(II) sulphate (CuSO₄ . 5 H₂O) have crystallised when the solution is cooled to 20 °C? 

Relative atomic masses: Ar(Cu) = 63.5; Ar(S) = 32; Ar(O) = 16; Ar(H) = 1 

Solubility of CuSO₄ at 20 oC: s = 20.9 g of CuSO₄ in 100 g of H₂O.  

Which of the following acid-base pairs is most suitable for keeping the pH constant at 9 in an aqueous solution? 

(a) CH₃COOH – CH₃COO^–   

(b) NH⁺₄ – NH₃

(c) H₂CO₃ –HCO^–₃

(d) H₂PO^–₄ –HPO^2-₄

(e) H₂C₂O₄ – HC₂O^–₄  

One of the following statements cannot be correct. State which one. 

(a) A water-soluble solid contains Mg²⁺, Cr³⁺, and Br^– . 

(b) A solid soluble in a sodium hydroxide solution contains Al³⁺, K⁺, and SO^2-₄. 

(c) A solid soluble in aqueous ammonia solution contains Ag⁺, Cu²⁺, and Cl^– . 

(d) A solid soluble in nitric acid contains Ba²⁺, Fe²⁺, and CO^2-₃ . 

(e) A solution neutral to litmus contains Na⁺, Ca²⁺, and PO^3-₄ .

Explain by means of generally used international symbols and formulas which compounds are named as peroxo compounds. Write summary formulas for six of them. 

Complete the following equation: H₃AsO₄ + Zn → AsH₃ + Zn²⁺ 

 The reaction is carried out in an acid solution. Fill in the missing particles and balance the reaction equation. 

A compound A contains 38.67 % of potassium, 13.85 % of nitrogen, and 47.48 % of oxygen. On heating, it is converted to a compound B containing 45.85 % of potassium, 16.47 % of nitrogen, and 37.66 % of oxygen. 

Problem: 

What are the stoichiometric formulas of the compounds? 

Write the corresponding chemical equation. 

The IUPAC name of the compound is:

(a) 5-bromo-1-hexanoic acid 

(b) 5-bromo-2-hydroxy-1-hexanal 

(c) 2-bromo-5-hydroxy-6-hexanal 

(d) 2-bromo-2-hydroxy-1-hexanal 

(e) 5-bromo-2-hydroxy-1-hexanone 

Quantitative analysis for carbon and hydrogen was originally carried out using a technique and apparatus (see figure) originally developed in 1831 by the famous chemist Justus Liebig. A carefully weighed sample of organic compound (C) is placed in a combustion tube (A) and vaporized by heating in a furnace (B). The vapours are swept by a stream of oxygen through a heated copper oxide packing (D) and through another furnace (E), which ensures the quantitative oxidation of carbon and hydrogen to carbon dioxide and water. The water vapour is absorbed in a weighed tube (F) containing magnesium perchlorate and the carbon dioxide in another weighed tube (G) containing asbestos impregnated with sodium hydroxide. 

 A pure liquid sample containing only carbon, hydrogen and oxygen is placed in a 0.57148 g platinum boat, which on reweighing weights 0.61227 g.The sample is ignited and the previously weighed absorption tubes are reweighed.The mass of the water absorption tube has increased from 6.47002 g to 6.50359 g, and the mass of the carbon dioxide tube has increased from 5.46311 g to 5.54466 g. 

(a) Calculate the mass composition of the compound. 

(b) Give the empirical formula of the compound.To estimate the molar mass of the compound,1.0045 g was gasified. The volume, measured at a temperature of 350 K and a pressure of 35.0 kPa, was 0.95 dm³. 

(c) Give the molar mass and the molecular formula of the compound. 

(d) Draw possible structures corresponding to the molecular formula excluding cyclic structures, stereo isomers, peroxides and unsaturated compounds.There are about 15 possibilities.Give 10 of them. 

When the compound is heated with a sodium hydroxide solution, two products are formed. Fractional distillation of the reaction mixture yields one of the substances.The other substance is purified by distillation after acidification and appears to be an acid. 

(e) What structures are possible for compound C? 

0.1005 g of the acid are dissolved in water and titrated with a sodium hydroxide solution with a concentration of 0.1000 mol dm^-3. The indicator changes colour on addition of 16.75 cm³ of hydroxide solution. 

(f) What was the original substance C? 

Write down equations for the reactions: 

Oxidation of chromium(III) chloride with bromine in alkaline solution (KOH).