You are required to determine the concentrations of hydrochloric acid and potassium iodate in the diluted solution containing both. 

Procedure: A solution containing potassium iodate and hydrochloric acid has already been measured into the volumetric flask provided. Fill the flask to the mark with distilled water using the wash bottle, close it with a stopper and shake it thoroughly. Fill the burette with the standard sodium thiosulphate solution using one of the beakers provided. (The exact concentration of the thiosulphate is given on the label of the bottle.) 

(a) First titration Pipette a 10.00 cm³ aliquot (portion) of the solution from the volumetric flask into a glass stoppered conical flask. Dilute it with 10 cm³ of distilled water, add 1 g (a small spatula end-full) of potassium iodide and acidify with 10 cm³ of 10 % sulphuric acid using a measuring cylinder. Titrate immediately the iodine formed with the standard sodium thiosulphate solution until the solution in the flask is pale yellow. Add with a pipette 1 cm³ of starch indicator solution and continue the titration to completion. Repeat the titration twice more and record your readings on the result sheet. 

(b) Second titration Pipette a 10.00 cm³ aliquot of the solution into another glass stoppered conical flask, dilute with 10 cm³ of distilled water, add 1 g of solid potassium iodide,and leave to stand for 10 minutes. Then titrate the iodine formed using the standard sodium thiosulphate solution, adding 1 cm³ of starch indicator solution when the mixture is pale yellow. Repeat the titration twice more, recording your readings on the result sheet. 

Task: Calculate the concentration of the HCl and the KIO₃ in the solution that you prepared by dilution (in mol dm^-3). 

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

A mixture of two solid elements with a mass of 1.52 g was treated with an excess of hydrochloric acid. A volume of 0.896 dm3 of a gas was liberated in this process and 0.56 g of a residue remained which was undissolved in the excess of the acid. In another experiment, 1.52 g of the same mixture were allowed to react with an excess of a 10 % sodium hydroxide solution. In this case 0.896 dm3 of a gas were also evolved but 0.96 g of an undissolved residue remained. In the third experiment, 1.52 g of the initial mixture were heated to a high temperature without access of the air. In this way a compound was formed which was totally soluble in hydrochloric acid and 0.448 dm3 of an unknown gas were released. All the gas obtained was introduced into a one litre closed vessel filled with oxygen. After the reaction of the unknown gas with oxygen the pressure in the vessel decreased by approximately ten times (T = const). 

Write chemical equations for the above reactions and prove their correctness by calculations. 

 In solving the problem consider that the volumes of gases were measured at STP and round up the relative atomic masses to whole numbers.

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? 

You are required to investigate seven inorganic compounds. Your test-tube rack is numbered 1 to 9.Two of the positions are empty.Each of the seven test-tubes provided contains only one compound in aqueous solution. Using only these solutions, pH indicator paper, and test-tubes, you are to identify as many of the ions present as you are able. For your information, record in the table the observations you make on mixing the solutions. Use the following symbols: 

elimination reactions: ↓ precipitate; ↑ gaseous product; 

 ↓s precipitate soluble in the excess of a precipitating agent. 

colours: w – white or colourless, b – blue, g – green, y – yellow, p – pink, r – red, br – brown. pH: a – acidic, b – alkaline, n – neutral. 

Equipment: 

A home-made rack contained 9 test-tubes with the unknown solutions, 30 empty Wassermann-tubes and one small beaker containing the pH indicator paper. Into each solution a dropper was inserted, and thus, the test-tubes need not to be removed from the rack while handling them. According to the original plan the following nine unknown solutions were expected to be given to the participants: 

CoCl₂,Fe(SCN)₃, NH₄OH,KI, AgNO₃, Na₂HAsO₄,HgCl₂, NiCl₂,CuCl₂. 

During the discussion of the International Jury it became known that in some countries the corresponding laws forbid the pupils in secondary schools to handle mercury and arsenic compounds. For this reason these two compounds were removed from the rack and consequently the number of ions to be detected – and the marks available – were reduced to 12 (from the original 15). (Under these conditions the alkali and nitrate ions cannot be detected.) 

The order of the test-tubes varied individually,but the first two contained invariably red solutions(CoCl₂ and Fe(SCN)₃), while the last two were the green NiCl₂ and CuCl₂ symbolizing the Hungarian national colours, red-white-green

Write down equations for the reactions: 

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

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 

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. 

A volume of 200 cm³ of a 2-normal sodium chloride solution (ρ = 1.10 g cm^-3) was electrolysed at permanent stirring in an electrolytic cell with copper electrodes. Electrolysis was stopped when 22.4 dm³ (at STP) of a gas were liberated at the cathode.

 Calculate the mass percentage of NaCl in the solution after electrolysis.  

Relative atomic masses: A_r(H) = 1; A_r(O) = 16; A_r(Na) = 23; A_r(Cl) = 35.5; A_r(Cu) = 64. 

You will follow the concentration change of one of the reactants by the method of comparative visual colorimetry. From data obtained experimentally plot graphically the change of the reactant concentration in dependence on time. 

1. Making of the comparative colorimetric scale of bromine solution Measure with a syringe into 10 identical test-tubes the following quantities of bromine water (0.01-molar): into the first one –10.0 cm³ ; 2nd – 9.0 cm³; 3rd – 8.0 cm³, ……. 9th – 2.0 cm³; into the tenth one – 1.0cm³. Then add to all the test-tubes (except the first one) distilled water to reach a total volume of 10.0 cm³ in each. Seal the test-tubes with stoppers and mix the solutions. Put the test-tubes in a stand with a white background. Finally calculate the concentration (in mol dm^-3) of bromine in the solutions in all testtubes. 

2. Reaction of bromine solution with formic acid Carry out the reaction by mixing 100.0 cm³ of bromine solution with 1.0 cm³ of 1.00- molar solution of formic acid. Immediately after mixing transfer 10.0 cm³ of the resulting solution to the test-tube identical with that used for colorimetric scale. By comparing the colour shade of the reaction mixture (in one-minute intervals) with that of the solutions in the scale, investigate changes of bromine concentration in dependence on time. Put the data in a table containing time (t) and concentration of Br₂. 

Task: Plot the bromine concentration in dependence on time a read the half-time of the reaction from the diagram.

1. Write the equation for the reaction of bromine with formic acid assuming that the reactants are in stoichiometric amounts. 

2. In analytical chemistry a volumetric solution of bromine can be prepared by dissolving a mixture of bromate and bromide in acid medium. Explain this mode of preparation by means of a chemical equation in ionic form.