Experiment 2.6.

Laboratory work 12

ELEMENTS of CHROME SUBGROUP

1. Materials and equipment: metallic chrome, metallic zinc, crystalline iodine, potassium iodide, potassium bromide, solutions of sulphuric acid, nitric acid, chrome (ІІІ) chloride, chrome (ІІІ) sulphate, ammonia, sodium hydroxide, sodium carbonate, sodium sulphide, potassium chromate, potassium dichromate, potassium iodide, sodium nitrite, sodium sulphite, ammonium molybdate, ammonium tungstenate, bromine water, hydrogen peroxide, concentrated hydrochloric acid, 100 ml beakers, test tubes, glass rods, clock glass.

Chemical properties of chrome

Experiment 2.1

№ experiment	Description of the experiment
	Put a piece of metallic chrome into a test tube, add 1-2 ml of 2N sulphuric acid solution and heat it up slightly. What colour does the solution have? Then transfer a droplet of the solution on a clock glass. What occurs? Give the equations of the relevant reactions and explain the reason of strong reducing properties of chrome (ІІ).
Observations
Equation of reaction

Experiment 2.2

№ experiment	Description of the experiment
	Place 2-3 ml of 0.5N chrome (ІІІ) chloride solution into a test tube, add 3-4 drops of concentrated hydrochloric acid and 1-2 granules of metallic zinc. What occurs? Give the equations of the relevant reactions.
Observations
Equation of reaction

Experiment 2.3

№ experiment	Description of the experiment
	Place 2-3 drops of chrome (ІІІ) sulphate solution into each of two test tubes and add 1-3 drops of ammonia solution to each one until precipitate forms. Add to this precipitate 3-5 drops of 2M hydrochloric acid solution into the first test tube, the same amount of 2M sodium hydroxide solution into the other one. What can you observe? Give the equations of the relevant reactions and make a conclusion of the acid-base properties of the obtained precipitate.
Observations
Equation of reaction

Experiment 2.4

№ experiment	Description of the experiment
	Measure with the help of the рH-meter hydrogen ionisation value of chrome (ІІІ) chloride solution. Then heat up the chrome salt solution and measure the value of pH again. What can you observe? Explain the difference of pH values of chrome salt solution at the ambient temperature and when heated. Give the equations of hydrolysis in the molecular and ionic forms.
Observations
Equation of reaction

Experiment 2.5.

№ experiment	Description of the experiment
	Place 4-6 drops of chrome (ІІІ) chloride solution into a test tube. Note the colour of the solution. Then heat up the test tube until the solution changes its colour. Stop heating and observe gradual reduction of the solution colour when cooled. Write down your observations and give the relevant explanation.
Observations
Equation of reaction

Experiment 2.6.

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