52nd International Chemistry Olympiad, Istanbul, TURKEY
Preparatory problems: PRACTICAL
Problem P2. Determination of the Total Carbon Content of Oltu Stone (Black Amber) Samples Erzurum is a city in the northeastern part of Anatolia and is called the peak of Turkey due to its high altitude of 1900 m. Erzurum has a unique black stone (Oltu stone, black amber). This stone has been carved since the 18th century to produce jewelry and different souvenirs. Different products of Oltu stone such as rings, earrings, necklaces, bracelets, tie pins, smoking pipes, cigarette holders, and prayer beads are produced by polishing and are sold in Taşhan (Rustem Pasha Caravanserai) Bazaar in Erzurum, which was established in 1561.
There are around 600 active quarries mining Oltu stone. The beds are about 80 cm in thickness and form by diastrophism and folding of fossilized trees. Oltu stone is soft when excavated but begins to harden when it is exposed to the air. It is generally black but can be dark brown, gray, or greenish too. Oltu stone is an important material for the electric and electronics industries because its graphite-like carbon black nature. Therefore, Oltu stone contains plenty of the element carbon. This task aims to quantitatively determine the amount of carbon in Oltu stone samples thanks to back titration, using dichromate solution. Carbon element in the sample is first oxidized to CO2(g) with dichromate and then excess dichromate is back titrated with a standard iron(II) sulfate solution. Note: This experiment can also be performed using another carbon-rich material such as coal or pencil graphite instead of Oltu stone. Caution: Potassium dichromate (K2Cr2O7) is a very strong oxidizer and corrosive. Its contact with other materials may cause a fire. Therefore, this experiment must be performed in a fume hood by using glassware, laboratory coat, and glove. After you complete the experiment, waste solutions and/chemicals should be placed in the waste container.
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