Example Problems for Entrance Examinations

Preliminary round

Problem 1.

Give an example of chemical reaction between a salt and an acid leading to the formation of another salt and a base.
(1 point) [Solution]

Problem 2.

Write the reactions involved in the following sequence of oxidation number transformations:
(2 points) [Solution]

P⁰ P^-3 P^-3 P⁺⁵ P⁺⁵

Problem 3.

Write the reactions of chromium (III) bromide with hydrogen peroxide in acidic and basic media.
(2 points) [Solution]

Problem 4.

Write the reactions involved in the following sequence:

C₁₀H₁₂ C₃H₆O₂ C₃H₅OCl C₁₀H₁₂O₂.

In the reactions, specify the structures of all substances.
(3 points) [Solution]

Problem 5.

Write the reactions involved in the following sequence of transformations:

Determine the unknown substances.
(4 points) [Solution]

Problem 6.

Three substances A, B, and C were mixed in the amount of three moles each. When the equilibrium
A + B 2C
was reached, five moles of substance C were found in the system. Calculate the equilibrium constant. Determine the equilibrium composition (in mol.%) of mixture, obtained by adding three moles of A and two moles of B to one mole of C at the same temperature.
(4 points) [Solution]

Problem 7.

Combustion of 10.7 g of unknown substance gave 30.8 g of CO₂, 8.1 g of Н₂O, and 1.4 g of N₂. The complete hydrogenation of the same sample of this substance required 9.0 l of hydrogen at temperature 227 ^oC and pressure 138.5 kPa. The gas obtained by complete evaporation of 3.21 g of the substance occupied the volume of 1.25 l at temperature 227 ^oC and pressure 99.7 kPa. Draw the four possible structures of the unknown substance.
(4 points) [Solution]

See also:

• Example problems in chemistry for the entrance exams (main round)
• Special Program developed for chemistry entrance examinations in Moscow State University.

Chemistry Department of Moscow State University