Chemistry 2015 Jamb Examination

When a combustible gas is burnt, the total volume of the gaseous products formed is usually greater than the volume of the reactant gas due to the combination with oxygen. However, for a stoichiometric mixture, the volume of the oxygen required for complete combustion is proportional to the gaseous volume involved. The total gaseous volume required for complete combustion of 45 cm³ of a mixture is twice its original volume. Therefore, the required gaseous volume is 90 cm³.

The kinetic theory of matter states that the temperature of a substance is directly proportional to the average kinetic energy of its particles. At absolute zero temperature (0 K), the particles theoretically have no kinetic energy because all molecular motion ceases. Hence, in the absence of temperature, the kinetic energy of the particles becomes zero.

Matter is made up of atoms, ions, and molecules, which are the fundamental building blocks of all substances. Salt, on the other hand, is not a fundamental particle but a compound made from ions. Therefore, while atoms, ions, and molecules represent the smallest units of matter, salt does not.

Let the oxidation state of chromium be \(x\).
Potassium has a fixed oxidation state of +1 and oxygen is −2.

Thus:\[ 2(+1) + x + 7(-2) = 0 \]\[ 2 + x - 14 = 0 \]\[ x = +12 \]\[ \therefore \; x = +6 \]Hence, the oxidation state of chromium in potassium dichromate (K₂CrO₇) is +6.

Uranium, particularly uranium-235, is widely used as a nuclear fuel because it can undergo fission to release large amounts of energy. When bombarded with neutrons, uranium-235 splits into smaller nuclei, releasing additional neutrons and a great deal of heat energy, which is harnessed for power generation in nuclear reactors.

Electromagnetic waves include white light, X-rays, infrared, radio waves, and others. A photon, however, is not an electromagnetic wave; it is a quantum particle that represents a packet of electromagnetic energy. Thus, while photons carry electromagnetic energy, they are not waves themselves.

In Cu₂S, copper has an oxidation state of +1 because sulphur is −2 and the compound is neutral:\[ 2x + (-2) = 0 \Rightarrow x = +1 \]In the products, copper is in its elemental state, hence oxidation state 0.
Thus, copper is reduced from +1 to 0, indicating a reduction process.

Boyle’s law states that the pressure of a gas is inversely proportional to its volume, provided the temperature and amount of gas remain constant. Mathematically, this is expressed as:\[ P_1V_1 = P_2V_2 \]This relationship shows that when pressure increases, volume decreases proportionally, and vice versa.

In electrolytes, electric current is carried by the movement of ions. Positive ions (cations) move towards the negative electrode (cathode), while negative ions (anions) move towards the positive electrode (anode). This movement of ions constitutes the flow of electric current in the electrolyte.

The discovery of proteins involved experiments using discharge tubes equipped with a central cathode. This configuration enabled the generation of cathode rays essential for studying the properties of atoms and molecules. The central cathode allowed for uniform discharge and helped scientists identify the presence of nitrogen-containing compounds, which were later linked to proteins. Such experimental setups provided insights into the molecular composition of biological substances, leading to the early understanding of protein structures and their elemental composition.