Waec 2024 chemistry answers








An electrochemical cell is a device that converts chemical energy into electrical energy or vice versa. It consists of two half-cells, each containing a electrodes (an anode and a cathode) immersed in an electrolyte, which facilitates the flow of ions between the electrodes.

(i)Spontaneity: Electrochemical cells are spontaneous, meaning they generate electricity on their own, while electrolytic cells require an external power source to drive the reaction.
(ii)Direction of Electron Flow: In electrochemical cells, electrons flow from the anode to the cathode, while in electrolytic cells, electrons flow from the cathode to the anode.
(iii)Purpose: Electrochemical cells are used to generate electricity, while electrolytic cells are used to drive non-spontaneous reactions, such as electroplating or water splittings.

(i)The blue color of the copper sulfate solution starts to fade as zinc replaces the copper.
(ii)Solid copper begins to precipitate out of the solution, forming a reddish-brown deposit at the bottom of the beaker.
(iii)The solution might gradually become colorless if all the copper ions are replaced.
(iv)Bubbles of hydrogen gas may be observed if the zinc is in excess, indicating the occurrence of further reactions involving the zinc and the sulfate or the acidic solution.

CH4(g) -> C(s) + 2H2(g)

Decomposition reaction

(i) hydrogen chloride (HCl)
(ii)sulfur dioxide (SO2).

(i)high temperature
(ii)presence of a catalyst
(iii)longer hydrocarbon chain length.

Noble gases are chemically inert because they have a completely filled outer shell of electrons, making them very stable and unlikely to react with other elements.

(i)Members have the same general formula
(ii)Members have similar chemical properties
(iii)Members have a gradual change in physical properties
(iv)Members have a constant difference in molecular formula between successive members

Global warming refers to the long-term rise in the average surface temperature of the Earth due to the increasing levels of greenhouse gases in the atmosphere.

increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to fossil fuel burning, deforestation, and land-use changes.


(I)Deliquescence is the process by which a substance absorbs moisture from the atmosphere until it dissolves in the absorbed water and forms a solution. This typically occurs with hygroscopic substances that have a high affinity for water.

(II)Efflorescence is the process by which a substance loses water to the atmosphere, resulting in the formation of a powdery surface deposit. This occurs when the vapor pressure of the water in the hydrated salt is greater than the partial pressure of water vapor in the air.

(I)Deliquescence: Calcium chloride (CaCl₂)
(II)Efflorescence: Sodium carbonate decahydrate (Na₂CO₃·10H₂O)

Ionization energy is the amount of energy required to remove an electron from an isolated gaseous atom or ion in its ground state. The first ionization energy refers to the energy needed to remove the first electron, while subsequent ionization energies refer to the removal of additional electrons.

The second ionization energy of sodium is greater than the first because, after the first electron is removed, the remaining electrons are closer to the nucleus and experience a stronger attractive force. Removing a second electron requires more energy as it disrupts the stable, noble gas configuration left behind.

Charles’ Law states that the volume of a given mass of gas is directly proportional to its absolute temperature, provided the pressure remains constant. Mathematically, it is expressed as:
V/T = k

Draw a diagram

1. Mining: Tin ore, usually cassiterite (SnO2), is mined from the Earth’s crust using methods such as open-pit mining or underground mining.
2. Concentration: The mined ore is crushed and ground to liberate the tin minerals from the surrounding rock. Then, gravity separation techniques are often used to concentrate the tin-bearing minerals.
3. Smelting: The concentrated tin ore is then heated in a furnace with carbon (usually in the form of coal) to reduce the tin oxide (SnO2) to metallic tin (Sn). This process typically occurs at high temperatures in the range of 1200 to 1500 degrees Celsius.
4. Refining: The crude tin obtained from smelting may contain impurities such as iron, copper, and lead. Therefore, the crude tin is refined through processes like liquation or electrolytic refining to obtain high-purity tin.
5. Casting and Fabrication: The refined tin is cast into ingots or other desired shapes, which can then be used for various applications such as soldering, plating, or manufacturing tin-based alloys.

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