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Waec 2024 Expo Correct Chemistry Answer

a) An electrochemical cell is a device that converts chemical energy into electrical energy through an oxidation-reduction reaction.

b) 1) An electrochemical cell produces electrical energy, while an electrolytic cell requires electrical energy to drive a non-spontaneous reaction.
2) In an electrochemical cell, the electron flow is from the anode to the cathode, while in an electrolytic cell, the electron flow is from the cathode to the anode.
3) In an electrochemical cell, the anode is where oxidation occurs, and the cathode is where reduction occurs, while in an electrolytic cell, the anode is where reduction occurs, and the cathode is where oxidation occurs.

c) When powdered zinc is added to a solution of copper (II) tetraoxosulphate (VI) in a beaker, a displacement reaction will occur. The zinc will undergo oxidation to form zinc ions in solution, while the copper ions will be reduced to form solid copper metal. This will result in a change in color of the solution from blue to colorless, as copper metal is deposited at the bottom of the beaker.
[5/22, 9:30 AM] Solution: 1(d) (i) CH4(g) -> C(s) + 2H2(g)
(ii) Decomposition reaction

(e) Two gases that should be prepared in a fume chamber are hydrogen chloride (HCl) and sulfur dioxide (SO2).

(f)

  1. high temperature, 2.presence of a catalyst
    3.longer hydrocarbon chain length.

(g) 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.

(h)

  1. Members have the same general formula
  2. Members have similar chemical properties
  3. Members have a gradual change in physical properties
  4. Members have a constant difference in molecular formula between successive members
    [5/22, 9:44 AM] Solution: (1a)
    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.

(1b)
(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.

(1c)
(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.

(1di)
CH4(g) -> C(s) + 2H2(g)

(1dii)
Decomposition reaction

(1e)
(i) hydrogen chloride (HCl)
(ii)sulfur dioxide (SO2).

(1f)
(i)high temperature
(ii)presence of a catalyst
(iii)longer hydrocarbon chain length.

(1g)
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.

(1h)
(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

(1i)
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.

No(j)
increasing levels of carbon dioxide (CO2) in the atmosphere, primarily due to fossil fuel burning, deforestation, and land-use changes.

Waec Expo 2024 Answer

4b
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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