Chemistry 2004 Jamb Examination

B. the formation of new substances.

Chemical reactions involve the transformation of reactants into products, resulting in the creation of new substances with different properties from the original reactants.

When a solid substance disappears completely as a gas upon heating, the substance is said to have undergone A. sublimation.

Sublimation is the process where a solid turns directly into a gas without passing through the liquid phase.

To determine the amount of copper (II) oxide that will react with 4.9 g of tetraoxosulphate (VI) acid (H₂SO₄), we first need to use the balanced chemical equation for the reaction between H₂SO₄ and copper (II) oxide (CuO):

\[ \text{H}_2\text{SO}_4 + \text{CuO} \rightarrow \text{CuSO}_4 + \text{H}_2\text{O}\]

Next, calculate the molar mass of H₂SO₄:\[ = (2 \times 1) + 32 + (4 \times 16) = 98 \text{ g/mol}\]

Calculate the moles of H₂SO₄ in 4.9 g:\[= \dfrac{4.9 \text{ g}}{98 \text{ g/mol}} = 0.05 \text{ moles}\]

According to the balanced equation, 1 mole of H₂SO₄ reacts with 1 mole of CuO. Therefore, 0.05 moles of H₂SO₄ will react with 0.05 moles of CuO.

Now calculate the molar mass of CuO:\[= 64 + 16 = 80 \text{ g/mol}\]

Finally, find the mass of CuO required:\[= 0.05 \text{ moles} \times 80 \text{ g/mol} = 4.0 \text{ g}\]

So, the correct answer is D. 4.0 g

The correct option is B. a double bond.

Vulcanization involves the removal of double bonds from the polymer chains. During vulcanization, sulfur is used to create cross-links between the polymer chains by converting double bonds into single bonds. This process enhances the elasticity, strength, and durability of the rubber.

The correct option is C. C_nH_2n+1.

The alkyl group is derived from alkanes by removing one hydrogen atom. Alkanes have the general formula C_nH_2n+2, so when one hydrogen is removed, the formula for the alkyl group becomes CnH_2n+1.

The correct option is D. C₂H₄.

In the reaction, ethanol (C₂H₅OH) is dehydrated by concentrated sulfuric acid (H₂SO₄) at 180°C to form ethene (C₂H₄) as the product. This process is known as dehydration of alcohols.

The correct option is C. decrease the solubility of the soap.

In the production of soap, concentrated sodium chloride (salt) is added to decrease the solubility of the soap in water. This causes the soap to precipitate out of the solution, making it easier to separate and collect.

The correct option is A. evolves a lot of heat when burnt.

An oxyacetylene flame is used for iron welding because it produces a very high temperature, capable of melting iron and other metals. The intense heat generated by the combustion of acetylene with oxygen makes it ideal for welding purposes.

The correct option is D. Copper (I) chloride.

Copper (I) chloride can confirm the presence of a triple bond, particularly in terminal alkynes. When a terminal alkyne reacts with copper (I) chloride, it forms a precipitate of a copper acetylide, indicating the presence of a triple bond.

The correct option is B. 2,3-dimethylhexane.

The compound has a hexane backbone (six carbon atoms in the longest chain) with two methyl groups attached at the 2nd and 3rd carbon atoms. Therefore, the IUPAC name is 2,3-dimethylhexane.