Question

Which of the following reactions is not a combination reaction?

• A. The reaction of iodine with white phosphorus
• B. The reaction of iron with sulfur
• C. Addition of water to lime
• D. Addition of concentrated sulphuric acid to sugar

Answer 1

The correct option is D

Addition of concentrated sulphuric acid to sugar

The explanation for correct option

Option (D)

• Combination reaction: It is the type of reaction in which an element or a compound will combine with another element or compound to form a single product.
• Addition of conc. sulphuric acid(H₂SO₄) to sugar(C₁₂H₂₂O₁₁) will result in the production of carbon black(C) and water(H₂O).
• $$\begin{gathered} {\mathrm{C}}_{12}{\mathrm{H}}_{22}{\mathrm{O}}_{11}\stackrel{{\mathrm{H}}_2{\mathrm{SO}}_4}{\to }11{\mathrm{H}}_2\mathrm{O}+12\mathrm{C} \\ \mathrm{Sugar}\mathrm{Water}\mathrm{Carbon} \end{gathered}$$
• Two products will form in this type of reaction. Therefore is not a type of combination reaction.

The explanation for incorrect options

Option (A)

• Reaction of iodine(I₂) with white phosphorus(P) will result in the formation of phosphorus triiodide(PI₃)
• $$\begin{gathered} {\mathrm{I}}_2\left(\mathrm{s}\right)+\mathrm{P}\left(\mathrm{s}\right)\to {\mathrm{PI}}_3\left(\mathrm{s}\right) \\ \mathrm{Iodine}\mathrm{Phosphorus}\mathrm{Phosphorus}\mathrm{triiodide} \end{gathered}$$
• It is a type of combination reaction. Two elements are combined to give products.

Option (B)

• The reaction of iron(Fe) with sulfur (S) will result in the formation of FeS(Iron sulfide)
• $$\begin{gathered} \mathrm{Fe}\left(\mathrm{s}\right)+\mathrm{S}\left(\mathrm{s}\right)\to \mathrm{FeS}\left(\mathrm{s}\right) \\ \mathrm{Iron}\mathrm{Sulfur}\mathrm{Iron}\mathrm{Sulfide} \end{gathered}$$
• It is also a type of combination reaction. Two elements are combined to give products.

Option(C)

• Addition of water(H₂O) to lime(CaO) will result in the formation of Ca(OH)₂ (Calcium hydroxide).
• $$\begin{gathered} \mathrm{CaO}\left(\mathrm{s}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{Ca}{\left(\mathrm{OH}\right)}_2\left(\mathrm{s}\right) \\ \mathrm{Lime}\mathrm{Water}\mathrm{Calcium}\mathrm{hydroxide} \end{gathered}$$
• It is also a type of combination reaction. Two elements are combined to give products.

Therefore, the correct option is option(D)