Question

The number of white coloured salts among the following is ___________.
(A) SrSO\(_4\), (B) Mg(NH\(_4\))PO\(_4\), (C) BaCrO\(_4\), (D) Mn(OH)\(_2\), (E) PbSO\(_4\), (F) PbCrO\(_4\), (G) AgBr, (H) PbI\(_2\), (I) CaC\(_2\)O\(_4\),(J) [Fe(OH)\(_2\)(CH\(_3\)COO)\(_2\)]

Answer 1

Correct Answer: 5

The problem asks to count the number of white colored salts from a given list of compounds. The color of an ionic compound is typically determined by the color of its constituent ions. Cations of s-block and p-block elements are generally colorless, leading to white salts unless the anion is colored. Cations of d-block (transition metals) are often colored due to d-d electronic transitions. Certain anions like chromate (CrO₄²⁻), dichromate (Cr₂O₇²⁻), and permanganate (MnO₄⁻) are also colored.

Step-by-Step Solution:

We will analyze the color of each salt individually.

1. (A) SrSO₄ (Strontium Sulfate):

   The cation is Sr²⁺ (Strontium, an s-block element) and the anion is SO₄²⁻ (sulfate). Both ions are colorless. Therefore, SrSO₄ is a white solid.

2. (B) Mg(NH₄)PO₄ (Magnesium Ammonium Phosphate):

   The cations are Mg²⁺ (s-block) and NH₄⁺ (ammonium), and the anion is PO₄³⁻ (phosphate). All three ions are colorless. Therefore, Mg(NH₄)PO₄ is a white solid.

3. (C) BaCrO₄ (Barium Chromate):

   The cation is Ba²⁺ (s-block), which is colorless. However, the anion is CrO₄²⁻ (chromate), which is distinctly yellow. Therefore, BaCrO₄ is a yellow salt, not white.

4. (D) Mn(OH)₂ (Manganese(II) Hydroxide):

   The cation is Mn²⁺ (a d-block transition metal ion). The Mn²⁺ ion has a d⁵ electron configuration. The d-d transitions are spin-forbidden, so its compounds are very pale in color. Freshly precipitated Mn(OH)₂ is a white solid, although it quickly oxidizes in air and turns brown. In its pure state, it is considered white.

5. (E) PbSO₄ (Lead(II) Sulfate):

   The cation is Pb²⁺ (a p-block element) and the anion is SO₄²⁻. Both ions are colorless. Therefore, PbSO₄ is a white solid.

6. (F) PbCrO₄ (Lead(II) Chromate):

   The cation is Pb²⁺, which is colorless. The anion is the yellow chromate ion, CrO₄²⁻. Therefore, PbCrO₄ is a bright yellow solid, not white.

7. (G) AgBr (Silver Bromide):

   The cation Ag⁺ and anion Br⁻ are both colorless. However, due to polarization and charge-transfer effects, AgBr is not pure white but rather a pale yellow or cream-colored solid. It is not considered white.

8. (H) PbI₂ (Lead(II) Iodide):

   The cation Pb²⁺ is colorless. The anion is I⁻ (iodide). Due to the high polarizability of the iodide ion, PbI₂ is a bright yellow solid, not white.

9. (I) CaC₂O₄ (Calcium Oxalate):

   The cation is Ca²⁺ (s-block) and the anion is C₂O₄²⁻ (oxalate). Both ions are colorless. Therefore, CaC₂O₄ is a white solid.

10. (J) [Fe(OH)₂(CH₃COO)₂] (Basic Iron(II) Acetate):

    This compound contains the Fe²⁺ (Iron(II)) ion, which is a transition metal ion. Fe²⁺ compounds are typically colored, often appearing pale green or greenish-white. They are not pure white.

Final Computation & Result:

Let's list the salts identified as white:

• (A) SrSO₄
• (B) Mg(NH₄)PO₄
• (D) Mn(OH)₂
• (E) PbSO₄
• (I) CaC₂O₄

Counting these salts, we find that there are 5 white colored salts in the given list.

The number of white coloured salts is 5.