The pH of pure water at 25°C is 7. This is because:
A. It is a strong acid
B. It contains equal concentrations of H⁺ and OH⁻ ions
C. It contains only OH⁻
D. It has no ions
Answer: Option B
Solution (By JKSSB Mock Tests)
Water self-ionizes: H₂O ⇌ H⁺ + OH⁻. At 25°C, [H⁺] = [OH⁻] = 10⁻⁷ mol/L, so Kw = 10⁻¹⁴ and pH = pOH = 7. A solution is neutral when [H⁺] = [OH⁻]. pH 7 is neutral only at 25°C; at higher temperatures, Kw increases, pH of neutrality drops but still [H⁺]=[OH⁻].
Explanation:
In electrolytic refining, impure copper is the anode, pure copper is the cathode, and CuSO₄ acidified with H₂SO₄ is the electrolyte. Copper dissolves from anode and pure copper deposits on cathode. Smelting is reduction with coke.
Explanation:
The standard reduction potential (E°) indicates the tendency of a species to gain electrons. A higher positive E° value means a greater tendency to be reduced, making it a stronger oxidizing agent. Fluorine (F2) has the highest standard reduction potential (+2.87 V), making it the strongest oxidizing agent among the choices.
Explanation:
Baking powder contains sodium bicarbonate (NaHCO₃) and a weak solid acid such as tartaric acid or cream of tartar (potassium hydrogen tartrate). When moistened, they react to produce CO₂, making dough rise. Baking soda alone requires an acidic ingredient (yogurt, lemon). The acid in baking powder ensures reliable leavening. Sodium chloride and calcium carbonate do not serve this purpose.
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