According to solubility rules, which statement best describes the solubility of Na3PO4 in 200 g of water at 40 °C?

• A. Na3PO4 is highly soluble in water, and almost all of it will dissolve at 40 °C.
• B. Na3PO4 is soluble only in hot water above 100 °C.
• C. Na3PO4 is generally insoluble in water, so only a very small amount will dissolve at 40 °C.
• D. Na3PO4 is moderately soluble in water, and a significant amount can dissolve at 40 °C.

Answer: (C)

Verified step by step guidance

1. Recall the general solubility rules for ionic compounds in water, which state that most sodium (Na⁺) salts are soluble in water regardless of the anion.
2. Identify that Na₃PO₄ (sodium phosphate) contains sodium ions (Na⁺) and phosphate ions (PO₄³⁻). According to solubility rules, all sodium salts are typically soluble in water.
3. Understand that solubility depends on temperature, but since sodium salts are generally highly soluble, Na₃PO₄ will dissolve well in water even at moderate temperatures like 40 °C.
4. Compare the given statements with the solubility rules: since Na₃PO₄ is a sodium salt, it is expected to be highly soluble, so the statement claiming it is generally insoluble is incorrect.
5. Conclude that the best description is that Na₃PO₄ is highly soluble in water, and almost all of it will dissolve at 40 °C.