Question

It is postulated that huge deposits of NaCl (rock salt) and CaCO3 (chalk and marble) are sites of erstwhile oceans, where the salts had been concentrated through weathering by rain and wind and leaching by rivers. Select the correct explanatory statement in this context.

• A. Both NaCl and CaCO3 are highly soluble in water.
• B. NaCl is soluble in water but CaCO3 is not. Hence, concentration of CaCO3 in the oceans through weathering is an untenable hypothesis.
• C. The solubility of CaCO3 in water is pH dependent and is enhanced by acidic atmospheric gases. Hence, CaCO3 may be leached into water during weathering.
• D. NaCl and CaCO3 are igneous rocks and have crystallized as such during the slow cooling process when the earth was born. Hence, the ocean postulates is baseless.
• E.

Hint:

Remember that the solubility of certain salts, like CaCO3, is affected by the pH of the surrounding environment. Acidic conditions increase the solubility of basic salts like CaCO3.

Answer 1

The Correct Option is C

While NaCl is highly soluble in water, CaCO3's solubility is pH dependent. In acidic conditions, like those caused by atmospheric CO2, CaCO3 becomes more soluble. This explains why CaCO3 could be leached into water during weathering.