Question

Which of the following is NOT soluble in water?
A.Salt
B.Sugar
C.Oxygen
D.Sand

Answer 1

Hint:For a solute to dissolve in a solvent, the molecules of the solvent must attract the molecules of the solute. The intermolecular forces of attraction are present between the solute and the solvent. Like dissolves like. The polarity of the solute is almost considered to be similar to that of the solvent.
Complete step by step answer:
The solubility of a substance tells us the maximum amount of the substance that can be dissolved in a specified amount of solvent at a particular temperature. Factors which affect the solubility of a substance are temperature, pressure and the nature of the solute and the solvent.
When a solute is added to the solvent, some amount of it dissolves and its concentration increases. This process is called dissolution.
In this case, the solvent is water. It is said that “like dissolves like” that means, a solute dissolves in a solvent only if the intermolecular interactions are similar in the two.
Now, water is a polar solvent. Hence polar solutes tend to dissolve in water. Let us look at the nature of the solute given to us.
Salt (NaCl) is an ionic compound and is polar in nature. Hence it dissolves in water.
Sugar $$(C_6{H}_5{O}_6)$$ or sucrose is a polar solute. The bonds between oxygen and hydrogen in sugar gives the oxygen a slightly negative charge and the hydrogen a slightly positive charge. Hence, sugar dissolves in water.
Oxygen is a gaseous solute and is non-polar in nature. However, it is soluble in water to a small extent. This dissolved oxygen sustains aquatic life.
Sand $\left(Si{O}_2\right)$ is a nonpolar solute. It does not have any intermolecular interactions with water. Also, the large size of the molecule makes it difficult to fit into the spaces between the water molecules. This makes it insoluble in water.
Hence, the correct answer is (D) sand.


Note: Temperature and pressure also play a great role in determining the solubility of a solute, especially gases. Here, we assume that the dissolution is taking place at Normal Temperature and Pressure (NTP). The solubility of oxygen gas decreases with increase in temperature and vice-versa. When the pressure of the gas is increased, the solubility is also increased. This is explained by Henry’s Law.