Massachusetts Tests for Educator Licensure (MTEL) Practice Test

What happens when salt dissolves in water?

1. Volume of water decreases

2. It forms sodium and chloride ions surrounded by water molecules

3. The density of water decreases

4. Temperature of the solution drops significantly

The correct answer is: It forms sodium and chloride ions surrounded by water molecules

When salt dissolves in water, it separates into sodium and chloride ions, which then become surrounded by water molecules. This process is known as dissociation. The positive sodium ions (Na⁺) are attracted to the negative parts of the water molecules (the oxygen atoms), while the negative chloride ions (Cl⁻) are attracted to the positive parts (the hydrogen atoms) of the water molecules. This interaction between the ions and the water molecules allows for the salt to disperse throughout the water, forming a homogeneous solution. The other choices do not accurately describe the process of salt dissolving in water. While the volume of water might change slightly, it does not decrease in a meaningful way due to the addition of salt. The density of the solution may change, but it does not necessarily decrease. Additionally, while the process of dissolving may cause a slight temperature change, it does not typically result in a significant drop in temperature unless the solution is prepared under specific conditions. Thus, the formation of sodium and chloride ions surrounded by water molecules is a clear and accurate depiction of what occurs when salt dissolves in water.