Final answer:
Surface tension increases with salinity due to enhanced intermolecular forces between water molecules and dissolved ions. Temperature rise leads to a decrease in surface tension because of reduced hydrogen bonding among water molecules.
Step-by-step explanation:
Surface tension increases with increasing salinity because the addition of salt leads to the strengthening of intermolecular forces within the solution. For water, surface tension is a measure of the energy required to increase its surface area, influenced largely by the cohesion between water molecules due to hydrogen bonding. When salt is dissolved in water, it disrupts the hydrogen bonding network, leading to modifications in the intermolecular forces. The ions from the salt may form ion-dipole interactions with water molecules, which can contribute to an increased order and overall stronger forces between molecules at the surface, resulting in a higher surface tension.
As the temperature of water increases, its surface tension decreases. This is because higher temperatures provide energy that overcomes the intermolecular forces, in particular hydrogen bonds, causing the molecules to move more freely and reducing their cohesion. The reduced intermolecular forces lessen the energy required to increase the surface area of the liquid, thus lowering the surface tension.