Question

Which of the following causes the density of seawater to increase? A) a decrease in temperature B) a decrease in salinity C) an increase in temperature D) a decrease in pressure

Short answer

A) a decrease in temperature increases the density of seawater.

Step-by-step solution

Understanding Density

Density is the mass of a substance per unit volume. In the case of seawater, its density can be influenced by factors such as temperature, salinity, and pressure.

Effect of Temperature on Density

As temperature decreases, particles move slower and become more closely packed. This generally results in an increase in density. Therefore, a decrease in temperature leads to an increase in the density of seawater.

Effect of Salinity on Density

Salinity refers to the amount of salt dissolved in the water. When salinity decreases, the mass of dissolved salts in a given volume of water decreases, leading to a decrease in density. Therefore, a decrease in salinity causes a decrease in seawater density.

Effect of Pressure on Density

As pressure decreases, particularly in fluids, the particles tend to occupy more space due to less external pressure compressing them, which usually decreases the density. Thus, a decrease in pressure leads to a decrease in the density of seawater.

Review and Choose the Correct Option

A decrease in temperature (Option A) increases the density of seawater, as outlined in the explanations. Options B, C, and D either decrease density or have the opposite effect. Therefore, A) a decrease in temperature, is the correct answer.

Key concepts

Temperature and Density

When we talk about seawater, its density is affected by temperature. Imagine particles in seawater. They move quite a bit, but as the temperature drops, these particles slow down. This is similar to how people move slower when it’s cold. This slowing down allows the particles to pack closer together, making the seawater denser.

As density increases, water molecules become more compact. You can think of it like squeezing a sponge. The more you squeeze, the denser it becomes.

• A decrease in temperature means increased density.
• The particles move less and settle in tighter spaces.

This principle explains why cold water is often denser than warm water.

Salinity and Density

Salinity is all about the saltiness of seawater. When seawater has a lot of salt, it weighs more in a given space, increasing its density. So, high salinity means high density.

Now, think about it the other way. If you have less salt in the water, there's less weight, and therefore, lower density. It’s like adding sugar to your tea. The more sugar, the thicker (or denser) it feels.

• More salinity results in higher density.
• Less salinity results in lower density.

So, changes in salinity can significantly impact how dense seawater is.

Pressure and Density

Pressure plays a crucial role in the density of seawater. When you apply pressure, it forces the particles in the water closer together, increasing the density. Think of this like pressing down on a pillow.

However, if the pressure is reduced, the particles have more room to move around, decreasing the density. You can see this effect when squeezing a toothpaste tube.

• Increased pressure packs particles tighter, increasing density.
• Decreased pressure allows particles to spread out, reducing density.

So, pressure changes affect how congested or loose the seawater particles are, which changes its density.