Seawater Temperature and Chemistry

Medium

How does warming seawater change its pH and saltiness? As oceans absorb heat, the water's chemistry shifts. This project measures those changes in a controlled setting. You fill ten beakers with seawater and heat each one to a different temperature, from 20 to 65 degrees Celsius. After 24 hours you measure the water level, pH, and specific gravity (density compared to pure water) in each beaker. The warmer beakers lose more water to evaporation. Both pH and specific gravity rise as the temperature goes up.

Hypothesis

The hypothesis is that increasing temperature causes the pH and salinity of seawater to increase.

Science Concepts Learned

Density

Temperature changes how much stuff is packed into a given volume of seawater. When you heat seawater, some water escapes as vapor. The remaining salts and minerals are now concentrated in less liquid — so the specific gravity (density compared to pure water) rises. You heat ten beakers of seawater to different temperatures, from 20 to 65 degrees Celsius, and measure the water level and specific gravity after 24 hours. The warmer beakers lose more water to evaporation, and both pH and specific gravity rise as the temperature goes up.

Salinity

This project starts with a pail of seawater, which has salt mixed in naturally. You heat the seawater across a range of 20 to 65 degrees Celsius, using ten beakers, and track how warming seawater shifts both its pH and saltiness.

Specific Gravity

The hypothesis predicts that salinity rises with temperature. Specific gravity — a number that tells you how heavy the water is compared to plain water — is the measurement that tracks that salinity change as the seawater warms.

Method & Materials

You will fill 10 beakers with seawater, measure the viscosity and pH levels, place a thermometer in each beaker, and place each beaker on a hot plate. You will regulate the hot plate so that the seawater in each beaker will reach a temperature of 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, 50 °C, 55 °C, 60 °C and 65 °C respectively.

You will need 10 beakers of the same size, 1 pail of seawater, 1 ruler, 10 hotplates, 10 thermometers, pH paper, and a hygrometer.

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Results

After 24 hours, the results showed that the level of water fell as the temperature of the seawater increased, indicating a higher rate of evaporation. The increasing temperature also increased the specific gravity and the pH of the seawater.

Why do this project?

By testing the effects of increasing temperatures on seawater, this experiment reveals a worrisome impact of global warming on ocean health.

Also Consider

Experiment variations include placing a fan in front of a basin containing the seawater, and repeating the experiment using containers with different surface areas, like pails or large trays.