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Separating Salts from Seawater

Separating Salts from Seawater
Contributors
Yiben Wang
Assistant Professor of Chemistry and Biochemistry | Villanova University
Learning Objets
Summary
The experiment "Separating Salts from Seawater" demonstrates the process of separating various salts from seawater. Students heat seawater to evaporate the water and precipitate solids. The procedure involves boiling seawater, allowing solids to settle, and using filtration and further evaporation to isolate different salts, primarily calcium carbonate, calcium sulfate, and sodium chloride. This experiment teaches concepts of mixtures, solubility, and chemical reactions, while emphasizing laboratory safety practices.
Keyword Tags
Analysis
Compounds and Mixtures
Link to external
Separating Salts from Seawater
Learning Goals/Student Objectives
See published resource
Object Type
Laboratory experiment
Audience
Middle School
High School (Secondary School)
Introductory Undergraduate
Green Chemistry Principles
Waste Prevention
Design for Energy Efficiency
Use of Renewable Feedstocks
U.N. Sustainable Development Goals (SDGs)
Clean Water and Sanitation
Responsible Consumption and Production
Life Below Water
Safety Precautions, Hazards, and Risk Assessment
See linked RSC resource
Teacher Recommendations or Piloting Data (if available)
Encourage the students to write down what they observe at each stage.

If no gradations are already present, teachers may wish to mark 250 cm3 beakers at the 60 cm3 level.

The artificial seawater contains calcium hydrogen carbonate owing to the reaction of limewater with excess carbon dioxide:

Ca(OH)2(aq) + 2CO2(g) → Ca(HCO3)2(aq)

When this solution is boiled, it soon precipitates calcium carbonate:

Ca(HCO3)2(aq) → CaCO3(s) + CO2(g) + H2O(l)

This is the identity of the predominant solid first left behind when the liquid is boiled. However, some calcium sulfate will also be present.

When hydrochloric acid is added to this solid, students should observe effervescence (fizzing), since the calcium carbonate is producing carbon dioxide gas:

CaCO3(s) + 2HCl(aq) → CaCl2(aq) + CO2(g) + H2O(l)

The solid which continuously crystallizes out on further evaporation is sparingly soluble calcium sulfate, which is the predominant solid filtered off when 30 cm3 of seawater remains.

The more soluble sodium chloride precipitates out during the final stages of evaporation.

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Submitted by

Yiben Wang
Published on
Moderation state
Published
Collection
Royal Society of Chemistry (RSC) Resources
Time required (if applicable)
60 mins