Seawater composition, salt extraction, electrolysis, water isolation: Practice Questions

Seawater is a homogeneous mixture. What term best describes the dissolved components, such as salts, within this mixture?

When electrolyzing an aqueous solution of sodium chloride with inert electrodes, how does the concentration of the sodium chloride solution generally affect the preferential discharge of ions at the anode?

When a dilute aqueous solution of sodium chloride is electrolysed using inert carbon electrodes, the results differ slightly from those of a concentrated solution. Which statement correctly identifies the products and explains their formation?

After evaporating most water from seawater to obtain impure common salt, further purification often involves recrystallization. What is the fundamental principle behind recrystallization as a purification method?

A coastal community aims to establish an efficient process to obtain both purified common salt and potable water from seawater using conventional physical separation methods. Considering large-scale practicality and the nature of seawater components, which combination of methods is most appropriate?

Seawater contains various dissolved salts. Name one anion, other than the chloride ion, that is commonly present in seawater.

In the electrolysis of aqueous sodium chloride using inert electrodes, explain why the concentration of chloride ions affects which product is formed at the anode.

During the electrolysis of seawater using carbon electrodes, a white cloudy precipitate is observed to form specifically around the cathode. Identify this precipitate and explain why its formation is characteristic of seawater electrolysis compared to the electrolysis of pure aqueous sodium chloride.
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Sodium chloride is the most abundant dissolved solid in seawater and can be extracted through evaporation.

(a) Explain why the salt remains in the evaporating dish while water escapes during the process in terms of the physical properties of the components.
(b) To confirm the presence of sodium ions in the extracted salt, a flame test is carried out. Describe the step-by-step procedure for this test, including how to clean the platinum wire and the expected observation.

Seawater is an abundant resource that provides essential substances through various chemical and physical processes.

(a) Name a major mineral, other than sodium chloride, that can be obtained from seawater.
(b) A student is provided with a sample of solid common salt extracted from seawater. Describe the procedure of a flame test to confirm the presence of sodium ions in the sample, including the expected observation.
(c) When concentrated seawater (brine) is electrolysed using graphite electrodes, a gas is produced at the anode that can turn moist blue litmus paper red and then bleach it.
(i) Identify this gas.
(ii) Write the ionic half-equation for the formation of this gas at the anode.
(iii) Explain why this gas is produced instead of oxygen gas, even though the concentration of hydroxide ions is non-negligible.