Answer: It introduces Al 3+ ions that coagulate negatively charged clay colloidal particles.
- A It acts as a catalyst that breaks down the water molecules themselves in most textbook accounts
- B It introduces Al<sup>3+</sup> ions that coagulate negatively charged clay colloidal particles
- C It generally raises the pH of the turbid water toward a neutral value during normal conditions
- D It causes the suspended impurities to evaporate out of the water as generally observed
Correct answer: B. It introduces Al<sup>3+</sup> ions that coagulate negatively charged clay colloidal particles
Explanation: Alum provides Al<sup>3+</sup> ions, which neutralize the charge on suspended colloidal clay particles, causing them to coagulate and settle.
A typical adsorption isotherm: x/m (mass adsorbed per gram of adsorbent) rises steeply at low pressure, then flattens into a saturation plateau as the adsorbent surface fills up.
Concept context
Explore the chemistry that happens at interfaces, from catalysts that speed up industrial reactions to colloids like milk, smoke, and gels that surround us every day.