Molecular Theory & Factors
Which of the following is NOT TRUE?
a. When soluble substance is dissolved in water, the surface tension of water increases. b. When sparingly soluble substance is mixed with water, surface tension of water increases. c. When insoluble impurity is added into the water, surface tension of water decreases. d. In case of molten copper or molten cadmium, the surface tension increases with increase in its temperature.
Show answer and solution
Answer: (a)
- a: A highly soluble substance (e.g. salt) increases surface tension. True.
- b: A sparingly soluble substance (e.g. soap, phenol) decreases surface tension, so 'increases' is false.
- c: Insoluble impurities (oil, dust) on the surface decrease surface tension. True.
- d: For molten copper and cadmium, surface tension increases with temperature (exception). True.
- So the statement NOT true is b, i.e. answer (a).