Question

which two statements about the substances in this experiment are true? a. soapy water has a higher surface tension than plain water. b. quartz is harder than chalk. c. water has a higher surface tension than salty water. d. graphite is harder than quartz.

Explanation:

• Surface Tension: Soapy water has lower surface tension than plain water because soap (a surfactant) disrupts the hydrogen - bonding network at the water's surface. Salty water (with dissolved ions) also has lower surface tension than pure water. So, options A is false and option C is true.
• Hardness (Mohs Scale): On the Mohs scale of mineral hardness, quartz has a hardness of 7, chalk (calcium carbonate) has a hardness of about 3 - 4, and graphite has a hardness of 1 - 2. So, quartz is harder than chalk (option B is true) and graphite is softer than quartz (option D is false).

Answer:

B. Quartz is harder than chalk, C. Water has a higher surface tension than salty water.