For solids and liquids, density can be expressed in which of the following units? 1. g/L 2. mg/mL 3. ...

(Answer to Q. 1)  ANS: D
For solids and liquids, density = grams (g)/liter (L) or grams (g)/cubic centimeter (cm3). Using d = g/L, divide both sides by 1000. Density can also be expressed in mg/mL.

(Answer to Q. 2)  ANS: D
Given density, d = mass (m)/volume (v), the equation can be solved for each variable: m = dv, v = m/d. When mass is substituted by weight, dw = w/v.

(Answer to Q. 3)  ANS: C
Surface tension is the force exerted by like molecules at the liquid's surface. The introduction of a surface-active agent (e.g., soap) would decrease the cohesive forces between the water drop-lets, thus reducing their surface tension at the surface. With liquids (e.g., water), surface tension can be made to increase or decrease, but it cannot be eliminated. See Figure 1-9.

(Answer to Q. 4)  ANS: D
Laplace's law, P = 2(ST/r), states that the pressure within a sphere is directly related to the sur-face tension of the liquid and inversely related to the radius of the sphere; that is, both surface tension and pressure within a sphere will change equally in the same proportion.

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