Marjorie is trying to determine the identity of an unknown substance. After running tests, she determines that the substance is insoluble in CCl4 with a density of about 2.2 g/mL.

Question

Substance Density Boiling Point Solubility (in water) Solubility (in CCl4)
NaCl 2.165 g/mL 1413°C soluble insoluble
C10H8 1.14 g/mL 255°C insoluble soluble
FeCl3 2.898 g/mL 315°C soluble insoluble
SiO2 2.634 g/mL 2590°C insoluble insoluble

Using the data above, which of the following substances is most likely Marjorie's unknown?
A.
NaCl
B.
C10H8
C.
FeCl3
D.
SiO2

Answer 1

To identify the unknown substance, we will compare its properties with the properties of the given substances:

1. Density: The unknown substance has a density of about 2.2 g/mL.
2. Solubility in Water: The unknown substance is insoluble in water (as implied but not directly stated, since NaCl and FeCl3 are soluble).
3. Solubility in CCl4: The unknown is insoluble in CCl4.

Now, let's examine the options one by one:

• A. NaCl

  • Density: 2.165 g/mL (close to 2.2 g/mL)
  • Solubility: soluble in water (not a candidate, as the unknown is insoluble in water)

• B. C10H8 (Naphthalene)

  • Density: 1.14 g/mL (much less than 2.2 g/mL)
  • Solubility: insoluble in water, soluble in CCl4 (not a candidate due to density)

• C. FeCl3

  • Density: 2.898 g/mL (higher than 2.2 g/mL)
  • Solubility: soluble in water (not a candidate, as the unknown is insoluble in water)

• D. SiO2 (Silicon Dioxide)

  • Density: 2.634 g/mL (higher than 2.2 g/mL, but it could be considered given the unknown is not specified with high precision)
  • Solubility: insoluble in water and insoluble in CCl4 (fits the criteria for both solubility properties)

Given this analysis, of the options, D. SiO2 is the most likely candidate for Marjorie's unknown substance because it is:

• Insoluble in water
• Insoluble in CCl4
• Has a density that is reasonably close to the unknown's density despite being slightly higher.

Thus, the answer is D. SiO2.