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.
SiO2
C.
C10H8
D.
FeCl3

Answer 1

To determine which substance is most likely Marjorie's unknown, we must consider the properties provided for each substance in relation to the information Marjorie has:

1. Density: The unknown substance has a density of about 2.2 g/mL.
2. Solubility in water: The behavior with water doesn't directly affect our choice based on the provided information.
3. Solubility in CCl4: The unknown is insoluble in CCl4.

Now let's evaluate each of the given substances:

A. NaCl

• Density: 2.165 g/mL
• Solubility in CCl4: insoluble

B. SiO2

• Density: 2.634 g/mL
• Solubility in CCl4: insoluble

C. C10H8 (naphthalene)

• Density: 1.14 g/mL
• Solubility in CCl4: soluble

D. FeCl3

• Density: 2.898 g/mL
• Solubility in CCl4: insoluble

Now, based on density alone:

• NaCl has a density close to the unknown (2.165 g/mL).
• SiO2 has a higher density than the unknown (2.634 g/mL).
• C10H8 has a significantly lower density (1.14 g/mL).
• FeCl3 has a higher density (2.898 g/mL).

Considering solubility in CCl4, NaCl and SiO2 are both insoluble, whereas C10H8 is soluble, and FeCl3 is insoluble, but has a density too high.

Based on compatibility of both density and solubility, NaCl (Density: 2.165 g/mL, Insoluble in CCl4) is the closest match.

Thus, the most likely identity of Marjorie's unknown substance is:

A. NaCl.