Question

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.

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**.