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.
C10H8
C.
SiO2
D.
FeCl3

Answer 1

To determine which substance Marjorie is analyzing, we need to consider the density, solubility in CCl4, and whether or not it is soluble in water.

- **Density of unknown substance**: 2.2 g/mL
- **Insoluble in CCl4**: This would eliminate any substance that is soluble in that solvent.
- **No information on solubility in water is provided for the unknown substance**.

Now, let's analyze the options:

A. **NaCl**
- Density: 2.165 g/mL
- Boiling Point: 1413°C
- Solubility in water: soluble
- Solubility in CCl4: insoluble

B. **C10H8 (Naphthalene)**
- Density: 1.14 g/mL
- Boiling Point: 255°C
- Solubility in water: insoluble
- Solubility in CCl4: soluble

C. **SiO2**
- Density: 2.634 g/mL
- Boiling Point: 2590°C
- Solubility in water: insoluble
- Solubility in CCl4: insoluble

D. **FeCl3**
- Density: 2.898 g/mL
- Boiling Point: 315°C
- Solubility in water: soluble
- Solubility in CCl4: insoluble

Given the density of the unknown substance is approximately 2.2 g/mL, the closest match would be NaCl (density 2.165 g/mL) but NaCl is soluble in water, which is inconsistent with the unknown's properties.

SiO2 has a higher density (2.634 g/mL) and is insoluble in both water and CCl4.

Therefore, the best choice given the properties provided is:

**C. SiO2**