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Reef Chemistry Question of the Day #242
Curiously, the density of a gas and density of a liquid do not necessarily track together when you look at different chemicals. In other words, the features that determine the density of the two phases are different.
Let's take the following four liquids at room temperature and pressure:
1. Bromine (Br2) molecular weight = 159.8 g/mmole
2. Water (H2O) molecular weight = 18.0 g/mole
3. n-Butane (C4H10) molecular weight = 58.1 g/mole
4. n-Dodecane (C12H26) molecular weight = 170.3 g/mole
The liquid densities rank as follows, from low to high:
n-Butane (0.6 g/mL) < n-Dodecane (0.75 g/mL) < water (1 g/mL) < Bromine (3.1 g/mL)
What is the rank order of the density of the gas phase (each chemical alone in the gas) at a constant temperature and pressure?
A. Bromine < Water < Butane < Dodecane
B. Water < butane < Dodecane < Bromine
C. Butane < Dodecane < Bromine < Water
D. Water < Butane < Bromine < Dodecane
Note that I have given you everything you need to answer the problem. No lookups needed. All you need to do is determine what attribute of a molecule determines its gas phase density at a fixed pressure and temperature.
Good luck!
.
Curiously, the density of a gas and density of a liquid do not necessarily track together when you look at different chemicals. In other words, the features that determine the density of the two phases are different.
Let's take the following four liquids at room temperature and pressure:
1. Bromine (Br2) molecular weight = 159.8 g/mmole
2. Water (H2O) molecular weight = 18.0 g/mole
3. n-Butane (C4H10) molecular weight = 58.1 g/mole
4. n-Dodecane (C12H26) molecular weight = 170.3 g/mole
The liquid densities rank as follows, from low to high:
n-Butane (0.6 g/mL) < n-Dodecane (0.75 g/mL) < water (1 g/mL) < Bromine (3.1 g/mL)
What is the rank order of the density of the gas phase (each chemical alone in the gas) at a constant temperature and pressure?
A. Bromine < Water < Butane < Dodecane
B. Water < butane < Dodecane < Bromine
C. Butane < Dodecane < Bromine < Water
D. Water < Butane < Bromine < Dodecane
Note that I have given you everything you need to answer the problem. No lookups needed. All you need to do is determine what attribute of a molecule determines its gas phase density at a fixed pressure and temperature.
Good luck!
.