Which of these designates a gas at room temperature?

#A)# #"HCl"(g)#
#B)# #"Br"_2(l)"/""alcohol"#
#C)# #"C"_(12)"H"_(22)"O"_(11)(aq)#
#D)# #"Cl"_2(g)"/""CCl"_4(l)#

1 Answer
Truong-Son N.
Jan 14, 2017

#"HCl"(g)#, as #"HCl"# is naturally a gas at room temperature and pressure. It boils below room temperature, at #-85.05^@ "C"#.

The way you can figure out what you're looking at is by looking at what is in parentheses:

  • #(g) = "gas"#
  • #(l) = "liquid"#, or very concentrated (high #"mol solute"/"L solution"#)
  • #(s) = "solid"#, or precipitate if within a reaction

The above are all phases, though #(l)# can indicate a concentrated solution.

Anything else specifies a solvent that the solute dissolves in (or a liquid that another liquid mixes with to form a liquid-liquid mixture), which is another way of saying that it is a solution:

#B)# specifies bromine liquid (#"Br"_2(l)#) dissolved in liquid alcohol (bromine is a liquid at room temperature and pressure). An alcohol can be anything containing only #"C"# connected to #"H"# (a hydrocarbon end), and #"OH"# (a hydroxyl group), such as ethanol and butanol.

#C)# is sucrose (common sugar, #"C"_(11)"H"_(22)"O"_(11)#) dissolved in water. #(aq)# denotes an aqueous solution, which is by definition something dissolved in water.

#D)# is chlorine gas (#"Cl"_2(g)#) dissolved in carbon tetrachloride liquid (#"CCl"_4(l)#). Chlorine is a gas at room temperature (check that its boiling point is less than #25^@ "C"#), while #"CCl"_4# has a boiling point higher than #25^@ "C"#.

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