The necessary point to acknowledge below is that sodium chloride is an electrolyte, which means that it will certainly dissociate in aqueous solution to give sodium cations, #"Na"^(+)#, and chloride anions, #"Cl"^(-)#

#"NaCl"_text((aq>) -> "Na"_text((aq>)^(+) + "Cl"_text((aq>)^(-)#

This means that one mole of sodium chloride will certainly produce 2 moles of ions in solution, one mole of sodium cations and one mole of chloride anions. Keep this in mind.

The equation for boiling-suggest elevation looks choose this

#color(blue)(DeltaT_b = i * K_b * b)" "#, where

#i# - the van"t Hoff factor;#K_b# - the ebullioscopic constant of the solvent;#b# - the molality of the solution. #DeltaT_b# - the poiling suggest elevation - identified as #T_"b" - T_"b"^

You are watching: A sodium chloride solution containing 120 g of water that has a melting point of -2.0 ∘c.

#

The ebullioscopic constant of water is equal to #0.512^
"C kg mol"^(-1)#

http://www.vaxasoftware program.com/doc_eduen/qui/tcriosebu.pdf

To determine the molality of the solution, use sodium chloride"s molar mass to help you find the number of moles you have actually in that #"31-g"# sample.

#31color(red)(cancel(color(black)("g"))) * "1 mole NaCl"/(58.44color(red)(cancel(color(black)("g")))) = "0.5305 moles NaCl"#

This suggests that the molality of the solution will be - perform not foracquire to transform the mass of the solvent from grams to kilograms

#color(blue)(b = n_"solute"/m_"solvent")#

#b = "0.5305 moles"/(559 * 10^(-3)"kg") = "0.949 molal"#

Now, the van"t Hoff factor, #i#, will certainly be equal to #2# because you obtain two moles of pwrite-ups per mole of sodium chloride included to the solution.

The boiling-point elevation will certainly thus be

#DeltaT_"b" = 2 * 0.512^
"C" color(red)(cancel(color(black)("kg"))) color(red)(cancel(color(black)("mol"^(-1)))) * 0.949 color(red)(cancel(color(black)("moles"))) color(red)(cancel(color(black)("kg"^(-1)))) = 0.97^
"C"#

This suggests that the boiling point of the solution will be

#DeltaT_"b" = T_"b" - T_"b"^
suggests T_"b" = T_"b"^
+ DeltaT_"b"#

#T_"b" = 100^
"C" + 0.97^
"C" = color(green)(101^
"C")# 