A #20*g# mass of #CaCl_2# was dissolved in #700*g# of water. What is the molality of the solution with respect to #"calcium chloride"#?

2 Answers
Jun 15, 2017

Answer:

#0.25# #molal#

Explanation:

Chemical formula of Calcium chloride= #CaCl_2#
Molar mass of #CaCl_2# =#110.98# #gmol^-1#
Mass of Calcium chloride (given) = #20g#

#Molality# = #m# = #("moles of solute")/"kg of solvent"#
Now, to calculate no. of moles:
No. of moles = #("mass")/"molar mass"#

No. of moles= #("20g")/"110.98g/mol"# = #0.180# moles
#g# of solvent = # 700 g #
Converting #g# #-># #kg#
#kg# of solvent = #0.7kg#
Water is solvent while #CaCl_2# is solute
Now,

#Molality# = #m# = #("moles of solute")/"kg of solvent"#
#Molality# = #("0.180 moles")/"0.7kg"#
#Molality# = #0.25# # molal#

Jun 15, 2017

Answer:

#"Concentration"-=0.257*"molal"#.........

Explanation:

#"Molality"# #-=# #"Moles of solute"/"Kilograms of solvent"#

And thus..............................................

#"molality"=((20*g)/(110.98*g*mol^-1))/(700*gxx10^-3*kg*g^-1)=0.257*mol*kg#.

Note that at (relatively!) low concentrations, the calculated #"molality"# would be almost the same as solution #"molarity"#. #"Molality"# is used because the expression is fairly independent of temperature. What is the #"molal concentration"# with respect to #"chloride ion"#?