Molality Colligative Properties
● One way to think of colligative properties in everyday life is through ice cream
○ Typically bought at the store
○ Some people make it at home using it contraption
■ A fairly simple set up
■ Has a motor on top
■ Buried inside is the working component we can see
■ Inner core where we put the milk and ingredients to make the ice cream
■ Around the outside of the core, we would put in ice or rock salt
■ What will happen is the salts and ices outside will sit in the middle, and the motor will spin it and take
about 20-30 minutes to make ice cream
● Why does this happen and why do we use salt?
○ Salt is a colligative property
○ A colligative property of matter is that whenever you dissolve a solute into a solvent (such as salt into water) the
particles of the salt lower the freezing point of water or ice
○ This is because it interferes with the packing of the ice
○ Lowers the freezing point, making it colder
○ Rock salt works well for making ice cream
● How do we determine how much salt to use
○ 1 part salt, 8 parts ice
● Looking at it in the lab
○ Molality - unit of concentration
○ Molality = number of MOLS of solute / kg of solvent = m
■ .30 mol / .50 kg = .60 m (molal) solution
○ One reason this unit is used for salt,water, and ice is because we use the unit kg for solvent
○ This is important because often the temperature will change, and mass does not change with temperature
● Molarity - a similar sounding unit
○ Molarity is defined as moles of solute / per volume L of solution
○ Solutions and solvents do change with temperature
○ They can compress, contract and expand
○ We rather use molality when dealing with temperature
Experiment: Making Ice Cream
● Using 2 different salts to demonstrate colligative properties; measuring the amount of salt in particular ice using the molaltiy
unit
● What we will do:
○ Weighed out ice
■ NaCl
■ CaCl2 (calcium chloride)
○ We have salt .5 mol weighed out (NaCl and CaCl2)
■ This is what will make it cold
○ And ice cream ingredients also weighed out and labeled as NaCl and CaCl2
■ Milk, vanilla, sugar and vanilla
● Going to make ice cream with 2 different salts to evaluate the impact that two difference salts are on the temp and
consistency of the ice cream
● Experiment:
○ Sodium Chloride
This study source was downloaded by 100000841138256 from CourseHero.com on 05-29-2023 03:25:11 GMT -05:00
, CHEM 103 LAB 7 MOLALITY COLLIGATIVE PROPERTIES
(PORTAGE LEARNING)
■ Take .5 mol sodium chloride and put it in with the ice in the Sodium Chloride bag
This study source was downloaded by 100000841138256 from CourseHero.com on 05-29-2023 03:25:11 GMT -05:00
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