properties of solutions

boiling point elevation

Antifreeze could also be called antiboil because it also raises the boiling point of the water in a car radiator. Hot weather combined with a hot engine can easily raise the temperature of the water in the radiator above 100 C, which is the boiling point of pure water. If the water boils, it could cause the engine to overheat and become seriously damaged. However, if antifreeze has been added to the water, the boiling point is much higher. For example a 50 percent antifreeze solution has a boiling point of 129 C. Unless the water gets hotter than this, it wont boil and ruin the engine.

freezing point depression

Pure water freezes at 0 C, but the salt water in the ocean freezes at -2.2 C because of freezing point depression. We take advantage of the freezing point depression of salt in water by putting salt on ice to melt it. Thats why the truck in the Figure 1.1 is spreading salt on an icy road. Did you ever see anyone add a fluid to their car radiator? The fluid might be antifreeze, like in the Figure 1.2. Antifreeze lowers the temperature of the water in the car radiator so it wont freeze, even when the temperature falls far below 0 C. For example, a 50 percent antifreeze solution wont freeze unless the temperature goes below -37 C.

textbook_image

textbook_image

how solutes affect solvents

Salt water in the ocean is a solution. In a solution, one substance, called the solute, dissolves in another substance, called the solvent. In ocean water, salt is the solute and water is the solvent. When a solute dissolves in a solvent, it changes the physical properties of the solvent. In particular, the solute generally lowers the freezing point of the solvent, which is called freezing point depression, and raises the boiling point of the solvent, which is called boiling point elevation. For example, adding either salt to water lowers the freezing point and raises the boiling point of the water.

instructional diagrams

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questions

salt water has a lower freezing point than pure water.

-->  a. true

b. false

when a solute dissolves in a solvent, it changes the chemical properties of the solvent.

a. true

-->  b. false

a solute generally raises the freezing point of a solvent.

a. true

-->  b. false

when antifreeze is added to water in a car radiator it causes

a) boiling point elevation.

b) freezing point depression.

c) changes in the physical properties of the water.

-->  d) all of the above

pure water boils at a temperature of 100 c. at which temperature might salt water boil?

a) 98 c

b) 99 c

c) 100 c

-->  d) 101 c

diagram questions

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