1. Module 4 Intro

1.7. Page 5

Lesson 1

Module 4—Properties of Solutions

Read

 

Read the section “Properties of Aqueous Solutions” on pages 193 and 194 in your textbook to learn more about the test for conductivity and the properties of acidic, basic, and neutral solutions.

 

The Aqueous Phase

 

As you read in the previous section, drinking water can contain many dissolved substances. Not only can dissolved substances provide colour or taste, but they can make a solution have other unique properties.

 

aqueous phase: a phase denoting a highly soluble substance that has been dissolved in water; denoted by (aq)

 

conductivity: the ability of a solution to transfer an electric current

 

electrolyte: a solution that conducts an electric current

 

nonelectrolyte: a solution that does not conduct an electric current

If sugar is dissolved in water, can it still it be written as C12H22O11(s)? The answer to this question is no, since the sugar molecules are no longer behaving as a crystalline solid—they are dispersed throughout the solution. The aqueous phase (aq) is used to indicate that a substance is dissolved in water. Note that a solute is said to be aqueous only if it is dissolved in water. If it is dissolved in a different solvent, such as alcohol, the phase would be written (alc).

 

Two other properties often considered when investigating solutions are conductivity and acidity. (Solubility is another property, which will be addressed in a later lesson.)

 

Some solutions demonstrate conductivity. A solution that conducts electricity contains electrolytes. Electrolytes are charged ions present within a solution. Their ability to move allows a current to be established within a solution. Tap water conducts electricity because the ions of dissolved solutes are present, while pure distilled water would not conduct electricity since no ions are present. Many molecular compounds form solutions that are nonelectrolytes because the solute does not form ions when it dissolves. Therefore, solutions containing dissolved molecular compounds do not conduct electricity.

 

Self-Check

 

SC 3. Examine the diagram below. Identify where an electrolyte and nonelectrolyte would appear on the chart.

 

A flowchart diagram is shown. The upper box contains the label “Does the solution conduct electricity?” Two branches are shown. The branch labeled yes ends at a box with the label “Does the solution affect litmus paper?” Three branches extend from this box. The first branch has the label “blue litmus turns red,” the box the branch extends to contains the label “It’s an acid.” The second branch has the label “No change to red or blue litmus.” the box the branch extends to has the label “It’s a neutral compound.” The third branch has the label “Red litmus turns blue.” The box at the end of the branch has the label “It’s a base.” The second branch from the first box is labeled “no,” the box at the end of the branch is labeled “It’s a neutral molecular solution”.

 

Check your work.
Self-Check Answers

 

SC 3.

 

A flowchart diagram is shown. The upper box contains the label “Does the solution conduct electricity?” Two branches are shown. The branch labeled yes ends at a box with the label “Does the solution affect litmus paper?” To the left of this box is the answer label “Electrolyte.” The second branch from the first box is labeled no. The box at the end of the branch is labeled “It’s a neutral molecular solution.” To the right of this box is the answer label “Nonelectrolyte.”