Unit 9 Review

If you have a beaker with 50 mL of 3M CaO solution, would the number of moles of solute change if you added water to the 70mL mark? 

• Yes, the number of moles of solute will increase because the total solution volume is increasing. 

• No, the number of moles of solute would not increase but the concentration of the solution would increase.

• Yes, the number of moles of solute will increase because the volume of water is increasing. 

• No, the number of moles of solute would not increase because the volume of water has no effect on the number of moles of solute. 

Answer explanation

Remember, concentration is moles/liters. If you add liters of volume, you do not change the moles of solute, but you do decrease the concentration by "watering it down"

How many moles of KCl are needed to prepare 7.0 L of a 2.0 M solution? 

• 0.67 moles

• 1.14 moles

• 10.0 moles

• 14.0 moles

Answer explanation

Since molarity is moles/volume, you can rewrite it to say moles = molarity * volume.

Of four different experiments, which of the following pH levels has the highest acidity?

• 1

• 3

• 5

• 6

Answer explanation

Acids have a pH of 1-6 and the lower the pH, the stronger the acidity.

The pOH of a solution is 8.7, calculate the pH 

• 8.7

• 5.3

• 5.7

• 8.3

Answer explanation

pH and pOH add up to 14, so to find one of them, take 14 and subtract from the pH/pOH you DO have.

• 9.3

• 7.6

• 11.4

Answer explanation

The formula for pH is:

-log[H], where [H] is the concentration of Hydrogen.

The pH of bleach is approximately 12.7.  Which of the following best describes bleach? 

• Strong Acid

• Strong Base

• Weak Acid

• Weak Base

Answer explanation

Bases are pH of 8-14 and the higher the number, the more basic it is.

What best describes the solvent in a solution? 

• The substance that absorbs energy

• The substance that releases gas.

• The substance that dissolves

• The substance that gets dissolved

Answer explanation

Solvent is the substance that does the dissolving

Solute is the substance that is dissolved.

You are given 4 aqueous solutions.  Each contains 1 mole of the solute, but they have varying amounts of solution: Blue = 5.0L / Green = 3.5L / Yellow = 6.0L / Red = 10.0L.   Which of them would have the highest molarity?  

• Blue

• Green

• Yellow

• Red

Answer explanation

Think of green being the "least watered down" because it has the least amount of volume of water, therefore it will have the highest molarity.

Which information would be the most useful for identifying whether a liquid is acidic or basic? 

• its density

• its pH

• its volume

• its melting point

Answer explanation

pH is the only indicator for acids and bases. Tastes are noted, but not a true indicator.

Vinegar is strongly acidic with a pH of approximately 2.3, so according to the scale it would have a pH closest to _______? 

• Lemon

• Tomato

• Water

• Soap

Answer explanation

Of the substances shown on the scale, lemon was closest to a pH of 2.3.