Module 8 DBA/Exam Review - ANSWER KEY
Chemistry V22; ID 5657 
Multiple Choice format questions:
1.	What happens to water when it warms above 212 ⁰F? (8.01)
a.	It contracts			c.  Its composition changes
b.	Its density decreases		d.  It forms a gas

212 ⁰F = 100 ⁰C. Water boils at this temperature so we would expect it to form a gas. The density would decrease and expand to fill the container/area. The composition would not change as this is a physical change, not a chemical change. 

2.	Which of the following is a correct property that makes water essential for life? (8.01)
a.	Frozen water is less dense than liquid	
b.	Water heats up quickly compared to other liquids
c.	It has a low surface tension		
d.	It is nonpolar

3.	What is the strongest intermolecular force experienced in water?  (8.01)
a.	London dispersion		c. Capillary action
b.	Hydrogen bonding		d. Cohesion

Be sure to understand all the terms.

4.	Which factor does not generally affect solubility of a solute? (8.01)
a.	Surface tension		c. Surface area
b.	Temperature			d. Pressure

Solid solutes: Increasing temperature and surface area will increase the solubility.  Pressure and surface tension has no effect on solubility.

Gas solutes:  increasing temperature will reduce the solubility.  Think of a can of soda.  If it is open and warms up, the CO2 gas comes out of solution quicker as it is not as soluble. Increasing the pressure will increase the solubility.  Think back to the can of soda. What happens when you open it?  You hear the whoosh as the gas escapes.  When you open the can, the pressure decreases and the CO2 gas is not as soluble. Surface tension has no effect on solubility.

5.	Which of the following is information you need to know to calculate molarity? (8.02)
a.	Liters solute			c. Moles solution
b.	Liters solution			d. Mass solute 		

6.	Which of the following is information you need to know to calculate molarity? (8.02)    
a.	Liters of solute 		c. Total mass of solution             			
b.	Moles solute			d. Moles solution

7.	What is the molarity of a 1.5-liter solution containing 98 grams of HCl? (8.02)
a.	18.2 M				c. 1.8 M
b.	10.2 M				d. 5.2 M

Make a list of what was given:
V = 1.5 L
Mass = 98 g HCl
 
The problem is asking for molarity.  So, we need the formula:
	Molarity (M) =   moles solute    	     	 
                           	   Liter solution

We need the moles of our solute.  The problem gave us grams, so we will need to convert:
98 g HCl  X   1 mole HCl   =   2.688 mol HCl
                                  36.45 g HCl

Now we can use the molarity formula:

Molarity (M) =   moles solute    =  2.688 moles HCl    			
	   Liter solution  	   1.5 L

Molarity = 1.8 M HCl

8.	 If 24.3 grams of NaCl are dissolved in 192 grams of water, what is the concentration of the solution in percent by mass? (8.02)
a.	11.2%				c. 5.3%
b.	9.35%				d. 2.3%

Make a list of what was given:
24.3 grams NaCl
192 grams H2O
 
This is percent by mass, so we need that formula:
% by Mass  =        mass of solute (g)	       X    100       
	Total mass of solution (g)     	                    

% by Mass =         mass of NaCl                X    100    
                   mass of NaCl + mass of H2O

% by Mass =               24.3 g NaCl             X    100        
          24.3 g NaCl + 192 g H2O

% by Mass = 0.1123 X 100
% by Mass = 11.2%

9.	How many grams of zinc metal will react completely with 2.54 L of 4.6 M HCl? (8.02)
Zn (s) + 2 HCl (aq) --> ZnCl2 (aq) + H2 (g)
a.	4.5 g				c. 280 g
b.	380 g				d. 75 g

We start by using the molarity formula to determine moles of HCl:
               M = mol / L            or         mol = M*L
                  
  11.684 mol HCl =  (2.54L)(4.6M)

Now, we take the moles of HCl and convert to moles of Zn using molar ratio (stoichiometry):
           11.684  mol HCl   X   1 mol Zn =  5.842 mol Zn
                                             2 mol HCl

Side note:  the 1 mol Zn / 2 mol HCl comes from the balanced equation-that is what we call the molar ratio)! Review module 5.

We now convert moles of Zn to grams of Zn using its molar mass (see lesson 5.01 for molar mass)
              5.842 mol Zn   X    65.38 g Zn   =  381.95 g Zn which is 380 g (sig figs)
                                              1 mol Zn

Side note:  molar mass is the mass, in grams of ONE mole according to the periodic table

10.	Which of the following is the correct formula for dilution? (8.02)
a.	MsVs = MdVd				c.  MsVd = MdVs
b.	Moles solute / grams solution		d.  Grams solute/ grams solution

11.	Which of the following is true when you make 2.3 liters of a 1.0 molar HCl solution from a 10.0 molar HCl stock solution? (8.02)
a.	The volume of the solvent used was less than 0.7 liters.
b.	The volume of stock solution used is less than 1.0 liter.
c.	The volume of the solvent used is less than 0.2 liters.
d.	The volume of the stock solution used is more than 2.3 liters.

2.3 L HCl   X   1.0 mol HCl   X           1 L stock            =  0.23 L stock is needed
                            1 L HCl          10.0 moles stock

To perform this dilution, we will take 0.23 L of the stock solution and add enough water to form a 2.3 L of a 1.0 M solution.  How much water?  Well, our final volume is 2.3 L and we need 0.23 L of the stock, so:  2.3 L - 0.23 L = 2.07 L water.

To put this in terms of the answers, we will need:

Volume stock used: 0.23 L		Volume solvent used: 2.07 L water 

12.	What is the mass of H2O2 required to make 500. grams of a 3.50% solution of H2O2? (8.02)
a.	23.1 g				c. 17.5 g
b.	147 g				d. 26.2 g
 
Percent by mass =    mass of solute (g)     X  100
                                Mass of solution (g)

3.50% =    mass of solute   X 100
                       500 g
(3.50%)(500) = mass of solute
     100

17.5 g = mass of solute

13.	Define acid. (8.04) An acid is a substance that produces hydrogen ions, H+ or more accurately, hydronium ions H3O+ in solution.
 
14.	What makes an acid to be classified as a ‘strong’ acid? (8.04)    An acid is classified as a "strong" acid if it completely dissociates or ionizes in water, producing a high concentration of hydrogen ions (H+). This means that when a strong acid is added to water, it reacts completely with water to form H+ ions and an anion, resulting in a low pH value.
●	Examples of strong acids include hydrochloric acid (HCl), sulfuric acid (H2SO4), and nitric acid (HNO3). They are very acidic and have a strong tendency to donate a proton (H+ ion) to water or any other base.
●	In contrast, weak acids only partially dissociate in water, producing a smaller concentration of H+ ions. Examples of weak acids include acetic acid (CH3COOH) and carbonic acid (H2CO3). They are less acidic and have a weaker tendency to donate a proton.

15.	List three general properties of acids. (8.04)  
●	Acids have a sour taste: This is because they release hydrogen ions (H+) when dissolved in water, which stimulate the taste buds on the tongue.
●	Acids react with bases to form salts and water: Acids and bases are two classes of compounds that react with each other in a chemical reaction called neutralization. During this reaction, the H+ ions from the acid combine with the OH- ions from the base to form water, and the remaining ions combine to form a salt.
●	Acids conduct electricity: When acids dissolve in water, they release H+ ions and anions, which can carry an electric charge. Therefore, solutions of acids can conduct electricity. The strength of the electrical conductivity depends on the concentration of H+ ions in the solution. Strong acids with a high concentration of H+ ions conduct electricity more effectively than weak acids.

16.	List 2 weak acids. (8.04) Note: be able to recognize weak and strong acids/bases in a multiple choice format and explain them in essay form. Hydrofluoric acid and pyridine, C5H5N

17.	List three general properties of bases. (8.04)  
●	Bases have a bitter taste and a slippery feel: When a base is dissolved in water, it releases hydroxide ions (OH-), which can interact with the taste buds on the tongue to produce a bitter taste. Bases also have a slippery feel because they react with the oils on the skin to form soap-like substances.
●	Bases react with acids to form salts and water: Bases and acids neutralize each other in a chemical reaction that forms water and a salt. During this reaction, the OH- ions from the base combine with the H+ ions from the acid to form water, and the remaining ions combine to form a salt.
●	Bases conduct electricity: Bases also produce ions when they dissolve in water. Hydroxide ions (OH-) can carry an electric charge, which allows solutions of bases to conduct electricity. The strength of the electrical conductivity depends on the concentration of hydroxide ions in the solution. Strong bases with a high concentration of hydroxide ions conduct electricity more effectively than weak bases.

18.	What is the salt and acid, respectively in the following reaction? (8.04)   
HCl + NaOH → H2O + NaCl  
In this reaction, NaCl is the salt and the HCl is the acid.  Acids and bases are reactants; salts and water are formed.

19.	Which of the following is not true for litmus paper indicators? (8.04) Note:  Please be sure to be able to describe the pros and cons for each of the four pH indicators discussed in the video on page 3 of the lesson.
a.	Litmus paper changes color in the presence of an acid or base. 
b.	The litmus paper cannot determine exact pH.
c.	Litmus paper turns blue at the level of 8.2 and higher and determines the substance to be an acid.
d.	The litmus paper turns deep red at the level of 4.5.

20.	 What could you do if you needed to increase the pH of the solution? (8.04)  If you need to increase the pH of a solution, you can add a base or remove an acid from the solution. This will help to neutralize the excess H+ ions in the solution and shift the equilibrium towards the production of OH- ions, leading to an increase in pH. 
●	Add a base: Bases are substances that can accept H+ ions and release OH- ions when dissolved in water. Adding a base to an acidic solution will neutralize the excess H+ ions and increase the pH. 
●	Dilute the solution (see lesson 8.02): Diluting an acidic solution with water will reduce the concentration of H+ ions and increase the pH. This is an effective method for weak acids, which do not completely ionize in water.
●	Remove an acid: Removing an acid from the solution will decrease the concentration of H+ ions and increase the pH. (Check our lesson 1.04 for separation techniques)

21.	Generally speaking, what is the relationship between pH and the concentration of hydrogen ions? (8.04)
a.	Linear; as hydrogen ions increase, the pH increases
b.	Inverse; as hydrogen ions increase, the pH decreases

22.	What is the pH of a solution with a concentration of 5.3 X 10-4 molar H3O+?   (8.05)
a.	3.28			c. 4.56
b.	9.25			d. 2.46

The formula is:  pH = - log [H3O+]
pH = - log (5.3 X 10-4)
pH = 3.275

23.	Which of the following would have a pH of 7. (8.05)
a.	Equal volumes of acid and base			
b.	Equal moles of acid and salt
c.	Equal concentrations of hydroxide and hydronium	
d.	Equal concentrations of salt and water

24.	What is the relationship between pH and concentration of hydroxide? (8.05)
a.	Linear; as hydroxide ions increase, the pH increases
b.	Inverse; as hydroxide ions increase, the pH decreases

25.	A solution has a hydroxide (OH-) concentration of 2.4 × 10−3 M. What is the hydronium (H3O+) concentration of the solution? (8.05)
a.	2.4 × 10−17 M		c. 4.2 × 10−17 M
b.	2.4 × 10−10 M		d. 4.2 × 10−12 M

The formula we need is: [ H3O+ ] × [OH−] = 1.0 × 10−14 M

What we know:  [OH−] =  2.4 × 10−3 M

[ H3O+ ] × (2.4 × 10−3 M) = 1.0 × 10−14 M

Rearrange:   [ H3O+ ] = (1.0 × 10−14 M) 
                                       (2.4 × 10−3 M) 

 [ H3O+ ] = 4.17  × 10−12 M

Essay format questions:
26.	What is the term for when water can move against gravity? (8.01)
a.	Cohesion			c.  Polarity
b.	Surface tension		d. Capillary action

Note: Be sure to be able to describe all terms in your own words

27.	Describe the pH range for acids and bases (don’t give just the values). (8.04) The pH scale is a measure of the acidity or basicity of a solution. It ranges from 0 to 14, with 7 being neutral. 
●	Acids have a pH below 7. The pH range for acids is typically from 0 to 6.9. Strong acids, such as hydrochloric acid (HCl) or sulfuric acid (H2SO4), have a pH close to 0, while weak acids, such as acetic acid (CH3COOH), have a pH closer to 7.
●	 Bases have a pH greater than 7. The pH range for bases is typically from 7.1 to 14. Strong bases, such as sodium hydroxide (NaOH) or potassium hydroxide (KOH), have a pH close to 14, while weak bases, such as ammonia (NH3), have a pH closer to 7.

Honors Extension (MC and Essay format)
28.	(8.06H) Are all renewable resources “clean” resources? 
a.	Yes			b.  No

29.	(8.06H) Which of the following statements is true about the use of coal?
a.	It is efficient and inexpensive.		
b.	It is a renewable resource
c.	This energy source does not pollute the atmosphere.
d.	It is a clean source of energy.

30.	(8.06H )Which of the following statements is true about the use of nuclear power? 
a.	They are very expensive to construct and maintain.
b.	They are relatively inexpensive, but requires lots of land
c.	It is considered clean, but could pollute land
d.	It is a clean source of energy

31.	(8.06H) Which energy best fits this description:  This energy makes use of garbage and agricultural waste while reducing our dependence on fossil fuels.
a.	Geothermal energy			b. Coal
b.	Nuclear Power				d. Hydropower