Module 7 Exam Review ANSWER KEY
1. Define acid. (7.01)
An acid is a substance that produces hydrogen ions, H+ or hydrodium ionsH3O+ in solution.
2. Compare the three theories of acids. (7.01)
An Arrhenius acid is a substance the increases the concentration of hydrogen ion, H+ or hydronium ions H3O+when dissolved in water. You must have water. A BrØnsted-Lowry acid is any substance that donates a hydrogen ion, H+ to another substance. A Lewis acid is any substance that accepts a lone pair of electrons. Yes, this is the same Lewis that wrote the Lewis Dot Structures in module 3.
3. What makes an acid to be classified as a ‘strong’ acid? (2.01) A strong acid is one that breaks apart close to 100% when in solution. HCl is an example. When HCl is dissolved in water, it breaks apart into H+ and Cl- ions. Not all acids break apart. Those chemicals that do not break apart well are considered ‘weak’ acids.
4. List three general properties of acids. (7.01)
Acids have a sour taste, they are corrosive, acids are electrolytes, acids react with active metals (group 1 or 2) to produce hydrogen gas, H2 and acids react with bases to produce salt and water.
5. Compare the three theories of bases. (7.01)
An Arrhenius base is any substance that increases the concentration of hydroxide ions (OH-) when dissolved in water. A BrØnsted-Lowry base is one that accepts a hydrogen ion, H+. A Lewis base is any substance that donates a lone pair of electrons.
6. List 2 weak acids. (7.01)
Ammonia, NH3 and pyridine, C5H5N
7. List three general properties of bases. (7.01)
Bases have a bitter taste, bases react with acids to produce salt and water (also called a neutralization reaction), and solutions that are basic feel slippery.
8. Identify the BrØnsted-Lowry acid and base in the forward reaction below. (7.01) HCl + NaHCO3 H2CO3 + NaCl
HCl is the BrØnsted-Lowry acid; NaHCO3 is the BrØnsted-Lowry base.
9. Write the neutralization reaction of hydrochloric acid and sodium hydroxide. (7.02) This requires segment 1 knowledge of common charges, polyatomic ions and writing formulas (lesson 3.08) HCl + NaOH H2O + NaCl
10. What salt is produced when phosphorous acid (H3PO3) reacts with lithium hydroxide (LiOH). (7.02) The salt is the ionic compound formed. So, we must write the full reaction to determine the salt. H3PO3 + LiOH H2O + Li3PO3 The salt formed is lithium phosphite, Li3PO3
11. What is the pH range for acids? What is the pH range for bases? (7.02) Acids have a pH range of less than 7; bases are higher than 7. On the pH scale, 7 is neutral. An acidic solution will have a greater hydrogen ion than hydroxide ion concentration; a basic solution has a greater hydroxide than hydrogen ion.
12. What could you do if you needed to increase the pH of solution? (7.03) You could add a base, thereby increasing the hydroxide ion concentration.
13. If 35.4 mL of LiOH with an unknown concentration is neutralized by 32.0 mL of 0.250 M HCl, what is the concentration of the LiOH? Show all work. (7.02) Since this is a simple neutralization reaction, we can use the following formula: M1V1 = M2V2. V1 = 35.4 mL LiOH
M1 = ? M LiOH
M1V1 = M2V2
V2 = 32.0 mL HCl
(? M LiOH) (35.4 mL LiOH) = (0.25 M HCl)(32 mL HCl) M2 = 0.205 M HCl M LiOH = 0.226 M
14. What is the pH of a solution with a concentration of 5.3 X 10-4 molar H3O+? Show all work. (7.03) The formula is: pH = - log [H3O+]
pH = - log (5.3 X 10-4)
pH = 3.275
15. Describe what a titration is. (7.03)
A titration is a laboratory technique used to calculate the concentration of a chemical. You are performing an acid-base neutralization reaction. For example, let’s say we have some HCl that we do not know the concentration. We can react it with a base, such as NaOH. You start by placing the substance of a known concentration in a buret, such as a 0.25 M NaOH solution. Then,...
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