Schedule

Weekly Web Work #13:

aAcids and Bases – What pHun!

This assignment was due by noon on Friday May 2, 2003.

Submissions are no longer accepted.


1. What strong acid and strong base combine in a neutralization reaction to yield Li2SO4?
 
Strong acid: H2SO4 Strong base: LiOH2  
 2. Pick an acid and a base from the list below. Write a balanced chemical equation for the neutralization reaction using the acid and base you chose. (I know you can't enter subscripts in the box.)
 
  Acid   Base
HNO3 Mg(OH)2
HClO4 Ca(OH)2
HBr Sr(OH)2
 

(Any combination of acid and base chosen from the list above would balance the same way because all the acids are monoprotic and all the bases are dibasic.)
2 Acid + Base --> Salt + 2 water
Example:
2 HNO3 + Mg(OH)2--> Mg(NO3)2 + 2 H2O

3. Assume that your base is available as an aqueous solution with a concentration of 0.200 M. What volume of your base will it take to neutralize 25.0 mL of your acid if your acid is 0.300 M. (Note: The answer is not 37.5 mL) You must explain the steps you used in your calculation.
 

Facts from the question:
acid: 25.0 mL of 0.300 M
HNO3, 0.300 N HNO3
base: 0.200 M
Mg(OH)2, or 0.400 N Mg(OH)2
NAVA = NBVB (Where N is normality and V is volume)

(0.300 N HNO3)(25.0 mL)=(0.400 N Mg(OH)2)(volume of base)
volume of base = 18.8 mL

(Any combination of acid and base chosen from the list above would give the same result because all the acids are monoprotic and all the bases are dibasic.)

4. At the end of your titration in question 3, what substances are present? (Hint: Is there any acid remaining? Any base?)
  Only your salt and water remain.
   
5. Consider a titration of 30 mL of acetic acid (0.200 M) with sodium hydroxide (0.200 M). What volume of NaOH is needed to neutralize the acid?
 

CH3COOH + NaOH --> CH3COONa + H2O

Facts from the question:
acid: 30.0 mL of 0.200 M
CH3COOH or 0.200 N CH3COOH
base: 0.200 M
NaOH or 0.200 N NaOH
NAVA = NBVB (Where N is normality and V is volume)

(0.200 N CH3COOH)(30.0 mL)=(0.200 N NaOH)(volume of base)
volume of base = 30.0 mL

6. What is the salt you are forming? What is the conjugate acid of the anion of this salt?
 

CH3COOH + NaOH --> CH3COONa + H2O
The salt is sodium acetate (CH3COONa). The anion is the acetate ion (CH3COO). The conjugate acid of the acetate ion is acetic acid, (CH3COOH).

7. What volume of sodium hydroxide would be used to get half-way to neutralization?
 

15.0 mL
(It would take 30.0 mL to be neutralized, see the calculation in question 5. Half of 30.0 mL is 15.0 mL.)

8. What substances are present in your flask when you have neutralized half of the acid?
  Acetic acid (CH3COOH) and the acetate ion (CH3COO)
9.

What is the name for the mixture in question 8? (Hint: See page 280 in your text.)

  A buffer. (A weak acid and its conjugate base form a buffer.)




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