CHEM 151 USF General Chemistry for Science and Engineering Lab Questions
Homework 3CHEM151: General Chemistry for Science and Engineering
Homework set 3 – Total points: 100
Instructions: Please type your answers to the following questions and submit an electronic copy of your
completed assignment on Canvas under Homework Set 1. Points for each question are indicated in front
of the question. Please name your file as CHEM151_HW3_FirstName
This homework set is on the material covered in week 3: Acids and Bases
Question 1 (4 pts)
(Fill in the blank) When added to water, an acid donates ____________________ and a base donates
______________. Name the chemical and write it’s chemical formula.
Question 2 (5 pts)
a. Describe what the equilibrium constant, Ka, of a dissociation reaction (for example an acid added
to water) represents in words.
b. Describe how it is related to the pKa.
Question 3 (5 pts)
a. How can you determine if an acid is strong or weak based on the Ka or pKa?
b. Why is it important to determine if an acid is strong or weak?
Question 4 (3 pts)
List the following acids from STRONGEST to WEAKEST: nitric acid, hydrofluoric acid, carbonic acid,
Question 5 (8 pts)
What is the pH of a solution containing 3*104 mg/L [OH-] (at 25 °C)?
Question 6 (20 pts)
Perchloric acid, HClO4, is a strong acid.
a. Write a balanced equation for this dissociation.
b. Calculate the pH of a solution containing 0.01 M HClO4.
c. What is perchloric acid used for?
Question 7 (15 pts)
Find the hydrogen ion concentration and the hydroxide ion concentration in a baking soda solution with a
pH of 8.5.
Question 8 (20 pts)
Hydrogen sulfide (H2S) is an odorous gas that can be stripped from solution. The reaction is
H2S ⇋ H- + HS-7
The equilibrium constant is Ka = 1.1*10 .
a. Find the ratio of hydrogen sulfide H2S to HS- at pH 6
b. Find the ratio of hydrogen sulfide H2S to HS- at pH 9.
c. At which pH do you have more hydrogen sulfide?
Question 9 (20 pts)
In lab, you made a solution of sodium carbonate (Na2CO3) by adding 0.1 grams to 50 mL of water. Then,
you titrated it with hydrochloric acid (HCl). When the solution changed color indicating the endpoint, you
read the buret and recorded that you had added 15 mL of HCl,
a. How many moles of HCl did you add? How do you know this number?
b. What was the concentration of the HCl? Check your units.