# 4 15 15

Topics: PH, Acid, Hydronium Pages: 2 (320 words) Published: April 16, 2015
﻿Name: Brent Creager
Date: 4-15-15
Unit Test, Part 2
Answer the questions below. You may use a scientific calculator for this test. When you have finished, submit this assignment to your teacher by the due date for full credit. (5 points)
1. Explain what is in a buffer. Discuss the function of a buffer. How will pH change when small amounts of acids or bases are added to the buffer solution? Answer: A buffer is an aqueous solution consisting of a mixture of a weak acid and its conjugate base or a weak base and its conjugate acid. Its pH changes very little when a small amount of strong acid or base is added to it and thus it is used to prevent changes in the pH of a solution

(5 points)
2. Cooks use baking soda to make cakes light and fluffy. You might have used baking soda yourself. Baking soda is NaHCO3. A 0.1 M solution of baking soda in water has a [H+] of about 4.0 × 10–9. (You may prefer to think of the hydronium ion concentration, [H3O+], as 4.0 × 10–9.) Write the formula for the calculation of pH, and then show each step as you calculate the pH of a 0.1 M solution of baking soda. Answer: pH = -log [H⁺] ←←[log without a specified base means log base 10] They give that a 0.1 M solution of NaHCO₃ has a hydrogen ion concentration of 4.0 x 10^(-9)

so pH = -log (4.0 x 10^(-9))

pH = 8.4

(5 points)
3. Before tackling this problem, be sure you know how to find the antilog of a number using a scientific calculator. A solution has a pH of 5.4. Write the formula you will use to calculate the [H+] and then show all your work leading to the determination of [H+]. Answer: pH = -log[H+]

[H+] = 10^(-pH)
3.98 * 10^-6 M