Unit 4 Lib B

Unit 4, Lab 1: Acids, Bases, and pH Buffers

Name: Date:

Experiment 1: Introduction to pH Indicators

Lab Results 

1. Fill in the table with the results from your lab notes.

Experiment #1: Introduction to pH indicators
Solution	Color after addition of bromothymol blue	pH after addition of bromothymol blue
water
acetone
5 M citric acid
5% vinegar
4 M ammonia
diluted bleach

Data Analysis 

2. Based on your results with bromothymol blue, what color would a solution that was pH 13.5 be?

Experiment 2: The Phosphate Buffer System

Lab Results

1. Fill in the following table with results from your lab notes.

Results
	HCl	NaOH
Tube Name	pH	pH after HCl	Change in pH	pH	pH after NaOH	Change in pH
water
NaH2PO4
Na2HPO4
NaH2PO4 and Na2HPO4

Data Analysis

2. Which of the four solutions tested is the best buffer against changes in pH caused by the addition of acid or base?

Experiment 3: The Buffering Capacity of a Phosphate Buffer

Lab Results

1. In the table below, record the results of the pH of the phosphate buffer solution versus the number of drops of HCl acid and NaOH base added to it.

Phosphate Buffer Results
Drops Acid	pH	Drops Base	pH
0		0
1		1
2		2
3		3
4		4
5		5
6		6
7		7
8		8
9		9
10		10
11		11
12		12
13		13
14		14
15		15

2. The strong acid and strong base used in this lab are the same concentration. Thus, the magnitude of the pH change caused by addition of a single drop will be the same on either side of the starting pH. Addition of acid lessens the pH, and addition of base raises the pH.  Construct a graph of the pH versus the number of drops of acid or base added to the phosphate buffer. To show the relative magnitudes, use a negative value for each drop of acid and a positive value for each drop of base. For example, use -7 to write 7 drops of acid and 5 to show 5 drops of base.

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