May/June 2017 – Vol. 29 No. 7

Acids and Bases Lab

Posted: Tuesday, February 1st, 2011

by Jeff Bradbury and Patricia Buchanan

Name ____________________

Date _____________________

Partners’ Name ____________

Question: When using materials to clean our house, are the products used usually acidic or basic, Why do you think so?

Purpose: To determine the importance of acids and bases while measuring the pH of different substances.

Part 1 Introduction:

In this lab you will be working in groups of two.

Acids were first recognized as substances that taste sour (The sour taste of lemons and limes is due to citric acid), will dissolve certain metals, and will dissolve some types of rocks.

Bases were characterized by their bitter taste and slippery feel (Hand soaps and toothpastes, for example).

A neutral solution is neither basic nor acidic.  Acids and bases will react together to form neutral solutions.  One can say that an acid will neutralize a base and vice-versa.

Indicators are substances that change color depending on whether they are in an acidic or basic solution.

In today’s lab you will observe some characteristic chemical and physical properties of acids and bases.

SAFETY

Safety goggles must be worn at all times. Hydrochloric acid, HCl, and acetic acid, HC2H3O2 can harm eyes, skin, and clothing.  Handle with care.  Any acid spilled on the skin or splashed into your eye should be rinsed with a large volume of water. NaOH and NH3(aq) solutions are corrosive to the skin and can harm your eyes.  Any base spilled on the skin or splashed into your eyes should be rinsed with a large volume of water.

Measuring pH with pH (Universal indicator) paper:

In your spot plate, obtain a sample (half-fill the wells) of each of the solutions shown in the table below.  Dip a small (1cm) piece of Universal Indicator paper into each well.  Record the color of the paper and match the color to the pH scale on the tube of paper.

Measuring pH with cabbage juice:

Make sure there is no Universal Indicator paper in the solution wells.  Obtain a piece of purple cabbage (one leaf) from the reagent bench.  Break it up into small pieces and boil it in about 150 ml of de-ionized water in a 250 ml beaker.  Add 15 drops of the cabbage juice extract to each of the wells of your spot plate.  Make sure you add the same amount of extract to each well.  Record the color of each solution.

Complete the table that compares the colors of each pH indicator at each pH

Table 1: Chemicals and their pH

Solution Color of cabbage juice Color of pH paper pH
.1 M HCL
.01 M HCl
.001 M HCl
.1 M NaOH
.01 M NaOH
.001 M NaOH
Windex
Milk
Orange Juice
Distilled water
Honey
Vinegar
NaCl
Tap water
Lemon juice

Compare your results with others in your group. Re-test those that are different.

Dispose of all solutions into the sink.

Complete the table showing the color of cabbage juice at each pH. 1-14.

Cabbage juice color pH
1
2
3
4
5
6
7
8
9
10
11
12
13
14

Acid Base Notes

Properties of Acids and Bases
Chemistry of Acids and Bases

Questions and Answers:

1.       Which substances had different pH’s than you expected?

2.       Why are acids and bases important?

3.       Were the household cleaners basic or acidic or both?

4.       What does pH mean to you now?

Jeff Bradbury is a professor of chemistry at Cerritos College in Norwalk and is community college director for CSTA; Patricia Buchanan is the Cal Grip Grant Project Assistant at Cerritos College. The original idea for this activity came from the Los Angeles County Office of Education 15 years ago, which the authors modified.

Written by California Science Teachers Association

California Science Teachers Association

CSTA represents science educators statewide—in every science discipline at every grade level, Kindergarten through University.

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