Testing the pH of Substances

 

 

Background:

pH is a measure of how many hydrogen atoms are in a solution. Acids generally have low pH’s while bases have high ones. Water tends to be neutral. The pH scale ranks acids and bases according to their strengths. The strong acids and bases are on complete opposite sides of the scale.

 

Purpose:

In this lab, students will:

·       Investigate the pH’s of a variety of substances

·       Learn how to use a pH meter

 

Materials:

-10 mysterious substances

-pH meters

-beakers

-pH paper

-paper towels

-water

 

Procedure:

1)     At each station/table, there will be a pH meter along with a mysterious substance.

2)     Press the On button of the pH meter. A 0.0 should appear on the screen.

3)     Take the pH meter out of the water and place the pH meter in the mysterious substance. The electrode must be covered to get a correct reading.

4)     Record the pH of the meter in data Table A. But, DO NOT SMELL THE SUBSTANCE!

5)     As a group, discuss what you think the liquid is based upon the pH reading and place the data in Table A. Use the pH scale for help.

6)     Then, in Table A write the reasons that led you to guess the substance.

7)     Place the pH meter back into the water beaker.

8)     The teacher will instruct you to rotate stations every five minutes. Wait for instruction.

 

Data:

 

Table A: pH Recordings

Station Number	pH Recording	Probable Liquid	Reasons Why?
1
2
3
4
5
6
7
8
9
10

 

Graph A: pH vs Station Number

Make a line Graph of the different pH’s at the different station. Place the Station Numbers on the x Axis and the pH’s on the y axis.

 

Conclusions:

In a paragraph, summarize what you observed in the lab. Include what stations had the highest and lowest pH’s. What were these substances and how could you tell?

 

 

Extension:

Answer the following questions in complete sentences in your lab report.

 

1) The stomach is filled with hydrochloric acid, which helps in digestion (breaking down food). What would happen if you were to eat a food that was really basic? Why?

 

 

2) For a dare, you drank a gallon of lemon juice. What do you think would happen to your stomach? Why? What should you do immediately following the dare?