Forest Ecology Pre-site Activity #1

Forest Ecology - Pre-site Activities/Teacher Led

Grade Level: 5
Content Area: Science
Time to Complete: 45 minutes
Title of Lesson: Using pH

South Carolina State Standards Addressed:

I.A.2.b.	Arrange objects in sequential order.
I.A.3.a.	Use standard (U.S. customary and metric) to estimate and measure mass, length, area, perimeter, volume, and temperature to the nearest whole unit (quantitative observations).
I.A.4.a.	Use drawings, tables, graphs, written and oral language to describe objects and explain ideas and actions.
I.A.5.a.	Explain or interpret an observation based in data and prior knowledge.
I.A.6.a.	Use prior knowledge and observations to identify and explain in advance what will happen.
I.A.7.a.	Devise a statement of assumption, based on observations, experiences, and research, that can be supported or refuted through experimentation.
I.B.1.c.	Use appropriate tools and techniques to gather, analyze, and interpret data.

Lesson Description:

Students will conduct activities to learn how to determine pH of water, and conduct an experiment to determine the pH level of different solutions.

Focus Questions:

1.	What is pH?
2.	What is a pH scale?
3.	Why is it important to know if a substance is acidic (acid) or basic (alkaline)?
4.	What are some factors that could affect the pH level of a lake or stream, or of soil?

Culminating Assessment:

Students will be able to draw and label the pH scale, and arrange sampled liquids based on resulting pH readings.

Materials/Equipment:

Provided	Recommended liquids to get
pH paper strips (35 per class)	tap water
50ml graduated beakers	distilled water
50 ml	milk
vocabulary	vinegar
	Coke or other soft drink
	orange juice or other juices

Teacher Preparation:

1.	Read background information.
2.	Be prepared to introduce pH.
3.	Collect and label different liquids for students to use to determine pH.

Background Information

The pH is a measure of how much acid is in a liquid. ‘H’ refers to hydrogen ions. Hydrogen is a common element that along with oxygen forms water (2 hydrogens + 1 oxygen = H²O).Water molecules can split, and at any instant in liquid water some water molecules break apart into positively charged hydrogen ions (H+) and negatively charged hydroxide ions (OH-). When they dissolve in water, acidic substances such as lemon juice release more H+ than OH-. Substances categorized as basic release more OH- than H+ when they dissolve in water. Thus, the more hydrogen ions that are formed in a solution, the more acidic it becomes. Scientists use a number line called the pH scale to rank the acidity of a fluid or substance. Pure water (not rain water or tap water) always contains the same number of H+ and OH- ions. This condition may occur in other fluids, and signifies neutrality. We assign neutrality a value of 7 at the midpoint of the pH scale, which ranges from 0 (most acidic, highest H+ concentration), to 14 (most basic or alkaline, lowest H+ concentration. Starting at neutrality, each change by one unit of the pH scale signifies a ten-fold increase or decrease in the H + concentration. The pH indicator strips change colors depending on the acidity or alkalinity of the substance being tested.

0	7	14
Acid	Neutral	Basic

The pH level is an important abiotic (nonliving) factor in determining what can live in a place. Animals have pH ranges within which they can live. Some can live in fairly acidic water or soil with a pH of 4. Others, like salamanders need a pH level closer to 6, or almost neutral. Knowing the pH of water is important in determining the quality of the water. Factors that can affect the pH of lakes, streams and forest soils include the amount of rainfall, the amount and types of leaves that fall (leaves contain tannic acid), and the type of soil near the lake or stream. Some minerals in soil can stabilize pH, acting as a buffer to counter shifts in acidity. Pollution can change pH. Knowing the pH is also important because very acidic solutions, like battery acid, and very basic solutions, like lye, are harmful to humans.

Procedures:

1.	Discuss pH as a measure of the acidity level in a liquid, and explain how to use the pH scale to determine if a sample is an acid, base, or neutral.
2.	Demonstrate to students the correct and safe way to use equipment, avoiding spills, cross-contamination of samples, and not drinking anything in the lab.
3.	Divide students into groups of 4 or 5. There are enough pH strips for 6 groups, with each group using 5 strips, and 5 beakers (use a new pH strip for each sample).
4.	Have students predict the pH level of each liquid.
5.	Collect 30 ml samples of five liquids to use during activity.
6.	Students dip one strip of ph indicator paper into a liquid for at least 1 minute, and compare all the segments to the chart on the back of the indicator paper box. Try to match all segments to the chart.
7.	Students record the pH reading.
8.	Students draw a pH scale, and arrange sampled liquids according to resulting pH readings.
9.	Discuss the important role of pH levels in determining what plants and animals can live in a place, since different organisms have different tolerances for acidity. Discuss factors that determine or change pH levels in water or soil, and the importance of knowing pH levels when assessing water or soil quality.
10.	With the students, come up with a statement of assumption that can be supported or refuted through experimentation. For example, “Solutions containing fruit juice will be more acidic than those not containing fruit juice, because fruit juices sometimes cause lips to sting, suggesting that maybe they are acidic.”
11.	Wash and dry the beakers.