Title: pH and Hydroponics

Discipline: Physical Science

Ability: 8^th Grade

NJ Core Curriculum Content Standards:

5.1 A, B, 5.5, 5.6, 5.8 A

Objective:

Students will gain an understanding of what the pH of a solution tells us. They will also learn what hydroponics is and why controlling the pH of hydroponics system is important for plant growth.

Note: This lesson was done with 8^th grade physical science class only

Materials:

Bean seeds; plastic cups; Perlite-inert medium

Aquarium pH increaser; Aquarium pH decreaser

Electronic pH probe; Wooden Popsicle sticks

Discussion:

What is hydroponics? The growing of plants without soil

Usually the nutrients and water is in the soil. Supply the plant with everything it needs-nutrients, light, water, support, correct pH then the plant will be healthy as possible without soil.

Soil- plants are expected to find the nutrients they need, if it is even there.

Hydroponics-nutrients given directly to plants in the proper amounts.

Nitrogen, Potassium, Phosphorous

Hydroponics= allows total control over pH, nutrients and nutrient strength. Don’t have this with soil

What is necessary for hydroponics?

• Inert growing –what the roots of the plant grow in, provides support. Plants get nothing from the medium. Very different from soil! Soil has control over the amount and type of nutrients and pH the plants are getting.
• Water
• Nutrient solution

Many different H systems. Us= passive system- no moving parts. Nutrients solution is drawn into the growing medium by the plant roots.

Why is hydroponics useful?

In areas where the soil is not good for farming, can grow crops using hydroponics. Can use hydroponics in space to grow fresh fruits and vegetables.

Control of pH is extremely important in hydroponics.

PH- a measure of how acidic a solution is. “The power of Hydrogen”- concentration of hydrogen ions in a solution.

Ion- if an atom does not have an equal amount of electrons and protons it will have a charge. More electrons, Neg charge. More protons, Pos charge.

Water molecule- 2 Hydrogen atoms and 1 oxygen atom

What is an Acid? Acid (HCL) is poured into the water; it gives up Hydrogen (H+) to the water to make hydronium (H3O+)

An acid has more hydronium in it.

H⁺ + H2O→H3O⁺

Separates into H+(positive ion) CL –(negative ion).

Acids- Hydrochloric acid, battery acid, vinegar

What is a BASE?

Base (NaOH) poured into water gives up a hydroxide ion(OH-) to the water

Abase has more OH- in it

Bases- bleach, Baking Soda

PH scale- ranges from 1(acidic) to 14(basic or alkaline). 7 is neutral. A change in one pH unit means a tenfold change in concentration.

Optimum pH level for plants. PH not at proper level= plants lose ability to absorb nutrients.

Activity:

We had been growing bean plants hydroponically for 2 weeks before we did this lesson. The beans had sprouted and were ready to be put in perlite. Mrs. G and I set up 8 different solutions at different pH levels from 4.5 to 8.5. In order to reinforce the importance of pH when growing plants we had the students decide what pH solution they wanted their plant to grow in. Students worked in groups. Each group planted one bean plant in a cup containing perlite. After the plant was in the perlite the students recorded the height, number of leaves and length of leaves on their plant. Then they placed their plant in the predetermined pH solution. After observing the plants growth for a week and comparing to other plants in other pH solutions, each group had to decide whether they wanted to move their plant to another pH solution or keep it where it was. The students made data tables containing plant and pH and recorded their own data as well as data from each group in the class.

Assessment:

Mrs. G felt the lesson could be improved by having less time between when the students initially planted their plant and their observations. The goal of the lesson might have lost by having so much time between lessons. We also needed a better lighting system