Acids and Bases Exploration Lab

One of the best ways to teach a concept is to allow your students to explore and experiment. In this lab activity, students can discover the acidity of different liquids by exploring the pH scale. This lab can be used as a part of a chemistry lesson or it can be applied to environmental science lessons with acid rain.

Grades: 6-8, 9-12

Background

Acidity is an important concept in chemistry. In order to understand acids, you’ll need to understand protons, electrons, and ions. Protons and electrons are the subatomic particles that make up an atom. Protons have a positive charge while electrons have a negative charge. An ion is an atom or molecule with a net electric charge due to the loss or gain of one or more electrons. Got it? Let’s move on to acids.

Acids are chemical compounds that either donate protons/hydrogen ions or accept electrons. The more hydrogen ions made by an acid means that it has a higher acidic concentration. The fewer ions it produces, the less acidic it is. Bases are chemical substances that release hydroxide ions, accepts protons, or releases electrons (which is quite opposite to what acids do).

We measure the acidity of a substance using the pH scale. The pH scale measures how acidic or basic a substance is on a scale of 1-14. The more acidic a substance is, the lower its pH is, and the more basic a compound is, the higher its pH will be.

Image result for ph scale

What You’ll Need

To do this experiment, I recommend the following materials. There are many more liquids you can test, but these liquids give you a nice range on the pH scale.

  • Litmus paper
  • pH color chart
  • plastic cups
  • tomato juice (pure)
  • vinegar
  • lemon juice
  • distilled water
  • salt water (3 tbs./1 cup distilled water)
  • ammonia
  • milk of magnesia
  • Alka-Seltzer

What to Do

Lab Goals:

  • The goal of this lab is to explore the acidity of different liquid substances and understand the components of acid rain.
  • Each student will test the acidity of different liquids by using litmus paper. Each liquid will be tested three times, and the average of each liquid will be calculated. Students will then compare the results of their experiments to determine the relative acidity of each liquid.

Lab Procedures:

  1. Test each sample of liquid by submerging half of the litmus strip into the liquid
  2. Use the pH color chart to determine the pH displayed on the litmus paper
  3. Record the pH on your paper
  4. Test the liquid two more times and calculate the average of that liquid
  5. Repeat this process for the other 7 liquids provided

Safety Guidelines:

  1. Report all accidents, injuries, and breakage of glass or equipment to the teacher immediately
  2. Do not taste or smell chemicals
  3. No running or horseplay in the lab
  4. Do not lift liquid solutions or equipment above eye level
  5. Follow all instructions provided by the teacher
  6. Long hair must be tied back and closed-toed shoes must be worn

Connecting Concepts

Develop models to describe the atomic composition of simple molecules and extended structures.

PS1.A: Structure and Properties of Matter

  • Substances are made from different types of atoms, which combine with one another in various ways. Atoms form molecules that range in size from two to thousands of atoms.
  • Solids may be formed from molecules, or they may be extended structures with repeating subunits (e.g., crystals).
Apply scientific principles to design a method for monitoring and minimizing a human impact on the environment.*

ESS3.C: Human Impacts on Earth Systems

  • Human activities have significantly altered the biosphere, sometimes damaging or destroying natural habitats and causing the extinction of other species. But changes to Earth’s environments can have different impacts (negative and positive) for different living things.
  • Typically as human populations and per-capita consumption of natural resources increase, so do the negative impacts on Earth unless the activities and technologies involved are engineered otherwise.
Use the periodic table as a model to predict the relative properties of elements based on the patterns of electrons in the outermost energy level of atoms.

PS1.A: Structure and Properties of Matter

  • Each atom has a charged substructure consisting of a nucleus, which is made of protons and neutrons, surrounded by electrons.
  • The periodic table orders elements horizontally by the number of protons in the atom’s nucleus and places those with similar chemical properties in columns. The repeating patterns of this table reflect patterns of outer electron states.
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