Introduction: (Initial Observation)
We all use the terms ‘acid’ and ‘base’ (or ‘alkali’ instead of base) with ease. We also know that some acids are ‘strong’ and others ‘weak’. This awareness is often reinforced by the hazard labels on the bottles, but that does not really substitute for a degree of theoretical understanding to match this practical awareness!
The terms ‘acid’ and ‘alkali’ were first used in recognition of their properties in solution. Acids possessed a sour taste, and alkalis were able to neutralize or reverse the action of acids.
In this project we will test different liquids for their acidic or basic properties.
Being able to identify the acid – alkali properties of different liquids is a skill that can help us with our health, with our environment and with our safety. The degree of acidity or alkalinity is important for human body, for plants and for the cleaning material that we use. Many antacid products sold in pharmacies may be avoided if we are familiar with the acidity of the food we eat. Balancing the pH in our stomach, in soil and in household cleaning material may be possible with food and household material.
Find out about acids and bases. Read books, magazines or ask professionals who might know in order to learn about the acids, bases and the methods that you can use to identify them. Keep track of where you got your information from.
Following are samples of information that you may find by reading books or interviewing a chemist:
Acids and alkalis are two groups of chemicals. All acids have a sour taste and a strong smell. Remember you must never taste chemicals! Strong acids will burn your skin, and can dissolve metals. Alkalis have a bitter taste and feel soapy.
Strong alkalis will also burn your skin and can dissolve things. Many household substances can be grouped into acid or alkali. We often describe acidity or alkalinity of a substance by its pH.
pH is the measurement of the acidity or alkalinity of a material. This measurement is expressed in a number system of 0 to 14. 0 being the most acidic and 14 being the most alkaline with 7 being neutral.
pH can be measured using electronic pH meters and pH indicator papers. pH meters with accuracy of 0.1 pH cost about $40 and they last a long time. (Left)
pH papers usually sell about $10 and they last for about 100 to 1000 tests. (Right)
How do you use pH papers?
Put each liquid you are testing in a separate beaker. Dip in a piece of indicator paper. The paper will change color depending whether the liquid is acid or alkali. The exact color change will depend on the make of indicator paper, but a general rule is:
- Red – Strong Acid
- Orange – Weak Acid
- Yellow – Neutral
- Green – Weak Alkali
- Blue – Strong Alkali
What do I need for my experiments?
Following are some material that you may use for your experiment:
Some universal indicator paper also known as pH paper
A number of 100ml glass beakers
Various household substances, such as lemon juice, orange juice, vinegar, cola, indigestion tablets (dissolved).
Need background information for your project?
Decide what liquids you want to test. Then gather information about each liquid separately. Information may include a list of ingredients and how they are made for each of the liquids.
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to test different liquid samples and see if most liquids contain either acid or alkali. We will try to test almost every liquid that we can find at home such as dairy products, juices, vinegar, salt solution, baking soda solution, beverages and detergents.
A specific question that you may choose to respond is:
How different household liquids vary in their pH?
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
The in dependent variable (also known as manipulated variable) is the type of liquid that we test to determine its pH.
The dependent variable (also known as responding variable) is the pH of the liquid.
Controlled variables are the temperature and test method. (We test all samples at room temperature and with the same method.)
If you don’t have access to a pH paper or pH meter and you are using cabage
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
My hypothesis is that most material that can be found at home are neutral, weak acid or weak base. This hypothesis is based on the potential hazards of strong acids and bases, so I think that health related government organizations prevent distribution of hazardous material for public use.
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1: (Cabbage Paper indicator)
You may use commercially available pH indicator papers to test different liquids for their acid or alkali contents, but you may also decide to make your own acid-base indicator. In this experiment we use cabbage to make our own indicator paper. Indicator papers that we make can be used in our later experiments to identify acidic or basic liquids found around the house.
- small red cabbage
- a jar (wide-mouthed)
- paper towels
- Shred the cabbage into small pieces.
- Place the cabbage in a saucepan covered with water.
- Bring the water to a boil.
- Allow the cabbage water to cool and strain into a jar.
- Tear strips of paper towel (5 cm in width) and soak them in the cabbage water for 30 seconds.
- Set the strips aside to dry completely.
When the cabbage and water is brought to a boil, the water will turn purplish-red.
Why does this happen?
In this cabbage water, there is a colored chemical that is called an indicator. Scientists use this chemical to indicate if other solutions are acids or bases. Dipping the strips of paper towel into the cabbage water is an easy way to make litmus paper. Your litmus paper can now be used to test other solutions that may be acids or bases! The pre-made litmus paper used in schools is colored by a kind of fungus, from lichen plants.
- 1. Test your “litmus” paper in the experiment, Acid or Base?
- 2. Experiment and make indicators from colored flower petals such as blue iris, violets, violet pansies, red tulips.
- Soak each kind in a cup of hot water for an hour to get the color out
- Test each solution using vinegar as an acid and baking soda as a base
- Observe the changes in color
Never eat or drink your science experiments!
Wear goggles at all times.
Always wear gloves.
This experiment is to be done with teacher or expert adult supervision at all times.
Experiment 2: (Identify liquids that are acid or base)
In this experiment we will use the litmus paper or cabbage water made in our previous experiment to test different liquids for their acidic or basic properties.
- 1-2 cups of red cabbage water *
- a clear colorless glass
- 1 teaspoon of white vinegar
- 1 teaspoon of laundry detergent
- 1 teaspoon of cream of tartar
- 1 teaspoon of baking soda
- 1 teaspoon of apple juice
- ginger ale
- club soda
- lemon juice
- see experiment 1 Cabbage Paper to make red cabbage water
Insert a small piece o litmus paper in different liquids and observe the color change. Red color in an indication for presence of acid and green color indicates the presence of a base. You may optionally use the red cabbage water for this experiment as described here.
- Pour a small amount of red cabbage water into a glass or a test tube.
- Select one of the liquids that you want to test and stir it into the glass.
- Observe what happens.
- wash the glass or use a new glass to repeat the same with every other liquid that you have selected for test.
- If any of the material that you have selected for test are not a liquid, first dissolve them in water and then use the solution for your test.
Depending on the ingredient added to the red cabbage water, the water will turn either green or pink. The concoction will also foam over at some point.
Why does this happen?
Red cabbage contains a chemical that acts as an indicator. Since both acids and bases can dissolve in water, they form solutions that often look alike. Scientists need to be able to identify which solutions are acids and which are bases. The indicator found in red cabbage is used for this. The pink color indicates the presence of acid. The green color indicates the presence of alkali or base.
Never eat or drink your science experiments!
Wear goggles at all times.
Always wear gloves.
This experiment is to be done in-class with teacher supervision at all times.
Materials and Equipment:
List of material can be extracted from the experiment section. You may use clear plastic cups instead of beakers. Lab supplies such as beakers and pH indicator papers may be ordered online or purchased from a local science supplier. Our affiliate online stores include www.ChemicalStore.com and www.ScienceProjectStore.com .
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Record the results of your experiments in a table like this:
Count the number of acidic, neutral and basic substances and write them in the last line of your table.
Make a Bar Graph:
Make a bar graph with 3 vertical bars. Use one bar for each of the three groups. The height of the bar will show the number of samples in that group.
One bar will show the number of acidic substances in your household; the other bar will show the number of neutral substances and finally the last bar will show the number of basic substances in your household.
No calculation is required for this experiment.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
Include a list of references for your report. That can include books, magazines, encyclopedia or internet.