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Shaking for Suds: Which Type of Water is the Hardest?

Difficulty
Time Required Short (2-5 days)
Prerequisites None
Material Availability Readily available
Cost Very Low (under $20)
Safety Be sure to wear safety goggles if you are using glass jars for testing.

Abstract

Do you want your hair to be shiny after you wash it? Do you want your clothes to stay bright and soft after laundering, and last a long time? You might think that a special shampoo or detergent can make this happen, but in this chemistry science fair project, you'll discover that how well people and things get clean has a lot more to do with the type of water used for washing than any special shampoo or soap. Did you know that water can be classified as either soft or hard? Soft water lathers and cleans better than hard water. Using this clue, you'll test different common water types to figure out which type is the softest and which is the hardest.

Objective

To determine the relative hardness of different common water types.

Credits

Kristin Strong, Science Buddies

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Last edit date: 2012-12-07

Introduction

Do you love to take a bubble bath filled with thick, hissing suds that you can sink down into? Do you like to take those bubbles and coat yourself from head to toe with white foam until you look like old man winter? Or do you sculpt the bubbles into towers and mountains, or hide your bath toys in them, so that your toys can't get eaten by an evil shark?

Chemistry Science fair project photo shows rubber duckies enjoying a bubbly bath (Wikimedia, 2006).
Figure 1. This photo shows rubber duckies enjoying a bubbly bath. (Wikimedia, 2006.)

However you enjoy your bath bubbles, you might be surprised to learn that when you pour a small amount of liquid bubble soap into the water coming out of your faucet, the amount of bubbles you can make depends upon the hardness of your water. You might be thinking "What? Water isn't hard! You can easily put your hand down into it, right?" That's true, but the term hardness, when used to talk about water has a different kind of meaning. Hardness is a word that geologists and other water scientists, like hydrologists, use to describe how many tiny particles of minerals are in the water.

Minerals are the building blocks of rocks. Minerals are not made by people, but by nature. If you've ever seen a diamond, emerald, or a ruby, you've seen a special and expensive kind of mineral, called a gem. In water, the common minerals that you will find are calcium and magnesium cations (pronounced CAT-eye-un). Cations are atoms that are missing some of their electrons (the negatively charged parts of an atom).


Chemistry Science fair project This photo shows examples of beautiful minerals. (Mila Zinkova, 2007).
Figure 2. This photo shows examples of beautiful minerals. (Mila Zinkova, 2007).

How do these minerals get into water? To understand this, you first need to know a little bit about acids and bases. Pure water is neutral, which means it is not acidic or basic; however, rainwater is slightly acidic, like orange juice. As this slightly acidic rainwater passes through mineral deposits, like the calcium-containing limestone that was used to build the Great Pyramids of Egypt, it reacts with the minerals and changes them into a form that can be dissolved in water, just as you can dissolve a spoonful of sugar in a glass of water. In this way, calcium and magnesium cations get into the water supply.

Is the hardness of water the same everywhere? No, take a look at the map below of the United States from the United States Geological Survey. The areas in deep blue are where the water is the "softest," with low levels of dissolved minerals in the water. The areas in medium blue and white have greater levels of dissolved minerals, and the levels in red are areas where the water is the hardest, with high levels of calcium and magnesium cations in the water. So, if you live in states like Maine, Vermont, the Carolinas, Alabama, or Georgia, you might have never even heard of hard water, but if you live in states like Utah, Wyoming, Colorado, Nebraska, or west Texas, hard water is something you deal with every day.

Chemistry Science fair project This map of the United States shows, by color, where water levels are hardest and softest. The red areas have the most dissolved calcium cations in the water and the hardest water, while the dark blue areas have the least dissolved calcium cations in the water, and therefore, the softest water. (USGS, 2005.)
Figure 3. This map of the United States shows by color where water levels are hardest and softest. The red areas have the most dissolved calcium cations in the water and the hardest water, while the dark blue areas have the least dissolved calcium cations in the water, and therefore the softest water. (USGS, 2005.)


What happens when you have hard water? Well, the harder the water (the more calcium and magnesium hardness minerals you have in the water), the more soap or detergent you need to get things clean. So, if you live in an area with hard water and you want to wash your clothes, dishes, or yourself, it will be harder to get these things clean than if you live in an area with soft water—water without a lot of dissolved minerals. Hard water interferes or reduces lathering (the formation of suds or bubbles). Because of hard water, a film can build up on shower doors and walls, or bath tubs, sinks, and faucets. Hair washed with hard water might look less shiny than hair washed with soft water. Clothing fabrics might be dull, gray, and scratchy, and wear out more quickly. Finally, water pipes in your house, and appliances that use water might not work very well over time because of build-up of hard water deposits. Is it bad to have hard water? No. In fact, the minerals in hard water are thought to contribute to human health. Hard water is mainly just a bother when it comes to cleaning, or in keeping pipes and water-using appliances working well.

So, how do you measure the hardness of water? There are chemistry kits that will tell you approximately how many tiny parts of calcium and magnesium you have in your water, but in this chemistry science fair project, you are going to use liquid soap to compare the hardness of different kinds of water. You will see how much soap you need for each water type to create a bubbly lather of the same height for each.

Terms and Concepts

  • Hardness
  • Geologist
  • Hydrologist
  • Particle
  • Mineral
  • Calcium
  • Magnesium
  • Cation
  • Electron
  • Acid
  • Base
  • Limestone
  • Dissolve

Questions

  • What is the difference between hard and soft water?
  • Is the hardness of water the same everywhere?
  • What problems does hard water cause?

Bibliography

For information about hard water, see these sources:

This source describes what minerals are:

For help creating graphs, try this website:

Materials and Equipment

  • Distilled water (1 gallon)
  • Bottled mineral water (1 gallon), sometimes called "spring water"; not the carbonated kind
  • Tap water (1 gallon)
  • Eye dropper; available at drug stores
  • Liquid dishwashing soap (1 bottle)
    • The kind for washing dishes by hand; not the kind for dishwashers
    • If possible, get regular liquid dishwashing soap; not the "concentrated" kind
  • Shaking jars, cups, or bottles with lids (3)
    • Should be equally sized and equally shaped
    • Any size is a possible option, but smaller sizes (like less than 2 cups) are easier to hold and shake.
    • Can be glass or clear plastic, though plastic does not have the risk of breakage.
    • If you use glass jars, then you will also need safety goggles.
  • If your jars do not have measurement marks on the side of your jars, you will also need:
    • A permanent marker
    • A ruler
  • Lab notebook

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Experimental Procedure

Preparing Your Shaking Jars

  1. If your jars have measurement marks on the side, then you do not need to make any level marks on your jars with a marker. Instead, identify two measurement marks on your jars:
    1. Find one measurement mark that is about one-third of the way up the jar. Write down which measurement mark you chose in your lab notebook. This will be the measurement mark you use to fill up the jar with water.
    2. Find a second measurement mark that is close to the lid of the jar. Write down the measurement mark that you found in your lab notebook. This will be the measurement mark you use to measure the height of the bubbles.
    3. Label the jars with the marker:
      1. You can write down 1, 2, or 3, or write the name of each water type on a different jar, so that you can keep track of which type of water is inside each jar.
    4. You can now go on to the next section, Preparing to Test.
  2. If your jars do not have measurement marks on the side, you will make some measurement marks using a ruler and a marker, so that you can compare the height of the bubbles in each jar.
  3. Using the marker, make a mark on a jar about one-third of the way up the side of the jar.
  4. Set the jar on a table and measure the distance from the table to the mark and write your measurement in your lab notebook.
  5. Using the measurement you wrote down and a ruler, mark the other two jars at the same height. This will be the mark you use to fill your jars with water.
  6. Now make a mark on a jar just a bit below the lid.
  7. Set the jar on the table and again measure the distance from the table to the mark below the lid. Write your measurement in your lab notebook.
  8. Using this second measurement and a ruler, mark the other two jars at the same height. This will be the mark you use to measure the final height of the bubbles in the shaking jar.
  9. Label the jars with the marker.
    1. You can write down 1, 2, or 3, or write the name of each water type on a different jar, so that you can keep track of which type of water is inside each jar.

Preparing to Test

  1. Fill each shaking jar to the first level mark using the appropriate type of water. For example, put distilled water in jar 1, bottled drinking water in jar 2, and tap water in jar 3.
    1. Get down so that you are eye-level with the mark as you are filling the jar.
  2. Create a data table in your lab notebook, like the one below:

Number of Liquid Soap Drops Required to Fill the Jar with Bubbles
Water Type Distilled Water Bottled Mineral Water Tap Water
Trial 1   
Trial 2   
Trial 3   
Average of trials   

Testing Your Waters

Important Notes Before You Begin Testing:

  • If you are using glass jars, safety goggles are recommended in case you drop a jar while shaking it and it breaks.
  • To test your waters, you will add liquid soap, drop by drop, and shake the jars in between the addition of the drops. You will need to decide how many times you want to shake the jar in between the additions of the drops of liquid soap. The most important thing is to shake the jar the same way every time you test. Don't shake it harder or longer at some times than at others. Also, don't wait too long after shaking to add the next drop of soap, since the bubbles will start to pop if they are left to stand.
  • Before you start testing, put the lid on a jar, and, without adding any liquid soap, practice shaking it up and down a few times. Figure out a number of times to shake the jar up and down that feels comfortable to you. It can be three times, five times, or whatever you think is best. Write down in your lab notebook the number of shakes you chose for testing.
  1. If using glass jars, put on your safety goggles.
  2. Add a drop of liquid soap to the jar containing distilled water.
  3. Put the lid on the jar.
  4. Shake the jar up and down the number of times that you chose in your practice.
  5. Set the jar on the table and see if the level of bubbles has reached the second measurement mark.
  6. If the bubbles have not reached the second measurement mark, then take off the lid, add another drop of liquid soap to the jar, and go back to step 3.
  7. If the bubbles have reached the second measurement mark, then stop testing and write down in your lab notebook the total number of drops of liquid soap that you added to the jar.
  8. Repeat steps 3–7 for the jar containing bottled mineral water.
  9. Repeat steps 3–7 for the jar containing tap water.
  10. Rinse your jars out thoroughly with tap water, dry them, and refill them to the first measure mark with the appropriate type of water.
  11. Repeat steps 1–10 two more times, so that you have a total of three trials for each jar. Repeating the trials ensures your results are accurate and repeatable.

Analyzing Your Data Table

  1. Calculate the average number of liquid soap drops that were required to reach the second measurement mark for each type of water. To get the average of the three trials, add up the results for trial 1, trial 2, and trial 3, and then divide by 3. Ask an adult if you need help with this step.
  2. Make a bar chart showing the average number of drops of liquid soap that were required. You can make the chart by hand or use a website like Create a Graph to make the graph on a computer and print it out.
  3. Looking at your chart, which type of water required the fewest number of liquid soap drops to make the bubbles reach the second measurement mark? Which type of water required the most? Which type of water do you think is the hardest? Which type do you think is the softest?

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Variations

  • Test rainwater, river water, ocean water, or water samples sent by your friends or family from different parts of the country.

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