Introduction: (Initial Observation)
Sugar, salt, baking soda, Epsom salt and some other solid chemicals can be found at home or local supermarkets. We often dissolve such substances in water before use. For example we add sugar to the tea, milk and other drinks, stir the liquid to dissolve the sugar and then it will be ready to drink.
While adding sugar to my tea, I noticed that some sugar is left at the bottom of the cup after a few minutes of stirring. Obviously I had added too much sugar. But how much is too much? How much sugar can be dissolved in certain amount of water?
Would the result be different if I was trying to dissolve salt or other substances?
This observation made me think about the solubility of substances and I decided to compare the solubility of some household substances in water. I already know that such substances dissolve in water and form a clear solution. Now I want to know if some of them dissolve at a higher rate.
Other uses of solubility:
The rate of solubility can also help chemists to identify a substance. Chemists have already performed experiments to identify the materials that dissolve in common solvents such as water, alcohol, acetone and mineral oil.
For example citric acid and sodium acetate are both white/clear crystals; however, citric acid dissolves in ethyl alcohol while sodium acetate does not. A simple solubility test can help a chemist to distinguish between a sample of citric acid and a sample of sodium acetate.
Find out about factors that may affect solubility. Read books, magazines or ask professionals who might know in order to learn about water and the material that can be dissolved in it. Also gather information about each of the materials that you are testing for their solubility in water. Keep track of where you got your information from.
Following are samples of information that you may find:
|Have you ever tried to dissolve sugar in iced tea? At first, it seems like the sugar has completely disappeared, but if you taste the tea, it tastes sweet! The sugar is still there, but the sugar particles are dissolved throughout the tea.
In the iced tea example, we call the mixture of iced tea and sugar a solution. The sugar that was dissolved gets a special name:”solute.” The solute is simply the stuff that gets dissolved. The ice tea is called the ” solvent,” which means the liquid that dissolves the solute.Source…
Water is a very common solvent. Many substances can be dissolved in this universal liquid due to its polarity. When an ionic or polar compound enters water, it is surrounded by water molecules. The relatively small size of water molecules typically allows many water molecules to surround one molecule of the solute. The partially negative dipoles of the water are attracted to positively charged components of the solute, and vice versa for the positive dipoles. In general, ionic and polar substances such as acids, alcohols, and salts are easily soluble in water, and nonpolar substances such as fats and oils are not. Nonpolar molecules stay together in water because it is energetically more favorable for the water molecules to hydrogen bond to each other than to engage in intermolecular interactions with nonpolar molecules. An example of an ionic solute is table salt; the sodium chloride, NaCl, separates into Na+ cations (electrically positively charged atom or molecule) and. Cl- anions (electrically negatively charged atom or molecule), each being surrounded by water molecules. The ions are then easily transported away from their crystalline lattice into the solution. An example of a nonionic solute is table sugar. The water dipoles hydrogen bond to the dipolar regions of the sugar molecule and allow it to be carried away into solution. The strong hydrogen bonds give water a high cohesiveness and consequently, surface tension. This is evident when small quantities of water are put onto an insoluble surface and the water stays together as drops.
For this project you will need substances such as table salt, sugar, baking soda, flour, and oil in order to dissolve them in water and observe their solubility. You may also chose to use different water temperatures to observe the effect of temperature on solubility. As with any project, you should always research and gather information before you begin.
How useful is this investigation?
Chemists and food scientists use their knowledge of solubility to decide what ratio of different chemicals they can add to a compound in order to obtain the necessary results. They know that excess amount of any substance does not dissolve and cause problems by precipitating in tanks, pipes and valves.
How does it contribute to making something better?
Do you like to have a soda drink in which some unknown particles are floating? That is exactly what happens when a substance is added to a product more than the amount that can dissolve. By knowing the ratios of solubility we can avoid such problems and have better products.
What is the importance of my findings in this project?
For students this is a hands on experiment similar to what scientists do in laboratories. You will not personally benefit from the results. You will only benefit from the method and practice. The solubility of the substances you test in this project are already known and are published in books. By knowing the method, you can repeat this experiment for new substances in future.
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 compare different household chemicals for their ability to dissolve in water. I will compare sugar, salt, Epsom salt, and baking soda.
You may include other chemicals in your study as well. Alum and citric acid are two other substances that can be purchased in a local supermarket.
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.
Independent variable (also known as manipulated variable) is the type of substance. Possible values are sugar, salt, Epsom salt, and baking soda.
Dependent variable (also known as responding variable) is the rate of solubility.
Controlled variable is the temperature. We make sure that all our samples are being tested at the same temperature.
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.
Sugar can dissolve better than other substances. My hypothesis is based on my observation of high viscosity syrups. It seems that adding more sugar will simply increase the viscosity of the solution.
Note that your hypothesis does not have to be correct. Later, the results of your experiments may support or reject your hypothesis.
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: Comparing solubility of Salt, Sugar and Baking soda
[You may use any other group of substances for your study.]
Introduction: The amount of solids that dissolve in water depend on the solubility of the solid in water. If the solubility is high, little or no solids will remain. If the solubility is low, most parts of the solid will remain un-dissolved. In this experiment we dissolve identical amounts of 3 solids in identical amounts of water and then compare the un-dissolved portion of solids.
- Get 3 identical test tubes. Use masking tape and a pen to label them as “Salt”, “Sugar”, and “Baking Soda”.
- Prepare 10 grams of Salt, Sugar and Baking soda and transfer them to the test tubes correspondingly. Measure and record the height of fine powder in each test tube.
- To each test tube add 10 mL water.
- Place your thumb or a rubber stopper on the top of each test tube and shake it for 5 minutes.
- Let all test tubes sit for a few hours so the un-dissolved portion of material will precipitate.
- Estimate the solubility of each substance. To do that subtract the final height of solids from the initial height of solids. Divide the the results by the initial height of solid. See the calculation section for other methods of finding the solubility.
Materials and Equipment:
Material used in the above experiment are:
- 3 test tubes 16 x 150mm
- 1 test tube rack
- 1 digital scale
- 1 10mL pipete
- Baking soda
- Masking tape and pen
Where to find?
Digital scale is available from MiniScience for about $35.00; however, you may use any inexpensive scale that can measure about 10 grams with accuracy of 0.1 gram or better.
Test tubes usually cost less than 50 cents each.
Test tube racks usually cost about $10.00 or less. For your experiment a test tube rack only holds the tubes vertical. If you don’t have a test tube rack, simply place your test tubes in a cup.
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.
Your results table may look like this:
|Matter||Initial Height||Final Height||Height Difference||Solubility rate|
- Initial height is the height of fine powder in test tube before adding water.
- Final height is the height of un-dissolved matter after 5 minutes shaking and about 4 hours sitting for precipitation.
- Solubility is calculated by dividing height difference by initial height.
Use the matter column and the solubility rate column to draw a bar graph. Make one bar for each substance. The height of bar will show the solubility rate of that substance. For example a one inch bar can be used to show 10% solubility. A 2 inch bar can be used to show 20% solubility, and finally a 10 inch bar can show 100% solubility.
The solubility calculation suggested in the above procedure is sufficient for lower grades; however, higher grades and more advanced students may calculate the solubility as described here.
- To all test tubes add enough material such that some un-dissolved substance remain at the bottom of all test tubes even after 5 minutes shaking. In this case the clear solution that stands above the un-dissolved substance is known as a saturated solution. A solution is saturated when it can not dissolve any more solute.
- Get some of each saturated solution and transfer them to separate petri dishes or watch glasses. Measure the mass of each solution.
- Let the water evaporate completely and measure the mass of the remaining solid. Evaporation of water takes many days; however in a warm space, it will be much faster.
- By having the mass of the evaporated water and the mass of the remaining solid, you can determine the solubility rate. Simply divide the mass of the solid by the mass of the evaporated water. In this way the solubility of table salt will be 0.36 .
- This means that 36 grams of table salt can be fully dissolved in 100 grams of water.
12.3 grams saturated solution of salt water is left to dry. After evaporation of all water, 3.26 grams of salt remained. By subtracting 3.26 from 12.3 we can see that 9.04 grams of water is evaporated. Divide 3.26 by 9.04 to find the solubility of salt in water.
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 the 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.
Visit your local library and find chemistry or physics books that discuss solubility. A librarian may be able to help you in finding the right book.
You may also search encyclopedias and online resources to find information about every substance that you would be testing.
Following are samples of online resources: