Introduction: (Initial Observation)
It often happens that people want to dry up something or somewhere, or they want to prevent drying for some other reasons. If sugar, salt or other chemicals be able to affect the evaporation of water, we can use them to decrease or increase the evaporation of water as we need it. In this experiment we will only test salt and sugar, because they are easily available at home. However many other chemicals are available for industrial use and can be tested for their affect on the evaporation of water.
If we find a chemical that can accelerate the evaporation of water and is environmentally safe, we may be able to use that to dry wetlands such as marshes or swamps and convert them to usable land. Also if we find something that can reduce the rate of evaporation, we can use them in dusty areas to keep the dust moist and heavy, creating a cleaner environment.
Information Gathering:
Find out about evaporation and factors that affect the rate of evaporation. Read books, magazines or ask professionals who might know in order to learn about the effects and applications of salt, sugar or any other material that you may want to test for this purpose. Keep track of where you got your information from.
Some links are offered here:
http://www.foodsci.uoguelph.ca/dairyedu/evapdehyd.html#evap3
Each sodium and chlorine ion actually is surrounded by a shell of water molecules held by strong ionic attraction between the ion and the polar water molecule. This attraction (hydration energy) is nearly as strong as that which the sodium and chlorine ions have for one another (this is why salt so readily dissolves in water). Therefore, the water molecules in this hydration shell are not as free to evaporate as those in a solution of pure water. The net effect is that there are fewer water molecules available for evaporation. This phenomenon is known as Raoult’s Law (Adams, 1973).
Source…
Question/ Purpose:
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.
We often need to control or modify the physical properties of different substances. For example in winter we want to stop water from freezing. In car radiators we want to stop water from boiling. Evaporation is another condition that we may want to control. For example the owner of a wet land may want to make it dry as fast as possible while the maker of modeling clay may want to keep it moist as much as possible. Such changes in the rate of evaporation of water may be controllable by adding chemicals such as salt and sugar.
The purposes of this project is to find out the effect of salt and sugar on the evaporation of water.
Identify Variables:
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 that we add to water. Values are salt, sugar, nothing.
Dependent variable (also known as responding variable) is the time it takes for each water to fully evaporate.
Controlled variables are heat, moisture, wind (air flow). In other words all test samples will be evaporated at the same temperature and the same level of air flow.
For the method of evaporation, you can let the waters evaporate naturally without any excess heat or air current. or you may choose to use heat or airflow to expedite the evaporation process.
Hypothesis:
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.
This is a sample hypothesis.
My hypothesis is that both salt and sugar will reduce the rate of evaporation. This hypothesis is based on my observation of using salt in winter to melt snow. I have noticed that after the snow gets melted the ground dries up, the area around the remained salt on the concrete remains wet for a longer time.
Note that the results of your experiment may show that your hypothesis is wrong.
Another way to write your hypothesis is:
If we add salt to the water, then the evaporation rate of water will reduce.
Experiment Design:
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:
Test the effect of salt and sugar in evaporation of water.
Material:
- 3 petri-dishes or any other flat identical plastic containers.
- 1 graduated cylinder or any other similar measuring device
- some sugar and some salt
Procedure:
- Place 25 ml water in each petri-dish.
- Label your dishes with “Water”, this is also the control
- Label two other dishes with “Salt water” and “Sugar water”
- In the dish labeled with salt add half teaspoon salt. shake or stir it carefully and slowly.
- In the dish labeled with sugar add half teaspoon sugar. shake or stir it carefully and slowly.
- Place all 3 dishes somewhere safe at room temperature and record date and time.
- Inspect the dishes every day until you see the one of them is dry. Record the date and time.
- Continue you observation until the second dish is also dry. Record the date and time again.
- Continue your observation until the last dish is dry. Record date and time and enter the final results of your experiment in a table lime this.
| Water | Salt Water | Sugar Water | |
| Dried after this number of days and hours |
Note: The amount of water in all three dishes must be the same, but they don’t have to be 25 ml. Change it to any amount that is best for your dishes.
Because of a cold weather it took more than a week for the water to evaporate. After completion of evaporation, we had some salt and some sugar crystals left on dishes containing salt water and sugar water.
Make a bar graph:
Use your results table (above) to make a bar graph with 3 vertical bars. Each bar represents one of the columns in your results table. Name the bars Water, Salt Water and Sugar Water. The height of each bar is the number of days or the number of hours it took for the solution to dry.
Also make sure to read the Chart and Graph instructions in the “How to Start” section of the control panel.
Experiment variations:
The same experiment can be done using test tubes or cups. If you are using a warm space (such as a low temperature oven) for your evaporation experiment, you may see that the water in all 3 petri-dishes are fully evaporated in your first observation. In this case using test tubes or cups are better choices. Start with same amount of water in each test tube. Add small amounts of sugar and salt to the first and second test tubes. Do not add anything to the third test tube. Mark the water level in all test tubes. Place them in a warm place and let them evaporate at the same conditions. Make observations and record the rate of evaporation after certain period of time.
If you are using cups for your evaporation experiment, add one or two table spoon sugar or salt in each cup. For test tube experiment, one teaspoon sugar or salt is enough.
Picture in the right shows a similar setup using glass graduated cylinders instead of test tubes.
Initial volume of liquid in each cylinder was 10 ml.
Cylinders were placed in an oven at 90ºC for 24 hours.
Following table shows how much of each liquid evaporated in 24 hours at 90º Celsius.
| Liquid | Evaporated in 24 hours |
| Water | 4 ml |
| Sugar Water | 3.8 ml |
| Salt Water | 4.2 ml |
Materials and Equipment:
Material:
- 3 petri-dishes or any other flat identical plastic containers.
- 1 graduated cylinder or any other similar measuring cup
- some sugar and some salt
- a room thermometer (optional)
Test tubes, petri dishes and graduated cylinders are available at MiniScience.com and other science project stores.
Results of Experiment (Observation):
Write which water dried faster?
Calculations:
If you do any calculation, write your calculation in your reports
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.
Conclusion:
This conclusion is the result of my experiment and some gathered information about salt.
When salt is dissolved in water, each salt molecule breaks up into one sodium ion (Na+) and one Chloride ion (Cl-). Just like magnets, charged particles are attracted to other particles of opposite charge that might also be floating around in solution. What you may not be aware of is that water molecules can also act like weak magnets and have both positively and negatively charged ends. When water molecules evaporate they have to absorb enough energy from their surroundings to break free of the attractive forces of the other molecules around them. When salt is dissolved in the water however, much stronger magnetic forces are present to hold the water molecules together. To break free (or evaporate) the molecules will require more energy than before the salt was added. For your experiment, you are adding the same amount of energy to each container but now the molecules in the salt water need more energy per molecule to break free. This means that fewer molecules will have evaporated from the salted solution. Another experiment that demonstrates this phenomenon is the temperature at which water boils when it is salted as opposed to when it is not salted.
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.
Possible Errors:
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.
References:
Visit your local library and find books related to physics. Look for topics related to evaporation. The effect of different substances (chemicals) on evaporation is often studied in Chemi Physics or physical chemistry.
