Which Freezes Faster? Water or Salt Water?

Introduction: (Initial Observation)

Freezing time and freezing temperature of different liquids are among the most important physical properties of that liquid. These physical properties may change when other material are dissolved in or mixed with liquids. This project will discover this subject using water and salt that are both safe and available in most households. We will perform some experiments and see which one freezes faster? water or Salt water?

Information Gathering:

Find out about freezing point of different material. Read books, magazines or ask professionals who might know in order to learn about the factors that may affect freezing time and freezing temperature. Keep track of where you got your information from.

As a part of information gathering we may want to perform some initial experiments to find out what happens during the freezing process of water. Simply place a cup of water with a thermometry on that inside the freezer and check it’s condition every five minutes. Conditions that you check are time, water temperature and water condition (frozen or not).

During this initial experiment you may make the notes like this:

C means Celsius or Centigrade
F mean Fahrenheit

The above experiment shows that in about 35 minutes water temperature drops to 0º C and then water freezes and in about 50 minutes the temperature of frozen water gets to -4ºC.

Also this experiment shows that the freezing temperature of distilled water that we used for our test is 0ºC.

What we learn from this experiment is that if the salt be able to increase the freezing temperature of water (from 0ºC to 5ºC for example) then water will freeze faster because it gets to that temperature in 25 minutes instead of 35 minutes. But if salt decreases the freezing temperature to a negative number such as -2º C, then it will take more time for water to freeze because it takes more time (about 45 minutes) to get to that temperature.

Remember that all these times depends on how cold your freezer is. Your results might be different.

Q. How did you type º ? I don’t have this on my keyboard!

A. Hold Alt in your keyboard while entering 167 on your numeric keypad of your keyboard (Those are numbers on the right side, not on the top row.)

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.
The purpose of this experiment is to determine the effect of salt on freezing temperature of water. Possibilities are no effect, slow down freezing and accelerate freezing.

Question:

Which one freezes faster, water or Salt water?

Identify Variables:

Both water and salt water that we choose to test must initially be at the same temperature. Also they must be the same amount. So our constants are:

• The amount of water
• Initial temperature of water
• temperature of freezer

Water type is an independent variable (also called manipulated variable). We call it independent because we set it or decide about it. This variable has two possible values (pure water and salt water)

Freezing point is a dependent variable because it depends on the type of water. What we are really doing here is testing the effect of salt on freezing point of water. (Freezing point means freezing temperature).

Hypothesis:

Based on your gathered information, make an educated guess about which one freezes faster? Water or Salt water?

A sample Hypothesis:

I believe, by adding Salt to the water, we will slow down freezing. My hypothesis is based on my previous observations that salt can melt ice and snow and prevents forming ice on the sidewalks in winters.

Experiment Design:

Perform an experiment to test which one freezes faster, water or Salt water.

Procedure:

Put a bowl on the counter and measure exactly one-quarter cup of water and pour the water into into a plastic cup. Fill up 6 cups in this way. All pouring and measuring should be done over the bowl to catch any excess waters.

It does not matter if you do your experiment with one quarter cup or more. What matters is that all cups must have the same amount of water. Try to have at least one inch of water at the bottom of each cup.

Mark two cups as “water”. Add one teaspoon Salt each to two other cups and mark them as ” Low Salt”. Add two teaspoon Salt each to the last two cups and mark them as “High Salt”. Stir the Salt until it is fully dissolved in water.

To do this experiment precisely you need to make sure that all your test samples (water and salt water), are at the same temperature. To do this, place them into the refrigerator for a long period of time before continuing this experiment. Also, at this time set the freezer to the desired temperature and do not change it until the experiment is done. I recommend to turn it as high as possible.

Then, place all 6 cups in your freezer equidistant from the freezer cooling radiators. Check every five minutes until you notice that they are starting to freeze. Now, check every minute. Once fully frozen, remove from freezer and record time immediately so you don’t forget it. Record the results in a table like this:

Note: As you noticed you don’t have to use a thermometer in this experiment, however if you have access to a thermometer that can display low temperatures, you may also record the temperature. If you have 6 thermometers, you may use one in each cup. Otherwise use thermometer only in your initial experiment or in one of the cups. You can not use one thermometer for multiple cups because it can transfer salt from one cup to the other.

Make a graph:

You may make a bar graph to visually present your results. Make one vertical bar for each liquid or each solution you test. The height of each bar will show the freezing temperature of the liquid it represents. Make sure to name each bar with the name of one of the liquids.

Materials and Equipment:

• 1 Large Bowl
• 1 1/8 Measuring Cup
• 1 ¼ Measuring Cup
• 1 Gallon of Water
• 6 Identical Containers such as plastic cups
• Supply of Salt
• 1 Freezer
• 1 Refrigerator
• Cleaning Tools (Towel, Soap, etc.)
• Thermometers (optional)

Results of Experiment (Observation):

          Measuring- All of the test samples will be a quarter of a cup. They will all be placed in identical containers and will be placed  equidistant from the cooling source inside the freezer. The time the waters take to freeze will be measured in minutes.

Data- The times that it took for all samples to start freezing and freeze completely is in this table.

Since we used two samples for each test we need to calculate the average of the results of each two identical sample. We write the average in a table like this and use that to draw a graph.

All of the freezing times were higher after adding Salt. In this experiment the amount of Salt was my independent variable. The dependent variable in my experiment was the freezing time. The Salt increased the freezing time. The graph below shows visually the time difference. (This graph is just a model and is not made based on real data. You need to do your own experiment and come up with real data)

Calculations:

In order to calculate the averages, we add two results and divide it by two. For example if one of the low Salt water samples froze in 27 minutes and the other froze in 29 minutes, add them up it becomes 56, then divide it by two the final result is 28.

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:

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.

This is a sample conclusion:

From this experiment I conclude that Salt does indeed slow down the freezing process. All the data in the above table and graphs show this. By studying the freezing times I have determined that my predictions about the effect of Salt in freezing of water must be correct and my hypothesis is supported from all the data and observations. Although most of my predictions were only inferences, I still believe them to be correct because they are supported by the data.

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 any possible books related to water, salt, general chemistry, chemical physics. Find out how different substances may affect the freezing point of water.

List such books in your bibliography as your references.

You must also include your online resources and electronic resources such as websites and encyclopedias on CDROMs.