The Science Notebook
Solids

  Home   Terms of Use   Safety  Contact Us   Experiment Pages   Downloads   Supplies   Useful Links!


 On this page...
SOLIDS
Examining a Solid
 
CHANGE OF STATE
 Changes in State
Sublimation
Changing the Melting Point of Water by Using Salt
Changing the Melting Point of Water by Using Pressure
 
TYPES OF SOLIDS
Amorphous Solids
Crystalline Solids
Growing Salt Crystals
Growing Sugar Crystals
One More Crystal Growing Experiment

SOLIDS

On this page, we will investigate solids, one of the three states of matter.  (There are investigations on the other two states - liquids and gases - elsewhere on this site.) 

A solid object has a definite volume and a definite shape. 


Examining a Solid

 

Materials Needed: A small wooden block such as a baby block; ruler.

Procedure: Look at the block.  You immediately see that it has a definite shape that does not change unless you do something to change it, such as carving a piece off of it.

Measure the length, width and height of the block.  You can calculate the volume of this block by multiplying it’s length times it’s width times it’s height.  Depending on the units you used, your answer will be in cubic inches or cubic centimeters.  Calculate the volume of your wooden block.  (For more information, go here on the Mesuring Volume page.

What Happened: Like a liquid, a solid has a definite volume.  But unlike a liquid, the shape of a solid will not change depending on what kind of container it is in.  In fact, a solid does not need a container to hold it’s shape.


CHANGE OF STATE

By now you know that matter exists in three states or forms on earth - solid, liquid and gas. (There is a fourth state of matter, called “plasma”, but this state only exists at very high temperatures, and it is usually associated with stars.)  Many substances can exist in all three states, but usually are found in only one in nature. For example, most metals are found as solids in nature, but metals can be melted by heating.  If you get them hot enough, they can even become gases.  But not all metals are solid at room temperature.  One metal, mercury, is a liquid at room temperature.  It is a silver colored and is often used in thermometers.

The air we breathe is a mixture of oxygen, nitrogen, and carbon dioxide gases.  All three of these gases may be cooled down to form other states.  Oxygen may be cooled to a very cold   -183 ºC to form  liquid oxygen. Nitrogen becomes a liquid at -196 ºC.  And if you cool carbon dioxide to about -79 ºC, it will form a solid.  We know this solid carbon dioxide as “dry ice”.

There is one substance, however, that can exist in all three states at a fairly narrow range of temperatures.  That substance is water, and it will allow us observe changes in state without having to produce extreme temperatures.


Changes in State


CAUTION!  Always be careful to follow all safety precautions when using a stove, and use with adult supervision only!

Materials Needed: Stove; small pot; ice; small room thermometer; candy thermometer. (A single lab thermometer that will measure at least from 0 ºC (32 ºF) to 100 ºC (212 ºF) may be substituted for both.)
  
Procedure: Fill a small pot about half full of ice.  Place the room or lab thermometer in the ice and measure the temperature.

Place the candy or lab thermometer in the ice and slowly begin to heat the ice on the stove until it melts and begins to boil.  Notice the temperature at which the water boils.

What Happened: You have just observed one of the most common compounds on the surface of the earth change from solid to liquid to gas.  As a substance goes from one state to another, we say that it “changes state”. 

Water has a definite temperature at which the solid form - ice - will melt.  This is called the “melting point”.  This is the same temperature at which liquid water will freeze.  This point is called the “freezing point”. For water, the freezing and melting point are 0 ºC (32 ºF).

Water also has a definite point at which it will begin to boil and change to it’s gas form - water vapor.  This is called the “boiling point” and is 100 ºC (212 ºF).

When you measured the temperature of the ice, it was probably very near 0 ºC (32 ºF), and when you measured the temperature of the boiling water; it was probably very close to 100 ºC (212 ºF).  However, the temperatures you measured might not have been exactly those, for a couple of reasons.  First, you thermometer may not be calibrated exactly.  Second, these points, particularly the boiling point, are also affected by air pressure.  These temperatures for freezing/melting and boiling are for sea level.  If you live in an area that is high above sea level, the temperature at which water boils will be several degrees lower.  If you live in one of these areas, you have to cook many foods for a longer time because the water isn’t as hot when it boils at a lower temperature.


Sublimation


Not all substances go from the solid state to the liquid state. Some go from the solid state directly to a gas.  This process is called “sublimation”.

CAUTION!  Mothballs or moth flakes are poisonous if eaten. Keep them away from younger children or pets!

Materials Needed: Mothballs or moth flakes; small bowl or other open container; thin cloth.

Procedure: Place a couple of mothballs or a spoonful of moth flakes in a small open container.  Place this container in a dry open area such as a garage and observe it over couple of days.  Mothballs have a very strong smell that most people find unpleasant, so you probably should not leave these out in the open on the inside.  Tape a piece of thin cloth over the container so that animals can’t get to them and be sure to keep them out of the reach of younger children.  (See caution.)

What Happened: Over a period of time, you saw the mothballs get smaller.  If you were using moth flakes, you probably saw the amount of solid flakes appear to decrease.

Many mothballs and moth flakes are made of a chemical called “naphthalene”.  Naphthalene does not melt unless it is heated.  When it is exposed to air, it will sublimate directly from a solid to a gas.  If you are anywhere near the mothballs, you can easily smell this gas because of its unique odor.

Going Further: Snow will often sublimate directly to water vapor when the atmosphere is dry, even if the temperature is less than the freezing point of water, 0 ºC (32 ºF).  If you live in an area where the weather is cold and dry, you may see several inches of snow a day appear to vanish without melting. Try placing a pan of ice cubes out on a sunny day when the temperature is below freezing and there is a breeze. Place the pan in the shade, and observe the pan from time to time for a few hours.  Do the ice cubes decrease in size? Do you see any liquid water?


Changing the Melting Point of Water by Using Salt


Materials Needed: Ice cube; salt. 

Procedure:   Pour a little salt onto the ice cube and observe what happens.

What Happened: The ice began to melt.  Salt lowers the melting point of water, so although the temperature of the ice is 0 ºC (32 ºF), it begins to melt. This principle is used when salt is sprinkled on an icy bridge to melt ice.  It is also used when making homemade ice cream.  When salt is added to the ice, it begins to melt, but in the process, the temperature of the ice and salt water mixture decreases and is actually less than 0 ºC (32 ºF).  This helps the ice cream mix freeze faster.


 Changing the Melting Point of Water by Using Pressure


Materials Needed: Ice cube; string; two large rocks or other weights; two cold glasses.

Procedure: Tie the two rocks to either end of a 15 cm (6 in) piece of string.  Place two glasses in a freezer for about 15 minutes to chill them.  Place the ice cube between the two glasses on the edge of each.  Place the string across the ice cube so that the weights hang down freely.  Observe the ice cube for a few minutes.

What Happened: The ice under the string began to melt.  This was due to the pressure from the string created by gravity pulling the two rocks.  As the melted water flowed back over the string, it refroze.  If you waited long enough, the string passed completely through the ice cube.  You may also have noticed that the cube melted some where it came in contact with the edge of the glasses. If so, this was also due to the pressure on the ice due to its wn  weight and the weight of therocks and string.  You had to chill the glasses to keep that melting to a minimum.


TYPES OF SOLIDS

Solids may be classified as either amorphous or crystalline.  An amorphous solid does not have as definite a melting point as does a crystalline one.  Instead, as it reaches it’s melting point, it begins to soften and then finally becomes a liquid.  Metals are usually amorphous, and so is glass.  Paraffin, or wax, as we will see in this experiment, is also amorphous.


Amorphous Solids



CAUTION!  Always be careful to follow all safety precautions when using fire, and use with adult supervision only!  Keep your alcohol lamp or candle in an aluminum pie pan, and keep the flame at least three feet away from anything that can burn, unless otherwise instructed.

Materials Needed: A small piece of paraffin or candle wax; lid from a food tin; candle or alcohol burner with safety pan; pliers or tongs; tooth pick.

Procedure:   Place a small piece of the paraffin or wax on a food tin lid.  Press this lump with the tooth pick.  How much does it “give”?

Using the pliers or tongs, hold the wax and tin over the flame for just a second or two.  Remove from the heat source and press with the tooth pick again.  Is there any difference? Return the wax and tin to the flame and hold it a little longer.  Again press with the tooth pick.  Is there any difference now?

Repeat this process holding the wax over the heat a bit longer each time until the wax melts.

What Happened: Since the paraffin or candle wax is an amorphous solid, it gradually softens as it approaches it’s melting point.


Crystalline Solids


Materials Needed: Salt; a good magnifying glass or a microscope.

Procedure: Observe several grains of salt under a magnifying glass or microscope.  What shape are the grains?

What Happened: The grains of salt were all box shaped.  Ordinary table salt is a chemical compound called “sodium chloride”.  In it’s solid form, it is “crystalline”.   In other words, it forms crystals.  Crystals of different solids may take different shapes, but every substance that forms crystals has it’s own unique shape. 
 
Going Further: Try this experiment with sugar crystals.  Do they look the same as the salt?  Also, look up “crystals” in an encyclopedia or online to see pictures of some other crystal solids.

You may have seen crystal growing kits in a toy store.  These next three experiment will show you how to grow crystals of salt, sugar and Epsom salts for next to nothing, and the crystals you grow can be every bit as impressive as the ones in the expensive kits.


Growing Salt Crystals


This experiment will allow you to grow some large crystals of salt that you can observe without a microscope.

CAUTION!  Always be careful to follow all safety precautions when using a stove, and use with adult supervision only!

Materials Needed: Salt; water; pencil; string; button; small pot; stove; small glass jar or bottle, such as a ½ liter (1 pint) container.

Procedure: Add ½ liter (2 cups) of water to a small pot.  Dissolve as much salt into the water as possible.  Slowly heat the water to boiling and continue to add salt until no more will dissolve.  You should be able to add more than ½ liter of salt to the water.

When you can add no more salt, allow the water to cool enough so that it will not crack the glass container.  Fill the container almost full.  

Pick a button that will not float.  Also, try to avoid a metal button.  Tie the button onto one end of a piece of string.  Tie the other end of the string to a pencil.  The string should be just long enough so that the button will almost reach the bottom when you place the pencil over the jar as shown.

This next step involves a lot of patience!  Place the container and string in a place where it will not be disturbed for several days.  Check your container every few hours the first day, and then once a day for several days.  What do you see?

After there is a good growth of salt crystals on the string, carefully remove the string and place it on a paper towel to dry.  Observe the crystals you have grown.  Do the shapes look similar to the ones you saw under the microscope?

What Happened: The salt water solution you made was a “supersaturated” solution.  By heating the water, you were able to dissolve more salt in the water.  When the water cooled, the salt stayed in solution.  Then, the string gave the dissolved salt a surface to attach to, and individual crystals began to come out of the solution.  As more crystals came out of solution, they attached themselves to the crystals which were already there, and stacked themselves together, something like building blocks, to make the larger crystals.

If you are patient, the crystals you grow from this experiment can be quite large.  It is important to let the crystals form slowly and not disturb them as they are forming.


Growing Sugar Crystals

In this experiment, you will be growing crystals of sugar.  You know this better as “rock candy”.  If you use clean utensils and a food jar or glass that nothing harmful has ever been stored in, you can eat the sugar crystals after you are through studying them.

CAUTION!  Always be careful to follow all safety precautions when using a stove, and use with adult supervision only!

Materials Needed: Same as the last experiment, except substitute sugar for the salt.

Procedure: Follow the same procedure as the last experiment, except use sugar instead of salt.

What Happened: The crystals of sugar were formed in much the same was as the salt, but the shape was different.


One More Crystal Growing Experiment

CAUTION!  Always be careful to follow all safety precautions when using a stove, and use with adult supervision only!

Materials Needed: Same as the last experiment, except this time, use Epsom salts (available from the pharmacy) instead of sugar.

Procedure: Follow the same procedure as the last two experiments to grow crystals of Epsom salts.

What Happened: Again, the crystals formed in the same manner as with the salt and the sugar, but the crystals were of a different shape.  A crystal’s shape is determined by the shape of the molecules of the substance which makes it, since each molecule has its own unique shape, the molecules fit together only one way.  The shape of crystals is one tool that scientists use to identify different crystalline substances.

Now that you know a little something about solids, why not visit our Liquids page?  Or, if you like, you can see what else there is to do on our Experiments page.

"The Science Notebook"  Copyright 2008-2017 - Norman Young