Wait a few minutes and look again. Have any of the other liquids separated? Alternate procedure: Rainbow in a glass. In the second glass, add two tablespoons of sugar, three in the third glass, and four in the last glass. Then add three tablespoons 45 ml of water to each glass, and stir until the sugar is dissolved. If the sugar in any of the glasses will not dissolve, add one more tablespoon 15 ml of water to all of the glasses, and stir again. When the sugar is completely dissolved, add two or three drops of red food coloring to the first glass, yellow to the second, green to the third, and blue to the last glass.
In the remaining glass we will create our rainbow. Fill the glass about a fourth of the way with the blue sugar solution. Next, carefully add the green solution to the glass.
Do this by putting a spoon in the glass, just above the level of the blue solution. Slowly pour the green solution into the spoon, raising the spoon to keep it just above the level of the liquid, until the glass is half full. Add the yellow solution, and then the red one in the same manner. What do you notice about the colored solutions? That means that there are only water molecules in the liquid. A mixture would be a glass of water with other things dissolved inside, maybe one of those powders you take if you get sick.
Each of the substances in that glass keeps its own chemical properties. So, if you have some dissolved substances in water, you can boil off the water and still have those dissolved substances left over.
If you have some salt NaCl in water and then boil off the water, the salt remains in the pan. The salt is left because it takes very high temperatures to melt salt even more to boil it. Mixtures are Everywhere There are an infinite number of mixtures. Anything you can combine is a mixture. Think of everything you eat. For example, shops sell cartons labelled as 'pure' orange juice. The label means that the contents are just orange juice, with no other substances added.
However, the juice is not pure in the chemical sense because it contains different substances mixed together. In chemistry:.
Hydrogen and oxygen are both gases. Together, as a mixture, hydrogen and oxygen can react and form water. Water is a compound of hydrogen and oxygen. There are important differences between the properties of a mixture and a compound. Vegetable soup is a heterogeneous mixture. Any given spoonful of soup will contain varying amounts of the different vegetables and other components of the soup.
A homogeneous mixture is combination of two or more substances that are so intimately mixed that the mixture behaves as a single substance. Another word for a homogeneous mixture is solution.
Thus, a combination of salt and steel wool is a heterogeneous mixture because it is easy to see which particles of the matter are salt crystals and which are steel wool. On the other hand, if you take salt crystals and dissolve them in water, it is very difficult to tell that you have more than one substance present just by looking—even if you use a powerful microscope.
On the right, the salt crystals have dissolved in the water so finely that you cannot tell that salt is present. The homogeneous mixture appears like a single substance. Identify the following combinations as heterogeneous mixtures or homogenous mixtures. Ordinary table salt is called sodium chloride. It is considered a substance because it has a uniform and definite composition. All samples of sodium chloride are chemically identical. Water is also a pure substance. Salt easily dissolves in water, but salt water cannot be classified as a substance because its composition can vary.
You may dissolve a small amount of salt or a large amount into a given amount of water. A mixture is a physical blend of two or more components, each of which retains its own identity and properties in the mixture. Only the form of the salt is changed when it is dissolved into water.
0コメント