Record whether the solution resulted in the light shining brightly, dimly, or not at all. A bright light indicates that the solid is an electrolyte; no light at all indicates that the substance is a nonelectrolyte. Based on this data alone, indicate whether your substances are ionic or molecular.
Melting Point. Pour a small amount of each of your unknowns on a piece of weighing paper or onto a watch glass. Tap the open end of a melting point tube into each of your unknowns so that about 2 to 3 mm height of your unknown is in the melting point tube.
Make sure that the temperature of the melting point apparatus is below o C. Place the tube in the melting point apparatus and turn on the heating dial to about 5. Look through the magnifying glass and record the temperature at which the solid just begins to melt and the temperature at which the sample has completely melted. This is known as the melting point range. If the unknown does not melt by o C, discontinue heating the sample and record the melting point as simply being greater than o C.
Make sure that you turn off the melting point apparatus. Some samples, especially molecular compounds, decompose before they melt. This is observed by the sample becoming charred. If the sample begins to char, record the temperature at which charring begins and discontinue heating. Color and Odor. Record the color and odor of each of your unknowns. This is one more piece of data that along with several others may help you in identifying the unknown.
Color or odor alone will not indicate whether a substance is ionic or molecular. A drop of hot cooking oil spattered on your arm causes brief, minor discomfort, whereas a pot of hot oil yields severe burns. Both the drop and the pot of oil are at the same temperature an intensive property , but the pot clearly contains much more heat extensive property. You may have seen the symbol shown in Figure 4 on containers of chemicals in a laboratory or workplace.
The system details flammability, reactivity, health, and other hazards. Within the overall diamond symbol, the top red diamond specifies the level of fire hazard temperature range for flash point. The blue left diamond indicates the level of health hazard. The yellow right diamond describes reactivity hazards, such as how readily the substance will undergo detonation or a violent chemical change. Each hazard is rated on a scale from 0 to 4, with 0 being no hazard and 4 being extremely hazardous.
While many elements differ dramatically in their chemical and physical properties, some elements have similar properties. We can identify sets of elements that exhibit common behaviors. For example, many elements conduct heat and electricity well, whereas others are poor conductors.
These properties can be used to sort the elements into three classes: metals elements that conduct well , nonmetals elements that conduct poorly , and metalloids elements that have properties of both metals and nonmetals. The periodic table is a table of elements that places elements with similar properties close together Figure 4. You will learn more about the periodic table as you continue your study of chemistry.
All substances have distinct physical and chemical properties, and may undergo physical or chemical changes. Physical properties, such as hardness and boiling point, and physical changes, such as melting or freezing, do not involve a change in the composition of matter. It is quite difficult to define a chemical property without using the word "change".
Eventually, after studying chemistry for some time, you should be able to look at the formula of a compound and state some chemical property. For example, hydrogen has the potential to ignite and explode given the right conditions—this is a chemical property. Metals in general have the chemical property of reacting with an acid. Zinc reacts with hydrochloric acid to produce hydrogen gas—this is a chemical property.
The more general term for rusting and other similar processes is corrosion. Other terms that are commonly used in descriptions of chemical changes are burn, rot, explode, decompose, and ferment. Chemical properties are very useful in identifying substances. However, unlike physical properties, chemical properties can only be observed as the substance is in the process of being changed into a different substance.
Physical properties include color, density, hardness, and melting and boiling points. A chemical property describes the ability of a substance to undergo a specific chemical change. To identify a chemical property, we look for a chemical change. A chemical change always produces one or more types of matter that differ from the matter present before the change. How does the chemical structure of water relate to its unique properties?
What properties of water cause surface tension? How do acids and bases affect the hydrogen ion concentration of a solution? How can acids and bases be identified and named? Why is hydrogen important to life?
Why is water an important solvent for living things? What is the significance of the high specific heat capacity of water?
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