When you have completed this activity, go to Status Check. Physical Science A Unit 1 Student Activity: Identifying Matter Name Date Objectives In this activity, you will: evaluate data on different physical and chemical properties of matter to determine the identity of unknown substances explain why various substances behave differently under specific conditions Activities Read the following information and, using your knowledge of different physical and chemical properties of matter, answer the questions that follow. Physical Properties. Imagine you are a sculptor and, for your next project, need a that is shiny and easy to bend. Suppose the should also have a very high melting point so that it can withstand a lot of heat. You should realize from the lesson on physical and chemical properties of matter that things such as melting point and boiling point, whether a bends easily, and its appearance are all different physical properties of s. Physical properties are characteristics that can be observed without changing the material. Some physical properties that you should be familiar with are the state of matter, ph, density, melting point, boiling point, brittleness, and hardness. You should recall that brittleness describes how easily different substances break or shatter. For example, you saw in the lesson that glass, which is very brittle, shatters when it is hit with a hammer. In contrast, aluminum, which is not very brittle, does not break, and only changes shape. Hardness describes how hard or soft a is. There are different scales used to measure and compare the hardness of different elements, which you can learn about later. In general, you should know that softer s are easier to bend and shape than harder s are. When you studied the lesson on the periodic table, you learned that s have certain physical properties that can be used to differentiate them from other elements. Two of these properties are malleability and ductility. Malleability is a measure of how easily a can be hammered into different shapes. Gold is the most malleable of all the s. In fact it is so malleable that as little as one ounce of gold can be hammered into a thin sheet about 100 square feet in size! Ductility describes how a can be shaped into wires. Gold is also extremely ductile. One ounce of gold can be stretched into a wire that extends about 8 kilometers in length! You also learned that s are usually good conductors of things such as heat and electricity. Thermal conductivity is a measure of how well a substance can transfer, or conduct, heat. In contrast, electrical conductivity is a measure of how well a substance can transfer electricity. Copper for example, has a high thermal conductivity, which is why it is often found on the bottoms of pots and pans. Copper also has a high electrical conductivity, which is why many electrical wires are made out of copper. In fact, copper has the highest electrical conductivity of any, except for silver. 1
Chemical Properties. In contrast to physical properties, chemical properties of matter describe how a substance behaves in a chemical reaction. Chemical properties include things such as reactivity, solubility, and corrosion. As you know, reactivity is a measure of how a substance reacts when placed with another substance. A chemical reaction occurs when one or more substances changes to form a new substance. For example, table salt is the result of a chemical reaction between two different elements, sodium and chloride. Some substances, such as chlorine, are highly reactive. Mixing chlorine with ammonia can produce a very toxic gas, which is why you should be careful not to mix household cleaning products. However, other substances, such as noble gases, are known as inert. Inert gases are gases that very rarely react with other substances. If you have ever stirred sugar in iced tea, you are familiar with solubility. Solubility is a measure of how much solute will dissolve in a solvent at a certain temperature. If you have studied the lesson on mixtures and solutions, you know that increasing the temperature will usually increase the rate at which solid and liquid solutes dissolve, and decrease the rate at which gases dissolve. You should also recall that a solute is a substance that is dissolved in another substance. A solvent is a substance that can dissolve other substances. For example, salt is highly soluble in water. When you mix the two, salt is considered the solute, and water is the solvent. Other substances, such as gold, have a low solubility in water and do not dissolve as easily. If you have ever seen pipes that look as though they have been eaten away, you are familiar with what is known as corrosion. Corrosion occurs when s break down after repeated exposure to air, water, or even other chemicals. For example, when some s are exposed to oxygen from water or air, they rust, turning a reddish-brown color. Rust forms when the reacts with oxygen, in a process known as oxidation. Corrosion commonly occurs on s such as iron and steel. However, adding things to some s can help prevent corrosion. For example, stainless steel is resistant to corrosion because it is a mix of iron, nickel, and chrome. In contrast, iron by itself is much more likely to corrode. Interestingly, corrosion occurs more quickly in moist air or when the s are exposed to salt. This is why cars near the ocean tend to experience more corrosion than cars farther inland. 2
1. Imagine you are a lab assistant helping Dr. Rusty Mettle identify different types of matter for various experiments that he is performing. Help Dr. Mettle complete his experiments by using the chart and answering the questions that follow. Physical Properties of Various Chemical Elements Element Appearanc e State of Matter @ 25 C Density (kg/m 3 ) @ 25 C Hardness (how easily it bends or breaks) Melting Point ( C) Boiling Point ( C) Electrical Conductivity Thermal Conductivity Argon colorless, odorless, tasteless gas 1.7824 N/A ( )189.19 ( )185.7 low low Barium silver solid 3,510 soft 729 1,898 low low Boron Bromine Calcium Chlorine Copper Fluorine Gold yellowbrown crystal red-brown with bad odor silvery yellowish green reddishorange greenish yellow brightyellow solid 2,340 hard 2,300 4,002 low low liquid 3,119 N/A 7.1 59.25 N/A low solid 1,550 soft 839 1,484 medium medium gas 3.214 N/A ( )100.84 ( )33.9 N/A low solid 8,920 soft 1,084.6 2,567 high high gas 1.69 N/A ( )219.52 ( )188.05 N/A low solid 19,300 soft 1,064.58 2,807 high high Iron silver-white solid 7,874 medium 1,811 3,134 low low Krypton colorless, odorless, tasteless gas 3.71 N/A ( )157.22 ( )153.2 N/A low Mercury silver liquid 13,570 soft 38.72 357 low low Rubidium silver-white solid 1,532 soft 39.64 688 low low Silver silver solid 10,490 soft 961 2,163 high high Sulfur pale-yellow non solid 1,960 soft 115.36 444.75 low low A. Suppose Dr. Rusty Mettle is looking for a that he can bend and shape very easily, which also conducts electricity well. He would like a that has between 15,000 and 20,000 kg per m 3. Which substance or substance should he choose? 3
B. Now, Dr. Mettle is looking for a that he can bend and shape easily. He wants to make wires out of the that will transfer electrical current very well. He can melt some s, but his melting equipment can only reach 1,000 C. Which substance or substances should he choose? C. Dr. Mettle needs a substance that does not conduct electricity well to take up some space in an experiment that requires pressure in the container. He needs a material that will remain in the gas phase unless it is at very cold temperatures. At cold temperatures, the material should change from a liquid to a gas very quickly, as long as Dr. Mettle adds heat. It should also change from a solid to a liquid to a gas within a temperature range of less than 10 Celsius. Which substance or substances could he use? D. Dr. Mettle is trying to identify a that he can pour into thin cylindrical tubes. The material needs to remain in the liquid phase over a wide range of temperatures. It should melt above 30 C but not boil below 350 C. The material needs to be very heavy with a mass of at least 10,000 kg/m 3. Which substance or substances should he choose? E. Dr. Mettle knows that if he tried to mix the element sodium (which is not shown in the chart) with water, it will explode. He needs to identify a different that is not as reactive, does not conduct heat very well, and changes from a solid to a liquid at a temperature between 1,775 C and 2,030 C. Using the information from the table, and this list, which substance or substances should he choose? Most Reactive sodium calcium iron copper silver gold Least Reactive 2. Suppose Dr. Mettle mixed 3 different substances in water labeled substance X, substance Y, and substance Z. Two grams of substance X dissolved at room temperature. When heat was added to the reaction, 3 grams of substance X dissolved completely. Only 1.5 grams of substance Y dissolved at room temperature and when heat was added to the reaction. Substance Z did not dissolve at all and sank to the bottom of the flask at many different temperatures. What does this tell you about the solubility of each of the 3 substances in water? 4
3. Suppose Dr. Mettle found some old pipes in his laboratory that had corroded away. He says that they are made of steel. You compare those with some other pipes that do not look nearly as worn down. He says that those pipes are made out of galvanized steel, which is coated with zinc. What does that tell you about zinc and steel in reference to corrosion? Explain. 4. Suppose Dr. Mettle has 2 flasks that he has filled with a liquid. He added a different gas to each flask but forgot to label them. Unfortunately, both of the gases are colorless, so he can not easily tell them apart. He knows that 1 gas is inert and that the other reacts with many different things. How can Dr. Mettle tell which gas he put into each flask? Explain. 5