Stainless steel is made by melting iron, chromium and nickel together. The metals spread evenly, and a factory can change how much chromium each batch contains. How is stainless steel best classified?

A flask holds distilled water. Every particle in it is the same, and each one contains two hydrogen atoms joined to one oxygen atom. How are the contents of the flask best classified?

A diving tank is filled with air: nitrogen, oxygen and argon spread evenly through the tank. The shop can raise the oxygen share for a special dive. How is the gas in the tank best classified?

A student stirs sand and iron filings together in a dish. The gray specks stay visible in the sand, and a magnet held above the dish pulls the filings out. How is the sample best classified?

A balloon is filled with helium. Every atom inside has the same atomic number, 2, and nothing in the balloon can be broken down into a simpler substance. How is the gas best classified?

Salt is stirred into a beaker of water until it disappears. Gently heating the beaker until the water evaporates leaves the salt behind as white crystals.

A lab tray holds four samples: brass, orange juice with pulp, aluminum foil, and ocean water. Which sample is a pure substance?

A student stirs two spoonfuls of sugar into a glass of iced tea until the crystals can no longer be seen. Which substance in the glass is acting as the solute?

A nurse prepares saline by dissolving 9 g of sodium chloride in 1000 mL of water. Which substance is acting as the solvent?

A sealed bottle of sparkling water holds carbon dioxide gas dissolved in liquid water. Opening the cap releases bubbles. Which substance in the sealed bottle is the solute?

Sterling silver is a solid solution of 92.5 percent silver and 7.5 percent copper, melted together and cooled. Which metal is acting as the solute?

Dry air is about 78 percent nitrogen, 21 percent oxygen and 1 percent argon and other gases. Treating dry air as a solution, which gas is the solvent?

A bottle of rubbing alcohol is labeled 70 percent isopropyl alcohol and 30 percent water, mixed evenly. Which substance is acting as the solvent in this solution?

To make tincture of iodine, a technician stirs solid iodine crystals into ethanol until every crystal disappears and the liquid turns brown. Which substance is the solute?

In a lab solution of copper sulfate in water, why is the water called the solvent rather than the solute?

Solid A melts sharply at 801 degrees C. Solid B begins to soften near 60 degrees C and finishes melting near 90 degrees C. What do these measurements indicate?

A clear liquid is heated. It begins to boil at 78 degrees C, and the thermometer holds steady at 78 degrees C until the flask runs dry. What does this result indicate about the liquid?

A student draws small samples from the top, the middle and the bottom of one jar of clear liquid. Each sample has a density of 1.03 g per cubic centimeter. What does this evidence best support?

A spot of black ink is placed on filter paper standing in water. As the water climbs, the spot separates into blue, red and yellow bands. What does this show about the ink?

A sample of clear pond water looks exactly the same throughout the beaker, so it must be a pure substance.