Solid, Liquid, Gas—Oh My!
Which state of matter has a definite volume but takes the shape of its container?
Liquid
Is a sample containing only pure iron, Fe, a pure substance or a mixture? Explain.
Pure substance. It contains only Iron atoms.
An element conducts electricity and can be hammered into thin sheets. Is it most likely a metal, nonmetal, or metalloid?
Metal. Conductivity and malleability are common metallic properties.
A particle model contains only identical, single atoms. Does it represent an element, compound, or mixture? Explain.
Element. Only one type of atom is present.
A cork floats on water. Is its average density greater than or less than water’s density?
Less than water’s density.
An ice cube melts into liquid water. Is this a physical or chemical change? Explain.
Physical change. Its state changes, but it remains water; no new substance forms.
A student says particles in a solid do not move. Correct the statement.
Solid particles vibrate in place. They do not normally move freely past one another.
Classify fully dissolved salt water and vegetable soup as homogeneous or heterogeneous mixtures.
Salt water: homogeneous. Vegetable soup: heterogeneous.
Where are most metals found on the periodic table? Where are metalloids generally found?
Most metals are on the left and in the center. Metalloids are along the stair-step boundary between metals and nonmetals.
A model contains only identical molecules. Each molecule has one carbon atom bonded to two oxygen atoms. Classify the substance.
A compound: carbon dioxide, CO₂. Different elements are chemically combined, and only one substance is present.
Oil, water, and syrup form separate layers. Oil is on top, water is in the middle, and syrup is on the bottom. Rank them from least dense to most dense.
Oil → water → syrup.
An iron nail develops a reddish-brown rust coating. Classify the change and identify supporting evidence.
Chemical change. Rust is a new substance, and the unexpected color change supports that conclusion.
Identify the state described by each model: A—particles vibrate in fixed positions; B—particles stay close but slide past each other; C—particles move freely throughout the container.
A: solid. B: liquid. C: gas.
Air contains several gases evenly mixed throughout. Is it a pure substance, homogeneous mixture, or heterogeneous mixture? Explain.
Homogeneous mixture. It contains different substances distributed evenly.
Silicon is used in computer chips because of its semiconductor properties. Which classification group contains silicon, and what makes that group distinctive?
Metalloids. They have a combination of properties associated with metals and nonmetals.
A model shows two different kinds of particles evenly distributed throughout the sample. They are not chemically bonded to one another. How should the sample be classified?
Homogeneous mixture. Different substances are evenly distributed.
An object sinks through oil but floats on water beneath it. Compare the object’s density with both liquids.
The object is denser than oil but less dense than water.
Two clear solutions are mixed, and a new insoluble white solid forms. What is this solid called, and what type of change does its formation support?
A precipitate. Its formation supports a chemical change because a new substance forms.
A liquid becomes warmer without changing state. What happens to its particles’ average kinetic energy and movement?
Average kinetic energy increases, and the particles move faster on average.
A student says, “Anything that looks the same throughout must be a pure substance.” Use sugar water to correct the claim.
A homogeneous mixture can also look uniform. Sugar water contains sugar and water, so it is a mixture even when the sugar is fully dissolved.
Neodymium is used in powerful magnets for motors and wind turbines. Identify its classification group and where neodymium appears on a typical classroom periodic table.
Rare Earth element. Neodymium is in the lanthanide row, usually shown below the main table.
A student labels a model of identical O₂ molecules as a compound because the atoms are bonded. Find the mistake and explain the correct classification.
It is an element. Bonded atoms do not automatically make a compound; O₂ contains only oxygen atoms.
Object A floats on water. Object B sinks through water but floats on syrup below it. Which object is denser? Explain using the water as your reference.
B. A is less dense than water, while B is more dense than water.
Boiling water and vinegar reacting with baking soda both produce bubbles. Explain why bubbles support a chemical change in only one of these examples.
Boiling is physical: the bubbles contain water vapor. Vinegar and baking soda react to form a new gas, carbon dioxide, so that change is chemical.
A liquid and a gas are each transferred into a larger container without losing any matter. Compare what happens to their shape, volume, and number of particles.
Both take the shape of their containers. The liquid keeps approximately the same volume; the gas expands to fill the larger container. Each keeps the same number of particles.
Compare pure water (H₂O) with salt water. Which is a pure substance? Which can be separated into its ingredients by physical methods? Explain.
Pure water is a pure substance containing only H₂O molecules. Salt water is a mixture; physical methods such as distillation can separate its ingredients. Physical mixtures can be physically separated.
Match each need to the most suitable group: A—conductive electrical wire; B—carbon and oxygen needed by living things; C—semiconductor for a chip; D—neodymium for a powerful magnet. Choose metals, nonmetals, metalloids, or rare Earth elements.
A: metals. B: nonmetals. C: metalloids. D: rare Earth elements. Their different properties make them useful for different purposes.
Model A contains two substances evenly distributed. Model B contains the same two substances separated into distinct regions. Classify each model and explain why neither is a pure substance.
A: homogeneous mixture. B: heterogeneous mixture. Both contain more than one substance; their distributions differ.
A student says, “If an object sinks in one liquid, it must sink in every liquid.” Evaluate the claim and describe a situation that disproves it.
Incorrect. An object can sink in a liquid less dense than itself but float in a liquid denser than itself. For example, it could sink in water but float on denser syrup.
A student says, “Any temperature or color change proves a chemical reaction.” Evaluate the claim using warm water cooling, food coloring mixing with water, and iron rusting.
The claim is incorrect. Cooling involves thermal energy transfer without forming a new substance. Food coloring mixing changes appearance without forming a new substance. Rusting is chemical because rust forms. These observations must be interpreted in context.