Properties and Classification
What two characteristics must something have to be considered matter?
Matter has mass and occupies space (has volume).
What is mass, and what is a common metric unit used to measure it?
Mass is the amount of matter in an object; common units include grams (g) and kilograms (kg).
What is the main difference between a physical change and a chemical change?
A physical change alters form, size, or state without forming a new substance; a chemical change forms one or more new substances.
State the law of conservation of mass.
Mass is conserved during a physical or chemical change; in a closed system, total mass remains the same.
Which state of matter has a definite shape and a definite volume?
A solid.
Explain why air in an inflated basketball is matter even though you cannot see it.
Air has mass and occupies space; the ball becomes inflated because the air takes up space.
How is mass different from weight?
Mass measures the amount of matter; weight is the force of gravity acting on an object.
Why is melting ice considered a physical change?
The state changes from solid to liquid, but the substance remains water (H₂O).
Why can a reaction appear to lose mass when it produces a gas in an open container?
The gas can escape into the surroundings, so not all products are included in the measurement.
Why does a liquid take the shape of its container but keep a definite volume?
Its particles are close together but can move/slide past one another, so the liquid flows while maintaining nearly the same volume.
A student describes a sample as shiny, silver-colored, and able to conduct electricity. Are these observations about physical or chemical properties
Physical properties; they can be observed without changing the substance into a new substance
A sample has a mass of 36 g and a volume of 12 cm³. Calculate its density.
Density = mass ÷ volume = 36 g ÷ 12 cm³ = 3 g/cm³.
Classify each change: cutting paper and iron rusting. Give one reason for each.
Cutting paper is a physical change; rusting iron is a chemical change because a new substance forms.
In a sealed container, the total mass before a reaction is 85 g. What should the total mass be after the reaction?
85 g, assuming the system remains sealed and the measurement is accurate
Use a particle model to describe how particles are arranged and move in a gas.
Gas particles are far apart and move freely in constant random motion, spreading to fill the available container.
Two samples look alike, but one is magnetic and the other is not. Why might magnetism help distinguish the samples?
Magnetism is a characteristic physical property that can help identify or distinguish materials.
Sample A has a mass of 20 g and a volume of 10 cm³. Sample B has a mass of 30 g and a volume of 10 cm³. Compare their densities.
A = 2 g/cm³; B = 3 g/cm³. Sample B is denser because it has more mass in the same volume.
A sample bubbles and changes temperature when mixed with another substance. Why should a scientist consider more than one observation before deciding a chemical reaction occurred?
Bubbles or temperature change alone are not conclusive; the scientist should consider multiple pieces of evidence and whether new substances formed.
A student measures 50 g before a reaction and 46 g afterward in an open cup. Give a possible explanation that is consistent with conservation of mass
A gas may have escaped from the open cup, or material may have spilled; the mass of the whole closed system would be conserved.
A solid ice cube keeps its shape, but liquid water flows across a plate. Explain the difference using particle arrangement and motion.
In ice, particles are held in fixed positions and vibrate; in liquid water, particles remain close but can move past one another.
A student says, “If I cannot see it, it is not matter.” Evaluate the claim using scientific evidence.
The claim is incorrect. Air and other gases are matter because they have mass and occupy space.
A student claims the larger object must be denser because it has more mass. Is the claim supported? Explain.
No. Density depends on mass per unit volume. Both mass and volume must be considered.
A student says every change that can be reversed is physical and every change that cannot be reversed is chemical. Evaluate this rule.
The rule is not reliable. Reversibility alone does not determine whether a change is physical or chemical; evidence of new substance formation matters.
A student concludes that mass was destroyed because the measured mass decreased in an open container. Is this a strong conclusion? Why or why not?
No. The student must account for matter that may have left the measured system, such as gas or spilled material.
A student says gas particles expand in size when a gas fills a larger container. Evaluate this explanation.
Incorrect. The particles themselves do not expand; they move farther apart and spread throughout the available space.