ELEMENTS & SYMBOLS
Which element is represented by the symbol Fe?
Iron
What does the formula H₂O tell you about a water molecule?
It contains 2 hydrogen atoms and 1 oxygen atom.
Which is a mixture?
A. Gold
B. Oxygen
C. Salt water
D. Carbon dioxide
C. Salt water
Which is a physical property?
A. Flammability
B. Color
C. Reactivity
D. Ability to rust
B. Color
Ice melts into liquid water. Physical change or chemical change?
Physical change
A scientist records Na on a container. Is the substance an element or a compound?
Element
Which formula represents a compound?
A. O₂
B. He
C. CO₂
D. N₂
C. CO₂
A container holds only one type of compound throughout the entire sample. Is it a pure substance or a mixture?
Pure substance
A scientist measures the boiling point of a liquid. Is boiling point a physical or chemical property?
Physical property
A piece of paper is cut into four smaller pieces. What type of change occurred?
Physical change
Which symbol represents calcium?
Ca
A substance has the formula CaCl₂. How many total atoms are in one formula unit?
3 atoms — 1 calcium + 2 chlorine.
A bowl contains iron filings and sand. Neither substance chemically bonds with the other. How should the bowl's contents be classified?
Mixture
A material can burn when exposed to oxygen. Is its ability to burn a physical or chemical property?
Chemical property
A silver-colored metal develops a new coating after reacting with substances in the air. What type of change is occurring?
Chemical change
A student says O₂ must be a compound because it contains two atoms. Is the student correct? Explain.
No. O₂ is an elemental molecule because both atoms are oxygen.
A student sees the formula C₆H₁₂O₆ and says it represents an element. Fully explain what mistake did the student make?
The formula contains three different elements, so it represents a compound, not an element.
A clear liquid is heated. After the liquid evaporates, sugar remain in the container. What does this evidence suggest?
The original liquid was likely a mixture containing a dissolved substance.
A student describes a mystery substance as shiny, dense, and able to conduct electricity. Are these physical or chemical properties?
Physical properties
A student mixes two liquids. The mixture becomes warm and produces bubbles. What evidence suggests that a chemical change may have occurred?
The temperature change and gas production suggest that a new substance may have formed.
A sample contains only one type of atom. The atoms are bonded together in groups of two. What is the best classification?
An elemental molecule.
Two samples are labeled N₂ and NH₃. Both contain nitrogen. Explain why one is an elemental molecule and the other is a compound.
N₂ contains only one type of atom, while NH₃ contains two different types of atoms chemically bonded together.
Sample A contains only CO₂ particles. Sample B contains CO₂ and O₂ particles. Which sample is a pure substance, and which is a mixture? Please Explain!
A scientist wants to identify whether an unknown substance is likely to react with another substance. Should the scientist focus on a physical property or a chemical property?
Chemical property, because it describes how a substance can react and form new substances.
A substance is crushed into a powder. Another substance produces a gas and a new solid when mixed with a liquid. Which change provides stronger evidence that a new substance formed?
The second change. Gas production and formation of a new solid can provide evidence of a chemical change.