What Happened?
What is a substance made of only one type of atom?
Answer: Element
What is the smallest unit of an element that still has the properties of that element?
Atom
How many elements are in H₂O?
List them
2
Hydrogen
Oxygen
Which area of the periodic table contains most metals?
A. Left side
B. Right side
C. Staircase only
D. Top row
Answer: A
A student says, “A chemical change only happens when a substance changes color.”
Is the student correct? Explain your answer and give an example of another type of evidence.
Answer: No. Other evidence can include gas production, light, precipitate formation, unexpected temperature change, or a new odor.
Is O₂ an element or a compound? Explain.
Answer: Element because it contains only one type of atom: oxygen.
Which element is a metalloid?
A. Sodium (Na)
B. Oxygen (O)
C. Silicon (Si)
D. Iron (Fe)
Answer: C
Crushing a can is what type of change?
Physical change
Why can't burning paper easily be changed back into paper?
A new substance called ash forms during the chemical change.
A student puts an ice cube in a cup. The ice melts, and the student says, “A new substance formed because the ice looks different.”
What mistake did the student make?
Answer: The student confused a change in appearance/state with the formation of a new substance. The ice is still water, so it is a physical change.
A dead leaf becomes brown, develops a new odor, and is broken down by decomposers. Which evidence BEST supports that a chemical change is occurring?
A. The leaf becomes smaller.
B. The leaf changes shape.
C. New substances with different properties are produced.
D. The leaf is moved by decomposers.
Answer: C
1. A student breaks a glass cup into several pieces. The pieces are smaller, but they are still glass. What type of change occurred? Explain your reasoning.
Answer: Physical change because the size and shape changed, but no new substance formed.
How many total atoms are in 2H₂O?
Answer: 6
2. A student leaves a wet towel outside. After several hours, the towel is dry. What happened to the water? Is this a physical or chemical change?
The water evaporated. It was a physical change because the water remained the same substance.
Compare O₂ and CO₂. How are they different even though both contain two oxygen atoms in their formulas?
Answer: O₂ contains only oxygen, so it is an element. CO₂ contains carbon and oxygen, so it is a compound.
Change A: Water is heated until it becomes steam.
Change B: A clear liquid is mixed with another clear liquid. The mixture unexpectedly turns yellow, becomes warm, and produces a new odor.
Which statement is correct?
A. Both are chemical changes because both involve a temperature change.
B. Change A is physical, while Change B is chemical.
C. Change A is chemical, while Change B is physical.
D. Both are physical changes because no solid formed.
Answer: B. Change A is physical, while Change B is chemical.
During an investigation, two substances are mixed. A solid suddenly forms and sinks to the bottom of the container.
Which observation provides evidence that a chemical change may have occurred?
A. The substances were mixed
B. A solid precipitate formed
C. The container was opened
D. The liquid took the shape of the container
B. A solid precipitate formed
3. A student mixes two solutions. A white solid suddenly appears at the bottom of the container. The student did not add any solid to the mixture. What happened?
You must use the sciencetific word.
Precipitate
A student eats an apple. First, the student chews the apple into smaller pieces. Later, enzymes in the digestive system break down the substances in the apple. Which statement correctly identifies the changes?
A. Both are physical changes because the apple is only being broken apart.
B. Chewing is a physical change, while enzyme digestion is a chemical change.
C. Chewing is a chemical change, while enzyme digestion is a physical change.
D. Both are chemical changes because the apple changes.
Answer: B.
A student sees NaCl and says, "There are two molecules because there are two element symbols." What is wrong with this reasoning?
Answer: The two symbols represent two different elements, not two molecules. NaCl is a compound made from sodium and chlorine
A student sees the formula 4NH₃. They say there are 4 nitrogen atoms and 3 hydrogen atoms. What is wrong with their answer?
Answer: The 4 is a coefficient, so it applies to the entire formula.
4NH₃ = 4 nitrogen atoms + 12 hydrogen atoms = 16 total atoms.
An unknown element is shiny, brittle, and can conduct electricity better than most nonmetals but worse than metals. Where would you most likely find it on the periodic table?
Answer: A metalloid, along the staircase.
How many total atoms are in 3H₂O? How many hydrogen atoms and oxygen atoms are there?
Answer:
A piece of metal is cut into smaller pieces. Another piece of metal is heated until it glows and then cools back down. Are these changes physical or chemical? Explain.
Answer: Both are physical changes. Cutting changes the size/shape, and heating changes the temperature/state, but neither creates a new substance.
Which contains more total atoms: H₂O or 2H₂O? How many more?
Answer: 2H₂O.
H₂O = 3 atoms
2H₂O = 6 atoms
3 more atoms