Chemical and Physical Changes — Answer Key
Part A: Multiple Choice
Circle the best answer for each question.
1. A Grade 5 student mixes sand and salt in a bowl. Which method best separates them?
A) Burn the mixture to remove the salt
B) Add water, filter the sand, then evaporate the water to get the salt
C) Wait for the mixture to chemically react and split apart
D) Use a magnet to pull out the salt
Adding water dissolves the salt; filtering catches the sand; evaporating the salty water leaves the salt behind, separating both parts of the mixture.
2. Which best describes salt water as a type of mixture?
A) A chemical compound formed from salt and water
B) A solution where salt is evenly dissolved in water
C) A pure substance with one kind of particle
D) A precipitate of salt at the bottom of the cup
Salt water is a solution because the salt particles spread out evenly and cannot be seen, but they are still salt — a physical mixture.
3. A baker notices the cake batter has risen, browned, and smells different after baking. Which change happened?
A) Only a physical change, because the batter was just heated
B) A chemical change, because new substances with new properties formed
C) No change, because the ingredients are still in the cake
D) A reversible physical change that can be undone by cooling
Browning, rising, and a new smell are signs of new substances forming, so baking is a chemical change.
4. Which scenario is a physical change rather than a chemical change?
A) A nail rusts after sitting in water for a week
B) A log burns in a fireplace and turns to ash
C) A glass of water evaporates and leaves it empty
D) Milk turns sour after sitting on the counter
Evaporation changes liquid water to water vapor — same substance in a different state — so it is a physical change. The other choices form new substances.
Part B: Fill in the Blank
Write the correct answer on each line.
1. A mixture is a combination of two or more substances that are physically mixed but not chemically combined.
Mixtures keep the original properties of each substance and can be separated without a chemical reaction.
2. When salt dissolves evenly in water, the result is called a solution because one substance is spread evenly through another.
A solution is a special mixture in which a solute dissolves uniformly in a solvent.
3. To get the salt back from salt water, you can evaporate the water until only solid salt remains in the dish.
Evaporation removes the water, leaving the dissolved salt behind, showing the change was physical.
4. Mixing iron filings and sand can be separated using a magnet to pull the iron out of the mixture.
Magnetic separation uses the magnetic property of iron to pick it out of a mixture without changing either substance.
5. Because mixtures and solutions can be separated again, mixing two substances together is usually a physical change, not a chemical one.
Physical changes do not create new substances, so most mixing and separating processes are physical changes.