Matter and chemical change

Ten questions of mixed difficulty, covering Matter and chemical change. Print it, or work through it on screen — the answer key starts on its own page.

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Matter and chemical change

Science 9 · maddyhelps.com

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Circle the best answer for each question. Show your work in the space provided.

Solid X melts at 800 °C, and its solution in water conducts electricity. Solid Y melts at 150 °C, and its solution does not conduct. Which conclusion do these results best support?
1. a) X is ionic and Y is molecular
2. b) Both are ionic, since both are solids
3. c) Both are molecular, since both dissolve
4. d) X is molecular and Y is ionic
A student drops identical antacid tablets into equal volumes of water at 10 °C, 25 °C and 40 °C and times how long each one fizzes. The manipulated variable is
1. a) the temperature of the water
2. b) the type of antacid tablet
3. c) the time the tablet fizzes
4. d) the volume of water used
The correct name of the molecular compound N₂O is
1. a) nitrogen oxide
2. b) nitrogen dioxide
3. c) dinitrogen monoxide
4. d) nitrogen monoxide
Steel wool is heated in air until it glows and turns into a dark powder. The powder has more mass than the steel wool had. The best explanation is that
1. a) the steel wool absorbed some of the flame's fuel
2. b) the heat from the flame added mass to the steel wool
3. c) oxygen from the air combined with the iron
4. d) mass is not conserved when a substance burns in air
Which WHMIS 2015 pictogram warns that a product is flammable, meaning it can catch fire easily?
1. a) A flame
2. b) A flame over a circle
3. c) An exploding bomb
4. d) An exclamation mark
An instant cold pack gets cold when you squeeze it to start the change inside. That change is
1. a) exothermic, because it releases energy to your hand
2. b) endothermic, because it gives off thermal energy
3. c) exothermic, because it releases cold into its surroundings
4. d) endothermic, because it absorbs thermal energy
A log burns completely in a fire pit, leaving a small pile of ash that is much lighter than the log was. The best explanation is that
1. a) the ash is lighter because the fire shrank the atoms in it
2. b) burning turned most of the log's mass into heat energy
3. c) most of it left as gases, such as carbon dioxide and water vapour
4. d) the mass was destroyed, and it was given off as the fire's heat and light
Rutherford fired tiny positive particles at thin gold foil. Most passed straight through, but a few bounced back. This showed that an atom
1. a) has electrons that move in fixed levels around the nucleus
2. b) is mostly empty space with a small, dense, positive nucleus
3. c) is a solid sphere that cannot be divided into smaller parts
4. d) is a ball of positive charge with electrons spread through it
Which of these is a chemical change?
1. a) A glass bottle shattering
2. b) Sugar dissolving in hot tea
3. c) A silver spoon tarnishing black
4. d) An ice cube melting in a glass
A calcium atom loses two electrons when it forms an ion. The ion is
1. a) Ca⁺
2. b) Ca²⁻
3. c) Ca²⁺
4. d) Ca⁻

Answer key · Matter and chemical change

Science 9 · maddyhelps.com

a) X is ionic and Y is molecular — Ionic compounds have high melting points and release ions when they dissolve, so the solution conducts. Molecular compounds such as sugar dissolve as whole neutral molecules, so no current flows; dissolving alone tells you nothing about the type.
a) the temperature of the water — The manipulated variable is the one the student deliberately changes, and here that is temperature. The fizzing time is the responding variable, which is measured; volume and tablet type are kept the same, so they are controlled variables.
c) dinitrogen monoxide — Molecular compounds use a prefix for how many of each atom: di- for the two nitrogens and mono- for the one oxygen, which is dropped only when it would come first. Leaving out a prefix names a different compound: nitrogen monoxide is NO and nitrogen dioxide is NO₂.
c) oxygen from the air combined with the iron — The iron combined with oxygen to form iron oxide, so the product includes the mass of the oxygen. Mass is conserved in every reaction; it only seems to change when a gas joins or leaves an open container.
a) A flame — The plain flame means the product itself burns. The flame over a circle marks an oxidizer, a substance that makes other things burn more fiercely, and it is the pictogram most often confused with the flame.
d) endothermic, because it absorbs thermal energy — An endothermic change takes in energy, so the pack draws thermal energy out of your hand and the air, and it feels cold. There is no such thing as releasing cold; cold is just less thermal energy.
c) most of it left as gases, such as carbon dioxide and water vapour — Carbon and hydrogen in the wood combined with oxygen and escaped as invisible gases. Collect those gases along with the ash and they weigh more than the log did, because oxygen from the air joined in: mass is conserved even when it looks lost.
b) is mostly empty space with a small, dense, positive nucleus — Most particles passing through means most of the atom is empty; the few bouncing back means they hit something small, dense and positive. That result overturned Thomson's model, in which the positive charge was spread evenly through the atom.
c) A silver spoon tarnishing black — Tarnish is a new substance formed when silver reacts with sulfur compounds in the air, and a colour change like that is evidence of a chemical change. Melting, dissolving and breaking change only the form or state; the substance is the same afterwards.
c) Ca²⁺ — Losing two negative electrons leaves two more protons than electrons, so the charge is 2+. Gaining electrons is what makes a negative ion, as when chlorine becomes Cl⁻.