Particles & States
What is matter?
Anything that has mass and takes up space.
Is colour a physical property or a chemical property?
A physical property: it can be observed without changing the substance into a new substance.
What do we call a pure substance containing only one type of atom?
An element.
What is a solute?
The substance that dissolves in a solvent.
A substance dissolves in water. Do we call it soluble or insoluble in water?
Soluble in water.
Which state has a fixed volume but takes the shape of its container?
A liquid.
Is flammability a physical property or a chemical property?
A chemical property: it describes a substance's ability to burn in a chemical reaction.
What is a compound?
A pure substance containing two or more different elements chemically bonded in fixed proportions.
Sugar dissolves in water. Identify the solute and the solvent.
Sugar is the solute; water is the solvent.
Which forms a solution when a small amount is stirred into enough water: salt or sand?
Salt. Sand remains an insoluble solid and does not form a solution with water.
Describe the arrangement and movement of particles in a solid.
They are closely packed and vibrate about fixed positions. They do not remain completely still.
Classify melting ice and burning wood as physical or chemical changes.
Melting ice is physical. Burning wood is chemical.
Classify pure gold, pure water and air as an element, a compound or a mixture.
Gold is an element; water is a compound; air is a mixture of gases.
What is a solution, and is it a pure substance or a mixture?
A uniform, homogeneous mixture formed when a solute dissolves in a solvent. It is a mixture.
A student says, "Salt water is a solution, so it is not a mixture." Correct the statement.
A solution is a type of mixture: a homogeneous mixture. Salt water contains salt and water evenly distributed.
A syringe contains air and its opening is sealed. When the plunger is pushed, the air occupies less space. Use the particle model to explain why the air can be compressed and why the particles themselves do not become smaller.
Gas particles have large spaces between them. Pushing the plunger moves particles closer together, reducing empty space. The size and number of particles remain unchanged.
A candle’s wax melts near the flame. Wax also burns. Explain why melting and burning are different types of change. Refer to whether new substances form.
Melting is physical: solid wax becomes liquid wax but remains the same substance. Burning is chemical: wax reacts with oxygen and forms new substances, including carbon dioxide and water.
Sample A contains only identical water molecules. Sample B contains water and sugar molecules evenly distributed throughout. Classify each and explain why a uniform appearance does not necessarily mean a substance is pure.
A is a pure compound containing only water molecules. B is a homogeneous mixture containing two substances evenly distributed. Both can look uniform, so appearance alone cannot establish purity.
Sugar dissolves completely in water. A student says, "The sugar is gone because we cannot see it." Use the particle model to correct the student and explain why the resulting mixture is homogeneous.
Sugar particles remain present, separate from the crystal and spread throughout the water. Individual particles are too small to see. Their even distribution makes the solution homogeneous.
A student adds a small amount of salt to one cup of water and sand to another, then stirs both. Predict the observations and explain which mixture can be separated using ordinary filter paper.
Salt dissolves in sufficient water to form a uniform solution. Sand remains as visible particles and may settle. Filter paper traps insoluble sand; dissolved salt passes through with the water.
Two sealed syringes contain equal volumes: one contains air and the other water. Their plungers are pushed with the same force. Predict which plunger moves farther. Explain using particle arrangement, then evaluate: "If the volume decreases, some particles must have disappeared."
The air plunger moves farther because gas particles have much more empty space between them. Water particles are already close together, so water compresses very little. Compression reduces spacing, not particle number. No matter escapes the sealed syringe, so its mass remains unchanged.
A student observes bubbles in A: boiling water, and B: two liquids mixed at room temperature. The student concludes, "Both must be chemical changes because gas is produced." Evaluate this conclusion. Explain what the bubbles could represent and suggest further evidence to investigate B.
Bubbles alone do not prove chemical change. In A they contain water vapour: water changes state without forming a new substance. In B they might be a new gas from a reaction or released dissolved gas. Investigating the gas’s identity and whether new substances formed would help. Temperature or colour changes can support the conclusion but are not conclusive alone.
A mixture contains sand, salt and water. All the salt has dissolved. Outline a sequence to recover dry sand and solid salt. Explain what happens to each substance at each stage and why filtering alone cannot recover both solids.
Filter first: sand remains as residue; salt solution passes through as filtrate. Rinse the sand with a little clean water to remove remaining salt solution, then dry it. Combine rinsings with the filtrate and evaporate the water to recover salt. Filtering alone cannot recover dissolved salt because its particles pass through ordinary filter paper with the water.
A closed jar contains 100 g of water and 10 g of sugar. The sugar dissolves completely. Evaluate both claims: 1. "The contents now have a mass of 100 g because the sugar disappeared." 2. "The clear liquid is now a pure substance." Use particle ideas and predict what would remain if the water were gently evaporated.
Both claims are incorrect. The contents have a mass of 110 g because no matter entered or left. Sugar particles remain among water particles. It is a homogeneous mixture of two substances even though it is clear. If opened and gently evaporated without losing or chemically changing the sugar, approximately 10 g of sugar remains.
Two colourless liquids look identical: pure water and a solution of an unknown, non-volatile solid in water. The solid does not chemically change under gentle heating. Without tasting, design a comparison to identify the solution. Include your method, what to keep the same, predicted results with reasoning, and one limitation.
Place equal measured volumes in separate clean, labelled evaporating dishes. Gently evaporate water under the same heating conditions with suitable laboratory precautions. Pure water should leave no solid residue; the solution should leave dissolved solid. Keep volumes, equipment cleanliness and heating procedure consistent. A residue indicates a non-volatile substance under the stated conditions but does not identify it. Contamination can also leave residue; clean equipment and repeated trials strengthen the conclusion.