Matter, Mixtures & Water Properties — Problem set, Grade 6
How can particle models and measurements account for matter across changes? Which parts of a stated sand–salt–water mixture can a filter separate, and where does the matter go?
Review the key ideas
States of Matter & the Particle Model
Solid, liquid and gas are not three different substances but three arrangements of the same particles, differing in how closely they are packed, how strongly they hold each other and how fast they move. Every melting point and boiling point in this lesson is a measurement of how strong that holding is.
Physical Properties & Physical Changes
A physical property can be measured without turning the substance into something else, and a physical change alters form while leaving identity intact. Because different substances share individual properties, identification always needs more than one.
Chemical Changes: Evidence & Conservation
A chemical change makes a substance that was not there before, and the way to tell is to compare properties afterwards rather than to watch for bubbles or colour. However dramatic the change looks, the total mass of everything involved is exactly the same before and after.
Mixtures, Solutions & Separation
In a mixture every component keeps its own properties, which is exactly why mixtures can be separated. Each separation method works by exploiting one property the components do not share, so choosing a method means first finding the difference you can use.
Water’s Properties: Density, Floating & Surface Effects
Water behaves oddly in several ways that matter enormously: its solid floats on its liquid, it holds more heat than almost any common substance, and its surface behaves as though it has a skin. Each of these follows from the same thing, which is how strongly water molecules hold on to one another.
Problem 1
Answer and explanation
Melting in the closed sample changes arrangement while retaining its 50 g of water. The open dish loses 6 g from the measured liquid; evaporation is a possible pathway into the air. The water has not been destroyed. Without further records, the mass loss alone does not exclude a spill or specify the evaporation rate over a particular time.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 2
Answer and explanation
Visibility is not the definition of matter. Gas particles have mass and occupy space; a suitable comparison or measurement can show these properties.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 3
Answer and explanation
48 ÷ 24 = 2 g/cm³. Reshaping changes outline while the modeled material and measured mass/volume remain. It is described as physical because no new substance is formed in this model, not simply because the shape might be restored.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 4
Answer and explanation
No. Blue depends on the observation conditions, and heavy depends on sample size and comparison. Measured properties and additional evidence are needed.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 5
Answer and explanation
Two A atoms and two B atoms are represented on each side. Their combinations change from A₂ and B₂ to two AB particles. The closed-system mass remains 60 g. This model directly states a rearrangement; a color change alone would not supply the same evidence of substance identity.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 6
Answer and explanation
No. Oxygen from the surroundings enters the material. Account for both the metal and the added oxygen rather than treating the exposed object as a closed system.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 7
Answer and explanation
After removing 3 g sand, 105 g of salt solution remains in the idealized model. After water enters the air, 5 g salt remains. The water is transferred, not destroyed. Real recovery may be incomplete; these assumptions do not show that the liquid was safe to drink.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 8
Answer and explanation
No. Filter pore size and other treatment properties matter. Visible clarity alone cannot establish removal of dissolved substances or drinking safety.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 9
Answer and explanation
Ice density is 0.9 g/mL. The hull displaces 60 g of modeled water, consistent with buoyancy balancing its weight. A hollow hull can float because of its overall geometry and average density; a compact piece of the same material may behave differently. Neither result is a rule for every temperature or liquid.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.
Problem 10
Answer and explanation
Ask for mass, volume or displacement, shape, enclosed air, and the liquid’s properties. Size alone does not determine average density or buoyancy.
Compare the scientific meaning and reasoning after an independent attempt. A different accurate supported response can be correct; human review is required.