Density and the 4 °C turning point
Answers are for parents and teachers.
1
A solid has a mass of 760 g and a volume of 800 cm³. Find its density and say whether it floats in water.
760 ÷ 800 = 0.95 g/cm³, which is less than 1 g/cm³, so it floats.
2
What volume do 1800 kg of pure water at 4 °C fill?
1800 ÷ 1000 = 1.8 m³.
3
Explain how density differences create ocean currents.
Colder, saltier water is denser and sinks, other water moves in to replace it, and deep water rises elsewhere, so the water circulates.
4
In two sentences, say why fish can survive under the ice of a frozen lake.
Ice floats and forms an insulating layer on top. The water below stays liquid, near 4 °C at the bottom.
5
Use the graph values: is fresh water at 10 °C denser or less dense than at 4 °C? Why is the difference small?
Less dense (999.7 against 1000.0 kg/m³). Water expands only a very little when its temperature changes by a few degrees.