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What does hard water leave behind in a kettle?

Water can carry dissolved minerals without looking cloudy. Hardness mainly describes calcium and magnesium in solution, while limescale is a deposit that can form when processes such as heating change the balance.

3–5 min

Questions you could explore

  • How is a dissolved mineral different from a visible deposit?
  • Why does hardness alone not establish drinking-water safety?

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Chemistry and materials

Why does ice take up more room than water?

An ice cube floats in the water it came from, and freezing water can push against its container. Ordinary ice arranges water molecules differently from the liquid, connecting a microscopic pattern with a familiar change in volume.

3–5 min

Why does ice take up more room than water?

Chemistry and materials3–5 minAn ice cube floats in the water it came from, and freezing water can push against its container. Ordinary ice arranges water molecules differently from the liquid, connecting a microscopic pattern with a familiar change in volume.

Chemistry and materials

How can light reveal an element you cannot touch?

A glowing gas can produce a pattern of spectral lines characteristic of its elements. Comparing several lines gives more evidence than spotting one color or one line alone. Scientists use spectra to investigate distant objects, while temperature, motion, and other conditions also affect what they observe.

5–7 min

How can light reveal an element you cannot touch?

Chemistry and materials5–7 minA glowing gas can produce a pattern of spectral lines characteristic of its elements. Comparing several lines gives more evidence than spotting one color or one line alone. Scientists use spectra to investigate distant objects, while temperature, motion, and other conditions also affect what they observe.

Chemistry and materials

Why is a lemon battery such a poor rocket engine?

A lemon with two different metal electrodes can become part of a battery. Turning that into a rocket power source is a much bigger question: a voltage reading does not tell you how much power the cell can deliver, how long it lasts, or how heavy the whole system becomes.

3–7 min

Why is a lemon battery such a poor rocket engine?

Chemistry and materials3–7 minA lemon with two different metal electrodes can become part of a battery. Turning that into a rocket power source is a much bigger question: a voltage reading does not tell you how much power the cell can deliver, how long it lasts, or how heavy the whole system becomes.

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