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From dissolved minerals to kettle limescale

Rainwater starts out soft, but as it percolates through limestone and chalk, it dissolves minerals that travel invisibly to your kitchen tap. That dissolved calcium and magnesium is what makes water 'hard', and when a kettle heats the water, the chemical balance shifts and leaves solid calcium carbonate behind as crusty limescale.

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

Identifying elements through patterns of light

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 line alone, while temperature, motion, and other conditions also affect the spectrum.

5–7 min

Identifying elements through patterns of light

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 line alone, while temperature, motion, and other conditions also affect the spectrum.

Chemistry and materials

Inside a lemon battery

A lemon with two different metal electrodes can become part of a battery. A voltage reading does not tell you how much power the cell can deliver, how long it lasts, or how heavy a larger power supply would become.

3–7 min

Inside a lemon battery

Chemistry and materials3–7 minA lemon with two different metal electrodes can become part of a battery. A voltage reading does not tell you how much power the cell can deliver, how long it lasts, or how heavy a larger power supply would become.

From dissolved minerals to kettle limescale | Speech Topic | speaking.app