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What is the easiest way to create a precipitation reaction at home, preferably with easily retrievable chemicals? I need this because I'm making a video for my film education.

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Here's one easy way :

Make a solution of salt ($\ce{NaCl}$) in water, and another solution of Silver Nitrate ($\ce{AgNO_3}$), which you can buy easily) in water.

Upon mixing the two, $\ce{AgCl}$ (Silver chloride, a white compound) will instantly precipitate.

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    $\begingroup$ Silver chloride is white. The grey colour is due to elemental silver (which AgCl is reduced to) $\endgroup$
    – orthocresol
    Mar 24, 2016 at 21:43
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    $\begingroup$ Silver nitrate is expensive, and not easy to buy without legal authorization. Furthermore, its solutions makes dark spots on skin and clothes, that appears only on the following day. But this spot is impossible to clean. $\endgroup$
    – Maurice
    Oct 7, 2021 at 21:11
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For a low-hazard experiment with standard household materials, some variation of the following should work:

Chemicals:

  1. $\ce{CaCl2}$ : Available as a type of ice melt (e.g., this)
  2. Acetic acid : White distilled vinegar
  3. $\ce{NaHCO3}$ : Baking soda

Procedure:

  1. Dilute the vinegar in water, at about $1$ part vinegar to $10$ parts water.
  2. Add a small handful of the $\ce{CaCl2}$ and stir to dissolve.
  3. In a separate container, mix $\sim 1~\mathrm{Tbsp}$ baking soda in $1~ \mathrm{cup}$ lukewarm water
  4. If all of the baking soda dissolves, keep adding more until it won't dissolve further.
  5. Let the baking soda solids settle to the bottom of the container, then carefully pour the liquid into a clear container, suitable for the demonstration.

For the demonstration, add the $\ce{CaCl2}$/vinegar solution drop-by-drop to the bicarbonate solution. If I've thought this through properly, a white $\ce{CaCO3}\!\left(\mathrm s\right)$ precipitate should hopefully form as each drop is added.

To note, I specified the dilute vinegar solution to try to avoid premature precipitation of $\ce{Ca(OH)2}$. If the demonstration solution fizzes too much when adding the drops of $\ce{CaCl2}$/vinegar solution, or if no precipitate forms at all, you could try eliminating the vinegar (skip step $1$) and just dissolve the $\ce{CaCl2}$ in tap water.

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    $\begingroup$ Use washing soda instead of baking soda. You are more guaranteed to get the calcium carbonate by adding a normal carbonate instead of a bicarbonate. $\endgroup$
    – Oscar Lanzi
    Sep 25, 2017 at 20:32
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    $\begingroup$ Indeed, @OscarLanzi, I tried this myself with bicarb, and it didn't really work. I'll have to try it again with the washing soda. $\endgroup$
    – hBy2Py
    Sep 25, 2017 at 21:46
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Mix solutions of washing soda (Na2CO3) and Epsom Salt (MgSO4) to get a precipitate of magnesium carbonate (MgCO3).

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  • $\begingroup$ As per magnesium carbonate, this actually produces a hydrated complex of magnesium hydroxide and magnesium carbonate. From the same wiki article, mixing solutions of sodium bicarbonate (“baking soda”) and magnesium sulfate (the typical hydrated form is “Epsom salt”) produces magnesium carbonate. $\endgroup$
    – Ed V
    Jan 23, 2021 at 2:24
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For an experiment of some practical value, try Epsom salt solution plus soapy water. Explain that the Epsom salt contains magnesium which is a source of water hardness and show what happens when you add the "hard water" to the soapy solution. Ewww! Now students will know why water softening is important.

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  • $\begingroup$ But hard water is good! $\endgroup$
    – Jan
    Sep 26, 2017 at 4:11
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Prepare a solution of table salt in boiling water until no more salt will dissolve. You can then transfer the solution to a different container and allow for the solution to cool. The salt should precipitate out. You should get about 10% of the total salt to precipitate out on cooling.

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Because to precipitate means to come out of solution, this word is commonly used in weather, chemistry and even in biology. For a science experiment that is safe for the kids and amazing for adults I recommend DNA extraction. Strawberry DNA extraction to be more precise, follow the online instructions to make a strawberry smoothie. Mix with the extraction buffer (soap and table salt), and save the last and final step for the demonstration. Describe the experiment to the kids or do it with them, once you add the chilled rubbing alcohol to the strawberry wash the strawberry DNA will precipitate out!

Enjoy, Mr. R

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The easiest way to make precipitation is using washing powder and water and then mixing it with baking powder and water. When they are mixed together the mixture goes from clear to cloudy and becomes hard water.

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