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How to Make Salt Crystals

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The Experiment

It takes a few days, but by growing the crystals, you’ll see how solutions are made and how the crystalline shapes of salt is formed.

What You’ll Need

To grow your own salt crystals you’ll need:

  • Table salt – sodium chloride
  • Distilled Water
  • A clean, clear glass container – a jam jar is perfect
  • String
  • A spoon for stirring

What To Do

Here’s what to do:

  1. Stir salt into boiling hot water until no more salt will dissolve (crystals start to appear at the bottom of the container). Be sure the water is as close to boiling as possible.
  2. Carefully pour the solution into your jar. (putting a spoon into the jar before adding the water should prevent the jar breaking.
  3. Suspend your string into the jar from the spoon laid across the top of the jar.
  4. Leave your jar somewhere it will not be disturbed and wait for your crystal to grow!

What To Look For

Once your crystals have grown, here are some things for you to look for in them:

  • Any impurities in the salt or the water will change the shape and colour of the crystals you grow. What shape and colour are yours?
  • Try using different types of table salt – try iodized salt, un-iodized salt, sea salt, or even salt substitutes. Is any difference in the appearance of the crystals?
  • Try using different types of water, such as tap water compared with distilled water. Is there any difference in the appearance of the crystals?

The Science Behind It – Using Chemical Reactions To Make Salt

Neutralisation

The reaction between an acid and a base is called Neutralisation. This is exactly how indigestion medicines works – it contain chemicals that react with and neutralise excess stomach acid. Industry uses this same method to produce a wide range of salts and products.

Here’s how neutralisation works:

Acidic solutions contain hydrogen (H+) ions.
Alkaline solutions contain hydroxide (OH) ions.

Here’s the word equation for a reaction between an acid and an alkali:

Acid + alkali → salt + water

The ionic equation for all neutralisation reactions is:

H+(aq) + OH(aq) → H2O(l)

The type of salt that is produced during the reaction depends on the acid and alkali used.

Acids, Alkalis and the Salts they Produce

Neutralising hydrochloric acid produces chloride salts.

Hydrochloric acid + sodium hydroxide → sodium chloride + water

Neutralising nitric acids produces nitrate salts.

Nitric acid + potassium hydroxide → potassium nitrate + water.

Neutralising sulphuric acid produces sulphate salts.

Sulphuric acid + sodium hydroxide → sodium sulphate + water.

Salt Crystals

Making Salts from Metal Oxides

Metal Oxides can also be used as bases and be reacted with acids to make salts and water.

Here’s word equation for a reaction between an acid and a metal base:

Metal oxide + acid → salt + water

For example:
Copper Oxide (CuO) + hydrochloric acid (2HCl) → copper chloride (CuCl2) + water (H20)

While fairly reactive metals can be reacted with acids to form salt and hydrogen, salts of very unreactive metals, such as copper, cannot be made this way because these metals do not react with acids.

And salts of very reactive metals, such as sodium, cannot be made this way because the reaction between the metal and the acid is too vigorous to be carried out safely.

Making Salt from Precipitation Reactions

Some insoluble salts can be made from the reaction between two solutions. Barium sulphate is an insoluble salt. It can be made by the reaction between solutions of barium chloride and sodium sulphate.

For example:
Barium chloride + Sodium Sulphate → barium sulphate + sodium chloride

Precipitation reactions can be used to remove unwanted ions from solutions. This technique is used to treat drinking water and treat effluent.

Making Salts from Metal Carbonates

Acids can be neutralised by metal carbonates to form salts. Most metal carbonates are insoluble, so they are bases, but they are not alkalis.

When acids are neutralised by metal carbonates, a salt, water and carbon dioxide are produced. This means that rocks, such as limestone, that contain carbonate compounds are damaged by acid rain.

Here’s the word equation of the reaction:

Metal carbonate + acid → salt + water + carbon dioxide

So there you have it! With a little patience and some common household items, you’ve grown your very own salt crystals and learned a surprising amount of science along the way. This experiment demonstrates the fascinating world of solutions, crystal formation, and even basic chemical reactions.

The next time you reach for the saltshaker, take a moment to appreciate the tiny crystals within. They’re a testament to the constant interplay between different substances and a reminder that there’s always more to learn about the world around us.

Don’t stop exploring! Try the variations suggested in the “What To Look For” section to see how different factors influence your crystal growth. There are countless other science experiments waiting to be explored at home, so keep your curiosity piqued and your thirst for knowledge strong!

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