Copper sulfate

Obtain beautiful copper sulfate crystals!

Difficulty:
Danger:
Duration:
10 minutes
Copper sulfate

Reagents

Safety

  • Put on protective gloves and eyewear.
  • Conduct the experiment on the plastic tray.
  • Observe safety precautions when working with boiling water.
General safety rules
  • Do not allow chemicals to come into contact with the eyes or mouth.
  • Keep young children, animals and those not wearing eye protection away from the experimental area.
  • Store this experimental set out of reach of children under 12 years of age.
  • Clean all equipment after use.
  • Make sure that all containers are fully closed and properly stored after use.
  • Ensure that all empty containers are disposed of properly.
  • Do not use any equipment which has not been supplied with the set or recommended in the instructions for use.
  • Do not replace foodstuffs in original container. Dispose of immediately.
General first aid information
  • In case of eye contact: Wash out eye with plenty of water, holding eye open if necessary. Seek immediate medical advice.
  • If swallowed: Wash out mouth with water, drink some fresh water. Do not induce vomiting. Seek immediate medical advice.
  • In case of inhalation: Remove person to fresh air.
  • In case of skin contact and burns: Wash affected area with plenty of water for at least 10 minutes.
  • In case of doubt, seek medical advice without delay. Take the chemical and its container with you.
  • In case of injury always seek medical advice.
Advice for supervising adults
  • The incorrect use of chemicals can cause injury and damage to health. Only carry out those experiments which are listed in the instructions.
  • This experimental set is for use only by children over 12 years.
  • Because children’s abilities vary so much, even within age groups, supervising adults should exercise discretion as to which experiments are suitable and safe for them. The instructions should enable supervisors to assess any experiment to establish its suitability for a particular child.
  • The supervising adult should discuss the warnings and safety information with the child or children before commencing the experiments. Particular attention should be paid to the safe handling of acids, alkalis and flammable liquids.
  • The area surrounding the experiment should be kept clear of any obstructions and away from the storage of food. It should be well lit and ventilated and close to a water supply. A solid table with a heat resistant top should be provided
  • Substances in non-reclosable packaging should be used up (completely) during the course of one experiment, i.e. after opening the package.

FAQ and troubleshooting

The CuSO4 isn’t dissolving. What should I do?

Copper sulfate won't dissolve completely under these conditions, so just pour the solution into a Petri dish, leaving the insoluble precipitate behind.

The crystals are growing very slowly or not at all.

Wait just a little longer – you’ll get your beautiful crystals in the end!

My crystals turned out small and rather unimpressive.

This is possibly because they were contaminated with dust or exposed to a temperature change during their formation.

But don’t be upset! You can change that. Wait until the crystals are completely formed. Dissolve the same crystals in 10 mL of boiling water and pour them back into the Petri dish. Try to protect the solution from dust and changes in temperature.

How can I preserve my crystals?

If you want to keep your crystals nice, coat them with a colorless nail polish. After the nail polish dries, store the crystals in a closed container.

The substance didn’t dissolve completely, and when I poured the solution into a Petri dish, I poured the sediment along with it. What should I do?

In this case, drain the solution back into the plastic cup and rinse the Petri dish with water. Carefully pour the solution back into the Petri dish, this time without the sediment.

Step-by-step instructions

Dissolve some copper sulfate CuSO4 in hot water. Copper sulfate dissolves much better in hot water than in cold water, so you can obtain a saturated solution much faster using heat.

crystals-v2_copper_en_iks-01

Leave your CuSO4 solution to cool and evaporate.

crystals-v2_copper_en_iks-02

Disposal

Dispose of solid waste along with household garbage.

Scientific description

The crystals formed in this experiment command an interesting trait — their structure contains water molecules H2O in addition to copper sulfate CuSO4. Funnily enough, there are more water molecules in a crystal of copper sulfate than there are ions of the Cu2+ and SO42- that comprise copper sulfate CuSO4—the ratio is 5 water molecules per one CuSO4. Moreover, it is the presence of water molecules that gives these crystals such a bright blue color.

Copper sulfate isn’t the only compound that forms these “watery” crystals. In fact, there are some substances that can include several molecules of water per one particle of the substance itself. Washing soda, or sodium carbonate Na2CO3, for example, usually contains ten water molecules per one unit of Na2CO3. Chemists call such substances crystalline hydrates.

Why do the crystals grow?

Copper sulfate belongs to those substances that dissolve in water better when heated. Conversely, their solubility decreases upon cooling, which in our case leads to copper sulfate precipitating as beautiful blue crystalline hydrate CuSO4·5H2O. Since the solution cools slowly, the crystals grow gradually and can become rather big.

Show more details

Why does the copper sulfate solution tend to form crystals, not a fine powder? Crystals are quite different from amorphous solids (such as carbon or glass): the particles they consist of are arranged in a strict geometrical order. Though such a clear complementary structure is often naturally unfavorable, the particles in crystal solids “feel” quite comfortable. Each atom is strongly connected to its surroundings and the positive charges interact closely with the negative charges.

Follow up

Big crystal

Small blue crystals of copper sulphate, without doubt, delight the eye. But what about growing a very big crystal? However, that is not so easy.

As a container, use a plastic cup (that way you can heat it just like the glass of tartaric acid or sugar in the other experiments of the kit) or a glass beaker. In the first case, you will need about 30 grams of copper sulfate CuSO4*5H2O. You can find it in a store where fertilizers are sold, or in a hardware store. If you decided to grow a very large crystal and to do it in a beaker, prepare in advance 60-70 grams of copper sulfate.

Fully dissolve the copper sulphate in hot water. Thoroughly mix the solution until there are no crystallites remaining. Use a piece of copper wire, thread or a splinter as the "support" of the crystal.

Now please be patient! A large crystal can grow for several days!

Crystallization in the refrigerator

How does the environmental temperature affect the rate and the result of crystallization? You can research that! Repeat the experiment, however prepare two test tubes with copper sulfate solution at the same time. In each of them you will need to add 5 grams CuSO4*5H2O, so use the solution and the crystals from the main experiment.

Stop after the 9th step in the instructions. Now, put one of the test tubes in a cup with hot water, as indicated in step 10, and put the second in the refrigerator (the temperature inside is about 4 Co).

Wait for 1-2 hours. Compare the results. Where did the crystal grow bigger? Where are there more of them and why?

Crystals of NaCl

Try to grow a crystal of the most common table salt - sodium chloride NaCl.

Dissolve 39 grams of salt in 100 ml of boiling water. Thoroughly mix the solution until there are no crystallites remaining. As the "support" for the crystal is best to use a thread wound on a splinter - lower its end into the solution. Tie a couple of knots on the end of the string - it may help.

Now all you have to do is wait! Make sure the glass is in a place where no one will shake or drop it over.

That's interesting!

Why grow crystals?

Many synthetic chemists discover and use different methods of single crystals growth in their work. So, why is it attractive and beneficial to professional chemists?

Besides an aesthetic effect (“I have synthesized a substance, and it forms beautiful crystals!”), there is a compelling need to asseamble molecules of new or unknown substances into perfectly ordered single crystals. Normally, after synthesizing a new compound, a chemist has to clarify (confirm) its molecular structure. Until he or she does that, no one in the world scientific community accepts his or her discovery.

There are numerous indirect methods to examine a substance molecular structure. For instance, chemists may expose a substance to visible or infrared light, strong magnetic field or another physical load, looking for hints about the order its atoms are arranged within molecules.

Among these methods, the most reliable and common approach to defining a new compound structure is a so-called X-ray crystallography analysis. It allows researchers to take a “snapshot” of a new substance lattice. This information, in turn, can immediately answer all questions about its molecular structure. Despite its effectiveness, though, this method has a very significant drawback: a substance must be analyzed in form of a single crystal.

It should be understood that each molecule, even if we are talking about very large molecules of polymers or proteins, is very, very small, which can only be detected with the help of special equipment and under strict conditions. Thus, unveiling the structure of a single molecule requires additional finesse. However, even a milligram of any substance contains a huge amount of identical molecules. If you assume that all the molecules respond equally to the same external exposure, and then sum up all these responses, then detection of that bulk signal becomes much easier.

As mentioned earlier, single crystals are unique in a way that their constituent “blocks” are in a strictly defined repetitive order. It allows for summing up the molecules responses to a certain effect, as they are all organized in space in the same way. X-ray analysis method assumes that substance molecules are responsive to X-ray irradiation. After these rays reach the substance molecules, they change their direction in a specific way, which depends on the arrangement of atoms in a single crystal.

Further, scientists analyze the pattern created by diffracted rays to define where atoms, which caused such a change, are located in the crystal. This knowledge makes it possible to figure out the substance molecular structure. Quite simply, if an atom is not a part of a molecule, then in most cases it will be detected being away from all other atoms in the molecule, at a distance of more than 3.5 angstroms, which is one hundred million times less than 3.5 centimeters.

By a curious coincidence, X-rays are also used to examine internal structures of a human body, as well as of many other living creatures. For example, in case of a bone fracture, X-ray radiograms (or just X-rays) of damaged body parts are taken, which lets a doctor know where exactly the fracture is located and how to treat it efficiently.