Limewater

• 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.

• 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.

• 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.

With time, thymol blue solution absorbs carbon dioxide CO₂ from air, which results in yellow coloring. Simply add 1 more drop of thymol blue into the test tube and continue with the experiment.

Perhaps, carbon dioxide escapes from the slits between the rubber stopper and the flask. Turn the rubber stopper in the flask neck while slightly pushing it down. Also, make sure that the tip is inserted all the way in. Ensure that the end of the hose is immersed in the solution.

Calcium carbonate is the main component of limescale – a hard white deposit. It often appears on the surface of heating elements after contact with hard water. Such water has a heightened content level of metal ions, especially those of magnesium Mg and calcium Ca.

So how does the limescale form? Tap water contains hydrogen carbonate HCO₃^-. With the increase of temperature (for example, when water boils) hydrogen carbonate turns into carbonate CO₃^2-:

HCO₃^- → CO₃^2- + H⁺ If the formed carbonate meets an ion of calcium Ca²⁺ or magnesium Mg²⁺, which are very well represented in hard water, a precipitate forms:

Ca²⁺ + CO₃^2- → CaCO₃↓

Mg²⁺ + CO₃^2- → MgCO₃↓

Insoluble carbonates of calcium and magnesium, this is what forms limescale. If you don’t clean your heating elements, they may even break down because of limescale.

Let us call thymol blue “Ind”. When it has very few protons, it is blue Ind^2-. If more protons appear in the solution, thymol blue becomes yellow Hind^-. In the presence of a large quantity of protons all of the thymol blue becomes red H₂Ind.

Such substances as thymol blue are called pH-indicators. You can read more about it in the description of the experiment «Magic liquid»