Hydroxides – properties and application
how the hydroxides are obtained and how to note down the corresponding reaction equations;
what are the indicators and how their colour changes in the presence of bases.
what are the most important properties of sodium, potassium and calcium hydroxides;
to name examples of hydroxides that can be called bases based on the solubility table;
to use the solubility table;
to describe the application of some hydroxides.
Properties of hydroxides
Before watching the movie „Testing the properties of sodium and potassium hydroxides”, formulate a research question and hypothesis. Also note down the observations and conclusions from the experiment.
Film dostępny na portalu epodreczniki.pl
Film przedstawia eksperyment pokazujący właściwości wodorotlenku sodu i wodorotlenku potasu. Do przeprowadzenia eksperymentu potrzebujemy: zlewki z wodą, probówki, pipety, łyżeczki, szalki Petriego, drewna, bibułki oraz tkaniny. W dwóch osobnych szalkach Petriego umieszczamy wodorotlenki, a następnie przenosimy je odpowiednio do dwóch probówek z wodą i mieszamy. Następnie umieszczamy kilka kropel każdej z nich na: drewnie, tkaninie i bibułce. Wodorotlenek potasu wsiąka w tkaninę, drewno i bibułę. Wodorotlenek sodu nie wsiąka w drewno, kropla pozostaje na powierzchni.
A laboratory vessel serving, among others for storage of hygroscopic substances is a desiccator.
Its cover is made of thick glass or plastic and adheres closely to the container in which there is a drying substance (e.g., potassium hydroxide). Some desiccators are equipped with a tap for removing air.
Before you watch teacher demonstration or conduct an experiment „Testing the properties of calcium and iron(III) hydroxides”, write down the research question and hypotheses. Then make a note of your observations and conclusions.
What are the characteristic properties of calcium and iron(III) hydroxides?
Calcium and iron(III) hydroxides are white solids which easily dissolve in water. Calcium and iron(III) hydroxides are solids with different colour and solubility.
2 tubes,
calcium hydroxide,
iron(III) hydroxide,
water,
glass rod.
In test tubes place small samples of the substance: in the first – calcium hydroxide, in the second – iron(III) hydroxide precipitated by the reaction of the soluble iron(III) salt with a solution of sodium or potassium hydroxide.
Add a small amount of water to the tubes, mix the contents with a glass rod.
Observe the changes.
Hydroxides are solids that can have different colours. Sodium and potassium hydroxides and hydroxides of other elements from the 1st group of the periodic table are very soluble in water. The solubility of the hydroxides of the 2nd group increases with the increase of the atomic number of the alkaline earth metals, and the hydroxides of the remaining metals are practically insoluble in water. Using the solubility table of hydroxides, it can be checked which of these are soluble in water and which precipitate in the form of sediments, i.e. are practically insoluble in water.
Concentrated solutions of sodium, potassium (formerly corrosive alkalises) and calcium hydroxides have caustic properties – destroy the paper. These work similarly on the skin – can cause severe burns. Molten sodium hydroxide damages (digest) glass, so it is stored in plastic packaging.
Application of hydroxides
Sodium and potassium hydroxides form water‑soluble compounds with fats, which is why these are used as components of preparations for agents unblocking pipes as well as for the production of washing agents. Calcium hydroxide forms a suspension with water – cream of limecream of lime. It is used for limewashing the fruit trees and building walls, because it has disinfecting properties, while white colour reflects a significant part of the sun's rays and prevents excessive heating. A clear colourless solution of calcium hydroxide is called lime water. It is used to detect carbon dioxide.
Lime mortar
The constituent of the lime mortar is, in addition to sand and water, slaked limeslaked lime, which is formed in the reaction of quicklime with water. The prepared dough‑like mixture has the ability to harden due to the chemical reaction of calcium hydroxide with carbon dioxide from the air.
Lime mortar | |
preparation | hardening |
Make a sketch showing the use of selected hydroxides. You can print it and add notes to create a poster.
Select the correct answer. Ca(OH)2 is:
- slaked lime
- cream of lime
- lime water
- quicklime
- calcium hydroxide
- calcium oxide
- calcium base
Summary
Hydroxides are solid substances of different colour.
Sodium and potassium hydroxides are highly hygroscopic substances, have similar properties, are used as ingredients for the production of soaps, detergents and preparations for the pipes unblocking agents.
Concentrated solutions of sodium, potassium and calcium hydroxides have corrosive properties.
Magnesium and aluminium hydroxides are among others components of antacids.
Prepare an infographic, presentation or speech showing the use of selected hydroxides as compounds for the various products used in your home.
Keywords
Hydroxides, application of hydroxides, sodium hydroxide, potassium hydroxide, bases
Glossary
higroskopijność – zdolność niektórych substancji do pochłaniania wilgoci (pary wodnej) z powietrza
mleko wapienne – zawiesina wodorotlenku wapnia w wodzie stosowana do dezynfekcji pomieszczeń o dużych powierzchniach (piwnice, magazyny) do neutralizacji kwasów (np. w ratownictwie chemicznym)
wapno gaszone – wodorotlenek wapnia , stosowany w budownictwie jako składnik zaprawy wapiennej