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Hydroxides - structure and identification using indicators

Dysprosium(III) hydroxide
Source: Leiem, licencja: CC BY-SA 4.0.

Link to the lesson

Before you start you should know
  • how to write the formulas of chemical compounds;

  • how to apply the rules of writing equations of chemical reactions;

You will learn
  • what a hydroxide is;

  • to name hydroxides based on their formulas;

  • to list and describe methods for the preparation of hydroxides and write the corresponding equations of reactions;

  • to give examples of metals and metals oxides reacting with water;

  • to identify products of reactions of active metals with water;

  • to give examples of acid‑base indicators and to determine their color in water and in bases.

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Nagranie dźwiękowe abstraktu.

Hydroxides – structure

HydroxideshydroxideHydroxides are chemical compounds with a constant state of aggregation, made of metal cations and hydroxide anions.
These ions are attracted by the action of electrostatic forces, creating crystal structurecrystal structurecrystal structure.

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The valency of the hydroxyl ions always equals I.

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The general formula of monovalent metal hydroxides:

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The general formula of metal hydroxides:

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Hydroxide names are created by adding to the name of the element that forms the compound the word “hydroxide”:

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If the metal forms two hydroxides, the Roman numeral in parentheses is added to the name, indicating the valency of the metal, for example:

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If the metal forms one hydroxide, the valency of the metal in the name is omitted:

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Indicators

The fact that the studied compounds have different properties can be seen using substances called indicators. Their action under the influence of other substances depends on the fact that they change the color in an easy to observe way. This allows us to determine whether the sample is the substance interesting for us.

In everyday life we also find indicators. Tea, to which we add lemon juice, changes its color to lighter. Similarly, when we add lemon juice (citric acid) or vinegar (acetic acid) to beetroot juice, the dye in this juice under the influence of acids will take on an intense red color.

An indicator changing colour in water solutions, to which we add metals and metal oxides (with the creation of a new chemical compound – hydroxide) is, among others, decoction of red cabbage.

Task 1

Formulate a research question and hypothesis before watching the video ‘Observation of colour indicators in bases’. Write down your observations and concluding remarks.

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Wykonaj ćwiczenie zgodnie z poleceniem.
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Film przedstawia eksperyment, w jaki sposób barwią się różne wskaźniki kwasowo-zasadowe w roztworach wodorotlenków Do przeprowadzenia doświadczenia potrzebujemy: wodę wapienną (wodny roztwór wodorotlenku wapnia), wodorotlenek potasu, wodorotlenek sodu, wywar z czerwonej kapusty, sok jagodowy, mieszadło, uniwersalne papierki wskaźnikowe oraz oranż metylowy i fenoloftaleinę. Do poszczególnych roztworów wodorotlenków dodajemy po kilka kropli badanego wskaźnika - za każdym razem do czystej porcji roztworu wodorotlenku. Powtarzamy eksperyment dla każdego badanego wskaźnika. Obserwujemy, jaką barwę przyjmują poszczególne wskaźniki w obecności roztworów wodorotlenków.
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An indicator or an indicating dye is a substance with which we can detect another substance, e.g. as a result of a change in color.

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Exercise 1
Which hydroxides form bases? Możliwe odpowiedzi: 1. na o ha, cu o ha dwa razy wzięte 2.na o ha, ce a o ha dwa razy wzięte 3. ka o ha, a el o ha trzy razy wzięte 4.ka o ha, ce u oha dwa razy wzięte

Summary

  • Hydroxides are chemical compounds made of metal cations and hydroxide anions whose general formula is M(OH)n.

  • Hydroxides are obtained as an effect of the reaction of active metal oxides (basic oxides) with water and of some metals with water.

  • Solutions of hydroxides that are easily soluble in water (all hydroxides of metals from the 1st group of the periodic table and selected metals from the 2nd group) are traditionally called bases.

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Grafika przedstawiająca tablicę szkolną, na której znajdują się zdania do dokończenia. Finish selected sentences. 1 It was easy for me (uzupełnij). 2 It was difficult for me (uzupełnij). 3 Today I learned (uzupełnij). 4 I understood that (uzupełnij). 5 It surprised me (uzupełnij). 6. Today I found out (uzupełnij). 7. I was interested in (uzupełnij). 8. I still have to repeat (uzupełnij).
Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.

Keywords

crystal web, hydroxide

Glossary

crystal structure
crystal structure
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Nagranie dźwiękowe słówka.

sieć krystaliczna – to szczególne ułożenie atomów lub cząsteczek w ciele stałym. Charakteryzuje się uporządkowaniem dalekiego zasięgu oraz symetrią.

hydroxide
hydroxide
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Nagranie dźwiękowe słówka.

wodorotlenek – związek chemiczny zbudowany z kationów metalu i anionów wodorotlenkowych