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Preparation of hydroxides

Soap obtained with sodium hydroxide
Source: domena publiczna.

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;

  • what a hydroxide is;

  • how to name hydroxides based on their formulas;

  • what the examples of acid‑base indicators are and how to determine their color in water and in bases.

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

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

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

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Nagranie audio prezentujące otrzymywanie wodorotlenków.

How hydroxides are formed

Task 1

Write the research question and hypotheses before watching the demonstration “Testing the behavior of sodium towards water”. Write also your observations and finally the conclusions.

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Wykonaj ćwiczenie zgodnie z poleceniem.
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Do wykonania eksperymentu służą: pippete, sodium, water, tweezer, red cabbage decotion. Do zlewki z wodą pipetą laborant dodaje kilka kropel fioletowgo red cabbage decotion. Roztwór miesza się całkowicie, ma barwę jasno fioletową. Następnie do tak otrzymanego roztworu laborant dodaje kawałek sody który zaczyna szybko pływać po powierzchni roztworu, tworząc brązowe ślady. Roztwór przyjmuje brązowy kolor, a następnie zielony.
Sodium/potassium reaction with water – teacher's demonstration
Experiment 1
Research problem

What happens if we put a piece of sodium or potassium in water?

Hypothesis

Sodium/potassium will dissolve in water.
A chemical reaction will occur between sodium/potassium and water.

You will need
  • crystallizer,

  • water,

  • red cabbage decoction,

  • a rice‑grain‑size piece of sodium or potassium,

  • tweezers,

  • blotting paper,

  • knife.

Instruction
  1. Pour water into the crystallizer and add a few drops of red cabbage decoction.

  2. Remove sodium or potassium from mineral oil or kerosene using tweezers, dry it thoroughly with blotting paper and cut a rice‑grain‑size piece.

  3. Add the prepared piece of sodium or potassium to the crystallizer filled with water with the addition of red cabbage decoction.

  4. Observe the occurring changes.

Summary
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Hydroxides are obtained as a result of the reaction of active metals with water (metals from the 1st and 2nd groups of the periodic table, except for beryllium). As a result, bases (aqueous solutions of hydroxides) are formed and hydrogen is produced.

 active metal oxide + water  hydroxide 

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Source: licencja: CC BY-SA 3.0.
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Source: licencja: CC BY-SA 3.0.

Alkali metals react with water more violently than alkaline earth metals. Magnesium reacts with water at increased temperature. Within the group, the activity of metals increases with the increase of the atomic number (this is related to the distance of valence electrons from the nucleus). The metals of other groups of the periodic table (e.g. copper) are less active and do not react with water. Hydroxides of metals from the 1st and 2nd groups of the periodic table are obtained by other methods.

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Ilustracja przedstawia kierunki zmian aktywności metali w grupie litowców i berylowców. Wzrost aktywności zgodnie z pomarańczową strzałką następuje od H do Fr (1H, 3Li, 11Na, 19K, 37 Rb, 55 Cs, 87 Fr) i od Be do Ra (4Be, 12 Mg, 20 Ca, 38 St,56 Ba, 88 Ra)
Task 2

Read the instructions before carrying out the experiment “Testing the behavior of a given oxide” Write the research question and hypotheses. Write also your observations and finally the conclusions.

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Wykonaj ćwiczenie zgodnie z poleceniem.
Experiment 2
You will need
  • beaker,

  • calcium oxide,

  • water,

  • glass rod,

  • thermometer,

  • phenolphthalein.

Instruction
  1. Pour a little calcium oxide into the beaker.

  2. Carefully add cold water and mix with the glass rod.

  3. Insert the thermometer into the beaker.

  4. Observe the thermometer indications.

  5. Add a few drops of phenolphthalein.

Summary
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Another way of obtaining hydroxides is the reaction of active metal oxides (belonging to the 1st and 2nd group of the periodic table, except for beryllium), called basic oxides, with water.

active metal oxide + water → hydroxide

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Source: licencja: CC BY-SA 3.0.
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Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.

These reactions generate bases – aqueous solutions of hydroxides.

Task 3

Watch the video “Preparation of hydroxide sparingly soluble in water”. Write your observations and conclusions, and then complete the equation of the reaction that occurred during the experiment shown in the video.

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Wykonaj ćwiczenie zgodnie z poleceniem.
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Do wykonania eksperymentu służą: sodium hydroxide ( przeźroczysta substancja w pierwszej probówce), copper(two) sulfate (turkusowa substancja w drugiej probówce). Laborant przelewa turkusową substancję do przeźroczystej i miesza je. Wytrąca się niebieski osad.
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Complete the chemical reaction observed in the experiment “Preparation of hydroxide sparingly soluble in water. Dostępne odpowiedzi: 1. 2NaSO4, 2. Na2SO4, 3. Cu2SO4, 4. CuSO4, 5. Na2SO2 Reakcja do uzupełnienia: (Uzupełnij) + 2NaOH → Cu(OH)2 + (Uzupełnij)
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Exercise 1
Which hydroxide cannot be obtained by the method: metal oxide + water? Możliwe odpowiedzi: 1. Cu(OH)2, 2. Ca(OH)2, 3. KOH, 4. NaOH
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Exercise 2
Several drops of phenolphthalein were added to 4 test tubes containing water; then to each of them a different hydroxide was added: Al(OH)3, NaOH, KOH, Ca(OH)2. In which test tube did phenolphthalein remain colorless? Możliwe odpowiedzi: 1. Al(OH)3, 2. Ca(OH)2, 3. KOH, 4. NaOH
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Exercise 3
What products are obtained from the reaction: active metal + water? Możliwe odpowiedzi: 1. hydroxide + hydrogen, 2. salt + hydrogen, 3. hydroxide + water, 4. hydroxide

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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Tablica interaktywna. How was this lesson? Did you like it? Finish selected sentences. Propozycje 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)..
Source: GroMar Sp. z o.o., licencja: CC BY-SA 3.0.
Homework
Wyjaśnij, w jaki sposób można wykorzystać w codziennym życiu zawarte w abstrakcie informacje.
Wyjaśnij, w jaki sposób można wykorzystać w codziennym życiu zawarte w abstrakcie informacje.

Keywords

hydroxides, preparation of hydroxides, bases, sodium hydroxide, potassium hydroxide

Glossary

hydroxide
hydroxide
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Nagranie słówka hydroxide.

wodorotlenek – związek chemiczny zbudowany z kationów metalu i anionów wodorotlenkowych