You get a bonus - 1 coin for daily activity. Now you have 1 coin

Laboratory Experiment 9. Amphoteric Properties of Aluminum Hydroxide

Lecture

Reagents: solutions of sodium hydroxide, hydrochloric acid, an aluminum salt AlCl3 or Al2(SO₄)₃.

1. Preparation of aluminum hydroxide. Add an alkali solution dropwise to an aluminum salt solution (2 cm³) until a precipitate forms.

2. Studying the amphoteric properties of aluminum hydroxide. Divide the precipitate obtained in the previous experiment into two parts. To one test tube add an acid solution, and to the other an alkali solution, until the precipitates dissolve.

Draw conclusions about the method of preparing aluminum hydroxide and its properties based on the experiment performed. Write the reaction equations in molecular and ionic form.

Procedure:

1. Preparation of aluminum hydroxide:

An alkali solution (NaOH) is added dropwise to an aluminum salt solution (for example, AlCl₃), forming a white gelatinous precipitate of aluminum hydroxide:

Molecular equation:

$A l C l_{3} + 3 N a O H \to A l (O H)_{3} ↓ + 3 N a C l$

Full ionic equation:

$A l^{3 +} + 3 C l^{-} + 3 N a^{+} + 3 O H^{-} \to A l (O H)_{3} ↓ + 3 N a^{+} + 3 C l^{-}$

Net ionic equation:

$A l^{3 +} + 3 O H^{-} \to A l (O H)_{3} ↓$

Laboratory Experiment 9. Amphoteric Properties of Aluminum Hydroxide

2. Studying the amphoteric properties:

Divide the precipitate obtained into two parts.

a) Action of acid (HCl):

Aluminum hydroxide dissolves in the acid, forming a salt:

Molecular equation:

$A l (O H)_{3} + 3 H C l \to A l C l_{3} + 3 H_{2} O$

Full ionic equation:

$A l (O H)_{3} + 3 H^{+} + 3 C l^{-} \to A l^{3 +} + 3 C l^{-} + 3 H_{2} O$

Net ionic equation:

$A l (O H)_{3} + 3 H^{+} \to A l^{3 +} + 3 H_{2} O$

Laboratory Experiment 9. Amphoteric Properties of Aluminum Hydroxide

b) Action of excess alkali (NaOH):

If an excess of alkali continues to be added, the precipitate dissolves, since aluminum hydroxide exhibits amphoteric properties:

The aluminum hydroxide precipitate dissolves in excess alkali, forming a complex anion:

Molecular equation:

Al(OH)3+NaOH→Na[Al(OH)4]

Ionic equation:

$A l (O H)_{3} + O H^{-} \to [A l (O H)_{4}]^{}$ $-$

Laboratory Experiment 9. Amphoteric Properties of Aluminum Hydroxide

Conclusions:

Aluminum hydroxide is formed when alkali is added to an aluminum salt solution.
It exhibits amphoteric properties, i.e. it can react both with acids and with bases:
- In acid — it dissolves, forming a salt.
- In excess alkali — it dissolves, forming a complex compound.

Comments

To leave a comment

If you have any suggestion, idea, thanks or comment, feel free to write. We really value feedback and are glad to hear your opinion.

To reply

Comment

To confirm that you are not a bot, answer:

Name

Email(not published)

Vote

Lectures and tutorial on "Неорганическая химия"

Terms: Неорганическая химия

Chapter I. Introduction to Inorganic Chemistry

1.1. Chemistry. Substance, chemical element, atom

1.2. Simple and complex substances. Substances of molecular and non-molecular structure

1.3. Main classes of inorganic compounds

1.3.1. Oxides

1.3.2. Acids: Classification, Chemical Properties, Nomenclature, Methods of Obtaining Acids

1.3.3. Bases

1.3.4. Salts

1.3.5. Relationships Between Classes of Inorganic Compounds

1.4. Quantitative Characteristics of a Substance

1.5. Basic Laws of Chemistry. The Law of Constant Composition of Matter. The Law of Conservation of Mass of Substances

1.6. Avogadro's Law as One of the Fundamental Laws of Chemistry

1.6.1. Molar concentration of a gas

Chapter II. ATOMIC STRUCTURE AND THE PERIODIC LAW 2.7. Atomic Structure

2.8. The Phenomenon of Radioactivity

2.9. The State of the Electron in the Atom

2.10. The Periodic Law in the Context of Atomic Structure Theory

2.11. Periodicity of changes in the properties of the atoms of chemical elements and of the substances they form

2.12. The significance of D. I. Mendeleev's periodic law and periodic table for the development of science

Chapter III. CHEMICAL BONDING AND THE STRUCTURE OF MATTER 3.13. The nature and types of chemical bonding

3.14. Properties of chemical bonds

14.1. Hybridization of atomic orbitals

Laboratory Experiment 1. Building Models of Molecules of Inorganic and Organic Compounds

3.15. Valence and Oxidation State

3.16. Types of Crystal Structures

3.17. Intermolecular Interaction and Hydrogen Bonding

Chapter IV. CHEMICAL REACTIONS 4.18. Classification and general characteristics of chemical reactions

4.18.1. Oxidation-Reduction Reactions. The Most Important Oxidizing Agents and Reducing Agents.

4.19. Thermal Effects of Chemical Reactions

4.20. The Rate of Chemical Reactions

4.21. Factors Affecting the Rate of Chemical Reactions

Laboratory Experiment 2. Investigating the Effect of Temperature and Acid Concentration on the Rate of Reaction Between Zinc and Hydrochloric Acid

4.21.1. The law of mass action

4.22. Chemical Equilibrium

Practical work 1. Chemical reactions: the ratio of the number and composition of starting substances and reaction products, the oxidation state of atoms, the release or absorption of heat, catalysts, and phase boundaries

Chapter V. CHEMISTRY OF SOLUTIONS 5.23. Dissolution as a Physicochemical Process

5.24. Preparation of Solutions

5.25. Electrolytic dissociation of substances in solutions

5.26. The Concept of the Hydrogen Index (pH) of a Solution. Acidity, Alkalinity

Laboratory Experiment 3. Determining the acidic or basic character of a solution using indicators

5.27. Chemical Properties of Acids, Bases, and Salts in Light of the Theory of Electrolytic Dissociation

Laboratory Experiment 3.1*. Ion Exchange Reactions

5.27.1. Hydrolysis of Salts

Laboratory Experiment 3.2*. Hydrolysis of salts (determining the pH of salt solutions)

Practical Work 2. Studying the Properties of Acids, Bases, and Salts in Light of the Theory of Electrolytic Dissociation

Practical Work 2.1*. Solving experimental problems on the topic "Solution Chemistry"

Chapter VI. NONMETALS. 6.28. General Characteristics of Nonmetals

6.29. Hydrogen as a chemical element

Laboratory Experiment 4. Testing solutions of hydrogen compounds of nonmetals with an indicator

6.29.1. Hydrogen Compounds of Nonmetals and Metals

6.29.2. Hydrogen Peroxide

6.30. Halogens as Chemical Elements

6.31. Compounds of the Halogens

6.32. Group VIA Elements. Oxygen and Sulfur

6.32.1. Ozone

6.33. Hydrogen Compounds of Oxygen and Sulfur

6.34. Oxygen compounds of sulfur

6.35. Sulfuric Acid

Laboratory Experiment 5. Investigating the Chemical Properties of a Dilute Sulfuric Acid Solution

6.36. Group VA Elements. Nitrogen and Phosphorus

6.37. Ammonia: Structure, Physical Properties, Preparation and Uses

Laboratory Experiment 6. Detecting ammonium ions in solution

6.37.1. Nitrogen Oxides NO and NO2

6.38. Nitric acid

6.39. Oxygen-Containing Compounds of Phosphorus

Laboratory Experiment 6.1*. Detecting phosphate ions in solution

6.40. The Most Important Mineral Fertilizers

6.41. Group IVA Elements. Carbon and Silicon

6.42. Carbonic and Silicic Acids, Their Salts

Practical Work 3. Solving Experimental Problems on the Topic "Non-Metals"

Practical work 3.1. Identification of mineral fertilizers

Chapter VII. METALS 7.43. Metals. General Characteristics

7.44. General chemical properties of metals

Laboratory Experiment 7. Reaction of Metals with Acid Solutions

7.45. General methods of obtaining metals

45.1. Obtaining Metals by Electrolysis of Aqueous Salt Solutions

7.46. Alkali Metals

7.47. Group IIA metals of the periodic system

Laboratory Experiment 8. Detection of Calcium Ions in Solution

Aluminum and Its Compounds

Laboratory Experiment 9. Amphoteric Properties of Aluminum Hydroxide

7.48.1. General Characteristics of Group B Metals

7.48.2. General Characteristics of the Acid-Base Properties of Oxides and Hydroxides of Group B Metals

49. Iron and Its Compounds

7.50. The most important compounds of iron

7.50.1. Chromium Compounds in Various Oxidation States

7.50.2. Compounds of Manganese in Various Oxidation States

7.50.3. Applications and Biological Role of Group B Metals and Their Compounds

Laboratory experiment 9.1*. Detection of iron(II) and iron(III) ions in solutions

Practical work 4. Solving experimental problems on the topic "Metals"

Practical work 4.1*. Solving experimental problems on the topic "Metals"

Chapter VIII. Chemical Substances in Human Life and Activity. 8.51. The Role of Chemistry in the Development of Civilization

8.51.1. Chemistry and agriculture

8.51.2 Medicinal Chemistry

8.51.2 Food Chemistry. Food Preparation Techniques, Food Industry

8.52. The Chemical Industry and Chemical Synthesis in the Service of Human Development

53. Ecology. Protecting the Environment from the Harmful Effects of Chemical Substances. "Green Chemistry"

Practical Work 7*. Solving Experimental Problems on the Topic "Preparation and Properties of Inorganic Compounds"

Appendix 1. Electronic Structure of Atoms of Chemical Elements of the Small Periods (I–III)

Appendix 2. Minerals and Their Hardness on the Mohs Scale

Appendix 3. Qualitative reactions

Appendix 4. Solubility table of acids, bases, and salts in water

Answers to Calculation Problems and Tests in Inorganic Chemistry