Acids

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Table of Content
Malaysia SPM Form 4 Chemistry, Chapter 7: Acid and Base.

1 Introduction
- 1.1 Organic Acid
- 1.2 Mineral Acid
2 Theory Of Acids And Alkalis
3 Bold text=Chemical Properties of Acid=

[edit] Introduction

Acids form a class of chemical substances which contain hydrogen ions in aqueous solution, H+ (aq), as the only positive ion.

Acids are usually classified into mineral or organic acids.

[edit] Organic Acid

The organic acids are usually weaker and less corrosive than mineral acids, but still have the 'sour' taste.
They are also naturally occurring acids, found in vegetables, fruit and other foodstuffs.
Some common organic acids are shown in Table 1.

Organic acid Where it is found lactic acid sour milk oxalic acid rhubarb plant citric acid limes, lemons (citrus fruit) formic acid insect bites and stinging nettles tartaric acid grape juice acetic acid vinegar malic acid apples and pears

[edit] Mineral Acid

Mineral acids are generally much stronger. Most do not occur naturally, but are man made, for laboratory and industrial use.
They usually have simpler molecules than do organic acids, and their chemical formulae are shown in Table 2.

Mineral acid Chemical formula sulphuric acid nitric acid hydrochloric acid carbonic acid sulphurous acid phosphoric acid Table 2 Mineral acids

[edit] Theory Of Acids And Alkalis

Acids are substances that form hydrogen ions ( $H^+_{(aq)}\,$ ) when dissolved in water.

Example
Hydrochloric acid $HCl\,$ gives $H^+\,$ (aq) and $Cl^-\,$ (aq) ions when dissolved in water.

$HCl \longrightarrow H^+ + Cl^-$

Sulphuric acid $H_2SO_4\,$ gives $2H^+\,$ (aq) and $SO_4^{2-}\,$ (aq) ions

$H_2SO_4 \longrightarrow 2H^+ + SO_4^{2-}$

and nitric acid $HNO_3\,$ gives $H^+(aq)\,$ and $NO_3^-\,$ ions.

$HNO_3 \longrightarrow H^+ + NO_3^-$

In water, some of the water molecules may decompose and form $H^+\,$ and $OH^-\,$ ions, which means hydrogen ions $H^+\,$ is also present in water.<br.

$H_2O \longrightarrow H^ + OH^-$

Nevertheless, the concentration of $H^+\,$ ions is equals to the concentration of $OH^-\,$ ions. Therefore, water is neutral.
In acid solutions there are more $H^+\,$ ions than $OH^-\,$ ions.

[edit] Bold text=Chemical Properties of Acid=

Although there is a wide variety of acids, they have certain general properties:
acids turn litmus from blue to red in colour;
acids are electrolytes, because in solution, they are ionic and therefore conduct electricity;

[edit] Reaction with Reactive Metal

Reaction Between Acid and Reactive Metal

Most dilute acids (except nitric acid) react and many metals (except copper, silver, gold) to form salt and hydrogen gas:

Acid + reactive metals ----> salt + hydrogen gas

[Reactive metals are those metals higher than hydrogen ion in Electrochemical Series]

Example

Magnesium + Sulphuric acid ----> Magnesium Sulphate + Hydrogen Gas

Equation:

Mg + H₂SO₄ ---> MgSO₄ + H₂

Zinc + Nitric Acid ---> Zinc Nitrate + Hydrogen gas

Equation

Zn + 2HNO₃ ---> Zn(NO₃)₂ + H₂

[edit] Reaction with Metal Oxide (Neutralisation)

Reaction Between Acid and Metal Oxide

Dilute acid react with metal oxide produces salt and water.

Acid + Metal Oxide ---> salt + water

This process is call neutralisation.

acids react and metal oxides to form a salt and water:
Example 1
copper (II) oxide + nitric acid ---> Copper(II) Nitrate + Water
Equation

CuO + 2HNO₃ ---> Cu(NO₃)₂ + H₂O

Example 2
Aluminium Oxide + Sulphuric acid ---> Aluminium Sulphate + Water
Equation

Al₂O₃ + H₂SO₄ ---> Al₂(SO₄)₃ + H₂O

[edit] Reaction with Alkali (Neutralisation)

Reaction Between Acid and Alkali

Acid react with alkali to form salt and water.

Acid + metal hydroxide ---> salt + water

This process is also called neutralisation.

Example 1 Sodium hydroxide + hydrochloric acid ---> Sodium Chloride + Water

NaOH + HCl ---> NaCl + H₂O

Example 2 Potassium hydroxide + ethanoic acid ---> Potassium Ethanoat + Water

KOH + CH₃COOH ---> CH₃COO^-K⁺ + H₂O

[edit] Reaction with Metal Carbonate

Reaction Between Acid and Metal Carbonate

Acids react with all metal carbonates to form a salt, water and carbon dioxide.

he reaction is effervescent, as lots of bubbles are produced:

Acid + Metal Carbonate ---> salt + water + carbon dioxide

Example 1

Calcium carbonate + hydrochloric acid

CaCO₃ + 2HCl ---> CaCl₂ + CO₂ + H₂O

Example 2
Sodium Carbonate + Sulphuric Acid ---> Sodium Sulphate + Carbon Dioxide + Water

Na₂CO₃ + H₂SO₄ ---> Na₂SO₄ + CO₂ + H₂O

[edit] The Ionic Equation

Acid + Oxide(Base)
Example:

2HCl + CaO ---> CaCl₂ + H₂O

Ions that present:

Ionic Equation

Acid + Hydroxide(Alkali)
Example:

2HNO₃ + Ca(OH)₂ ---> Ca(NO₃)₂ + 2H₂O

Ions that present:

2H⁺ + 2 NO₃^- + Ca²⁺ + 2OH^- ---> Ca²⁺ + 2NO₃^- + 2H₂O

Ionic Equation

H⁺ + OH^- ---> H₂O

Acid + Metal
Example:

H₂SO₄ + Ca ---> CaSO₄ + H₂

Ions that present:

Ionic Equation

Acid + Carbonate
Example:

2H₃PO₄ + 3CaCO₃ ---> Ca₃(PO₄)₂ + 3CO₂ + 3H₂O

Ions that present:

Ionic Equation

[edit] Acidity Needs Water

The presence of water is essential for the formation of hydrogen ions and it is only the presence of these ions which causes acidity.
A hydrogen ion, H+, is a hydrogen atom which has lost its electron and is therefore just a proton.

The proof of the importance of water for acidity is shown in Table 3.
Here, a solution of hydrogen chloride in water, which is hydrochloric acid, is compared and *hydrogen chloride gas not dissolved in water, but in an organic solventsuch as methylbenzene.
The comparison is made by using typical acid tests like those discussed in the previous Section.

Test And hydrochloric acid And hydrogen chloride gas dissolved in methylbenzene dry litmus Paper turns red shows no change conducting Electricity is an electrolyte is a non-electrolyte adding Magnesium powder shows violent bubbling, producing hydrogen gas shows no reaction adding copper oxide and heating shows the blue colouration of the salt formed shows no reaction adding Calcium carbonate produces bubbles of carbon dioxide gas shows no reaction Table 3 The importance of water for acidity

Hydrogen chloride gas is a covalent compound composed of molecules.
When it is dissolved in water, it forms hydrochloric acid, which is ionic and composed of hydrated hydrogen and chloride ions:

hydrogen chloride gas + water ¾¾® hydrochloric acid

                HCl (g)           +    H2O (l) ¾¾® H3O+ (aq) + Cl- (aq)

Hydrochloric acid behaves as a typical acid, as shown in Table 3, but hydrogen chloride gas dissolved in methylbenzene has no acidic properties, as it does not contain any hydrogen ions.
This is because hydrogen ions can only exist in the presence of water.
These aqueous or hydrated hydrogen ions, H+ (aq), are sometimes shown as H3O+ (aq) and are called the hydroxonium ions.

H+ (aq) + H2O (1) ¾¾® H3O+ (aq)

Some other example Sulphurus Acid SO2 + H2O ¾¾® H2SO3 H2SO3 + H2O ¾¾® 2H3O+ + SO32-

Carbonic Acid CO2 + H2O ¾¾® H2CO3 H2CO3 + H2O ¾¾® 2H3O+ + CO32-

[edit] Base and Alkali

Compounds which react with acid to form a salt and water only are called bases.
A soluble base is called an alkali and in aqueous solution it produces hydroxide ions (OH-).
Alkalis are substances that form hydroxide ions (OH-(aq)) in water

Example sodium hydroxide NaOH gives Na+(aq) and OH-(aq) ions, NaOH ¾¾® Na+ + OH- calcium hydroxide Ca(OH)2 gives Ca2+(aq) and 2OH-(aq) ions.

Ca(OH)2 ¾¾®

Ammonia give NH4+ and OH-

NH3 + H2O ¾¾®

[Note: an alkali is a base soluble in water.]

In alkaline solution there are more OH- ions than H+ ions.

[edit] Bases: Properties and Reactions

Bases form a class of chemical substances which include all metal oxides and metal hydroxides.
A soluble base is called an alkali and in aqueous solution it produces hydroxide ions (OH-).
Alkalis are always metal hydroxides because when a metal oxide dissolves in water it forms a metal hydroxide which produces hydroxide ions.
For example, when the base, calcium oxide, dissolves in water, it forms the alkali called calcium hydroxide. This, in solution, produces hydroxide ions:

calcium oxide + water ¾¾® calcium hydroxide

   CaO (s)     +   H2O (1) ¾¾® Ca(OH)2 (aq)

Common bases and alkalis
Common name	Chemical name	Formula	Solubility
caustic soda	sodium hydroxide	NaOH	soluble alkalis
caustic potash	potassium hydroxide	KOH
ammonia solution	aqueous ammonia	NH4+ (aq)
slaked lime	calcium hydroxide	Ca(OH)2
milk of magnesia	magnesium oxide	MgO	insoluble bases
verdigris	copper(II) oxide	CuO
rust	iron(III) oxide	Fe203

Alkalis are often described as being the 'opposite' to acids.
When an alkali is added to an acid, it 'cancels' out the acidity. This is called neutralisation.

Alkalis have certain general properties:

alkalis turn litmus from red to blue in colour;
alkalis feel soapy to touch — this is because they dissolve the natural oils in the skin, to form soap.

[edit] Chemical properties

[edit] Reaction with Ammonium Salt

Ammonium Salt + Alkali ¾¾® Salt + Ammonia + Water

alkalis, when gently warmed with ammonium salts, give off ammonia gas; this is used in the laboratory preparation of ammonia:

ammonium chloride + sodium hydroxide ¾¾® sodium chloride + water + ammonia

[edit] Reaction with Acid

Acid + Alkali ¾¾® Salt + Water

alkalis react with acids to form a salt and water — this is a neutralisation reaction:

Potassium hydroxide + Nitric Acid ¾¾® Potassium Nitrate + Water

[edit] Neutralisation: Reaction of Hydrogen Ions and Hydroxide Ions

Neutralisation is the reaction of hydrogen ions from an acid with hydroxide ions from a base or alkali to form water molecules.
A salt is also produced. All neutralisation reactions can be represented by the ionic equation

H+(aq) + OH-(aq) ¾¾® H2O(1) from acid from alkali neutral

[edit] Mere Oxide: Basic, Acidic, Neutral, or Amphoteric

Metal oxides are basic oxides and those that dissolve in water are called alkalis.
Some non-metal oxides dissolve in water to form acids, and are called acidic oxides.
Other metal oxides can behave as both acids and bases and are said to be amphoteric oxides.

Amphoteric react with acids to form a salt and water, thereby acting as a base:

zinc oxide + sulphuric acid ¾¾® zinc sulphate + water ZnO (s) + H2SO4 (aq) ¾¾® ZnSO4 (aq) + H2O (1)

In the same way, they can also react with an alkali, to form a salt and water, thereby acting as an acid.

zinc oxide + sodium hydroxide ¾¾® sodium zincate + water ZnO (s) + 2NaOH (aq) ¾¾® Na2ZnO2 (aq) + H2O (1)

Finally, there are some non-metal oxides which have none of the properties mentioned above.
They are called neutral oxides.
Such oxides are usually insoluble in water and therefore they have no reaction with acids or alkalis.
An example would be carbon monoxide, a poisonous gas found in exhaust fumes.

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Acids

From OneSchoolWiki

Contents

[edit] Introduction

[edit] Organic Acid

[edit] Mineral Acid

[edit] Theory Of Acids And Alkalis

[edit] Bold text=Chemical Properties of Acid=

[edit] Reaction with Reactive Metal

[edit] Reaction with Metal Oxide (Neutralisation)

[edit] Reaction with Alkali (Neutralisation)

[edit] Reaction with Metal Carbonate

[edit] The Ionic Equation

[edit] Acidity Needs Water

[edit] Base and Alkali

[edit] Bases: Properties and Reactions

[edit] Chemical properties

[edit] Reaction with Ammonium Salt

[edit] Reaction with Acid

[edit] Neutralisation: Reaction of Hydrogen Ions and Hydroxide Ions

[edit] Mere Oxide: Basic, Acidic, Neutral, or Amphoteric

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