(O level Chem) Are reactions of acids redox reactions?

Acids and Alkalis is one of the easiest chapters to many students. The basic thing is that acids are substances that produce protons H⁺(aq) or hydroxonium ions H₃O⁺ when dissolved in water, not in alcohol or any other solvents. Do get the habit of writing “H⁺(aq)” instead of just “H⁺” because the proton is simply too unstable by itself. Because the concentration of H⁺(aq) in the acidic solutions is greater than the concentration of OH^-(aq), acidic solutions turn blue litmus to red, and yellow methyl orange to red. They have a pH (= -lg [H⁺]) of less than 7.

The properties of acids are due to their protons. 

H⁺(aq) ions are also responsible for the various properties of acids. They combine with OH^-(aq) in alkalis to produce water. This gives the general equation, acid + alkali --> salt + water, that's a neutralization. Its ionic equation is H⁺(aq) + OH^-(aq) --> H₂O(l). Note that the salt, which is soluble, don't appear in the ionic equation because they are spectator ions.

Acids can also be neutralized by carbonates. Carbonates are compounds that contain the ion CO₃^2-. Carbonates are either soluble such as Na₂CO₃ (Remember that all sodium compounds are soluble.) or insoluble such as CaCO₃ (in limestone) and CuCO₃. Effervescence is observed during the neutralization of an acid by a carbonate. The colorless gas gives a white precipitate with limewater indicating that it's carbon dioxide. The general equation is acid + carbonate --> salt water + carbon dioxide. The ionic equation is H⁺(aq) + CO₃^2-(aq) --> H₂O(l) + CO₂(g).

Acids also corrode metals producing a colorless and odorless gas that extinguishes a burning splint with a “pop” sound. The general equation for the reaction is acid + metal --> salt + hydrogen. If an acid reacts with zinc, then the ionic equation is Zn(s) + H⁺(aq) --> Zn²⁺(aq) + H₂(g). This is called a displacement reaction because the hydrogen is displaced by the metal. Remember, however, that dilute HCl and H₂SO₄ do not react with copper which is unreactive.

So, are the above three reactions redox reactions? To identify a redox reaction, we look for whether there are oxidation and reduction occurring in the reaction. The best way is to look for changes in oxidation states which are charges of atoms. When there's an increase in oxidation state, we say oxidation has occurred. When there's a decrease in oxidation state, we say reduction has occurred. A redox reaction has to have both oxidation and reduction occurring simultaneously. In the following, the oxidation states of atoms are already calculated for you. You've got to know how to calculate them. Only one of the reactions is a redox reaction. Which one? 

(O Level Chem) Formulas and dot-and-cross diagrams of ionic compounds

Ionic compounds contain cations (usually metal ions) and anions (non-metal ions).

When atoms form ions, they tend to achieve the electronic configuration of noble gases.

Examples:

• Beryllium (electronic configuration: 2,2) loses 2 electrons to form the duplet structure of helium (electronic configuration: 2). 

• Oxygen (electronic configuration: 2,6) gains 8 - 6 = 2 electrons to form the octet structure of neon (electronic configuration: 2,8).
  

Be --> Be²⁺ + 2e (loss of electrons: oxidation)

O + 2e --> O^2- (gain of electrons: reduction) 

What if you're asked to write out the formulas of unfamiliar ionic compounds like strontium chloride, silver astatide or gallium(III) sulfide? First, refer to the Periodic Table to find out which Group each element belongs to. Then decide the number of each type of ions needed to balance each others' charges.

• Strontium chloride: Sr (Group II) forms Sr²⁺ and chlorine (Group VII) forms Cl^-. One Sr²⁺ balances the 2 x -1 = -2 charge of two Cl^-. Formula: SrCl₂.
  
• Silver astatide: Silver is known to form Ag⁺ as in AgCl and AgNO₃. Astatide (Group VII) forms At^-. One Ag⁺ balances the -1 charge of one At^-. Formula: AgAt.
  
• Gallium(III) sulfide: As indicated by “(III)”, we write Ga³⁺. Sulfur (Group VI) forms S^2-. Two Ga³⁺ balances the 3 x -2 = -6 charge of three S^2-. Formula: Ga₂S₃.
  

What if you're asked to draw the dot-and-cross structures of unfamiliar ionic compounds and the question asks for only the valence (outer-most) electrons? We shall use dots for electrons from the metal atom and crosses for electrons from the non-metallic atom. The valence shell of the resultant cation should be empty, while the valence shell of the resultant anion should be full (have both dots and crosses). Remember to include charges as superscripts and number of ions as subscripts.

In the formation of ionic compounds, the outer electrons of the metal atom is transferred to the non-metallic atom.

Now, complete this table. Then form dot-and-cross ionic structures of your own using only the Groups I-VII elements.

Group number	Number of electrons involved to form an ion	Formation of ions
I (alkali metals)	1 valence electron ==> Atom will lose 1 electron	M --> M+ + e e.g. K --> K+ + e (oxidation)
II (alkaline metals)
III
IV
V
VI
VII (halogens)
0	2 (duplet) or 8 (octet) ==> Atom will neither lose nor gain electrons

Answer:

Group number	Number of electrons involved to form an ion	Formation of ions
I (alkali metals)	1 valence electron ==> Atom will lose 1 electron	M --> M+ + e e.g. K --> K+ + e (oxidation)
II (alkaline metals)	2 valence electrons ==> Atom will lose 2 electrons	M --> M2+ + 2e e.g. Ca --> Ca2+ + 2e (oxidation)
III	3 valence electrons ==> Atom will lose 3 electrons	M --> M3+ + 3e e.g. Al --> Al3+ + 3e (oxidation)
IV	4 valence electrons ==> Atom will gain 8 – 4 = 4 electrons	X + 4e --> X4- (reduction)
V	5 valence electrons ==> Atom will gain 8 – 5 = 3 electrons	X + 3e --> X3- e.g. N + 3e --> N3- (reduction)
VI	6 valence electrons ==> Atom will gain 8 – 6 = 2 electrons	X + 2e --> X2- e.g. O + 2e --> O2- (reduction)
VII (halogens)	7 valence electrons ==> Atom will gain 8 – 7 = 2 electrons	X + e --> X- e.g. Cl + e --> Cl- (reduction)
0	2 (duplet) or 8 (octet) ==> Atom will neither lose nor gain electrons