ACIDS, BASES AND SALTS
Properties of Acids, Bases and Salts:
Acids (Latin word acidus, meaning sour like lemon)
- Acids taste sour.
- Their aqueous solutions conduct electric current (electrolyte solutions)
- Acids turn blue litmus to red.
- pH less than 7
- Examples of acids:
HNO3 – nitric acid
HCl – hydrochloric acid
CH3COOH – acetic acid (ethanoic acid) => (Organic acids contain -COOH group)
H2SO4 – sulfuric acid
H3PO4 – phosphoric acid
- Acids react with bases and form salt and water. This reaction type is called neutralization reaction.
HCl + NaOH –> NaCl + H2O
Bases (Alkali: Arabic word for the ashes that come from burning certain plants; water solutions feel slippery and taste bitter like soap)
- Their taste is bitter like shampoo.
- Their solutions with water conduct electric current (electrolyte solutions)
- Bases are slippery.
- Bases turn red litmus to blue.
- Bases turn phenolphthalein to purple
- pH greater than 7
- They react with acids and form salt and water. (Neutralization reactions)
The Arrhenius theory: Swedish scientist Svante Arrhenius (1859–1927) proposed a theory explaining the nature of acids and bases according to their structure and the ions produced when they dissolve in water.
- Acids are any substances that dissociate to produce hydrogen ions (H+) when dissolved in water.
HA(aq) –> H+(aq) + A–(aq)
Hydrochloric acid: HCl(aq) –> H+(aq) + Cl–(aq)
Nitric acid: HNO3(aq) –> H+(aq) + NO3–(aq)
Acetic acid: CH3COOH(aq) –> H+(aq) + CH3COO–(aq)
- In fact the hydrogen ion (H+) will associate with a water molecule to form H3O+. One way to write the equation for an acid ‘HA’ dissolving in water is:
HA + H2O(l) –> H3O+(aq) + A–(aq)
- Bases are any substances that dissociate to produce hydroxide ions (OH–) when dissolved in water.
MOH(aq) –> M+(aq) + OH–(aq)
Sodium hydroxide: NaOH(aq) –> Na+(aq) + OH–(aq)
Barium hydroxide: Ba(OH)2(aq) –> Ba2+(aq) + 2OH–(aq)
Ammonia: NH3(aq) + H2O –> NH4+(aq) + OH–(aq)
Salts (Ionic compounds)
- Ionic compounds that can result from the neutralization reaction of an acid and a base.
- They are composed of cations (positively charged ions) and anions (negative ions) so that the product is electrically neutral (without a net charge).
- Ionic compounds are dissociated into ions when they are dissolved in water.
Sodium Chloride: NaCl(s) + water –> Na+(aq) + Cl–(aq)
Magnesium bromide: MgBr2(s) + water –> Mg2+(aq) + 2Br–(aq)
Potassium nitrate: KNO3(s) + water –> K+(aq) + NO3–(aq)
Sodium acetate: CH3COONa(s) + water –> CH3COO–(aq) + Na+(aq)
Exercise: Dissociation equations of acids
Exercise: Dissociation equations of bases
Acidic Oxides & Basic Oxides:
Nonmetal oxides: (=Acidic oxides if #Oxygen>#Nonmetal)
CO2, NO2, N2O3, N2O5, P2O5, SO2, SO3, etc. Acidic oxides form acids when they’re dissolved in water.
CO2(g) + H2O(l) –> H2CO3(aq) (Carbonic acid)
SO2(g) + H2O(l) –> H2SO3(aq) (Sulfurous acid)
SO3(g) + H2O(l) –> H2SO4(aq) (Sulfuric acid)
N2O5(g) + H2O(l) –> 2HNO3(aq) (Nitric acid)
Metal oxides: (=Basic oxides except amphoteric metal oxides)
Na2O, K2O, MgO, CaO, etc. Basic oxides form bases when they’re dissolved in water.
Na2O(s) + H2O(l) –> 2NaOH(aq)
CaO(s) + H2O(l) –> Ca(OH)2(aq)
- Acids react with bases and form salt and water. This reaction type is called neutralization reaction and also double-displacement reactions.
- The number of H+ ions should be equal to the number of OH– ions for neutralization to form water (H+OH–).
HCl + KOH –> KCl + H2O
H2SO4 + 2NaOH –> Na2SO4 + 2H2O
- How many moles of NaOH is needed to neutralize 0.5 moles of HNO3?
- If 0.2 moles of H2SO4 reacts with 0.5 moles of KOH, how many moles of with substance remain without reaction?
Neutralization Reactions of Oxides:
Na2O(aq) + HCl(aq) –> NaCl(aq) + H2O(s)
Basic Acid Salt Water
NaOH(aq) + SO3(aq) –> Na2SO4(aq) + H2O(s)
Na2O(aq) + SO3(aq) –> Na2SO4 (aq)
Exercise: Complete and balance the following neutralization reactions.
- Ca(OH)2(aq) + HCl(aq) –>
- H2SO4(aq) + CaO(aq) –>
- H3PO4(aq) + Mg(OH)2(aq) –>
- NH3(aq) + HCl(aq) –>
- N2O5(aq) + HBr(aq) –>
- K2O(aq) + CO2(aq) –>