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:

Monoprotic acids

HNO3 – nitric acid

HCl – hydrochloric acid

CH3COOH – acetic acid (ethanoic acid) => (Organic acids contain -COOH group)

Diprotic acid

H2SO4 – sulfuric acid

Triprotic 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

Let’s go to make an experiment about daily life acids and 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)

NEUTRALIZATION REACTIONS:

  • 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

Exercise:

  1. How many moles of NaOH is needed to neutralize 0.5 moles of HNO3?
  1. 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:

Sample:

Na2O(aq) +   HCl(aq) –>  NaCl(aq) +  H2O(s)

Basic             Acid                Salt            Water  

Exercises:

NaOH(aq) +  SO3(aq) –>  Na2SO4(aq) + H2O(s)

                                                                                  

Na2O(aq) +  SO3(aq) –> Na2SO4 (aq)

                                                             

Exercise: Complete and balance the following neutralization reactions.

  1. Ca(OH)2(aq) + HCl(aq) –>
  2. H2SO4(aq) + CaO(aq) –>
  3. H3PO4(aq) + Mg(OH)2(aq) –>
  4. NH3(aq) + HCl(aq) –>
  5. N2O5(aq) + HBr(aq) –>
  6. K2O(aq) + CO2(aq) –>

OXIDES