Sodium Through Argon
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All of the second- and third-row metals are found in the crust of the Earth in the form of silicates (which we will discuss in the next section), carbonates, oxides, and nitrates. Sodium carbonate, Na2CIO3, is the salt of a strong base, NaOH, and a weak acid, H2CO3 (See 1). Carbonic acid is weak because the carbonate ion has nearly as strong an affinity for protons as water does. About half of the carbonic acid remains in undissociated form in water solution, half exists as bicarbonate ion, HCO3-, and very little CO32- is present (See 2). When sodium carbonate is dissolved in water, the carbonate ions thus released take protons away from water molecules and make bicarbonate and hydroxide ions (See 3). This is called hydrolysis, or "cleaving with water," under the original but erroneous impression that water simply takes sodium carbonate apart, rather than the carbonate ion pulling the water molecule apart. A solution of sodium carbonate, or of any salt of a strong base and weak acid, will be mildly basic. |
Na2CO3, or washing soda, is used as a mild source of hydroxide ions in the home and in industry. It dissolves grease and oils by turning them into soaps that can be washed away, but is not as corrosive to people or property as sodium hydroxide is. Sodium bicarbonate, NaHCO3, is an even weaker base because only the second hydrolysis (See4)) can take place and is used internally as an ant-acid (see 5). It is also used as a raising agent in baking as even with mild acetic acid it produces CO2 gas. (see 6) (1) 2NaOH + H2CO3 ------> Na2CO3 + 2H2O (2) Na2CO3 ------> 2Na+ + CO3- (3) CO3- + H2O ------> HCO3- + OH- (almost completely) (4) HCO3- + H2O ------> H2CO3 + OH- (only halfway) (5) Na+ + HCO3- + H2O ------> Na+ + H2CO3 + OH- (6) H+ + HCO3- ------> H2CO3 ------> H2O + CO2(gas) |
