Sodium carbonate and sulfuric acid have opposite pH properties. Soda ash can be made from sodium hydroxide and carbonic acid. Sodium carbonate is used in glassmaking and laundry detergents. Sulfuric acid is important for phosphate fertilizers, rayon manufacturing, and other industries. Sodium sulfate has various uses, including in papermaking and medicine.
Sodium carbonate and sulfuric acid—important chemicals singly and in combination—are on opposite sides of the pH scale; sodium carbonate (Na2CO3) is a fairly basic salt, while sulfuric acid (H2SO4) is one of the strongest mineral acids. Careful consideration of its chemical structure reveals that soda ash can be made from sodium hydroxide (NaOH), plus carbonic acid (H2CO3); the salt of such a weak acid with such a strong base is not neutral, but basic. The equation for this is 2 NaOH + H2CO3 → Na2CO3 + 2 H2O. Alternatively, if left exposed to air, sodium hydroxide very slowly absorbs carbon dioxide (CO2) from the atmosphere, obeying the relationship 2 NaOH + CO2 → Na2CO3 + H2O. In both cases, the reaction between soda ash and sulfuric acid is Na2CO3 + H2SO4 → Na2SO4 + H2O + CO2, where Na2SO4 is the chemical formula of sodium sulfate.
Sodium carbonate bears the historical familiar name of “washing soda”, because thanks to its alkaline, or basic, properties, it improves the functioning of laundry detergents. Another name is soda ash, as an early primary source came from tree ashes, algae, and other organic material. Its most important use today – accounting for nearly half of its total production level – is in glassmaking. Nearly 30% of its use, however, is for the production of chemicals. Sodium carbonate and sulfuric acid are used in the laboratory as standards against which other substances can be evaluated.
Sulfuric acid is among the most important industrial chemicals worldwide, particularly in Asia and the United States, and is especially critical for the production of phosphate fertilizers. Rayon, originally a substitute for silk, uses sulfuric acid in its manufacture. Sodium sulfate, an important byproduct in rayon manufacturing, is generally not derived from the combination of soda ash and sulfuric acid. Rather, it results when sodium hydroxide (NaOH) – so-called caustic soda – is used to neutralize the “spent” acid. The acid is also used in automotive batteries, steelmaking, and explosives manufacturing.
Water molecules associate with the simple Na2SO4 molecule to form hydration products, including the building-damaging heptahydrate (Na2SO4·7H2O). The damage occurs because soluble salts can travel into the pores and exert stressful pressure; Fortunately, another hydrate, Glauber’s salt (Na2SO4 10H2O), decahydrate, is being evaluated for positive use in latent heat storage in heating and cooling systems. The pulp industry uses sodium sulfate in the Kraft process for making paper. In medicine, salt is used as a cathartic, diuretic and purgative.
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