Properties of sulfuric acid, its reactions with metals
What properties are typical for sulfuric acid?
Sulfuric acid is one of the strongest mineral acids. It is an oil hydroscopic liquid without smell or color. It is a strong oxidizer, and forms two rows of salts – sulfates and hydrosulfates.
Obtaining sulfuric acid
There are two main methods for obtaining sulfuric acid – contact and nitrous. In the first case, the reaction equations for obtaining sulfuric acid are the following:
- S + O₂ = SO₂ (to obtain the dioxide, molecular sulfur or pyrite FeS₂ is burnt);
- 2SO₂ + O₂ = 2SO₃ (sulfur trioxide is obtained in the oxidation of dioxide in the presence of vanadium V₂O₅);
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- SO₃ + H₂O = H₂SO₄ (by adding water to the trioxide (white hydroscopic crystals), sulfuric acid of a concentration of 92-94% can be obtained).
Sometimes trioxide is enriched with sulfuric acid, creating oleum: SO₃ + H₂SO₄ = H₂S₂O₇ (acid of the required concentration is obtained by adding oleum).
There is also the nitrous (tower) method of obtaining sulfuric acid by the reaction:
SO₂ + NO₂ + H₂O = H₂SO₄ + NO.
The result is acid with a concentration of 75%.
Chemical properties of sulfuric acid
Sulfuric acid is a strong mineral acid. Like any other acid, sulfuric acid enters into a neutralization reaction with bases, forming two rows of salts depending on the ratio of reagents – sulfates and hydrosulfates:
H₂SO₄ + 2NaOH = Na₂SO₄ + 2H₂O (sodium sulfate);
H₂SO₄ + NaOH = NaHSO₄ + 2H₂O (sodium hydrosulfate).
Many sulfates dissolve well in water.
Diluted sulfuric acid also reacts typically with all metals which are located before hydrogen in the reactivity row:
H₂SO₄ + Fe = FeSO₄ + H₂.
Diluted acid does not react with metals located after hydrogen. Concentrated sulfuric acid may react with reactive and low-reactive metals according to these equations:
Cu + 2H₂SO₄ = CuSO₄ + SO₂ +2H₂O;
3Zn + 4H₂SO₄ = 3ZnSO₄ + S + 4H₂O.
Concentrated sulfuric acid passivates iron and aluminum.
Other reactions of sulfuric acid:
With primary oxides: H₂SO₄ + CuO = CuSO₄ + H₂O;
With non-metals: 2H₂SO₄ + S = 3SO₂ + 2H₂O (with heating, concentrated acid);
With salts: H₂SO₄ + Na₂CO₃ = Na₂SO₄ + CO₂ + H₂O;
With sulfur trioxide: SO₃ + H₂SO₄ = H₂S₂O₇;
With hydrogen halides: 2HBr + H₂SO₄ = Br₂ + SO₂ + 2H₂O;
With salts: H₂SO₄ + BaCl₂ = BaSO₄ + 2HCl;
With formic acid: H₂SO₄ + HCOOH = CO + H₂SO₄*nH₂O.
Sulfuric acid is also often used to create acidic mediums – for example for the behavior of oxidation-reduction reaction with potassium permanganate. Acid is capable of dehydrating and carbonizing organic matter:
С₂Н₅ОН = С₂Н₄ + Н₂О (dehydration of alcohol);
C₆H₁₂O₆ + 12H₂SO₄ = 18H₂O + 12SO₂ + 6CO₂ (decomposition).
Sulfuric acid is also used in industry in organic synthesis (as a dehydrating agent). With sulfuric acid, ores are treated in cases when rare metals need to be obtained from them. Sulfuric acid is used for manufacture of batteries, and also in the oil, leather and textile industries.