Physical properties of sulfuric acid:
Heavy oily liquid (“oil of vitriol”);
density 1.84 g/cm3; non-volatile, highly soluble in water - with strong heating; t°pl. = 10.3°C, t°boil. = 296°C, very hygroscopic, has water-removing properties (charring of paper, wood, sugar).
The heat of hydration is so great that the mixture can boil, splash and cause burns. Therefore, it is necessary to add acid to water, and not vice versa, since when water is added to acid, lighter water will end up on the surface of the acid, where all the heat generated will be concentrated.
Industrial production of sulfuric acid (contact method):
1) 4FeS 2 + 11O 2 → 2Fe 2 O 3 + 8SO 2
2) 2SO 2 + O 2 V 2 O 5 → 2SO 3
3) nSO 3 + H 2 SO 4 → H 2 SO 4 nSO 3 (oleum)
Crushed, purified, wet pyrite (sulfur pyrite) is poured into the kiln on top for firing in " fluidized bed". Air enriched with oxygen is passed from below (counterflow principle).
Furnace gas comes out of the furnace, the composition of which is: SO 2, O 2, water vapor (the pyrite was wet) and tiny particles of cinder (iron oxide). The gas is purified from impurities of solid particles (in a cyclone and electric precipitator) and water vapor (in a drying tower).
In a contact apparatus, sulfur dioxide is oxidized using a catalyst V 2 O 5 (vanadium pentoxide) to increase the reaction rate. The process of oxidation of one oxide to another is reversible. Therefore, optimal conditions for the direct reaction are selected - increased pressure (since the direct reaction occurs with a decrease in the total volume) and a temperature not higher than 500 C (since the reaction is exothermic).
In the absorption tower, sulfur oxide (VI) is absorbed by concentrated sulfuric acid.
Absorption by water is not used, because sulfur oxide dissolves in water with the release of a large amount of heat, so the resulting sulfuric acid boils and turns into steam. To prevent the formation of sulfuric acid fog, use 98% concentrated sulfuric acid. Sulfur oxide dissolves very well in such an acid, forming oleum: H 2 SO 4 nSO 3
Chemical properties of sulfuric acid:
H 2 SO 4 is a strong dibasic acid, one of the strongest mineral acids; due to its high polarity, the H – O bond is easily broken.
1)
Sulfuric acid dissociates in aqueous solution
, forming a hydrogen ion and an acidic residue:
H 2 SO 4 = H + + HSO 4 - ;
HSO 4 - = H + + SO 4 2- .
Summary equation:
H 2 SO 4 = 2H + + SO 4 2- .
2) Interaction of sulfuric acid with metals:
Dilute sulfuric acid dissolves only metals in the voltage series to the left of hydrogen:
Zn 0 + H 2 +1 SO 4 (diluted) → Zn +2 SO 4 + H 2
3)
Reaction of sulfuric acidwith basic oxides:
CuO + H 2 SO 4 → CuSO 4 + H 2 O
4)
Reaction of sulfuric acid withhydroxides:
H 2 SO 4 + 2NaOH → Na 2 SO 4 + 2H 2 O
H 2 SO 4 + Cu(OH) 2 → CuSO 4 + 2H 2 O
5)
Exchange reactions with salts:
BaCl 2 + H 2 SO 4 → BaSO 4 ↓ + 2HCl
The formation of a white precipitate of BaSO 4 (insoluble in acids) is used to detect sulfuric acid and soluble sulfates (qualitative reaction to sulfate ion).
Special properties of concentrated H 2 SO 4:
1) Concentrated sulfuric acid is strong oxidizing agent ; when interacting with metals (except Au, Pt), it is reduced to S +4 O 2, S 0 or H 2 S -2 depending on the activity of the metal. Without heating, it does not react with Fe, Al, Cr - passivation. When interacting with metals with variable valency, the latter oxidize to higher oxidation states than in the case of a dilute acid solution: Fe 0→ Fe 3+ , Cr 0→ Cr 3+ , Mn 0→Mn 4+,Sn 0→ Sn 4+
Active metal
8 Al + 15 H 2 SO 4 (conc.) → 4Al 2 (SO 4) 3 + 12H 2 O + 3 H2S
4│2Al 0 – 6 e— → 2Al 3+ — oxidation
3│ S 6+ + 8e → S 2– recovery
4Mg+ 5H 2 SO 4 → 4MgSO 4 + H 2 S + 4H 2 O
Medium activity metal
2Cr + 4 H 2 SO 4 (conc.) → Cr 2 (SO 4) 3 + 4 H 2 O + S
1│ 2Cr 0 – 6e →2Cr 3+ - oxidation
1│ S 6+ + 6e → S 0 – recovery
Low-active metal
2Bi + 6H 2 SO 4 (conc.) → Bi 2 (SO 4) 3 + 6H 2 O + 3 SO 2
1│ 2Bi 0 – 6e → 2Bi 3+ – oxidation
3│ S 6+ + 2e →S 4+ - recovery
2Ag + 2H 2 SO 4 →Ag 2 SO 4 + SO 2 + 2H 2 O
2) Concentrated sulfuric acid oxidizes some non-metals, usually to the maximum oxidation state, and is itself reduced toS+4O2:
C + 2H 2 SO 4 (conc) → CO 2 + 2SO 2 + 2H 2 O
S+ 2H 2 SO 4 (conc) → 3SO 2 + 2H 2 O
2P+ 5H 2 SO 4 (conc) → 5SO 2 + 2H 3 PO 4 + 2H 2 O
3) Oxidation of complex substances:
Sulfuric acid oxidizes HI and HBr to free halogens:
2 KBr + 2H 2 SO 4 = K 2 SO 4 + SO 2 + Br 2 + 2H 2 O
2 KI + 2H 2 SO 4 = K 2 SO 4 + SO 2 + I 2 + 2H 2 O
Concentrated sulfuric acid cannot oxidize chloride ions to free chlorine, which makes it possible to obtain HCl by the exchange reaction:
NaCl + H 2 SO 4 (conc.) = NaHSO 4 + HCl
Sulfuric acid removes chemically bound water from organic compounds containing hydroxyl groups. Dehydration of ethyl alcohol in the presence of concentrated sulfuric acid produces ethylene:
C 2 H 5 OH = C 2 H 4 + H 2 O.
The charring of sugar, cellulose, starch and other carbohydrates upon contact with sulfuric acid is also explained by their dehydration:
C 6 H 12 O 6 + 12H 2 SO 4 = 18H 2 O + 12SO 2 + 6CO 2.
Undiluted sulfuric acid is a covalent compound.
In the molecule, sulfuric acid is tetrahedrally surrounded by four oxygen atoms, two of which are part of the hydroxyl groups. The S–O bonds are double, and the S–OH bonds are single.
The colorless, ice-like crystals have a layered structure: each H 2 SO 4 molecule is connected to four neighboring strong hydrogen bonds, forming a single spatial framework.
The structure of liquid sulfuric acid is similar to the structure of solid one, only the integrity of the spatial framework is broken.
Physical properties of sulfuric acid
Under normal conditions, sulfuric acid is a heavy, oily liquid without color or odor. In technology, sulfuric acid is a mixture of both water and sulfuric anhydride. If the molar ratio of SO 3: H 2 O is less than 1, then it is an aqueous solution of sulfuric acid; if it is greater than 1, it is a solution of SO 3 in sulfuric acid.
100% H 2 SO 4 crystallizes at 10.45 ° C; T kip = 296.2 °C; density 1.98 g/cm3. H 2 SO 4 mixes with H 2 O and SO 3 in any ratio to form hydrates; the heat of hydration is so high that the mixture can boil, splash and cause burns. Therefore, it is necessary to add acid to water, and not vice versa, since when water is added to acid, lighter water will end up on the surface of the acid, where all the heat generated will be concentrated.
When aqueous solutions of sulfuric acid containing up to 70% H 2 SO 4 are heated and boiled, only water vapor is released into the vapor phase. Sulfuric acid vapor also appears above more concentrated solutions.
In terms of structural features and anomalies, liquid sulfuric acid is similar to water. There is the same system of hydrogen bonds, almost the same spatial framework.
Chemical properties of sulfuric acid
Sulfuric acid is one of the strongest mineral acids; due to its high polarity, the H–O bond is easily broken.
Sulfuric acid dissociates in aqueous solution , forming a hydrogen ion and an acidic residue:
H 2 SO 4 = H + + HSO 4 - ;
HSO 4 - = H + + SO 4 2- .
Summary equation:
H 2 SO 4 = 2H + + SO 4 2- .
Shows properties of acids , reacts with metals, metal oxides, bases and salts.
Dilute sulfuric acid does not exhibit oxidizing properties; when it interacts with metals, hydrogen and a salt containing the metal in the lowest oxidation state are released. In the cold, the acid is inert towards metals such as iron, aluminum and even barium.
Concentrated acid has oxidizing properties. Possible products of the interaction of simple substances with concentrated sulfuric acid are given in the table. The dependence of the reduction product on the acid concentration and the degree of activity of the metal is shown: the more active the metal, the more deeply it reduces the sulfate ion of sulfuric acid.
Interaction with oxides:
CaO + H 2 SO 4 = CaSO 4 = H 2 O.
Interaction with bases:
2NaOH + H 2 SO 4 = Na 2 SO 4 + 2H 2 O.
Interaction with salts:
Na 2 CO 3 + H 2 SO 4 = Na 2 SO 4 + CO 2 + H 2 O.
Oxidative properties
Sulfuric acid oxidizes HI and HBr to free halogens:
H 2 SO 4 + 2HI = I 2 + 2H 2 O + SO 2.
Sulfuric acid removes chemically bound water from organic compounds containing hydroxyl groups. Dehydration of ethyl alcohol in the presence of concentrated sulfuric acid produces ethylene:
C 2 H 5 OH = C 2 H 4 + H 2 O.
The charring of sugar, cellulose, starch and other carbohydrates upon contact with sulfuric acid is also explained by their dehydration:
C 6 H 12 O 6 + 12H 2 SO 4 = 18H 2 O + 12SO 2 + 6CO 2.
Any acid is a complex substance whose molecule contains one or more hydrogen atoms and an acid residue.
The formula of sulfuric acid is H2SO4. Consequently, the sulfuric acid molecule contains two hydrogen atoms and the acidic residue SO4.
Sulfuric acid is formed when sulfur oxide reacts with water
SO3+H2O -> H2SO4
Pure 100% sulfuric acid (monohydrate) is a heavy liquid, viscous like oil, colorless and odorless, with a sour “copper” taste. Already at a temperature of +10 ° C it hardens and turns into a crystalline mass.
Concentrated sulfuric acid contains approximately 95% H2SO4. And it hardens at temperatures below –20°C.
Interaction with water
Sulfuric acid dissolves well in water, mixing with it in any proportion. This releases a large amount of heat.
Sulfuric acid can absorb water vapor from the air. This property is used in industry for drying gases. The gases are dried by passing them through special containers with sulfuric acid. Of course, this method can only be used for those gases that do not react with it.
It is known that when sulfuric acid comes into contact with many organic substances, especially carbohydrates, these substances become charred. The fact is that carbohydrates, like water, contain both hydrogen and oxygen. Sulfuric acid takes these elements away from them. What remains is coal.
In an aqueous solution of H2SO4, the indicators litmus and methyl orange turn red, which indicates that this solution has a sour taste.
Interaction with metals
Like any other acid, sulfuric acid is capable of replacing hydrogen atoms with metal atoms in its molecule. It interacts with almost all metals.
Diluted sulfuric acid reacts with metals like an ordinary acid. As a result of the reaction, a salt with an acidic residue SO4 and hydrogen is formed.
Zn + H2SO4 = ZnSO4 + H2
A concentrated sulfuric acid is a very strong oxidizing agent. It oxidizes all metals, regardless of their position in the voltage series. And when reacting with metals, it itself is reduced to SO2. Hydrogen is not released.
Сu + 2 H2SO4 (conc) = CuSO4 + SO2 + 2H2O
Zn + 2 H2SO4 (conc) = ZnSO4 + SO2 + 2H2O
But gold, iron, aluminum, and platinum group metals do not oxidize in sulfuric acid. Therefore, sulfuric acid is transported in steel tanks.
The sulfuric acid salts that are obtained as a result of such reactions are called sulfates. They are colorless and easily crystallize. Some of them are highly soluble in water. Only CaSO4 and PbSO4 are slightly soluble. BaSO4 is almost insoluble in water.
Interaction with bases
The reaction between acids and bases is called neutralization reaction. As a result of the neutralization reaction of sulfuric acid, a salt containing the acid residue SO4 and water H2O are formed.
Examples of sulfuric acid neutralization reactions:
H2SO4 + 2 NaOH = Na2SO4 + 2 H2O
H2SO4 + CaOH = CaSO4 + 2 H2O
Sulfuric acid reacts with neutralization with both soluble and insoluble bases.
Since the sulfuric acid molecule has two hydrogen atoms, and two bases are required to neutralize it, it is classified as a dibasic acid.
Interaction with basic oxides
From the school chemistry course we know that oxides are complex substances that contain two chemical elements, one of which is oxygen in the oxidation state -2. Basic oxides are called oxides of 1, 2 and some 3 valence metals. Examples of basic oxides: Li2O, Na2O, CuO, Ag2O, MgO, CaO, FeO, NiO.
Sulfuric acid reacts with basic oxides in a neutralization reaction. As a result of this reaction, as in the reaction with bases, salt and water are formed. The salt contains the acidic residue SO4.
CuO + H2SO4 = CuSO4 + H2O
Interaction with salts
Sulfuric acid reacts with salts of weaker or volatile acids, displacing these acids from them. As a result of this reaction, a salt with an acidic residue SO4 and an acid are formed
H2SO4+BaCl2=BaSO4+2HCl
Application of sulfuric acid and its compounds
Barium porridge BaSO4 is capable of blocking X-rays. Filling the hollow organs of the human body with it, radiologists examine them.
In medicine and construction, natural gypsum CaSO4 * 2H2O and calcium sulfate crystalline hydrate are widely used. Glauber's salt Na2SO4 * 10H2O is used in medicine and veterinary medicine, in the chemical industry - for the production of soda and glass. Copper sulfate CuSO4 * 5H2O is known to gardeners and agronomists, who use it to combat pests and plant diseases.
Sulfuric acid is widely used in various industries: chemical, metalworking, oil, textile, leather and others.
