Properties of sulfuric acid, its reactions with metals

What properties are typical for sulfuric acid?

Solid sulfuric acid [Wikimedia]

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:

  1. S + O₂ = SO₂ (to ob­tain the diox­ide, molec­u­lar sul­fur or pyrite FeS₂ is burnt);
Celestite is a mineral that contains sulfur [Wikimedia]
  1. 2SO₂ + O₂ = 2SO₃ (sul­fur tri­ox­ide is ob­tained in the ox­i­da­tion of diox­ide in the pres­ence of vana­di­um V₂O₅);

Click here for amaz­ing ex­per­i­ments with sul­fur diox­ide.

  1. 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).

Pyrosulfuric acid molecule (H₂S₂O₇) [Wikimedia]

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%.

Sulfuric acid chemical structure [Wikimedia]

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:

  1. Cu + 2H₂­SO₄ = Cu­SO₄ + SO₂ +2H₂O;

  2. 3Zn + 4H₂­SO₄ = 3Zn­SO₄ + S + 4H₂O.

[Wikimedia]

Con­cen­trat­ed sul­fu­ric acid pas­si­vates iron and alu­minum.

Oth­er re­ac­tions of sul­fu­ric acid:

  1. With pri­ma­ry ox­ides: H₂­SO₄ + CuO = Cu­SO₄ + H₂O;

  2. With non-met­als: 2H₂­SO₄ + S = 3SO₂ + 2H₂O (with heat­ing, con­cen­trat­ed acid);

  3. With salts: H₂­SO₄ + Na₂­CO₃ = Na₂­SO₄ + CO₂ + H₂O;

  4. With sul­fur tri­ox­ide: SO₃ + H₂­SO₄ = H₂S₂O₇;

  5. With hy­dro­gen halides: 2HBr + H₂­SO₄ = Br₂ + SO₂ + 2H₂O;

  6. With salts: H₂­SO₄ + Ba­Cl₂ = Ba­SO₄ + 2HCl;

  7. 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.