Sulfuric acid

 

Sulfuric acid

Chemical formula	H2SO4
OTP appearance	oily liquid
Molar Mass(g/mol)	98.79
Density(g/cc)	1.84
Melting Point(°C)	10
Boiling Point(°C)	337
Solubility in water(g/L)	misc
Water azeotrope(mol%)	88.5
Water azeotrope(%v/v)	95.8
Water azeotrope(%w/w)	98
NFPA 704	0 3 2 W

Sulfuric acid is a strong acid. It is not the strongest acid, but it is arguably the source of most other acids, weaker or stronger. In fact, according to most sources, sulfuric acid is the primary industrial chemical on earth, and a nation's ability to produce it may be a good indicator of it's industrial strength.

Uses

Primary

• Sulfuric acid is the preeminent industrial chemical.
• The precursor to many mineral acids including hydrochloric acid, phosphoric acid and nitric acid

Secondary

• purification of copper
• in lead-acid voltaic cells
• as a chemical dehydrating agent, particularly during nitration of hydrocarbons.

Natural Occurrence

• Sulfuric acid does occur naturally, primarily in post-volcanic acid rain and as acidic rock drainage from sulfide minerals.

Hazards

N.B. Sulfuric acid is among the most hazardous chemicals we list in this project. Treat it with the utmost care.

• Sulfuric acid will dissolve most metals and virtually all organic matter. Spills of concentrated acid are often essentially unfixable: adding a correspondingly strong alkali in the hopes of neutralizing the acid can result in even more heat being produced and splatters of acid (and concentrated alkali) flying in all directions. Sometimes it is best to wait until the reactions stop of their own accord, then repair the damage.
• Sulfuric acid, in the process of breaking down most organics, produces substantial amounts of heat. Often enough to start fires where there were none before. In fact, a mixture of sulfuric acid added to organics was (for a while) used as a fire starting mechanism before reliable strike matches were available. Be very careful.

Character

Stoichiometry

228g (190.5L, a sphere with R=35.66cm, D=71.32cm, or a cube 58cm on an edge) of (dry, 20°C) air contains 1.5 mol of O₂. (48g or 3 mol of O)

32g (16cc) of sulfur contains 1 mol of S

18g (18cc) of water contains 1 mol of H₂O

So...

1.5 mol O₂ + 1 mol S + 1 mol H₂O = 1 mol H₂SO₄

48g O₂ + 32g S + 18g water = 98g H₂SO₄

Production

Synthesis

via other mineral acids

See mineral acid intraconversion

via electrolysis

copper sulfate

Using a copper anode, and a graphite, platinum, lead, or lead dioxide anode, pass 300-600 Am^-2 at 1-2.5V through a concentrated solution of copper sulfate:

2 CuSO₄(aq) + 2 H₂O

{

→

1-2.5V}

2 Cu(s) + 2 H₂SO₄(aq) + O₂(g)

magnesium sulfate

Using a porous ceramic partition (such as a low-fired clay pot)draw the sulfate through the partition and form sulfuric acid on the anode side, leaving magnesium hydroxide on the cathode side of the partition. pH paper should show progressively more acidity in the anolyte and more alkalinity on the cathode side.

via sulfur trioxide

Sulfuric acid is produced by dissolving sulfur trioxide in water. This is a very exothermic reaction.

H₂O + SO₃ → H₂SO₄

cf. Chamber process

via sulfur dioxide

One way to bypass sulfur trioxide is to oxidize the sulfur dioxide in situ using an oxidizer:

hydrogen peroxide

Bubble sulfur dioxide through hydrogen peroxide, producing sulfuric acid directly:

H₂O₂(l) + SO₂(g) → H₂SO₄(l)

potassium permanganate

Bubble sulfur dioxide through a solution of potassium permanganate, producing sulfuric acid

5 SO₂ + 2 KMnO₄ + 2 H₂O → 2 H₂SO₄ + 2 MnSO₄ + K₂SO₄

copper chloride

Sulfur dioxide will reduce two molecules of copper (II) chloride and in turn be oxidized to SO3 which immediately reacts with water producing sulfuric acid. The remaining hydrogens pick up the freed chlorine and make hydrochloric acid.

1. Bubble sulfur dioxide through a concentrated solution of copper (II) chloride, giving sulfuric acid, hydrochloric acid and copper (I) chloride.

   SO₂(g) + 2 CuCl₂(aq) + 2 H₂O → H₂SO₄(aq) + 2 HCl(aq) + 2 CuCl(aq)

   64.066 + 2(134.45) + 2(18.015) → 98.079 + 2(36.46) + 2 (98.999)

   64.066 + 268.9 + 36.03 → 98.079 + 72.92 + 197.998

   368.996 → 368.997±0.001

   So approximately 64ubm of sulfur dioxide will be absorbed by approximately 305ubm of solution giving 369ubm of product, including approximately 98ubm of sulfuric acid

   NB: The solubility of CuCl2 in water at 25°C is 1:10.2, so you can't dissolve 2 moles of CuCl2 in 2 moles of water. Therefor, there will either be undissolved CuCl2 or an excess of water when the reaction begins.

2. Decant/Filter the solid copper salts as needed, leaving mixed acids with some small amount of dissolved copper salts
3. Distill off the hydrochloric acid

   H₂SO₄(aq) + HCl(aq)

   {

   →

   ~100°C}

   H₂SO₄(aq) + HCl(g) // possibly also CuSO4(s) and CuCl(s) on both sides

4. Decant/Filter the solid copper salts as needed, leaving sulfuric acid
5. Regenerate HCl/CuCl solution to CuCl₂(aq) by bubbling air through it

   4 HCl(aq) + 4 CuCl(aq) + O₂(g) → 4 CuCl₂(aq) + 2 H₂O(l)

Purification

Sulfuric acid vs dissolved sulfur dioxide

drying

Water with dissolved sulfur dioxide will dry completely under moderate airflow. sulfuric acid will not evaporate at OTP to any great degree.

1. Take a small sample, spread it out on a warm dry surface.

   Danger: The other possibility is that this is sulfuric acid, so the surface and the device used to spread the solution should be acid tolerant!

2. Smell the spread-out solution.
3. If it smells of eggs, or emits a greyish gas, you've got substantial dissolved sulfur dioxides.
4. Attempt to air-dry the solution by blowing air over it
5. If it dries completely from airflow at OTP, there was (essentially) no sulfuric acid present.

boiling

Sulfur dioxide is soluble in water at lower temperatures, but much less so at elevated ones. Check the pH of a sample the solution, boil it to half its volume, and check again. If the pH has decreased (become more acidic) even slightly, then the solution is mostly sulfuric acid. If the pH has increased, then the solution was mostly dissolved sulfur dioxide.

Testing

Concentration

Mass fraction H2SO4	Density (kg/L)	Concentration (mol/L)	Common name
10%	1.07	~1	dilute sulfuric acid
29–32%	1.25–1.28	4.2–5	battery acid (used in lead–acid batteries)
62–70%	1.52–1.60	9.6–11.5	chamber acid fertilizer acid
78–80%	1.70–1.73	13.5–14	tower acid Glover acid
98%	1.83	~18	Azeotropic concentrated sulfuric acid

Molarity

In order to get a feel for how much sulfuric acid you have in your water, add a vast excess of magnesium carbonate. Magnesium carbonate is sparing soluble (0.1g/L) in water, but will react with sulfuric acid to produce magnesium sulfate, which is quite soluble. You may add more (distilled) water to assure yourself that all the magnesium sulfate is dissolved, but this should not be necessary. Evaporate and weigh the magnesium sulfate, calculate the moles of sulfuric acid in the original solution.

1. Place dilute sulfuric acid of unknown strength in a container
2. Add an equal mass of water to the acid
3. Add an excess of magnesium carbonate

   H₂SO₄(aq) + MgCO₃(s) → H₂O + CO₂(g) + MgSO₄(aq)

4. Filter
5. The residue is magnesium carbonate. Recycle.
6. Evaporate the filtrate (magnesium sulfate)
7. Weigh the filtrate
8. Multiply the mass (in grams) by 4.06×10^-3 to get moles of H₂SO₄ in the original solution. (256.366g/mol magnesium sulfate heptahydrate, normal at SPRT)

Storage

• Sulfuric acid does not dissolve silicon dioxide, so glass or quartz containers are recommended.
• Sulfuric acid does not dissolve lead, so it too can be used as a container.
• While sulfuric acid does not dissolve copper, it does dissolve copper oxides, so copper is probably not a good choice.
• Sulfuric acid is strongly, even dangerously, hygroscopic and will absorb water (and other detritus) directly from the air, so a good seal on the container is recommended.

Disposal

• Combining sulfuric acid with almost any copper (II) salt (such as copper carbonate or copper hydroxide will result in copper sulfate, which is GRAS and occurs naturally; other predictable side products (carbon dioxide, water, hydrogen chloride, etc)

Cu(OH)₂ + H₂SO₄ → CuSO₄ + 2 H₂O // copper hydroxide

Cu₂CO₃(OH)₂ + 2 H₂SO₄ → 2 CuSO₄ + 3 H₂O + CO₂ // copper carbonate

CuCl₂ + H₂SO₄ → CuSO₄ + 2 HCl // copper chloride

• Combining sulfuric acid with almost any calcium salts will create gypsum, a naturally occurring mineral and listed as GRAS.

See Also

• The Chamber Process
• von Wagner, Rudolf (1892) "Sulfuric Acid"
  Manual of Chemical Technology J & A Churchill, London
  link courtesy Hathi Trust.
• "Ch 15 Oxidation (Inorganic)"
  Handbook of Commercial Catalysts; pp221. 
  link courtesy Google Books.
• Cooley, Arnold James (1897) "Sulfuric Acid"
  Cooley's Cyclopædia of Practical Receipts and Collateral Information in the Arts, Manufactures, Professions, and Trades, Including Medicine, Pharmacy, and Domestic Economy: Designed as a Comprehensive Supplement to the Pharmacopœia and General Book of Reference for the Manufacturer, Tradesman, Amateur, and Heads of Families; pp1592. J. & A. Churchill
• Ibusuki, Takashi; Barnes, H.M. (1984) "Manganese(II) catalyzed sulfur dioxide oxidation in aqueous solution at environmental concentrations".
  Atmospheric Environment 18(1); pp145-151. 
  DOI:10.1016/0004-6981(84)90237-3
• Mineral acid intraconversion

References