Sulfur

Properties of Sulfur

• Yellow solid at room temperature
• Second only to carbon, sulfur is found in large number of allotropes (various forms). For examples: disulfur (S2), trisulfur (S3), tetrasulfur (S4), cyclo-pentagon (cyclo-S5), and so-on. 

Here are the common sulfur allotrope:

Rhombic sulfur

Monoclinic sulfur

Powder

• Sulfur reacts with metal to form metal sulfide (sulphide)

             mg(s)          +     S(s)    --->      MgS(s)

             magnesium  +    sulfur   --->     magnesium sulfide

             Zn(s)           +     S(s)    --->      ZnS(s)

             zinc             +     sulfur  --->     zinc sulfide

• Sulfur reacts with oxygen to produce sulfur dioxide 

             S(s)           +     O2 (g)     --->    SO2 (g)

             sulfur         +     oxygen    --->   sulfur dioxide

• Sulfur is a non-metallic element, does not conduct electricity and insoluble in water
• Sulfur atomic number = 16

Sulfur atom

Sources of Sulfur

Sulfur may be obtained from the following sources:

1. Copper pyrite (CuFeS2)
2. Zinc blend (ZnS) is heated in air (to produce zinc oxide and sulfur dioxide)
3. Fossil fuel/ natural gas and oil/petroleum
4. Sulfur ore (sulfide/sulphide) from volcanic activity
5. Elemental sulfur from sulfur beds in Poland, Russia and US (Louisiana)  

Recovery sulfur from refinery of petroleum/natural gas  using Claus process

Mining sulfur ore from active volcano area

Sulfur minor carrying sulfur ore

Frasch process, named after Hermann Frasch. 

Highly heated  water and compressed air is forced into the sulfur beds. 

Sulfur becomes molten and is forced out together with water. 

Molten sulfur can be easily separated from water. 

99.5% purity may be obtained.

Uses of Sulfur

Sulfur is very important in the chemical industry as the following:

1. to produce sulfuric acid

• millions of tonnes of sulfuric acid are produced worldwide every year. 
• sulfuric acid is used to make chemicals, paints & pigments, detergents, soaps, synthetic fibres, dyes, metal salts, fertilisers, and so-on.

1. to vulcanise rubber, a process which makes the rubber harder and increases its elasticity.
2. in manufacture of matches, fireworks and fungicides
3. as a sterilising agent in medicines
4. to produce bleaching agent (sulfur dioxide gas) for paper manufacture 
5. to produce food preservative (sulfur dioxide gas) by killing bacteria ( also called fumigation; to exterminate pests or disinfect)

For knowledge only:
The standard method to control postharvest decay of grapes is to fumigate with sulphur dioxide gas the fruit immediately after harvest and during storage.  However, the concentration of sulphur dioxide necessary to inhibit fungal infections may induce injuries in both rachis and berries, in addition sulphur dioxide application has been restricted in many Countries for the human health risks due to the sulphite residues. Several studies have shown the efficacy of heat treatments on harvested fruits to control biological agents, delay ripening and preserve quality of fresh-cut table grapes.
(source:http://www.freshplaza.com/article/97631/How-to-preserve-the-quality-of-ready-to-eat-grapes#SlideFrame_1)

Salts - preparing insoluble salts by precipitation

Tips: Before preparing a salt, find out if the salt is soluble or insoluble. A soluble salt is made from an acid. An insoluble salt is prepared by precipitation.

Table 1 Soluble Salts and Insoluble Salts

Soluble Salts	Insoluble Salts
All (group I) sodium, potassium, and ammonium
All nitrates
Most chlorides	Silver chloride and lead chloride
Most sulfates (sulphates)	Calcium sulfate, barium sulfate and lead sulfate
Most bromide and iodides	Silver bromide, silver iodide, lead bromide and lead iodide
Sodium, potassium(group I), and ammonium carbonates	All other carbonates

Preparing Insoluble Salts by Precipitation

Example: 

preparing insoluble barium sulfate salt.

• Barium sulfate salt is made of Ba²⁺ ions and SO₄^2- ions.
• So, we have to prepare two soluble salts solutions of which one contains Ba²⁺, its positive metal ions and the other contains the SO₄^2-, its negative non-metal ions. 
• These two ions will react and form a precipitation as barium sulfate salt. 

          Ba²⁺ (aq) + SO₄^2-  (aq) ---> BaSO₄ (s)

The precipitate of barium sulfate salt(residue) is gathered using a filter funnel, rinsed with distilled water to remove any impurities and dried. The filtrate contains the spectator ions which remained unchanged in the reaction.

Another way to separate the precipitate from the solution is using a centrifuge. This technique is used when the solid particles are very small and dispersed in the solution. The fast spinning of the tube in a centrifuge (see picture below) causing the solid gathers at the bottom of the tube due to higher density and gravity force. The liquid can be then decanted leaving the solid in the tube.

A centrifuge

More examples of preparing insoluble salts:

Table 2. Preparing Insoluble Salts 

Preparing insoluble salts	‘+’ ions	‘- ' ions	Solution used	Solution used	Salt precipitation	Spectator ions (no changes in reaction)
Barium sulfate BaSO4	Ba2+	SO42-	Barium nitrate with Ba2+	Sodium sulfate with SO42-	Barium  sulfate BaSO4	NaNO3 sodium nitrate soluble and remained unchanged as Na+ ions and NO3- ions
Reaction: Ba(NO3)2 (aq) + Na2SO4(aq) ---> BaSO4 (s) + 2 NaNO3 (aq)
Barium sulfate BaSO4	Ba2+	SO42-	Barium chloride  with Ba2+	Sodium sulfate with SO42-	Barium  sulfate BaSO4	NaCl  sodium chloride soluble and remained unchanged as Na+ ions and Cl- ions
Reaction: BaCl2 (aq) + Na2SO4(aq) ---> BaSO4 (s) + 2 NaCl2 (aq)
Barium sulfate BaSO4	Ba2+	SO42-	Barium chloride  with Ba2+	Magnesium sulfate with SO42-	Barium  sulfate BaSO4	MgCl2  magnesium chloride soluble and remained unchanged as Na+ ions and Cl- ions
Reaction: BaCl2 (aq) + MgSO4(aq) ---> BaSO4 (s) + 2 MgCl2 (aq)
Silver chloride AgCl	Ag+	Cl-	Silver nitrate with  Ag+	Sodium chloride with Cl-	Silver chloride AgCl	NaNO3  sodium nitrate soluble and remained unchanged as Na+ ions and NO3- ions
Reaction: AgNO3 (aq) + NaCl(aq) ---> AgCl (s) + NaNO3 (aq)
Lead iodide PbI2	Pb2+	I-	Lead nitrate with  Pb2+	Sodium iodide with  I-	Lead iodide PbI2	NaNO3 sodium nitrate soluble and remained unchanged as Na+ ions and NO3- ions
Reaction: Pb(NO3)2 (aq) + NaI (aq) ---> PbI2 (s) + NaNO3 (aq)

Pictures of insoluble salts:

White precipitate
silver chloride, AgCl 

Creamy precipitate
silver bromide, AgBr

Yellow precipitate
silver Iodide, AgI

White precipitate
barium sulfate, BaSO₄

Yellow precipitate
lead iodide, PbI₂

Salts - normal salts, acid salts

Salts are very important to us.

Table 1 Example of salts

Salt	Use
Ammonium chloride	Torch batteries
Ammonium nitrate	Fertilisers
Calcium carbonate	Extraction of iron, making cement, making glass
Calcium chloride	Extraction of sodium, drying agent
Calcium sulphate	Making plaster boards and casts for injured limbs
Iron(II) sulphate	Iron tablets
Magnesium sulphate	Medicines
Potassium nitrate	Fertiliser, gunpowder
Silver bromide	Photography
Sodium carbonate	Making glass, washing powders, water softener
Sodium chloride	Making hydrochloric acid, food flavouring, hospital saline, making sodium carbonate
Sodium stearate	Soaps
Tin(II) flouride	Additive to toothpaste

 

Ammonium chloride in a battery

Ammonium nitrate fertilisers

Calcium carbonate

Iron sulphate for making Iron supplement,
also named as ferrous tablet

Magnesium sulphate

Silver bromide

Sodium carbonate

Sodium chloride

Sodium stearate

Normal Salts

A Normal salt is formed when all the hydrogen ions(H⁺) of an acid, have been replaced by metal ions or by the ammonium ions(NH4⁺), All the salts listed in table 1 are normal salts. 

Normal salts may be soluble or insoluble in cold water.

• all nitrates salts are soluble
• all common sodium, potassium and ammonium salts are soluble
• all chlorides salts all soluble except lead, silver and mercury 
• all sulfates salts are soluble except lead, barium and calcium

Table 2 Normal Salts

Acid	Type of salt	Example
Carbonic acid H2CO3	Carbonates	Sodium carbonate Na2CO3
Sulfuric acid H2SO4	sulphates	Sodium sulfate Na2SO4
Ethanoic acid CH3COOH	Ethanoates	Sodium ethanoate CH3COONa
Hydrochloric acid HCl	Chlorides	Potassium chloride KCl
Nitric acid HNO3	Nitrates	Potassium nitrate KNO3

Acid Salts

An acid salt is formed where not all of the hydrogen ions of an acid have been replaced by metal ions or the ammonium ions. For examples:

Acids such as sulfuric acid and carbonic acid which have two hydrogen ions per molecule, when only one of the hydrogen ions is replaced with a metal ion, the salts formed still contain hydrogen ions.

Table 3 Acid Salts

Acid	Type of acid salt	Example
Carbonic acid H2CO3	Hydrogencarbonate	Sodium hydrogencarbonate NaHCO3
Sulfuric acid HsSO4	Hydrogensulfate	Potassium hydrogensulfate KHSO4