Chloroauric Acid Formula – Structure, Properties, Uses, Sample Questions

Chloroauric acid is also known as “gold chloride” and “gold chloride tetrahydrate.”  It is soluble in water, ethanol, ether, and chloroform. Anhydrous chloroauric acid may be crystallized using an ethanol solution. It decomposes in the presence of heat, and at 120° C, it decomposes into gold trichloride. Gold hydroxide precipitates with the addition of a cold potassium hydroxide solution.  It was converted to gold powder using sulfur dioxide. 

Chloroauric Acid

Chloroauric acid is an orange-yellow solid composed of inorganic chemicals. This acid also acts as a precursor to other gold compounds. Furthermore, this chemical is used as a gold purifying step. This acid is also known as gold chloride and gold chloride tetrahydrate. Because the acid is caustic and harmful, it should be avoided. 

Chemical formula of Chloroauric Acid

The chemical formula is HAuCl₄ • 4H₂O.

Structure of Chloroauric Acid 

Chloroauric Acid 

AuCl₃ occurs as a dimer in both solid and vapor form; the bromide AuBr₃ follows the same trend. Each Au center has a square planar shape. This structure resembles the bitetrahedral structures used by AlCl₃ and FeCl₃. The majority of the bonding in AuCl₃ is covalent, reflecting gold’s high oxidation state and very strong electronegativity (for a metal). 

Physical Properties of Chloroauric Acid 

IUPAC name	hydrontetrachlorogold(1-)
Chloroauric Acid Molecular formula	HAuCl4
Chloroauric Acid Molecular mass	339.785 g/mol (anhydrous) 393.833 g/mol (trihydrate) 411.85 g/mol (tetrahydrate)
Chloroauric Acid Density	3.9 g/cm3 2.89 g/cm3
Chloroauric Acid Melting point	254°C
Chloroauric Acid Appearance	Yellow-orange needle-like crystals

Chemical properties of Chloroauric Acid 

• Chloroauric acid is a high-molecular-weight monoprotic acid. The crystalline tetrahydrate contains H₅O₂⁺ as well as AuCl₄. It also contains two water molecules.
• In solid form, chloroauric acid is a hydrophilic (ionic) protic solute. Furthermore, chloroauric acid is water-soluble. In addition, this acid is water-soluble and as well as soluble in a number of oxygen-containing solvents such as ethers, esters, alcohols, and ketones.
• When chloroauric acid is treated with a normal base, it is transformed into water, metal, and tetrachloroaurate. The thallium salt, which is similar, is poorly soluble in all non-reacting solvents. Experts are familiar with the salts of quaternary ammonium cations. 
• Gold nanostructures may be created from chloroauric acid via a two-phase redox reaction. The simultaneous attachment of thiol monolayers that self-assemble on the expanding nuclei results in the formation of metallic clusters in this reaction.
• After partial reduction, chloroauric acid yields oxonium dichloroisocyanurate(1). Furthermore, when organic ligands are available, reduction may result in the production of additional gold(I) complexes. 

Uses of Chloroauric Acid 

• A precursor used in the electrolytic purification of gold is hydrogen tetrachloroaurate(III). It is used for gold recovery, concentration, purification, and analytical determination.
• Gold has usually been refined with chloroauric acid.
• Due to the improvements in nanotechnology, gold nanoparticles with diameters ranging from 5 nm to 400 nm have been produced from chloroauric acid.
• Chloroauric acid is used as a gold toner in photography, which is one of its most prevalent uses. Toning is a chemical process that changes the color of an image.
• Cranberry glass, often known as “Gold Ruby,” is a red glass made by adding colloidal gold or chloroaurate into molten glass. 

Sample Questions 

Question 1: How to determine the ph level of Chloroauric Acid?

Answer:

To distinguish the influence of reaction mixture pH from that of precursor reactivity, tests ‘E’ and ‘F’ were carried out with chloroauric acid kept at pH 2.1 and tannic acid kept at pH 7.1 and 9, resulting in final reaction mixture pH values of 5.0 and 7.1, respectively. 

Question 2: When gold chloride is heated, what happens?

Answer:

When aqueous AuCl₃ solutions react with an aqueous base, such as sodium hydroxide, an Au(OH)₃ precipitate is formed, which dissolves in excess NaOH to produce sodium aurate (NaAuO₂). When gently heated, Au(OH)₃ decomposes to gold(III) oxide, Au₂O₃, and eventually to gold metal. 

Question 3: How is gold precipitated from auric chloride?

Answer: 

The most popular method for producing auric chloride is to dissolve gold in aqua regia and then evaporate the liquid to dryness at the lowest temperature feasible. 
As a result, a brownish-red mass is formed, containing AuCl3 mixed with different proportion of proto chloride and hydrochloric acid .

Question 4: Can we generate gold artificially?

Answer: 

The chemical element gold contains 79 protons in each of its atomic nuclei. Every atom with 79 protons is a gold atom, and all gold atoms act chemically in the same way. Nuclear reactions include the addition or removal of protons from a nucleus. As a result, no chemical process can ever generate gold. 

Question 5: How do you get gold out of an aqua regia solution?

Answer:

To remove the nitric acid from the excess aqua-regia used in digestion, boiling or a chemical reaction is used. A reducing reagent is used to convert the gold chloride into solid gold particles while keeping the other metal chlorides undamaged and in solution, allowing the gold to be recovered as metal. 

Question 6: What exactly are gold nanoparticles?

Answer:

Gold nanoparticles (AuNPs) are tiny gold particles with diameters ranging from 1 to 100 nm that, once dispersed in water, are also referred to as colloidal gold. 

Question 7: Is chlorine effective in eating gold?

Answer:

Chlorine may corrode and discolour metals (such as gold and platinum), as well as gradually destroy the finish and shine of gemstones. Dirt and tiny rocks are abrasive and should be avoided when playing in the sand (or gardening). Your jewellery may be permanently destroyed if it is not cleaned immediately.