A quick guide to hydrochloric & sulphuric acid: how do they differ?
Hydrochloric acid and sulphuric acid are two strong mineral acids with wide-ranging applications. Looking to learn a little more? Join our team of product experts as we explore these two versatile commodity chemicals.
As a leading UK supplier and distributor of bulk chemicals, including hydrochloric acid and sulphuric acid, we’re perfectly placed to explore the varying ways these acids differ, as well as the ways they are applied across a range of industries.
Hydrochloric acid quick profile
Hydrochloric acid (HCl), also sometimes known as muriatic acid, is an aqueous solution created when hydrogen chloride gas dissolves in water. It consists of a hydrogen and chlorine atom.
Colourless and with a distinctive pungent smell, many people do not know that hydrochloric acid is a component of gastric acids that live within the digestive systems of most animals, including humans.
Around the industrial revolution, it was discovered that the process of converting salt to soda ash released hydrogen chloride as a by-product. By the early 20th century, it became possible to produce soda ash from salt without HCl as a by-product. However, by then, HCl had become an important industrial chemical.
Modern methods of creating HCl are integrated with the production of other chemicals, where hydrogen chloride is a by-product. This is then dissolved in water.
The acid is produced in solutions of various strengths up to 38%, classified as concentrated grade. The majority of industrial grade HCl is 30–35% to minimise product loss through evaporation.
As well as being used as a reagent in laboratory settings, it is a key fixture in the chemical industry with wide-ranging commercial applications.
- Plastics: HCl is used in industrial production of vinyl chloride, which is then used in the production of PVC. It is one of the chemicals used to create polyurethane foam.
- Cleaning: Used in cleaning with consideration for materials that are able to withstand its effects. Commonly used for cleaning of masonry. Also found in small quantities in household cleaners for stubborn stain removal. Particularly useful for tiles and porcelain cleaning (including toilet bowls) because of its corrosive properties. Sometimes referred to as ‘spirits of salt’ when used for domestic cleaning.
- Steel pickling: Used for pickling of steel to remove rust and iron oxide as part of processing.
Agrochemical: In the agrochemical sector, HCl is often used in the manufacture of fertilisers and dyes. It can be used to acidify water and soil, lowering its pH level to help plants grow.
- Swimming pools: HCl helps to adjust the pH for neutralisation, sanitation and maintenance. It helps to optimise the levels of chlorine in the water.
- Oil and gas: Used for acidizing oil wells to maximise productivity.
- Calcium chloride production: When HCl is mixed with or reacted with limestone, the result is calcium chloride, a salt commonly used for gritting roads, but also as an antimicrobial agent. Calcium carbonate is also used in food production and baked goods.
- Neutralising agent: With high acidity, hydrochloric acid is commonly used for neutralising alkalis.
- Bleaching agent: Across the food, metal, textile, dye manufacturing and rubber industries.
- Metal and mining: Used in the ore refining process for the production of tin and tantalum, and in both the pickling of steel and the removal of rust or iron oxide before it is processed.
- Food production: Used as a buffer and neutralising agent and to process products like cookies, ketchups, cereals, soft drinks and as an acidifier in sauces, canned foods and vegetable juices. Its pH regulation properties mean it can act as a preservative.
- Other: Also used in battery production, fireworks, leather processing and in producing gelatin products.
HCl is extremely corrosive and is classified as a strong acid. It should not be stored in metal containers, but plastic containers such as those made from PVC. If misused, HCl can cause chemical burns to skin or eyes and can result in loss of sight, as well as severe internal damage if ingested.
For more information on uses, handling and safety, see our hydrochloric acid product page and download an MSDS.
Sulphuric acid quick profile
Sulphuric acid (H2SO4) is a mineral acid composed of elements of sulphur, oxygen and hydrogen. An odourless, colourless solution, its highly corrosive power comes from its powerful dehydrating effect. Because it has a strong affinity for water vapour, sulphuric acid does not exist naturally.
The primary method of production for high volume industrial use is the ‘contact process’. This involves burning sulphur to form sulphur dioxide, which is then purified and oxidised in presence of a catalyst (usually vanadium oxide), forming sulphur trioxide. The addition of sulphuric acid forms oleum (also known as ‘fuming sulphuric acid’). This oleum is diluted with water to form concentrated sulphuric acid.
Another less common production method, the ‘wet method’, sees sulphur recovered from gases to generate sulphuric acid through a system of heating and cooling the gases.
The most popular grades of sulphuric acid are 98% (concentrated) and 77%, with other strengths also able to be diluted. Around 260 million metric tons are produced globally each year.
Sulphuric acid is a key commodity chemical with applications across a variety of industries, most prominently agriculture.
- Agriculture: The production of phosphate fertilisers accounts for 50–60% of all sulphuric acid manufactured. Sulphuric acid can also be sprayed on fields of potato when they are due to be harvested, speeding up the drying out of the stem and helping with use of equipment.
- Cleaners: Used in cleaning agents, detergents and domestic drain cleaners (particularly for removing hair and grease).
- Textile chemicals and dyes: Used in the manufacture of dye solution, paints, enamels, printing inks, paper, fabrics and in the process of making nylon.
- Oil and gas industry: Sulphuric acid is utilised in the refining of crude oil, where an acid is often used as a catalyst.
- Metal processing: Used in metal processing to remove oxidation, rust and scaling from rolled sheet metals that are required for the appliance and car industries.
- Chemical synthesis: Used as part of a reaction to produce other chemicals.
- Other: Also used in pharmaceuticals, antifreezes, insecticides, synthetic resins, mining and mineral processing, wastewater processing, explosives, lead acid batteries, cellophane, lubricants and as a catalyst in engineering.
When it contacts bodily tissue, sulphuric acid can cause severe chemical burns, even in a diluted state. Adding the water to the acid can release extreme heat that boils the solution and causes droplets to spray.
Like hydrochloric acid, extreme caution should be taken when handling sulphuric acid. It should be stored away from sunlight and heat in a cool, dry place that does not exceed 37.8°C (100°F).
For more information on safety and uses, see our sulphuric acid product page and download an MSDS.
The key differences between hydrochloric and sulphuric acid
Both hydrochloric and sulphuric are strong, corrosive mineral acids. As major commodity chemicals, millions of tonnes of each are produced globally each year. Both have wide-ranging roles — including certain common uses in industrial cleaning, agriculture and textiles — but their central industrial applications differ greatly.
The most popular applications for hydrochloric acid are the production of PVC, steel pickling and pool pH maintenance. Sulphuric acid is mainly used for the manufacture of phosphate fertilisers — accounting for over half of all sulphuric acid produced globally — followed by metal processing.
- Molecular: Hydrochloric acid is composed of hydrogen (H) and chlorine (Cl) atoms; sulphuric acid is composed of hydrogen (H), sulphur (S) and oxygen (O).
- Chemical properties: Hydrochloric acid is monoprotic — it releases one proton per molecule — while sulphuric acid is diprotic, which means it releases two. Hydrochloric acid is a non-oxidising (reducing) agent with no dehydrating property, whereas sulphuric acid is a very strong oxidising agent and dehydrating agent.
- Appearance and smell: Both are colourless liquids. Hydrochloric acid has a pungent smell, whereas sulphuric acid has no odour.
So, did that help?
At Airedale Chemical, we are leading suppliers and distributors of quality bulk chemicals, of course including hydrochloric acid and sulphuric acid in a range of sizes to suit your needs.
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