WHAT IS DRY ACID
Dry Acid also known as sodium bisulphate occurs as an odourless, hygroscopic white powder that is soluble in water. Its solutions are strongly acidic and corrosive. It is manufactured by reacting sodium hydroxide with sulphuric acid. Sodium bisulphate acts as a technological additive, a preservative, a disinfectant, an acidity regulator, a cleaner and a flavour enhancer. It is used in agriculture, metal, oil, food, cleaning and textile industries. Sodium bisulfate is frequently used as a replacement for Sulphuric Acid in many applications as sulphuric Acid is highly dangerous to transport.
Properties and specification of Dry Acid :
- Synonyms: Sodium hydrogen sulfate; sodium hydrogen sulphate; sodium bisulphate; sodium bisulfate; Sodium acid sulfate; Bisulfate of soda; Sodium acid sulphate; dry acid; pH Decreaser; pH down; pH minus.
- CAS No: 7681–38–1
- EINECS: 231–665–7120.06 g/mol
- Molecular weight: 120.06 g/mol
- Purity: 92% min
- Formula: NaHSO4
- Appearance: In the form of sperules white or slightly yellow.
- Chloride content: 0.1% max
- Iron (Fe): 0.015% max
- Insoluble content: 0.01% max.
- Solubility in Water: 1080g/l @ 25 C
- Density: 2.742 g/cm3
- Melting point: 315 C decomposes
- pH: 1.2 – 1.3 @ 1.2% w/w solution
Sodium bisulphate is decomposed by alcohols producing sodium sulphate and sulphuric acid.
Uses for Dry Acid :
- Household cleaners, toilet cleaners etc
- Acid cleaner for industry, breweries, dairies etc
- Silver pickling See below for more details
- To reduce alkalinity and pH in swimming pools. Commercially it is sold as “pH Decreaser”, pH Reducer”, “pH Minus” or “pH Down”. See below for more details on how to use
- As a preservative for soil and water samples in analytical laboratory analysis
- Used for the dhydration of castor oil.
- An auxillary agent for the bleaching and dyeing of wool.
- A polishing and grinding agent for glass.
- A pickling salt for the plumping and bleaching of skins in the leather industry.
- As a flux for metal pickling. See below for more details
- In the mineral oil industry for the extraction of nitrogen compounds from hydrocarbons (gas scrubbing).
- As a silage additive.
- Food grade sodium bisulphate is used as a food preservative.
- When mixed with potassium dichromate it is used as a bleach in photography.
- It has been used to reduce ammonia from manure in animal and poultry housing to reduce the number of flies. For more information click here
How to use sodium bisulfate / Dry acid in pools & spas
Sodium bisulfate is used to lower the pH and to maintain total alkalinity TA in swimming pools and spas. It is safer and easier to use than hydrochloric acid (muriatic). It is easier to store but it also must be handled with care. The ideal pH of pool water should be 7.0–7.6 and total alkalinity should be maintained between 80 and 120ppm.
Pre-dissove the dry acid first by adding the dry acid into a large plastic bucket of water and then pouring the acid solution into the deep end of the pool, away from the skimmer and the fixtures. The Acid should be added when the pump is on and running. Retest the pH of the water in 4 hours and add more acid if needed. To calculate the amount of dry acid required to reduce the total alkalinity Click here
Helpful Tips: Do not add more than 150g of dry acid per 10,000 litres of pool water at any one time. Never add dry acid more than 3 times per day. Do not adjust the pH without first testing the Total Alkalinity. Dry acid may be used in a spa or hot tub.
Using Sodium Bisulphate as silver / metal pickle
The purpose of the sodium bisulphate solution is to remove ‘borax glass’ or fire scale left on metal during the heating process. The pickle solution can be made a 30% solution i.e. 300g per litre of water. Leave in the pickle until the surface appears white and free of fire scale. Note: Pickle should be kept warm, but not boiling. The warmer the solution the paster the process takes place. The optimum temperature is 57C to 95C. Sodium bisulphate is Acidic and it is an electrolyte. Never put iron into pickle. This will impart a copper tone to sterling silver.
Health & safety
R-phrases: R41 Risk of serious damage to eyes.
S-phrases: S24 Avoid contact with skin. S26 In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.
For full details see MSDS for Dry Acid / sodium bisulfate