chemistry

Sodium bisulfite

Sodium bisulfite is a chemistry topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Sodium bisulfite rather than just read about it. In short: Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite is not a real compound, but a mixture of salts that dissolve in water to give solutions composed of sodium and bisulfite ions.

Key takeaways

Sodium bisulfite belongs to chemistry; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Sodium bisulfite to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sodium bisulfite from memory before moving on to harder problems.

Reference excerpt

Sodium bisulfite (or sodium bisulphite, sodium hydrogen sulfite) is a chemical mixture with the approximate chemical formula NaHSO3. Sodium bisulfite is not a real compound, but a mixture of salts that dissolve in water to give solutions composed of sodium and bisulfite ions. It appears in form of white or yellowish-white crystals with an odor of sulfur dioxide. Sodium bisulfite is used in a variety industries such as a food additive with E number E222 in the food industry. It is also used as a reducing agent for applications in the textile and cosmetics industries.

Synthesis Sodium bisulfite solutions can be prepared by treating a solution of suitable base, such as sodium hydroxide or sodium bicarbonate with sulfur dioxide.

SO2 + NaOH → NaHSO3 SO2 + NaHCO3 → NaHSO3 + CO2 Attempts to crystallize the product yield sodium metabisulfite (also called sodium disulfite), Na2S2O5. Upon dissolution of the metabisulfite in water, bisulfite is regenerated:

Na2S2O5 + H2O → 2 Na+ + 2 HSO3− Sodium bisulfite is formed during the Wellman-Lord process.

Uses

Cosmetics Sodium bisulfite functions as a hair-waving/straightening agent. As of 1998, sodium bisulfite was used in 58 cosmetic products including hair conditioners, moisturizers, and hair dyes.

Food industry Sodium bisulfite is used to prevent discoloration, bleach food starches, and delay spoilage of the product. In the US, EPA, FDA, and American Conference of Governmental Industrial Hygienists established a working place threshold limit value for sulfur dioxide (which is formed from bisulfite) of 2ppm averaged over 8 hours, and a 3-hour level of 5ppm. Even with this threshold established, the FDA recognized sodium bisulfite as "generally recognized as safe" compound. Sulfites in food can be assayed by the Monier-Williams type procedure, HPLC after extraction, and Flow Injection analysis.

Textile industry Sodium bisulfite is used as an antichlor in the textile industry. Antichlors are very useful in the textile industry because bleaching of compounds using chlorine is a standard practice.

Safety The International Agency for Research on Cancer concluded that there was inadequate evidence that sodium bisulfite was carcinogenic. Under specific conditions such as acidity and concentration level, sodium bisulfite was able to cause negative alterations to the genome such as catalyzing transamination, and to induce sister-chromatid exchanges suggesting possible genotoxicity. In a study using Osbourne-Mendel strain rats, it was concluded that oral toxicity was not significant if the consumed concentration was less than 0.1% (615 ppm as SO2). A study by Servalli, Lear, and Cottree in 1984 found that sodium bisulfite did not produce membrane fusion in hepatic and murine glial cells and human fibroblasts, so there is no oral toxicity. These clinical studies concluded that sodium bisulfite was safe to use in cosmetic formulations. The concentrations of sodium bisulfite that could be dangerous are well beyond the concentrations discussed in the cosmetic and food industry, thereby indicating it is extremely unlikely to pose an environmental threat. The World Health Organization Expert Committee on Food Additives concluded that 0-0.7 mg of sulfur dioxide equivalent/kg of body weight per day will cause no harm to an individual consuming this compound as a food additive. Sulfites exhibit no genotoxicity and carcinogenicity.

See also Sodium metabisulfite Calcium bisulfite Potassium bisulfite Croscarmellose sodium Sulfurous acid

References

Illustrations

Worked examples

Example 1 — a first encounter with Sodium bisulfite

Start with the simplest possible case. Write down what Sodium bisulfite claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In chemistry, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Sodium bisulfite before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Sodium bisulfite ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Sodium bisulfite

In research: Sodium bisulfite appears in chemistry research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Sodium bisulfite in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Sodium bisulfite is common in secondary-school and first-year university syllabi. It links to neighbouring topics Bisulfites, E-number additives, Food additives, so understanding it makes those chapters shorter.
In everyday life: Look for Sodium bisulfite outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Sodium bisulfite in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sodium bisulfite means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Sodium bisulfite out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sodium bisulfite in simple terms?

Why does Sodium bisulfite matter?

Because it connects several chemistry ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Sodium bisulfite?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Sodium bisulfite.