Sodium cyanide

Key takeaways

Sodium cyanide 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 cyanide to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Sodium cyanide from memory before moving on to harder problems.

Reference excerpt

Sodium cyanide is a compound with the formula NaCN and the structure Na+ −C≡N. It is a white, water-soluble solid. Cyanide has a high affinity for metals, which leads to the high toxicity of this salt. Its main application, in gold mining, also exploits its high reactivity toward metals. It is a moderately strong base.

Production and chemical properties Sodium cyanide is produced by treating hydrogen cyanide with sodium hydroxide:

HCN + NaOH → NaCN + H2O Worldwide production was estimated at 500,000 tons in the year 2006. Formerly it was prepared by the Castner process involving the reaction of sodium amide with carbon at elevated temperatures.

NaNH2 + C → NaCN + H2 The structure of solid NaCN is related to that of sodium chloride. The anions and cations are each six-coordinate. Potassium cyanide (KCN) adopts a similar structure. When treated with acid, it forms the toxic gas hydrogen cyanide:

NaCN + H+ → HCN + Na+ Because the salt is derived from a weak acid, sodium cyanide readily reverts to HCN by hydrolysis; the moist solid emits small amounts of hydrogen cyanide, which is thought to smell like bitter almonds (not everyone can smell it—the ability thereof is due to a genetic trait). Sodium cyanide reacts rapidly with strong acids to release hydrogen cyanide. This dangerous process represents a significant risk associated with cyanide salts. It is detoxified most efficiently with hydrogen peroxide (H2O2) to produce sodium cyanate (NaOCN) and water:

NaCN + H2O2 → NaOCN + H2O

Applications

Cyanide mining

Gold cyanidation (also known as the cyanide process) is the dominant technique for extracting gold, much of which is obtained from low-grade ore. More than 70% of cyanide consumption globally is used for this purpose. The application exploits the high affinity of gold(I) for cyanide, which induces gold metal to oxidize and dissolve in the presence of air (oxygen) and water, producing the salt sodium dicyanoaurate (or sodium gold cyanide) (NaAu(CN)2):

4 Au + 8 NaCN + O2 + 2 H2O → 4 Na[Au(CN)2] + 4 NaOH A similar process uses potassium cyanide (KCN, a close relative of sodium cyanide) to produce potassium dicyanoaurate (KAu(CN)2). These soluble forms of gold (and silver) can be converted back to the metals by electrolysis.

Chemical feedstock Some commercially significant chemicals are derived from cyanide: cyanuric chloride, cyanogen chloride, and cyanogen. Several specialty nitriles may be produced by alkylation of cyanide, a strong nucleophile. Illustrative is the synthesis of benzyl cyanide by the reaction of benzyl chloride and sodium cyanide:

C6H5CH2Cl + NaCN → C6H5CH2CN + NaCl

Electroplating Cyanide baths (solutions) of metal ions are used to electroplate many metals, including platinum, gold, and silver. Cadmium plating gives excellent corrosion resistance and is achieved using cadmium oxide and sodium cyanide. Copper 'strikes' (thin high quality layers) are traditionally formed using cyanide electroplating, these thin interstitial layers allow adhesion between metals that are usually incompatible, such as chromium and aluminium.

Niche uses Being highly toxic, sodium cyanide is used to kill or stun rapidly such as in collecting jars used by entomologists and in widely illegal cyanide fishing. It was used as an insecticide, rodenticide and antibacterial, but these uses were cancelled by the EPA in 1987.

Toxicity

Sodium cyanide, like other soluble cyanide salts, is among the most rapidly acting of all known poisons. NaCN is a potent inhibitor of cellular respiration, acting on mitochondrial cytochrome oxidase and hence blocking electron transport. This results in decreased oxidative metabolism and oxygen utilization. Lactic acidosis then occurs as a consequence of anaerobic metabolism. An oral dosage as small as 200–300 mg can be fatal.

Disposal Due to toxicity considerations, the disposal of cyanide is subject to stringent regulations. Industrial cyanide effluent is typically destroyed by oxidation using peroxysulfuric acid, hydrogen peroxide, sulfur dioxide/copper salts ("Inco process") or all three ("Combiox Process"). Use of sodium hypochlorite, traditional for laboratory-scale wastes, is impractical on a commercial scale. Hydrolysis at higher temperatures is highly effective, but requires specialized equipment. Lastly, cyanide wastes can be acidified for recovery of hydrogen cyanide.

References

External links Institut national de recherche et de sécurité (INRS), "Cyanure de sodium. Cyanure de potassium", Fiche toxicologique n° 111, Paris, 2006, 6 pp. (PDF file, in French) International Chemical Safety Card 1118 Hydrogen cyanide and cyanides (CICAD 61) National Pollutant Inventory - Cyanide compounds fact sheet NIOSH Pocket Guide to Chemical Hazards EINECS number 205-599-4 CID {{{1}}} from PubChem CSST (Canada) Sodium cyanide hazards to fish and other wildlife from gold

Illustrations

Worked examples

Example 1 — a first encounter with Sodium cyanide

Start with the simplest possible case. Write down what Sodium cyanide 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 cyanide 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 cyanide 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 cyanide

In research: Sodium cyanide 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 cyanide 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 cyanide is common in secondary-school and first-year university syllabi. It links to neighbouring topics Cyanides, Photographic chemicals, Sodium compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Sodium cyanide 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.

How to study Sodium cyanide in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Sodium cyanide 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 cyanide out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Sodium cyanide in simple terms?

Sodium cyanide is a compound with the formula NaCN and the structure Na+ −C≡N. It is a white, water-soluble solid.

Why does Sodium cyanide 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 cyanide?

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 cyanide.