Monochloramine

Key takeaways

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

Reference excerpt

Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia. It is a colorless liquid at its melting point of −66 °C (−87 °F), but it is usually handled as a dilute aqueous solution, and it is sometimes used as a disinfectant in this form. Chloramine is too unstable to have its boiling point measured.

Water treatment

Chloramine is used as a disinfectant for water. It is less aggressive than chlorine and more stable against light than hypochlorites.

Drinking water disinfection Chloramine is increasingly used in low concentrations as a secondary disinfectant in municipal water distribution systems as an alternative to chlorination, as monochloramine is much less reactive and does not dissipate as rapidly as elemental chlorine (referred to in water treatment as free chlorine). Chloramine also has a much lower, but still active, tendency than free chlorine to convert organic materials into chlorocarbons such as chloroform and carbon tetrachloride. Such compounds have been identified as carcinogens and in 1979 the United States Environmental Protection Agency (EPA) began regulating their levels in US drinking water. Some of the unregulated byproducts may possibly pose greater health risks than the regulated chemicals. Due to its acidic nature, adding chloramine to the water supply may increase exposure to lead in drinking water, especially in areas with older housing; this exposure can result in increased lead levels in the bloodstream, which may pose a significant health risk. Fortunately, water treatment plants can add caustic chemicals at the plant which have the dual purpose of reducing the corrosivity of the water, and stabilizing the disinfectant.

Swimming pool disinfection In swimming pools, chloramines are formed by the reaction of free chlorine with amine groups present in organic substances, mainly those biological in origin (e.g., urea in sweat and urine). Chloramines, compared to free chlorine, are both less effective as a sanitizer and, if not managed correctly, more irritating to the eyes of swimmers. Chloramines are responsible for the distinctive "chlorine" smell of swimming pools, which is often misattributed to elemental chlorine by the public. Some pool test kits designed for use by homeowners do not distinguish free chlorine and chloramines, which can be misleading and lead to non-optimal levels of chloramines in the pool water. There is also evidence that exposure to chloramine can contribute to respiratory problems, including asthma, among swimmers. Respiratory problems related to chloramine exposure are common and prevalent among competitive swimmers. Though chloramine's distinctive smell has been described by some as pleasant and even nostalgic, its formation in pool water as a result of bodily fluids being exposed to chlorine can be minimised by encouraging showering and other hygiene methods prior to entering the pool, as well as refraining from swimming while suffering from digestive illnesses and taking breaks to use the bathroom, instead of simply urinating in the pool.

Safety US EPA drinking water quality standards limit chloramine concentration for public water systems to 4 parts per million (ppm) based on a running annual average of all samples in the distribution system. In order to meet EPA-regulated limits on halogenated disinfection by-products, many utilities are switching from chlorination to chloramination. While chloramination produces fewer regulated total halogenated disinfection by-products, it can produce greater concentrations of unregulated iodinated disinfection byproducts and N-nitrosodimethylamine. Both iodinated disinfection by-products and N-nitrosodimethylamine have been shown to be genotoxic, causing damage to the genetic information within a cell resulting in mutations which may lead to cancer. Another newly-identified byproduct of chloramine is chloronitramide anions, whose toxicity has not yet been determined.

Lead poisoning When a community water supply switches from chlorine to monochloramine as a disinfectant, lead is known to leach from lead pipes. Chlorine's oxidative nature stabilizes a passivation layer of lead dioxide in lead pipes, but chloramine is a weaker oxidant than elemental chlorine. Thus, when chlorine is replaced by monochloramine in water supplies, lead dioxide can be reduced to more water-soluble forms of lead, leading to increased lead concentrations in drinking water.

Synthesis and chemical reactions Chloramine is readily soluble in water and ether, but less so in chloroform and carbon tetrachloride. It is highly unstable when concentrated. Pure chloramine decomposes violently above −40 °C (−40 °F). When in a gaseous form and an aqueous solution, it is thermally slightly more stable.

Production In dilute aqueous solution, chloramine is prepared by the reaction of ammonia with sodium hypochlorite:

NH3 + NaOCl → NH2Cl + NaOH Chloramine also occurs from the reaction of urea in urine:

2 HClO + CO(NH2)2 → CO2 + H2O + 2 NH2Cl Gaseous chloramine can be obtained from the reaction of gaseous ammonia with chlorine gas (diluted with nitrogen gas):

2 NH3 + Cl2 ⇌ NH2Cl + NH4Cl Pure chloramine can be prepared by passing fluoroamine through calcium chloride:

2 NH2F + CaCl2 → 2 NH2Cl + CaF2

Decomposition The covalent N−Cl bonds of chloramines are readily hydrolyzed with release of hypochlorous acid:

RR′NCl + H2O ⇌ RR′NH + HOCl The quantitative hydrolysis constant (K value) represents the bactericidal power of chloramines, and generally ranges from 10−4 to 10−10 (2.8×10−10 for monochloramine). It is given by the formula below:

… excerpt ends here. Continue reading the full article.

Illustrations

Worked examples

Example 1 — a first encounter with Monochloramine

Start with the simplest possible case. Write down what Monochloramine 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 Monochloramine 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 Monochloramine 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 Monochloramine

In research: Monochloramine 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 Monochloramine 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: Monochloramine is common in secondary-school and first-year university syllabi. It links to neighbouring topics Drinking water, Inorganic amines, Inorganic chlorine compounds, so understanding it makes those chapters shorter.
In everyday life: Look for Monochloramine 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 Monochloramine in 20 minutes

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

Frequently asked questions

What is Monochloramine in simple terms?

Monochloramine, often called chloramine, is the chemical compound with the formula NH2Cl. Together with dichloramine (NHCl2) and nitrogen trichloride (NCl3), it is one of the three chloramines of ammonia.

Why does Monochloramine 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 Monochloramine?

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 Monochloramine.