chemistry

Haloacetic acids

Haloacetic acids 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 Haloacetic acids rather than just read about it. In short: Haloacetic acids or HAAs are carboxylic acids in which one or more halogen atoms take the place of hydrogen atoms in the methyl group of acetic acid. In a monohaloacetic acid, a single halogen replaces a hydrogen atom: for example, in bromoacetic acid.

Key takeaways

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

Reference excerpt

Haloacetic acids or HAAs are carboxylic acids in which one or more halogen atoms take the place of hydrogen atoms in the methyl group of acetic acid. In a monohaloacetic acid, a single halogen replaces a hydrogen atom: for example, in bromoacetic acid. Further substitution of hydrogen atoms with halogens can occur, as in dichloroacetic acid and trichloroacetic acid. Haloacetic acids are a common contaminant in treated drinking water, particularly water subjected to chlorination.

Contaminants in treated water Haloacetic acids (HAAs) are a common undesirable by-product of water treatment by chlorination. Exposure to such disinfection by-products in drinking water, at high levels over many years, has been associated with a number of health outcomes by epidemiological studies. HAAs can be formed following chlorination, ozonation, or chloramination of water, as chlorine from the water disinfection process can react with organic matter and small amounts of bromide present in water. HAAs are highly chemically stable, and therefore persist in water after formation. A study published in August 2006 found that total levels of HAAs in drinking water were not affected by storage or boiling, but that filtration was effective in decreasing levels.

HAA5 In the United States, the EPA regulates the five HAAs most commonly found in drinking water, collectively referred to as "HAA5." These are:

Chloroacetic acid (MCA) (ClCH2−CO2H) Dichloroacetic acid (DCA) (Cl2CH−CO2H) Trichloroacetic acid (TCA) (Cl3C−CO2H) Bromoacetic acid (BrCH2−CO2H) Dibromoacetic acid (Br2CH−CO2H) The regulation limit for these five acids combined is 60 parts per billion (ppb). The sum of bromodichloroacetic acid, dibromochloroacetic acid and tribromoacetic acid concentrations is known as HAA3.

HAA9 The designation "HAA9" refers to a larger group of HAAs, including all of the acids in HAA5, along with:

Bromochloroacetic acid (ClBrCH−CO2H) Bromodichloroacetic acid (Cl2BrC−CO2H) Dibromochloroacetic acid (ClBr2C−CO2H) Tribromoacetic acid (Br3C−CO2H) The level of these four acids in drinking water is not regulated by the EPA. HAA6 refers to the sum of HAA5 and bromochloroacetic acid concentrations.

Health effects Haloacetic acids are readily absorbed by the human body after being ingested, and can be absorbed slightly through the skin. At high concentrations, HAAs have irritating and corrosive properties; however, typical concentrations of HAAs found in drinking water are extremely low. HAAs are typically eliminated from the body through normal processes between 1 day and 2 weeks after ingestion, depending on the type of acid. Highly concentrated HAAs have been found to cause toxicity in various organs, including the liver and pancreas, in animal studies. This includes an increased risk of cancer, particularly of the liver and bladder. For this reason, the EPA considers a few HAAs (namely DCA and TCA) as potential human carcinogens. They may also cause developmental and reproductive problems during pregnancy. However, short-term adverse health effects are unlikely after ingesting dilute quantities of HAAs, and the long-term low-level risks associated with drinking treated water with residual HAAs are much lower than the risks of drinking untreated water.

Chemistry Haloacetic acids have a general chemical formula X1X2X3C−CO2H, where X is hydrogen or halogen, and at least one X is a halogen. The inductive effect caused by the electronegative halogens often results in the higher acidity of these compounds by stabilising the negative charge of the conjugate base.

See also Fluoroacetic acid (FCH2−CO2H) Difluoroacetic acid (F2CH−CO2H) Trifluoroacetic acid (F3C−CO2H) Iodoacetic acid (ICH2−CO2H) Diiodoacetic acid (I2CH−CO2H) Triiodoacetic acid (I3C−CO2H) Bromodifluoroacetic acid (F2BrCH−CO2H)

References

Further reading ANSI National Institute of Health

External links Haloacetic Acids (For Private Water and Health Regulated Public Water Supplies) "Drinking Water Contaminants – Standards and Regulations". US Environmental Protection Agency.

Illustrations

Worked examples

Example 1 — a first encounter with Haloacetic acids

Start with the simplest possible case. Write down what Haloacetic acids 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 Haloacetic acids 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 Haloacetic acids 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 Haloacetic acids

In research: Haloacetic acids 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 Haloacetic acids 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: Haloacetic acids is common in secondary-school and first-year university syllabi. It links to neighbouring topics Acetic acids, Carboxylic acids, Haloacetic acids, so understanding it makes those chapters shorter.
In everyday life: Look for Haloacetic acids 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 Haloacetic acids in 20 minutes

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

Frequently asked questions

What is Haloacetic acids in simple terms?

Why does Haloacetic acids 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 Haloacetic acids?

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 Haloacetic acids.