Why does acidity increase with the number of oxygens

Water molecules are made up of one oxygen atom and two hydrogens. Distilled water has a neutral pH of 7. The pH scale helps scientists measure whether or not a solution is acidic or basic. In chemistry, a solution is defined by one substance being dissolved in another. Solutions are easiest to understand as a liquid, but it is important to note that they also exist in gas and solid forms. An acid is a solution that has a higher concentration of positively charged hydrogen ions H than negatively charged hydroxide ions OH.

Common examples of acids are lemon juice and vinegar. A base has a higher concentration of OH ions. Common examples are baking soda and household ammonia. The scale ranges from 0 to Smack dab in the middle 7 is considered neutral, which is neither acidic nor basic. And what substance do you suppose comes in at that number? Our happy water molecule. When water is in a pure or distilled state, it measures a pH of 7. And the higher the number 7 to 14 , the more basic it is.

Carboxylic acids can be seen as reduced or alkylated forms of the Lewis acid carbon dioxide; under some circumstances they can be decarboxylated to yield carbon dioxide. Privacy Policy. Skip to main content. Acids and Bases. Search for:. Acid Strength and Molecular Structure Binary Acids Binary acids are certain molecular compounds in which hydrogen is bonded with a nonmetal.

Learning Objectives Explain the periodic trends that affect binary acid strength. Oxoacids An oxoacid is an acid that contains oxygen. Learning Objectives Discuss the periodic trends that help determine oxoacid strength. Carboxylic acids are an important subclass of organic oxoacids and the most common type of organic acid. Carboxlic acids are characterized by the presence of at least one carboxyl group and have a general formula of R-COOH, where R is some monovalent functional group.

Key Terms oxyacid : an acid containing oxygen, as opposed to a hydracid oxoacid carboxylic acid : any of a class of organic compounds containing a carboxyl functional group a carbon with one double bond to an oxygen and a single bond to another oxygen, which is in turn bonded to a hydrogen. As with the alkanes, an increased amount of LDFs in alcohol containing molecules also causes in increase in boiling point.

In addition to forming hydrogen bonds with themselves, alcohols can also engage in hydrogen bonding with water molecules Figure 9. Thus, whereas the hydrocarbons are insoluble in water, small alcohols with one to three carbon atoms are completely soluble. As the length of the chain increases, however, the solubility of alcohols in water decreases; the molecules become more like hydrocarbons and less like water.

We frequently find that the borderline of solubility in a family of organic compounds occurs at four or five carbon atoms. Hydrogen bonding between the OH of methanol and water molecules accounts for the solubility of methanol in water.

Molecules that contain two alcohol functional groups are often called glycols. Ethylene glycol, one of the simplest glycols, has two major commercial uses. It is used as a raw material in the manufacture of polyester fibers and for antifreeze formulations. The addition of two or more -OH groups to a hydrocarbon substantially increases the boiling point and solubility of the alcohol. For example, for ethylene glycol, the boiling point is Thus, ethylene glycol is a useful cooling substance for automobile engines.

Ethylene glycol is often used as a cooling agent in antifreeze mixtures due to its low freezing point and high boiling point. Ethylene glycol is poisonous to humans and other animals, and should be handled carefully and disposed of properly. As a clear liquid with a sweet taste, it can lead to accidental ingestion, especially by pets, or it can be used deliberately as a murder weapon.

Ethylene glycol is difficult to detect in the body, and causes symptoms—including intoxication, severe diarrhea, and vomiting—that can be confused with other illnesses or diseases. Its metabolism produces calcium oxalate, which crystallizes in the brain, heart, lungs, and kidneys, damaging them; depending on the level of exposure, accumulation of the poison in the body can last weeks or months before causing death, but death by acute kidney failure can result within 72 hours if the individual does not receive appropriate medical treatment for the poisoning.

Some ethylene glycol antifreeze mixtures contain an embittering agent, such as denatonium, to discourage accidental or deliberate consumption. Typical antifreeze mixtures also contain a fluorescent green dye which make it easier to find and clean up antifreeze spills. Compounds in which an -OH group is attached directly to an aromatic ring are called phenols and can be abbreviated ArOH in chemical equations.

Phenols differ from alcohols in that they are slightly acidic in water. Similar to double displacement acid-base neutralization reactions, they react with aqueous sodium hydroxide NaOH to form a salt and water. The simplest phenol containing compound, C 6 H 5 OH, is itself called phenol. An older name, emphasizing its slight acidity, was carbolic acid. Phenols are widely used as antiseptics substances that kill microorganisms on living tissue and as disinfectants substances intended to kill microorganisms on inanimate objects such as furniture or floors.

The first widely used antiseptic was phenol. Joseph Lister used it for antiseptic surgery in Phenol is toxic to humans, however, and can cause severe burns when applied to the skin. In the bloodstream, it is a systemic poison , meaning that it is carried to and affects all parts of the body. Its severe side effects led to searches for safer antiseptics, a number of which have been found. Picture is painted by Gaspare Traversi. Currently, phenol is only used in very small concentrations in some over-the-counter medical products like chloraseptic throat spray.

More complex compounds that contain phenolic functional groups are commonly found in nature, especially as plant natural products. For example, some of the major metabolites found in green tea are the polyphenolic catechin compounds, represented in figure 9.

Drinking green tea has been shown to have chemopreventative properties in laboratory animals. The biological activity of the catechins as antioxidant agents is thought to contribute to this activity and other health benefits attributed to tea consumption.

A Green tea contains catechin compounds like epigallocatechin gallate ECGC and the epicatechins that are thought to provide some of the anticancer health benefits attributed to green tea.

B Marijuana contains many biologically active phenolic compounds, including the hallucinogenic component of marijuana, tetrahydrocannabinol THC and the metabolite cannabidiol CBD. Cannabidiol does not have psychoactive properties and is currently being studied as a potential medical treatment for refractive epilepsy syndromes.

Ethanol has an -OH group and only 2 carbon atoms; 1-hexanol has one -OH group for 6 carbon atoms and is thus more like a nonpolar hydrocarbon than ethanol. Answer the following exercises without consulting tables in the text. Ethers are a class of organic compounds that contain an oxygen between two alkyl groups. The C — O bonds in ethers are polar and thus ethers have a net dipole moment. The weak polarity of ethers do not appreciably affect their boiling points which are comparable to those of the alkenes of comparable molecular mass.

Ethers have much lower boiling points as compared to isomeric alcohols. This is because alcohols molecules are associated by hydrogen bonds while ether molecules cannot form hydrogen bonds with other ether molecules. Ethers can form hydrogen bonds with water, however, as water contains the partially positive hydrogen atoms required for H-bonding. Thus, ethers containing up to 3 carbon atoms are soluble in water, due to the formation of H-bonds with water molecules. The solubility of ethers decreases with an increase in the number of carbon atoms.

The relative increase in the hydrocarbon portion of the molecule decreases the tendency of H-bond formation with water. Ethers are appreciably soluble in more nonpolar organic solvents and in fact, can be used as a solvent to dissolve nonpolar to mildly polar molecules. In addition, ethers are very non-reactive. In fact, with the exception of the alkanes, cycloalkanes and fluorocarbons, ethers are probably the least reactive common class of organic compounds.

The inert nature of the ethers relative to the alcohols is undoubtedly due to the absence of the reactive O—H bond. A general anesthetic acts on the brain to produce unconsciousness and a general insensitivity to feeling or pain. This painting shows an operation in Boston in in which diethyl ether was used as an anesthetic. Inhalation of ether vapor produces unconsciousness by depressing the activity of the central nervous system.

Diethyl ether is relatively safe because there is a fairly wide gap between the dose that produces an effective level of anesthesia and the lethal dose. However, because it is highly flammable and has the added disadvantage of causing nausea, it has been replaced by newer inhalant anesthetics, including the fluorine-containing compounds halothane, and the halogenated ethers, desflurane, isoflurane, and sevoflurane.

The halogenated ethers, isoflurane, desflurane, and sevoflurane, show reduced side effects when compared with diethyl ether. Unfortunately, the safety of these compounds for operating room personnel has been questioned. For example, female operating room workers exposed to halothane suffer a higher rate of miscarriages than women in the general population. Ethers are also common functional groups found in natural products and can have unique biological activities. In fact, some very large compounds containing multiple ethers, called polyethers , have been found to cause neurotoxic shellfish poisoning.

In this example, the dinoflaggelate, Karina brevis , which is the causative agent of red tide algal blooms, produces a class of highly toxic polyethers called the brevatoxins. Brevatoxin A is depicted in Figure 9. Symptoms of this poisoning include vomiting and nausea and a variety of neurological symptoms such as slurred speech. The dinoflaggelate, Karina brevis , shown in the upper left is the causative agent of red tide harmful algal blooms.

These marine algal blooms can be quite extensive as shown in the photo of a red tide upper right occurring near San Diego, CA. Brevatoxin A is depicted as an example. Filter feeding clams and muscles become contaminated with the dinoflaggelate and can cause neurotoxic shellfish poisoning if eaten. Red tides can have severe economic costs as fisheries and shellfish harvesting has to be closed until toxin levels in commercial products return to acceptable levels. Aldehydes are typically more reactive than ketones.

These structures can be found in many aromatic compounds contributing to smell and taste. As discussed before, we understand that oxygen has two lone pairs of electrons hanging around.

These electrons make the oxygen more electronegative than carbon. The polarizability is denoted by a lowercase delta and a positive or negative superscript depending on the atom.

In aldehydes, the carbonyl group has a hydrogen atom attached to it together with either. For the purposes of this section, we shall ignore those containing benzene rings. Below are some examples of aldehydes. Notice that these all have exactly the same end to the molecule. All that differs is the complexity of the other carbon group attached.

When you are writing formulae for these, the aldehyde group the carbonyl group with the hydrogen atom attached is always written as -CHO — never as COH. That could easily be confused with an alcohol. In ketones, the carbonyl group has two carbon groups attached. Again, these can be either alkyl groups or ones containing benzene rings. Notice that ketones never have a hydrogen atom attached to the carbonyl group.

That means that ethanal boils at close to room temperature. Larger aldehydes and the ketones are liquids, with boiling points rising as the molecules get bigger. The size of the boiling point is governed by the strengths of the intermolecular forces. There are two main intermolecular forces found in these molecules:. The polarization of carbonyl groups also effects the boiling point of aldehydes and ketones which is higher than those of hydrocarbons of similar size.

However, since they cannot form hydrogen bonds, their boiling points tend to be lower than alcohols of similar size. Note that compounds that have stronger intermolecular forces have higher boiling points.

Due to the polarity of the carbonyl group, the oxygen atom of the aldehyde or ketone engages in hydrogen bonding with a water molecule.

The solubility of aldehydes and ketones are therefore about the same as that of alcohols and ethers. As the carbon chain increases in length, solubility in water decreases.

The borderline of solubility occurs at about four carbon atoms per oxygen atom. All aldehydes and ketones are soluble in organic solvents and, in general, are less dense than water. Similar to the other oxygen-containing functional groups discussed thus far, aldehydes and ketones are also widespread in nature and are often combined with other functional groups. Examples of naturally occurring molecules which contain a aldehyde or ketone functional group are shown in the following two figures.

The hypohalous acid series does a good job showing increasing acid strength with increasing electronegativity of the Y atom in this case, a halogen atom. Anytime the O-H bond is weakened the stronger the acid will be. In the example above, the O-H bond is weakened by increasing the electronegativity of the Y atom. Think of the Y atom as an electron vacuum cleaner that sucks the electrons out of the O-H bond so that they no longer get shared with the proton and end up on the conjugate base molecule.

The stronger the vacuum pulling the electrons out the bond, the stronger the acid will be. The same principle holds for acids that contain the same Y atom but different numbers of oxygen atoms. Oxygen atoms are also like electron vacuum cleaners. They weaken the O-H bond through the central Y atom and stabilize the negatively charged product. As a result, the more oxygen atoms are attached to the central Y atom, the stronger the H n YO m acid.

Increasing the number of oxygen atoms that are attached to the central atom also increase the oxidation number of the central atom. High oxidation numbers of the central atom represent positive charge on that atom. Since opposite charges attract, a very positive central atom would be more attracted to the negative charge from the electron lone pair on the neighboring oxygen atom.

In order for the neighboring oxygen to get the coveted lone pair electrons, it transfers a proton and acts as an acid. While the above trends and examples will be useful, you will inevitably have close encounters with alien molecules. Reminds us of an old Spielberg movie. When we need to compare the acidity of molecules we haven't seen before, try to determine how many electron vacuum cleaners if any there are on the molecule. These "vacuum cleaner" atoms are typically those with high electronegativities, like oxygen.