Many of the foods you eat contain acids. These foods have a tart or sour taste. corn has pH of 5.2 lentils pH of 6.3 Blueberries have a pH of 3.3 cranberry juice pH of 2.3 White bread has pH of 5 White rice has pH of 6. Vegetables Grains Dairy Products Milk pH is 6.4 American cheese has pH of 5 Egg yolks pH of 6.1 Nuts pH 5.4 Coke pH 2.5, coffee pH= 5 Fruits Beverages Phytic acid Phosphoric acid Chlorogenic acid Lactic acid Citric acid

Many substances you are familiar with contain bases. Egg whites Bases have a bitter taste and a slippery feel.

able to burn or corrode organic tissue Most acids and bases are:

A base is any compound that yields hydroxide ions (OH - ) when dissolved in water. An acid is any compound that yields hydrogen ions (H + ) when dissolved in water.

Arrhenius Acids and Bases Acids are compounds that contain hydrogen and ionize to yield hydrogen ions ( H + ) in aqueous solution. Bases are compounds that contain OH and ionize to yield hydroxide ions ( OH - ) in aqueous solution. HCl (g) H + (aq) + Cl - (aq) H2OH2O According to Arrhenius: NaOH (g) Na + (aq) + OH - (aq) H2OH2O (acid) (base)

Arrhenius Acids Acids are compounds that contain hydrogen and ionize to yield hydrogen ions ( H + ) in aqueous solution.

Not all compounds that contain hydrogen are acids. Only a hydrogen that is bonded to a very electronegative element can be released as an ion (highly polar bonds). Methane (CH 4 ) is not an acid. The C-H bonds are only weakly polar so these hydrogens do not ionize.

Acetic acid The three hydrogens attached to carbon are in weakly polar bonds, so the do not ionize. Only the hydrogen bonded to the highly electronegative oxygen can be ionized.

HCl (g) H2OH2O Hydrogen chloride HCl (aq) H + (aq) + Cl - (aq) Hydrochloric acidHydrogen ion Chloride ion In reality, hydrogen ions are not present in aqueous solution. Instead, the hydrogen ions are joined to water molecules as hydronium ions (H 3 O + ). (an acid)

H2OH2O H3O+H3O+ H+H+ +

HCl (g) H2OH2O Hydrogen chloride HCl (aq) H 3 O + (aq) + Cl - (aq) Hydrochloric acidHydronium ion Chloride ion H + same as H 3 O +

Arrhenius Bases Bases are compounds that contain OH and ionize to yield hydroxide ions ( OH - ) in aqueous solution. NaOH (s) H2OH2O Na + (aq) + OH - (aq) NaOH (aq) Sodium hydroxide Sodium ions Hydroxide ions NaOH is extremely caustic (can burn or eat away materials). This is why NaOH is a major component of products used to clean clogged drains. Sodium hydroxide (base)

Contain group 1 metals Contain group 2 metals Their solutions are always very dilute, even when saturated. Concentrated solutions Dilute solutions A saturated solution of magnesium hydroxide has only g of Mg(OH) 2 per 100 g of water.

Their solutions are always very dilute, even when saturated. Dilute solutions A saturated solution of magnesium hydroxide has only g of Mg(OH) 2 per 100 g of water. Mg(OH) 2

Bronsted-Lowry Acid An acid is a hydrogen-ion donor. HCl (g) + H 2 O (l) Hydrogen chloride H 3 O + (aq) + Cl - (aq) Hydronium ion Chloride ion Water (acid) Donates H + H

A base is a hydrogen-ion acceptor. Bronsted-Lowry Base OH - NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) (base) (acid) Accepts H + ?

NH 3 NH 4 +

Identify the acid and base. acidbase

Why is NaOH a base? HCl(aq) + H2O(ℓ) →H3O+(aq) + Cl−(aq) Hydrochloric acid in water increases the concentration of H3O+ ions and is therefore an acid. NaOH(s) + H2O(ℓ) → Na+(aq) + OH−(aq) + H2O(ℓ) Sodium hydroxide in water increases the concentration of OH− ions and is therefore a base. However, this definition can only be used for acids and bases in water. Since there are many reactions which do not occur in water, it was important to come up with a much broader definition for acids and bases. Arrhenius described an acid as a compound that forms H3O+ when added to water. An Arrhenius acid therefore increases the concentration of H3O+ions ( [H3O+] ) in water. Arrhenius described a base as a compound that dissociates in water to form OH− ions. An Arrhenius base therefore increases the concentration of OH− ions ([OH−] ) in water. The Brønsted-Lowry theory does not go against the Arrhenius theory in any way - it just adds to it. Hydroxide ions are still bases because they accept hydrogen ions from acids and form water. An acid produces hydrogen ions in solution because it reacts with the water molecules by giving a proton to them. SKIP

A Bronsted-Lowry acid is defined as anything that releases H 1+ ions; a Bronsted-Lowry base is defined as anything that accepts H 1+ ions. This definition includes all Arrhenius acids and bases but, as we will soon see, it is a bit more general. The Bronsted-Lowry concept is based on the transfer of a proton from one substance to another. The ionization of HCl in water can be viewed as a Bronsted-Lowry acid-base reaction with HCl behaving as the acid (H 1+ ion donor) and water serving as the base (H 1+ ion acceptor). Just as we saw with Arrhenius acids, the acidic hydrogens are usually written at the beginning of the chemical formula of a Bronsted-Lowry acid. So, for instance, we can tell from the formulas that HCl, HNO 3, and HCH 3 O 2 are monoprotic acids, each liberating one H 1+ ion per acid molecule, whereas H 2 SO 4 is diprotic, and H 3 PO 4 is triprotic. The reaction of HCl with water can be called either an Arrhenius acid-base reaction or a Bronsted-Lowry acid-base reaction. There are many acid-base reactions, however, for which the Arrhenius definition is inappropriate. Let's consider the gas phase reaction of HCl with ammonia, NH 3, which occurs as shown in the chemical equation below. The arrows represent the movement of electron pairs as bonds are formed and broken.Arrhenius In this reaction the ammonia behaves as the proton acceptor, a Bronsted-Lowry base, while the HCl serves as the proton donor, a Bronsted-Lowry acid. Notice that a pair of nonbonding electrons on the base is used to form a covalent bond with the hydrogen of the acid. The covalent bond between the hydrogen and the chlorine atom is broken, and this pair of electrons becomes nonbonding on the chlorine atom. To function as a Bronsted-Lowry base a substance must have a pair of nonbonding electrons that can be used to form a bond to H 1+. Be careful though, because the presence of nonbonding electrons is not always apparent. When we write chemical formulas, the nonbonding electrons are not shown explicitly so it may not be obvious that systems such as PH 3, F 1-, or amines are bases. SKIP

HCl (g) + H 2 O (l) H 3 O + (aq) + Cl - (aq) NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) ? donated H + acid Is water an acid or a base? Water can act as either an acid or a base. ? accepts H + base

The whole HCl molecule is acting as a Lewis acid. It is accepting a pair of electrons from the ammonia, and in the process it breaks up. Lewis acids don't necessarily have to have an existing empty orbital. What about more obviously acid-base reactions - like, for example, the reaction between ammonia and hydrogen chloride gas? NH3(g)+HClg)→NH+4(s)+Cl−(s) What exactly is accepting the lone pair of electrons on the nitrogen. Textbooks often write this as if the ammonia is donating its lone pair to a hydrogen ion - a simple proton with no electrons around it. That is misleading! You don't usually get free hydrogen ions in chemical systems. They are so reactive that they are always attached to something else. There aren't any uncombined hydrogen ions in HCl. There isn't an empty orbital anywhere on the HCl which can accept a pair of electrons. Why, then, is the HCl a Lewis acid? Chlorine is more electronegative than hydrogen, and that means that the hydrogen chloride will be a polar molecule. The electrons in the hydrogen-chlorine bond will be attracted towards the chlorine end, leaving the hydrogen slightly positive and the chlorine slightly negative. The lone pair on the nitrogen of an ammonia molecule is attracted to the slightly positive hydrogen atom in the HCl. As it approaches it, the electrons in the hydrogen-chlorine bond are repelled still further towards the chlorine. Eventually, a coordinate bond is formed between the nitrogen and the hydrogen, and the chlorine breaks away as a chloride ion. coordinate bond This is best shown using the "curly arrow" notation commonly used in organic reaction mechanisms. SKIP

Lewis Acid An acid is a substance that can accept a pair of electrons to form a covalent bond. acid Accept … Acid

Lewis Base A base is a substance that can donate a pair of electrons to form a covalent bond. base Donate … base

Identify the Lewis acid and Lewis base. acid base

Lewis acids are electron pair acceptors. In the above example, the BF 3 is acting as the Lewis acid by accepting the nitrogen's lone pair. On the Brønsted-Lowry theory, the BF 3 has nothing remotely acidic about it. This is an extension of the term acid well beyond any common use.

Identify the Lewis acid and Lewis base. H + + H 2 O H 3 O + acidbase

Identify the Lewis acid and Lewis base. AlCl 3 + Cl - AlCl 4 - acidbase