BBA2106: Basics in Natural Science(FBA)Lecture

Acids, Bases and pH What is an acid? What is a base?Acids

have sour taste (think of lemon juice!);

ability to change the color of litmus from blue to red;

react with certain metals to produce hydrogen gas;

react with bases to form a salt and water.

react with carbonates and bicarbonates to produce carbon dioxide gas.

Bases

have bitter taste;

slippery or soapy feeling when applied to the skin;

ability to turn red color of litmus to blue;

ability to react with acids to form salts and water.

their aqueous (water) solutions conduct electric current;

Examples of Common Acids

citric acid (from certain fruits and veggies, notably citrus fruits)

ascorbic acid (vitamin C, as from certain fruits)

vinegar (5% acetic acid)

carbonic acid (for carbonation of soft drinks)

lactic acid (in buttermilk)

stomach acid (HCl)

Examples of Common Bases

antacid [milk of magnesia, magnesium hydroxide Mg(OH)2] antacid [maalux, aluminium hydroxide Al(OH)3] liquid soap(Potassium hydroxide, KOH) lye (Sodium hydroxide, NaOH)

stabilizer for plastics [barium hydroxide, Ba(OH)2]

Neutralization Reaction

When acids and bases are added to each other they react to neutralize each other if an equal number of hydrogen and hydroxide ions are present.

When this reaction occurs -salt and water are formed.

HCl + NaOH(Acid) (Base)---(Salt) (Water)

What Makes a Strong Acid or Strong Base?

Strong electrolytes are completely dissociated into ions in water. The acid or base molecule does not exist in aqueous solution, only ions. Weak electrolytes are incompletely dissociated.

Strong Acids: Acids that completely ionize in water, forming H+ and an anion are called strong acids. There are six strong acids. The others are considered to be weak acids.

HCl - hydrochloric acid

HNO3 - nitric acid

H2SO4 - sulfuric acid

HBr - hydrobromic acid

HI - hydroiodic acid

HClO4 - perchloric acid

Weak Acids: A weak acid only partially ionizes in water to give H+ and the anion. Examples of weak acids include hydrofluoric acid (HF), acetic acid (CH3COOH), formic acid (HCOOH) etc. Weak acids include: Organic acids containing one or more carboxyl group, -COOH. The H is ionizable.

Lemon juice is about 5% citric acid, a weak acid.

Strong Bases: Strong bases ionize 100% into the cation and OH- (hydroxide ion). The hydroxides of the Group I and Group II metals usually are considered to be strong bases.

LiOH - lithium hydroxide

NaOH - sodium hydroxide

KOH - potassium hydroxide

RbOH - rubidium hydroxide

CsOH - cesium hydroxide

Ca(OH)2 - calcium hydroxide

Sr(OH)2 - strontium hydroxide

Ba(OH)2 - barium hydroxide

Weak Bases: Examples of weak bases include ammonia, NH3, NaHCO3, Mg(OH)2, Al(OH)3 diethylamine, (CH3CH2)2NH etc. Most weak bases are anions of weak acids. Weak bases do not furnish OH- ions by dissociation. Instead, they react with water to generate OH- ions.

What is acid rain?:Different types of oxides such as NOx, SOx and COx are available in the environment due to combustion which result in the production of acids with rain water:

NO and NO2 react with water to give strong nitric acid (HNO3).

SO2 and SO3 react with water to give strong sulphuric acid (H2SO4).

CO and CO2 react with water to give carbonic acid (HCO3).

The acids thus produced in the atmosphere are collectively known as acid rain.

Why do onions make you cry when you cut onios?Inside the onion cells there are some chemical compounds that contain sulfur. When you cut an onion its cells are broken and those chemical compounds then undergo a reaction that transforms them into a more volatile sulfur products, which are released into the air.These sulfur compounds react with the moisture in your eyes forming sulfuric acid, which produces a burning sensation. So you cry to keep your eyes protected from the acid.

pH conceptHistory

The concept of p[H] was first introduced by Danish chemist Sren Peder Lauritz Srensen at the Carlsberg Laboratory in 1909[3] and revised to the modern pH in 1924 to accommodate definitions and measurements in terms of electrochemical cells. In the first papers, the notation had the "H" as a subscript to the lowercase "p", like so: pH.

The exact meaning of the "p" in "pH" is disputed, but according to the Carlsberg Foundation pH stands for "power of hydrogen".[4] It has also been suggested that the "p" stands for the German Potenz (meaning "power"), others refer to French puissance (also meaning "power", based on the fact that the Carlsberg Laboratory was French-speaking); others refer to "potential". Other suggestions have surfaced over the years that the "p" stands for the Latin terms pondus hydrogenii, potentia hydrogenii, or potential hydrogen. It is also suggested that Srensen used the letters "p" and "q" (commonly paired letters in mathematics) simply to label the test solution (p) and the reference solution (q).[5]Current usage in chemistry is that p stands for "decimal cologarithm of", as also in the term pK, used for acid dissociation constants The strength of an acid or base in a solution is measured on a scale called a pH scale.

The pH scale is a measure of the hydrogen ion concentration.

It spans from 0 to 14 with the middle point (pH 7) being neutral (neither acidic or basic).

Any pH number greater than 7 is considered a base and any pH number less than 7 is considered an acid. 0 is the strongest acid and 14 is the strongest base.

The chart shown above will help to know pH level of common substances very much in touch with our daily life. Especially note that

most foods are slightly acidic;

the principal "bodily fluids" are slightly alkaline, as is seawater not surprising, since early animal life began in the oceans.

the pH of freshly-distilled water will go downward as it takes up carbon dioxide from the air; CO2 reacts with water to produce carbonic acid, H2CO3. the pH of water that occurs in nature varies over a wide range. Groundwaters often pick up additional CO2 respired by organisms in the soil, but can also become alkaline if they are in contact with carbonate-containing sediments. "Acid" rain is by definition more acidic than pure water in equilibrium with atmospheric CO2, owing mainly to sulfuric and nitric acids that originate from fossil-fuel emissions of nitrogen oxides and SO2. A neutral solution is one in which the concentrations of H+ and OH ions are identical.

pH of Some CommonSubstances:

Acids0 - Hydrochloric Acid (HCl)1.0 - Battery Acid (H2SO4 sulfuric acid)2.0 - Lemon Juice2.2 - Vinegar3.0 - Apples4.0 - Wine and Beer4.5 - Tomatoes6.6 - Milk

Neutral7.0 - Pure Water

Bases7.4 - Human Blood8.3 - Baking Soda (Sodium Bicarbonate)10.5 - Milk of Magnesia11.0 - Ammonia12.4 - Lime (Calcium Hydroxide)13.0 - Lye14.0 - Sodium Hydroxide (NaOH)

Worked Chemistry Problems

Q: Which of the following statements is true concerning acids and bases?

(a) acids and bases don't react with each other (b) acids mixed with bases neutralize each other (c) acids mixed with bases make stronger bases (d) acids mixed with bases make stronger acids

Q: True or false: bases are sometimes called alkalis.

(a) true (b) false

Q: Which is the correct set of acid properties?

(a) sour taste, corrosive, change litmus from red to blue (b) sour taste, corrosive, change litmus from blue to red (c) sweet taste, slippery, change litmus from blue to red (d) sour taste, slippery, change litmus from blue to red EMBED Unknown

Acids, Bases & pH (Updated on May 15, 2011)Page 3