ACID BASE AND SALT

ACID BASE AND SALT

from Femosky110 on 06/12/2020 01:18 PM

ACID BASE AND SALTS
Various definitions of Acids and Bases

 

There are various definitions of acids and bases. Although these definitions don't disagree with one another, they differ in their comprehensiveness. Apart from the already established definitions of Acids, bases and salts Antoine Lavoisier, Humphry Davy, and Justus Liebig as well discovered few things about acids and bases, but they didn't make their definitions formal.

Svante Arrhenius defined acid in terms of their behavior in water.

In 1884 Svante Arrhenius observed that salts like NaCl dissociate in water to provide particles he called ions.

H2O

NaCl(s) Na+(aq) + Cl-(aq)

3 years after that he extended his theory by explaining that acids are neutral compounds that ionize when they dissolve in water to give H+ ions and an equivalent negative ion. His theory describes hydrogen chloride as an acid because it ionizes in aqueous solution to produce hydrogen (H+) and chloride (Cl-) ions as s demonstrated below:

H2O

HCl(g) H+(aq) + Cl-(aq)

In summary, his theory of acids states that:

• Acids are compounds which generate H+ ions in aqueous solutions eg.

• Bases are compounds which generate OH- ions in aqueous solutions

• His definition only works in the presence of water. The definition is only valid in aqueous solutions.

• His definition only allows protic acids that are able to produce hydrogen ions

The definition also only allows hydroxide bases.

Arrhenius also dispute that bases are neutral compounds that also dissociate or ionize in water to produce OH- ions and a positive ion. NaOH is an example of Arrhenius base due to the fact that it dissociates in water to give the hydroxide (OH-) and sodium (Na+) ions.

H2O

NaOH(s) Na+(aq) + OH-(aq)

An Arrhenius acid is therefore any material that ionizes when dissolved in water to produce the H+, or hydrogen ion.

An Arrhenius base is therefore any material that produces the OH-, or hydroxide, ion when dissolved in water.

Examples of Arrhenius acids are compounds like HCl, HCN, and H2SO4 that ionize in water to produce H+ ion. Examples of Arrhenius bases are ionic compounds that have the OH- ion, like NaOH, KOH, and Ca(OH)2.

The Arrhenius theory explains the reason why acids posses related properties. The distinguishing properties of acids are as a result of the presence of the H+ ion produced when an acid is dissolved in water. It also gives explanation to why acids neutralize bases and why bases neutralize acids. Acids supply the H+ ion; bases supply the OH- ion; and these two ions join together to form water.

H+(aq) + OH-(aq) H2O(l)

Disadvantages of the Arrhenius theory
1. It can be relevant only to reactions that take place in water because it defines acids and bases in terms of their behavior when dissolved in water.

2. It gives no explanation to why a number of compounds that has hydrogen with an oxidation number of +1 like HCl dissolve in water to yield acidic solutions, while others like CH4 don't.

3. It is just the compounds that hold the OH- ion that are graded as Arrhenius bases. The Arrhenius theory does not give explanation to why compounds like Na2CO3 have the distinguishing properties of bases.

Johannin es Nicolaus Brønsted - Thomas Martin Lowry theory of acid defined acids as

• Proton donors and

• Bases as proton acceptors

• The definition also works in aqueous solutions

• The definition works for bases apart from hydroxide bases.

• The definition only allows protic acids.

Gilbert Newton Lewis defined
• Acids as electron pair acceptors

• Bases as electron pair donors

Properties of Acids
1. Acid tastes sour and must not be tasted.

2. Acids turn blue litmus paper to red.

3. Aqueous solutions of acids conduct electric current. They are therefore good electrolytes

4. Acids react with bases to form salts and water

5. Acids give out hydrogen gas when they are reacted with an active metal like alkali metals, alkaline earth metals, zinc and aluminum.

Properties of Bases
1. Bases taste bitter and must not be tasted

2. They sense slippery or foamy. You must not by chance feel them

3. Bases don't alter the color of litmus paper but can they can turn red or acidified litmus paper to blue

4. Aqueous solutions of bases conduct electricity and are therefore good electrolytes.

5. Bases react with acids to form salts and water

Examples of regular Acids
• Citric acid from particular fruits and vegetables especially citrus fruits

• ascorbic acid-vitamin C from as from certain fruits

• vinegar which contains about 5% acetic acid

• carbonic acid that are useful during the carbonation process of soft drinks

• lactic acid is available in buttermilk

Examples of regular Bases
• Detergents

• Soap

• Soduim hydroxide (NaOH)

• Aqueous ammonia

pH and pH Meter
In chemistry, pH is an evaluation of the acidity or basicity of an aqueous solution. Solutions that have a pH value that is below 7 are said to be acidic and solutions that have pH value greater than 7 are considered basic or alkaline. The pH of pure water is about 7.

Acid-Base Indicators
Weak Acids and Bases can be used as Acid-Base indicator. An acid-base indicator is a weak acid or a weak base. An Indicator acid base indicator does not change color from pure acid to pure alkali solution at particular hydrogen ion concentration, but to a certain extent, color change takes place over a range of hydrogen ion concentrations. This range is termed the color change interval and is articulated as a pH range.

The use of acid base indicators

Weak acids are titrated in the presence of indicators that alter a little in alkaline situations. Weak bases ought to be titrated in the presence of indicators that alter their colours under a little acidic condition.

Popular acid-base indicators:

Examples of acid-base indicators are:

• Thymol blue

• tropeolin OO

• methyl yellow

• methyl orange

• bromphenol blue

• bromcresol green

• methyl red

• bromthymol blue

• phenol red

• neutral red

• phenolphthalein

• thymolphthalein

• alizarin yellow

• tropeolin O

• nitramin

• trinitrobenzoic acid.

Common Acid-Base Indicators
Indicator pH Range Qty per 10 ml Acid Base
Thymol Blue 1.2-2.8 1-2 drops 0.1% solution in aqueous red yellow
Pentamethoxy red 11.2-2.3 1 drop 0.1% soln. in 70% alcohol red-violet colorless
Tropeolin OO 1.3-3.2 1 drop 1% of aqueous solution red Yellow
Tropeolin OO 1.3-3.2 1 drop 1% of aqueous solution red Yellow
2,4-Dinitrophenol 2.4-4.0 1-2 drops 0.1% solution in 50% alcohol colourless Yellow
Methyl yellow 2.9-4.0 1 drop 0.1% solution in 90% alcohol red Yellow
Methyl orange 3.1-4.4 1 drop 0.1% aqueous solution red Orange
Bromphenol blue 3.0-4.6 1 drop 0.1% aqueous solution yellow blue-violet
Tetrabromphenol blue 3.0-4.6 1 drop 0.1% aqueous solution yellow blue
Alizarin sodium sulfonate 3.7-5.2 1 drop 0.1% aqueous soln yellow Violet
α-Naphthyl red 3.7-5.0 1 drop 0.1% solution in 70% alcohol red Yellow
p-Ethoxychrysoidine 3.5-5.5 1 drop 0.1% aqueous solution red Yellow
Hydrolysis
Hydrolysis is a chemical reaction that results to molecules of water (H2O) being divided into hydrogen cations H+ and hydroxide anions (OH−) in the process of a chemical reaction. The cation is usually known as protons. Hydrolysis is the kind of reaction that is used to break down definite polymers, principally those prepared by step-growth polymerization. Such dilapidation of polymer is frequently catalyzed by either acid or alkali example concentrated sulfuric acid (H2SO4) and sodium hydroxide (NaOH) respectively.

Types of hydrolysis
Hydrolysis is a chemical reaction in which a particular molecule is divided into two parts with the addition of one molecule of water. One part of the reacting molecule gains a hydrogen ion (H+) through the water molecule added. The remaining part takes up the other hydroxyl group (OH−).

The most widespread hydrolysis takes place when a salt of a weak acid or /and a weak base is dissolved in water. Water automatically ionizes into negative hydroxyl ions and positive hydrogen ions. The salt splits into positive and negative ions. For instance, sodium acetate in water dissociates into sodium and acetate ions. Sodium ions react sparingly with hydroxyl ions while acetate ions join with hydrogen ions to form neutral acetic acid, and the overall result is a comparative overload of hydroxyl ions, resulting to a basic solution.

Nevertheless, under standard conditions, just a small number of reactions occur between water and organic compounds. Commonly, strong acids or bases have to be incorporated to be able to attain hydrolysis where water has no consequence. The acid or base would act as a catalyst. They are used to hasten up a reaction but they remain unchanged at the end of the reaction.

Acid–base catalyzed hydrolyses reaction are extremely widespread. An instance is the hydrolysis of amides or esters. Their hydrolysis takes place when the nucleophile ie nucleus hunting agent, for example water or hydroxyl ion reacts with the carbon of the carbonyl group of the ester or amide. In an aqueous base solution, hydroxyl ions are more of better nucleophile than dipoles like water. In acid, the carbonyl group becomes protonated which results to a better nucleophilic attack. The products for the two types of hydrolysis reaction are compounds with carboxylic acid groups.

Acidic, Basic, and Neutral Salts

Some examples of Ions of Neutral Salts

Cations

Na+ + K+ Rb+ Cs+

Mg2+ Ca2+ Sr2+ Ba2+

Anions

Cl- Br- I-,

ClO4- BrO4- ClO3- N03-

A salt is a compound formed when an acid is reacted with a base. Normally, a neutral salt is formed when a strong acid neutralizes a strong base in the reaction. See example below:

H+ + OH- = H2O

The passerby ions in an acid-base reaction result into a salt solution. The majority of neutral salts contain cations and anions listed below: They have less affinity with water. Therefore, salts that contain any of these ions are neutral salts. For instance: NaCl, KNO3, CaBr2, CsClO4 are neutral salts.

Acidic Ions

NH4+ Al3+ Pb2+ Sn2+

Transition metal ions

HSO4- H2PO4-

Basic Ions

F- C2H3O2- NO2- HCO3-

CN- CO32- S2- SO42-

HPO42- PO43-

During a reaction between weak acids and bases, the comparative strength of the reacting acid-base pair in the salt establishes the pH of the solutions. The salt, or the solution of the salt formed can either be acidic, neutral or basic. Acid salt is formed between a strong acid and a weak eg. NH4Cl.Abasic salt is formed between a weak acid and a strong base .eg. NaCH3COO.

Hydrolysis of Acidic Salts
Acid salt is formed between a strong acid and a weak eg. NH4Cl. Ammonia is a weak base, and a salt of ammonia with every strong acid result to a solution with a pH below 7. For instance in the reaction between hydrocholic acid and ammonia below:

HCl + NH4OH = NH4+ + Cl- + H2O

Here, the NH4+ ion reacts with water through the process of hydrolysis as shown in the equation below:

NH4+ + H2O = NH3 + H3O+ .

The acidity constant can be obtined from Kw and Kb.

[H3O+] [NH3] [OH- ]

Ka = ---------------- ------

[NH4+] [OH-]

= Kw / Kb

= 1.00e-14 / 1.75e-5 = 5.7e-10. Where a =acid, b =base and w = water.