Acid Bases And Salt For Chemistry Students

ACID BASE AND SALTSVarious definitions of Acids and BasesThere 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.H 2 ONaCl(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:H2OHCl(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 ionsThe 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.H2ONaOH(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) H 2 O(l)Disadvantages of the Arrhenius theory1. 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 CH 4 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 donorsProperties of Acids1. 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 electrolytes4. Acids react with bases to form salts and water5. Acids give out hydrogen gas when they are reacted with an active metal like alkali metals, alkaline earth metals, zinc and aluminum.Properties of Bases1. Bases taste bitter and must not be tasted2. They sense slippery or foamy. You must not by chance feel them3. Bases don't alter the color of litmus paper but can they can turn red or acidified litmus paper to blue4. Aqueous solutions of bases conduct electricity and are therefore good electrolytes.5. Bases react with acids to form salts and waterExamples 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 buttermilkExamples of regular Bases• Detergents• Soap• Soduim hydroxide (NaOH)• Aqueous ammoniapH and pH MeterIn 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 IndicatorsWeak 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 indicatorsWeak 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 pHIndicator Range 1.2-Thymol Blue2.8 11.2-Pentamethoxy red2.3 1.3-Tropeolin OO3.2 1.3-Tropeolin OO3.2 2.4-2,4-Dinitrophenol4.0 2.9-Methyl yellow4.0 3.1-Methyl orange4.4 3.0-Bromphenol blue4.6Tetrabromphenol 3.0-4.6 blueAlizarin sodium 3.7- sulfonate5.2 3.7-α-Naphthyl red5.0p- 3.5-5.5EthoxychrysoidineHydrolysisHydrolysis 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 hydrolysisHydrolysis 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 SaltsSome examples of Ions of Neutral SaltsCationsNa + + K + Rb + Cs +Mg 2+ Ca 2+ Sr 2+ Ba 2+AnionsCl -Br -I -,ClO 4 -BrO 4 -ClO 3 -N0 3 -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- = H2OThe 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 IonsNH 4 + Al 3 + Pb 2 + Sn 2 +Transition metal ionsHSO 4 -H 2 PO 4 -Basic IonsF -C 2 H 3 O 2 -NO 2 -HCO 3 -CN -CO 3 2-S 2 -SO 4 2-HPO 4 2-PO 4 3-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 SaltsAcid 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 + NH 4 OH = NH 4 + + Cl -+ H 2 OHere, the NH 4 + ion reacts with water through the process of hydrolysis as shown in the equation below:NH 4 + + H 2 O = NH 3 + H 3 O + .The acidity constant can be obtined from Kw and Kb.[H 3 O + ] [NH 3 ] [OH -]Ka = ---------------- ------[NH 4 + ] [OH -]= Kw / Kb= 1.00e-14 / 1.75e-5 = 5.7e-10. Where a =acid, b =base and w = water.