At the end of this lesson, students are able to: • State the meaning of acid, base and alkali. • State uses of acids, bases and alkalis in daily life. • Explain the role of water in the formation of hydrogen ions to show the properties of acids. • Explain the role of water in the formation of hydroxide ions to show the properties of alkalis. • Describe chemical properties of acids and alkalis.
Arrhenius’ definition: ACID BASE ALKALI Chemical Chemical Bases that can dissolve in water to compound that compound that produces ionises to produce can neutralise an hydroxide ion, OH- H+ or H3O+ in acid to form salt water. and water. H2O H2O Ex: HCl H+ + Cl- Base + acidsalt + Ex: NaOH (s) Na+ water + OH- Ex: MgO, ZnO, NaOH, KOH
The properties of acid is due to the presenceOf hydrogen ions, H+ (aq) H2O Acid H+Without water, acid will not behave as anacid.
The properties of alkali is due to the presenceOf hydroxide ions, OH- . H2O Alkali OH-Without water, alkali will not behave as analkali.
ACID ALKALI• Sour taste • Bitter taste• pH < 7 • pH > 7• Turn blue litmus • Turn red litmus paper to red paper to blue• React with bases to • React with bases to form salt & water form salt & water
Salt & Hydrogen gas Salt & water With With metal ACID baseEx: H2SO4 + Zn Ex: HCl + NaOH ZnSO4 + H2 NaCl + H2O With metal carbonates Salt, carbon dioxide gas & water Ex: 2HCl + CaCO3 CaCl2 + CO2 + H2O
Metal hydroxide Salt & water With WithEx: Fe3+ + 3OH- metal ALKALI Fe(OH)3 acid Ex: HCl + NaOH ion (precipitate) NaCl + H2O Heat with ammonium salt Ammonia gas, water and salt Ex: NH4+ + OH- NH3 + H2O
To clean metals beforeelectroplating.To makepaints, detergents, fertilizers,electrolyte.To coagulate latex.
To preserve foodA component of vinegarTo make carbonated acid
MgOH: neutralises acids Uses Of Al(OH)3, Mg(OH)2 : alkali Alkali neutralise excess acid in our stomach NaOH NH3 solution
To make Fertilizers, to keeplatex in liquid form, as a sinkcleaning agent.To make soap, detergents.To make toothpaste, gastricpills (antacids).
7.1 : ASIDS AND BASES The following is some information on magnesium hydroxide: Magnesium hydroxide is one of the ingredients found in toothpaste and potassium hydroxide is used as the electroyte in alkaline batteries. Magnesium hydroxide is a base and potassium hydroxide is an alkaline.a) What is base?b) How is alkali different from a base?c) State three physical properties of an alkali.d) Write a balanced chemical equation to show the reaction between hydrochloric acid and magnesium hydroxide.
What is base? A base is a substance that react with an acid to form salt and water only.How is alkali different from a base? An alkali is a soluble base that forms a solution when dissolved in water and ionises to produce hydroxide ions.State three physical properties of an alkali. Alkali is bitter. Slippery. Turn red litmus paper blue.Write a balanced chemical equation to show the reaction between hydrochloric acid and magnesium hydroxide. Mg(OH)2 (s) + 2HCl (aq) MgCl2 (aq) + 2H2O (l)