Ammonia (NH3) Metal oxides Metal hydroxides A BASE is a compound which reacts with an acid to form a salt and water only. Examples of base: Ammonia (NH3) Metal oxides Metal hydroxides 16.1 Introducing bases and alkalis

Alkali Soluble Bases Only a few bases are soluble in water. This means that all alkalis are bases, but not all bases are alkalis. 16.1 Introducing bases and alkalis

Bases e.g. CuO, Cu(OH)2 Alkalis e.g. NaOH Figure 16.1 All alkalis are bases, but not all bases are alkalis. 16.1 Introducing bases and alkalis

ammonia sodium hydroxide sodium hydroxide COMMON ALKALIS IN DAILY LIFE ammonia sodium hydroxide sodium hydroxide Figure 16.2 These household cleaners contain alkalis. 16.1 Introducing bases and alkalis

COMMON ALKALIS IN LABORATORY Figure 16.3 Alkalis commonly used in a laboratory. 16.1 Introducing bases and alkalis

How to prepare limewater? 16.1 Introducing bases and alkalis

Preparation of limewater Calcium hydroxide is an alkali. It is a white solid, slightly soluble in water. Limewater is a saturated aqueous solution of calcium hydroxide. 16.1 Introducing bases and alkalis

Preparation of limewater 1. Stirring solid calcium hydroxide with water for a long time. 2. Filtering the suspension. 3. The clear filtrate obtained is the limewater. 16.1 Introducing bases and alkalis

Electrical conductivity 16.2 CHARACTERISTICS AND CHEMICAL PROPERTIES OF AQUEOUS ALKALIS Taste Aqueous solutions of alkalis usually taste bitter. (Never try to check this yourself!) Feel Dilute solutions of alkalis have a soapy feel. Effect on litmus They change red litmus paper to blue colour. Electrical conductivity Like acids, alkalis are electrolytes. They dissolve in water to form solutions that conduct electricity.

Chemical properties of alkalis alkali + acidic substance salt + H2O(l) (neutralization) (no heating) e.g1. NaOH (aq) + HCl (aq)  NaCl (aq) + H2O (l) e.g2. NH3 (aq) + HCl (aq)  NH4Cl (aq) e.g3. 2NaOH (aq) + CO2 (g)  Na2CO3 (aq) + H2O (l) e.g4. Ca(OH)2 (aq) + CO2 (g)  CaCO3 (s) + H2O (l) limewater test All ammonium compounds (NH4+) are soluble in water

Chemical properties of alkalis B. alkali + NH4+ compound  salt + NH3(g) + H2O(l) (heating) e.g1. NaOH (aq) + NH4Cl(aq)  NaCl(aq) + NH3(g) + H2O(l) e.g2. KOH (aq) + NH4Cl (aq)  KCl(aq) + NH3(g) + H2O(l) NH3(g)+ NH4Cl(aq)  NH4Cl(aq) + NH3(g) + H2O(l) Same reactants and products This is not a possible reaction. NH3(g) can turn red limus paper blue.

Chemical properties of alkalis C. alkali + metal ions (aq)  hydroxides + salt (no heating) e.g1. 2NaOH (aq) + CuSO4 (aq)  Cu(OH)2(s) + Na2SO4(aq) e.g2. NaOH(aq) + Cu(NO3)2 (aq) Cu(OH)2(s) + NaNO3(aq) e.g3. 2H2O(l)+ 2NH3(aq)+ CuSO4(aq) Cu(OH)2(s)+ (NH4)2SO4(aq) e.g4. NaOH(aq) + KNO3(aq) KOH(aq) + NaNO3(aq) No ppt formed. 2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s) 2OH- (aq) + Cu2+ (aq)  Cu(OH)2 (s)

Metal Hydroxides Gp 1 hydroxides can dissolve in water(no ppt formed). Hydroixdes of main group metals are white, while those are transition metals are coloured. In excess NaOH: Pb(OH)2 (s) , Al(OH)3 (s), Zn(OH)2 (s), are soluble in excess NaOH.

Water is important to alkalis (OH- ions) e.g1 NaOH(aq)  Na+(aq) + OH-(aq) e.g2 Strong alkali NH3(aq) + H2O(l) NH4+(aq) + OH–(aq) Weak alkali

A16.5 (a) (i) Fe2(SO4)3(aq) + 6NaOH(aq)  2Fe(OH)3(s) + 3Na2SO4(aq) (ii) Fe3+(aq) + 3OH-(aq)  Fe(OH)3(s) (b) (i) Cu(NO3)2(aq) + 2KOH(aq)  Cu(OH)2(s) + 2KNO3(aq) (ii) Cu2+(aq) + 2OH-(aq)  Cu(OH)2(s)

p32A Q14 Zinc dissolved/ colourless gas bubbles evolved. Zn(s) + 2HCl (aq) ZnCl2(aq) + H2(g) (b) Dirty green precipitates formed. 2NaOH (aq) + FeSO4 (aq)  Fe(OH)2(s) + Na2SO4(aq) or 2OH- (aq) + Fe2+ (aq)  Fe(OH)2(s)

Alkalis (soluble bases) Concept map Complete the following concept map. Bases examples metal oxides ____________ metal hydroxides ammonia Alkalis (soluble bases) Insoluble bases Concept map

Alkalis (soluble bases) dissolve in water to give properties examples OH-(aq) KOH(aq) NaOH(aq) NH3(aq) Ca(OH)2(aq) Dilute alkalis taste bitter feel soapy turn red litmus _______ conduct ____________ react with ______ to give salt and water react with __________ oxides to give salts and water react with ammonium compounds to give salt,__________ and water react with ______ ions to form insoluble hydroxide (except K+ and Na+ ions) blue electricity acids Concentrated alkalis _____________ non-metal very corrosive ammonia metal Concept map

How can we tell a solution is acidic, neutral or alkaline?

All aqueous solution contain 17.1 pH AND INDICATORS THE pH SCALE H+(aq) All aqueous solution contain OH-(aq)

How can we tell a solution is acidic, neutral or alkaline? It depends on the difference in H+(aq) concentration and OH-(aq) concentration. 17.1 pH and indicators

Difference in H+(aq) and OH-(aq) concentration H+(aq) concentration > OH-(aq) concentration H+(aq) concentration = OH-(aq) concentration H+(aq) concentration < OH-(aq) concentration acidic neutral alkaline Difference in H+(aq) and OH-(aq) concentration Solution Table 17.1 Difference in H+(aq) and OH-(aq) concentration for acidic, neutral and alkaline solution. H2O  H+ + OH- HCl  H+ + Cl- 17.1 pH and indicators

H+ (aq) concentration express by pH value 17.1 pH and indicators

pH scale : a measure of acidity and alkalinity Increasingly alkaline Neutral Increasingly acidic Increasingly alkaline 7 14 On the pH scale: An acidic solution has a pH value less than 7. An neutral solution has a pH value of exactly 7. An alkaline solution has a pH value greater than 7. 17.1 pH and indicators

(a) limewater (b) rainwater (c) soft drinks Q17.1 what can you tell about the relationship between H+(aq) and OH-(aq) concentration of the following substances? (a) limewater (b) rainwater (c) soft drinks A17.1 (a) H+(aq) concentration < OH-(aq) concentration (b) H+(aq) concentration > OH-(aq) concentration (c) H+(aq) concentration > OH-(aq) concentration 17.1 pH and indicators

increasingly alkaline neutral acidic 1 2 3 4 5 6 7 8 9 10 11 12 13 14 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH 1 M NaOH 0.1 M NaOH limewater Na2CO3 solution Milk of Magnesia, household ammonia soap solution NaHCO3 solution blood rainwater pure water ordinary distilled water (NH4)2SO4 solution soft drink orange juice vinegar, 0.1 M CH3COOH lemon juice 0.1 M HCl 1 M HCl neutral increasingly alkaline acidic

(a) Add a piece of magnesium ribbon to dilute hydrochloric acid. Q17.3 State whether the pH value increases or decreases in each of the following cases: (a) Add a piece of magnesium ribbon to dilute hydrochloric acid. (b) Dissolve hydrogen chloride gas in water. A17.3 (a) Increases (b) Decreases 17.1 pH and indicators

COMMON ACID-BASE INDICATORS An acid-base indicator is a special dye added to the solution to be tested. Figure 17.2 Three common acid-base indicators. 17.1 pH and indicators

Different acid-base indicators show different colours in different pH ranges. Methyl orange Indicator pH scale Litmus red purple blue orange yellow 3.1 4.4 5 8 Phenolphthalein very pale pink colourless 8.3 10 1 2 3 4 6 7 9 11 12 13 14 Figure 17.3 Different colours of acid-base indicators in different pH ranges. 17.1 pH and indicators

pH meter Universal indicator MEASURING pH OF A SOLUTION pH meter Measuring pH value Universal indicator 17.1 pH and indicators

A mixture of several indicators Universal indicator A mixture of several indicators Gives different colours in different pH ranges Available as a solution or paper (pH paper) 17.1 pH and indicators

Figure 17.4 pH paper and pH colour chart. 17.1 pH and indicators

universal indicator solution Figure 17.5 Finding the pH value of a solution by universal indicator solution. Put the solution in front of a piece of white paper to see the colour easily. 17.1 pH and indicators

Do not dip the pH paper into the solution to be tested! Why? Q17.4 Do not dip the pH paper into the solution to be tested! Why? A17.4 The dyes on the pH paper may go into the solution and contaminate it. 17.1 pH and indicators

pH meter To measure pH values accurately, use a pH meter. electrodes 17.1 pH and indicators

Normal functioning of body fluids IMPORTANCE OF pH Keeping a constant pH value is important in many cases, for example: Normal functioning of body fluids Water supply Food production 17.1 pH and indicators