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Acids, bases and salt
- 1. ACIDS, BASES ANDSALT BASE A base is a substance which contains the oxide ion or hydroxide ion and reacts with acid to give salt and water only Or A base is a soluble substance which accepts a proton A soluble base is called Alkali The Alkali’s are The solution of Ca(OH)2 in water is called lime water Magnesium hydroxide (milk of magnesia ………Mg(OH)2 It’s also sparingly soluble The soluble bases when in solution produce OH- as their only negative ion PROPERTIES OF BASES 1. Alkalis have a soapy feeling (slippery)
- 2. 2. Alkalis havebitter taste 3. Alkalis turn red to blue litmus paper 4. They react with acids and water only Question: which bases combine to form NaCl? 5. Alkalis yield ammonia when warmed with ammonium salts USES OF BASES QUESTION: Calculate percentage of hydrogen in compound (HCL) H + Cl 1 + 35.5 = 36.5 (atomic masses) H% = 1/36.5 x 100% Cl% = 35.5/36.5 x 100% What kind of equation is? Answer: Special case reaction ACIDS
- 3. These are thesubstances which when in solution produce hydrogen ions as their only positive ions An acid is a substance which turns blue litmus to red and which contains hydrogen replaceable by a metal TYPES OF ACIDS There are two types of acids i) Mineral acids ii) Organic acids A: Mineral Acids These are derived from substances formed from minerals, for example; from minerals Acid Formula Source Formula Hydrochloric acid HCl Common salt NaCl Sulphuric acid H2SO4 Sulphur S Nitric acid HNO3 Chilean salt petre NaNO3 Carbonic acid H2CO3 Limestone CaCO3 The mineral salts that can be derived from the oxides are called oxy - acids (from the acidic/ non – metal oxides) B. ORGANIC ACIDS These are derived from plants and animals source animal source (organic sources) Example;
- 4. Acid Source Lactic acidSour milk Acetic acid Vinegar Tartaric acids Grapes Citric acid Citreous fruits STRENGTH OF ACIDS Strength of acids are classified into two i) Strong acids ii) Weak acids STRONG ACIDS These are acids which ionize completely in aqueous solution WEAK ACIDS These are acids which ionize partially in aqueous solution All organic acids are weak QUESTION; Is phosphoric acid a strong or weak acid? What are strong bases or weak bases? PROPERTIES OF ACIDS 1. Have sour taste
- 5. 2. Action onindicators Indicator is a substance which changes color in acids or bases Example; litmus, methyl orange, phenolphthalein etc Indicators Color in acids Color in alkali Methyl orange Pink Yellow Phenolphthalein Colorless Pink Bromothymol blue Yellow Blue Litmus Red blue 3. Corrosive action A concentrated acid is a water molecule aspires. Acid dries any substance of water content in vigorous action, thus burns skin of animals, leaves and stems of plants. 4. Action with metal Any metal which is above hydrogen in the activity series will replace hydrogen from the acid. The products of these reactions are salt and hydrogen gas 5. Action with metal oxides and hydroxides to form salt and water only 6. Action with carbonates and hydrogen carbonates (bicarbonates)
- 6. Acids react withcarbonates and bicarbonates producing salt, water and CO2 7. Action with sulphates When acids react with sulphates, SO2, water and salts are produced BASICITY OF ACIDS The basicity of an acid is the numbers of hydrogen ions (H+) produced by one mole of an acid in aqueous solution NB: All organic acids are monobasic PH SCALE;- It isn’t possible to know exactly how strong an acid or base is by using an indicators. The term PH is used to describe or show the exact strength of an acid or base. It shows the number of hydrogen ion concentration The PH scale can be represented diagrammatically as show below;
- 7. 1-4 Strong acid 5-6Weak acid 7 Neutral 8-9 Weak alkali 10-14 Strong alkali USES OF ACIDS Acids have the following uses; a) Preparation of salts, for example; from fertilizers From bases / metals. Ca(OH)2 † 2HCl → CaCl2 † 2H2O NH4OH + H2SO4 → (NH4)2SO4 + 2H2O b) Preparation of other acids; e.g.Pb(NO3)2 + H2SO4 → PbSO4 + 2HNO3 Example; c) Manufacture of artificial silk d) Clearing of metals, acids can combine with them to form salts can be easily removed out e) Necessary for digestion of protein in the stomach. SALTS Definition: A salt is a compound consisting of a positive metallic ion (or) and negative ion derived from an acid
- 8. Types of salts; I)Acidic salts ii) Normal salts iii) Basic salts 1. Acidic salts This is the salt which contains part of the hydrogen ions of an acid Example; Sodium hydrogen – sulphate Calcium hydrogen carbonate 2. Normal salts These are the salts which contain neither H+ ions from the acid nor O2- or OH- ions from the base Example; NaCl, MgCl2,MgSO4 ,FeCl2 ,CaCO3 3. Basic salts These are salts containing or ions from the base Example; MgOHCl, ZnOHCl Magnesium hydroxyl chloride and zinc hydroxyl chloride O is incorrect because oxygen exists in molecule state but not in atomic In previous salts was classified according to the nature of salts but in terms of solubility there are two types of salts (i ) Soluble salt ( ii ) Insoluble salt. SOLUBILITY RULE states; Soluble salts are;- a) All salts of (made of) K, Na and NH+ 4 Example; KNO3,KCl,K2SO4 ,K3PO4 ,K2CO3,NaHCO3 This is an acidic salt (because it gives out 2 positive ions of Na and H) 1. All nitrates
- 9. Example; KNO3 ii) Allhydrogen carbonates Example; NaHCO3 b) All chlorides except i) Silver chloride (AgCl) ii) Mercury (I) Chloride (HgCl) iii) Lead (II) chloride (PbCl2) which is soluble in hot water N.B: In reactions the compound above are considered as solids (s) c) All sulphates except i) - Barium sulphate. ii) - Lead (II) sulphate. iii) - Calcium sulphate is slightly soluble in water. Insoluble salt are; a) All carbonates except those of K, Na, NH4 b) All hydroxyl except those of K, Na, and Ca (which is slightly soluble in water) Salt of strong acid and bases do not react with water Solubility rule (summary) i) All salts of K, Na and are soluble ii) All nitrates are soluble iii) All sulphates are soluble except those Ba, lead (II) and Ca Vi) All chlorides are soluble except those Ag, lead (ii) and mercury (x) All carbonates and hydroxides are insoluble except those of K, Na, NB: - All acids are soluble unless when concentrated (aq)
- 10. - All oxidesare labeled by solids (s) Examples; METHODS OF PREPARING SALTS A: SOLUBLE SALTS i) Direct combination of elements Example; Burning Mg in chlorine gas Mg + Cl2 → MgCl2 Pass hot Al in Chlorine gas. 2Al(hot) + 3Cl → 2AlCl3 ii) Addition of a metal to a dilute acid. But this method is restricted to metals above hydrogen in the reactivity series. A metal below hydrogen cannot displace hydrogen Example; Zn + 2HCl2 + H2(g) Na + H2SO4 → Na2SO4 + H2(g) 1. Addition of carbonates to a dilute acid. Products = salt, water and carbon dioxide. CaCO3(s) + 2HCl → CaCl2(aq) + H2O(l) + CO2(g) 2. Addition of an oxide to a dilute acid. CaO + H2SO4 → CaSO4 + H2O(l) + H2O v) The general method for preparing soluble salts is called crystallization, for example; Preparation of ZnSO4 Procedure;
- 11. a) Add excessZn to dilute in a beaker Add few crystals of and few drops of concentrated to speed up the reaction rate 1. If the reaction is still slow warm the mixture 2. When the reaction is over, filter and put the filtrate in an evaporating dish c) Crystallization The filtrate is evaporated and cooled. Check if the crystals are formed. If they are formed stop evaporating and leave it for clay. The water attached or associated to the crystals is called water of crystallization. ZnSO4.7H2O is called zinc sulphate hepta hydrate. B. INSOLUBLE SALTS The insoluble salts are prepared by ionic precipitation also called double decomposition Here two soluble salts are mixed and react by interchanging their radicals ion forming both soluble and insoluble salts. BaCl2(aq) + Na2SO4(aq) → BaSO4(s) +2NaCl Ba2+ (aq) + 2Cl(aq) + 2Na+ (aq) + SO4 2- (aq) → BaSO4(s) + 2Na+ (aq) + 2Cl- (aq) Ba2+ (aq) + SO4 2- (aq) → BaSO4(s) QUESTION; Ions to get solid, what is the name of the reaction? It’s a double decomposition reaction or ionic precipitation. PROPERTIES OF SALTS 1. COLOUR Some salts are coloured For example; i) Iron (ii) salts are green ii) Iron (ii) salts are yellow iii) Iron (ii) salts are pale blue
- 12. iv) Nickel (ii)salts are green v) Cobalt (ii) salts are pink The colours of the above mentioned salts are due to the color of hydrated ion Coloured salts are formed only in the group of transition elements. All elements in first 20 elements are not colored. Other salts are not colored, for example; salts of Na, K, Ca, Pb, Zn, Al, Mg 2. Hydrolysis This is the reaction of salts and water giving an acid or alkaline solution Example: NH4Cl(aq) + H2O → NH4OH(aq) + HCl(aq) Na2CO3(aq) + H2O(L) → NaOH(aq) + H2CO3(aq) a) All salts of weak bases and strong acids hydrolyze to give acid solution Example; NH4, Cl, FeCl2, CuCl2,Al2(SO4) etc. b) All salts of strong bases and weak acids are hydrolyzed to give an alkaline solution Example; Na2CO3 ,CH3COONa, etc. N.B: Salts of strong bases and strong acids are not undergoing hydrolysis. They only ionize when in solution: Example; NaCl + H2O → There's no reaction. 3. EXPOSURE TO AIR When salts are exposed to air they either lose water of crystallization or absorb water from the atmosphere a) Hygroscopic Is the action of absorbing water from the atmosphere without changing into solution NaCl, anhydrous copper II sulphate (CuSO4) and NaNO3 others are concentrated and copper II sulphate b) Deliquescent
- 13. This is theaction of absorbing water from the atmosphere by a solid to form a solution Example; MgCl2, CaCl2, FeCl3, Ca(NO3)2 Others are the hydroxides of K and Na c) Fluorescence This is the action of giving up water of crystallization of the solid to the atmosphere Examples; i) Hydrate sodium carbonate Na 2 CO 3 .10H 2 O → Na 2 CO 3 .H 2 O+ 9H 2 O ii) Hydrated sodium sulphate Na2SO4.10H2O → Na2SO4 + 10H2O iii) Hydrated magnesium sulphate MgSO4.7H2O → MgSO4.H2O + 6H2O 4. HEAT EFFECTS ON SALTS Different salts behave differently on heating. Most of the hydrated salts loose water of crystallization when heated. The anhydrous salts undergo chemical change when heated
- 14. c) When iron(ii) sulphate is heated strongly it decomposes to form black iron (iii) oxide, and SO3 and SO2(g) 2FeSO4 → Fe2O3(s) + SO3(g) + SO2(g) White black d) Iron (iii) sulphate when heated strongly it decomposes to form black iron (iii) oxide and SO3 only. Fe2(SO4)3(s) → Fe2O3(s) + 3SO3(g) White black II) Chlorides All chlorides of metals are hydrated except those of K, Na, Pb, Hg and Ag when heated, chlorides undergo a chemical change called hydrolysis (i.e. they don’t form anhydrous chlorides) in which hydrogen chloride gas (and water involve and a basic salts of chloride or oxide are formed Example; MgCl2.6H2O(s) MgOHCl(s) + HCl(g) + 5H2O(g)
- 15. AlCl3.6H2O(s) AlO3(s) +8H2O(g) + 6HCl(g) ZnCl2.6H2O(s) ZnOHCl(s) + HCl + 5H2O(g) Ammonium chloride sublimes when heated NH4Cl(s) NH3(g) + HCl(g) III) Carbonates and hydrogen carbonates Carbonates of sodium and potassium are unaffected by heat (even at very high temperature) Ammonium carbonate decomposes readily on heating to form NH3(g), CO2(g) and H2O(g) (NH4)2CO3(s) 2NH3(g) + CO2(g) + H20(g) All other carbonates decompose to give oxide and CO2 Al2(CO3)3 Al2O3 + CO2 K2CO3 NO Reaction All hydrogen carbonates decompose to give metal carbonates water and CO2 on heating Mg(HCO3)2 → MgCO3 + H2O + CO2 2NaHCO3 → Na2CO3 +H2O + CO2 IV) Nitrates Na and K nitrates decompose when heated to give corresponding nitrite and oxygen
- 16. NaNO3 → NaNO2+ O2 KNO3 → KNO2 + O2 - Ammonium nitrate decomposes on heating to give dinitrogen oxide and water NH4NO3 → N2O + H2O - While the nitrite gives nitrogen and water NH4NO2 → N2 + H2O - The metal nitrates (i.e. those of Ca, Mg, Al, Zn, Fe, Pb, Cu) decompose on heating to give the corresponding oxide, nitrogen dioxide and oxygen Ca(NO3)2(s) → CaO(s) + NO2(g) + O2(g) Mg(NO3)2(s) → MgO(s) + NO2(g) + O2(g) - Nitrates of heavy metals (Ag and Hg) decompose to give a metal, NO2 and 02 on heating. AgNO3 → Ag + NO2 + O2 Hg(NO3)2 → Hg + 2NO2 + O2 V) Hydroxides The hydroxide of Na and K are stable to heat ie. Don’t decompose on heat even at very high temperature. All other metal hydroxides decompose on heating to give the corresponding oxides and water vapor KOH No Reaction Mg(OH)2 MgO + H2O
- 17. 5. SOLUBILITY ANDSOLUBILITY CURVES Solubility of a salt in a liquid is the maximum amount of the salt that will dissolve in 100cm3 of a liquid at any given temperature Solubility Curve These are the graphs which show the variation of solubility with temperature Solubility of a salt increases with the increase in temperature. The steeper the solubility curve the more soluble the salt and the easier it is to crystallize that salt SOLUBILITY AND SOLUBILITY CURVES. The diagram above is a graph of solubility against temperature. The vertical component is a solubility of substance in gram per dm3 , where by horizontal component is temperature of a substance. The graph drawn in the plane is analysis of two related variables (solubility and temperature). The change of solubility related to change of temperature. From the accumulated data due to the test of salts NaCl, KCl and KNO3 analyzed in the graph as drawn above. (i) A graph of NaCl interpret that, it has a constant solubility at any temperature. The increase or decrease of temperature does not affect its solubility. (ii) A graph of KCl is a smooth linear graph which interpret that for every change of temperature
- 18. give the effectchange of solubility. Therefore KCl is more soluble than NaCl. (iii) A graph of KNO3 is a curved graph interpret that the change of temperature gives a rapid solubility. Therefore a salt KNO3 is more soluble than NaCl and KCl. Assignment; Take a salt of NaNO3(S) to examine its solubility. Procedure (i) Measure 1litre of distilled water and pour it into the beaker. (ii) Measure 1g of NaNO3 by electronic balance and pour into the beaker. (iii) By heat source, tripod stand, wire gauze, retort stand and thermometer make connection and heat both water and sample salt. (iv) Watch a disappearance of salt particles until all finish and record the temperature as follows;
- 19. (v) Repeat procedure(ii) for except 2,3,4,5,6,7 and 8 (vi) Draw a graph of solubility against temperature. USES OF SALT IN DAILY LIFE Salt is essential for life, because it has more than 14000 users in daily. But the common uses categorized into Food, Agriculture,Water conditioning, High way Deicing and Industrial chemicals. 1. FOOD i) A salt of sodium chloride is mixed with food as flavoring, (common salt). ii) A salt of sodium chloride (NaCl)is mixed in the food industrial product as both flavoring and preservative. iii) A salt of sodium bicarbonate (NaHCO3) 'bicarb' is used in cooking as raising agent for cakes, bread e.t.c. Baking powder Is a mixture of sodium hydrogen carbonate and tartaric acid, The mixture helps to keep the PH neutral. 2. AGRICULTURE A salt is very important in agriculture since used as land additive nutrients. A fertilizers of Ammonium sulphate (NH4SO4(S)) and Sodium nitrate (NaNO3) salt are used to make land fertility to help healthier growing of crops. 3. WATER CONDITIONING i) In the purification of urban water (Permutit process),the salt of Aluminum silicate is used to remove permanent hardness of water (Al(SiO3)3). ii) Sodium carbonate (Na2CO3(S)) called washing soda, is used to make water soft by replacing calcium ions by sodium ions. iii) Sodium chloride is used in a water softener to generate the ion exchange column. 4. HIGH WAY DEICING
- 20. A salt ofsodium chloride (NaCl) is mixed with grit and spread on roads to prevent road freezing in cold condition. 5. INDUSTRIAL USES i) The salt of potassium Iodide (KI) is added to sodium chloride (common salt) to prevent a lack of Iodine in the diet. ii) The salt of sodium carbonate is used in the manufacture of glass.