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Acids and bases chapter 8 - Coggle Diagram
Acids and bases chapter 8
Types of acids
Ethanoic acid
CH3 COOH ->H+ + CH3 COO -
Eg:Lemon juice tenderises meat
The toughness of meat, a protein food, is partly due to protein collagen and fibre in it.The citric acid in lemon juice breaks down the protein and fibre, making the food more tender
hydrochloric acid
HCl=H+ + Cl -
nitric acid
HNO3->NO3 - + H +
sulfuric acid
H2SO4 -> SO4 2- + 2H+
What are strong and weak acids
Some animals use acids as a form of protection.Formic acid found in an ant's bite causes a stinging sensation and some sea slugs defend themselves by squirting sulfuric acid and cause burns on victims
Formic acid is a weak acid whereas sulfuric acid is a strong acid.The difference in strength causes differing effects
The term strenght in acids refers to the extent of the ionisation of an acid when dissolved in water
Properties of acids
Acids have a sour taste
Acids produce ions when dissolved in water.These ions allow the resulting aqueous solution to conduct electricity
Acid turns litmus blue paper red
Acids react with reactive metals
metal + acid -> salt + hydrogen
potassium, sodium and calcium are too reactive to be used in an experiment, potentially injuring someone during the explosion
When a piece of magnesium is added to dilute sulfuric acid, bubbles of hydrogen gas can be seen
Equation for the reaction= magnesium+dilute sulfuric acid ->magnesium sulfate + hydrogen
Chemical equation is: Mg(s) + H2SO4(aq) ->MgSO4(aq)+H2(g)
Magnesium sulfate is the salt produced when magnesium reacts with sulfuric acid.Salts are called:
Sulfates when formed from sulfuric acid
Nitrates when formed with nitric acid
Chlorides when formed from hydrochloric acid
presence of hydrogen gas formed by the reaction can be tested by placing a burnt splint at the mouth of the test tube
If hydrogen is present,it will extinguish the burning splint with a "pop" sound
Acids and unreactive metals
Not all metals react with acids to give a salt and hydrogen gas
When unreactive metals usch as copper or silver are added to dilute acids, there is no reaction
lead appears not to react with hydrochloric acid and sulfuric acid.The intital reaction between lead and the acid produces a layer of lead chloride or lead sulfate
This layer is insoluble in water and quickly forms a coating around the metal.The coating protects the metal from further reaction with the acid
The unreactive metals are gold, silver, platinum, palladium and copper
Acids reacts with bases(metal oxides and hydroxides)
Neutralisation occurs when an acid reacts with a base to form a salt and water.The base can be a metal oxide or metal hydroxide
In general, H+ ions from the acid react with the O 2- ions from a metal oxide or OH - ions from the metal hydroxide, forming water molecules, H2O.The resulting mixture is neutral
The general equation for neutralisation reaction of bases with acids is:Acid + Base-> salt + water
for eg: magnesium oxide is a base that reacts with dilute sulfuric acid.magnesium oxide + dilute sulfuric acid ->magnesium sulfate + water
MgO(s)+H2SO4(aq) ->MgSO49aq) +H2O(L)
Copper hydroxide is another base that reacts with dilute nitric acid:Copper(ii) hydroxide+ dilute nitric acid->copper nitrate(ii) + water
Cui(OH)2(s) + 2HNO3(aq)->Cu(NO3)2(aq)+2H2O(L)
The surfaces of copper objects become tarnished as they react with the oxygen in the surroundings to form copper oxide(ii)
Copper oxide(ii) is a base that reacts with acids
For eg, if a tarnished copper coin is inserted into a citrus fruit and taken out after some time, the part that was inside the citrus fruit becomes clean as the copper oxide was reacting with the acid of the citrus fruit
Acids reacts with carbonates
Scales of calcium carbonate, or hard water stains, found on taps and sinks can be cleaned off easily using acids
Acids react with carbonates to form salt, water and carbon dioxide.Carbonate + acid= salt + water + carbon dioxide
For eg:the reaction between calcium carbonate and dilute hydrochloric acid produces calcium chloride, water and carbon dioxide
CaCO3(s) + 2HCl(aq)->CaCl2(aq) + H2O(L)+CO2(g)
Presence of carbon dioxide from the reaction can be tested by bubbling it through limewater.Carbon dioxide gas forms a white precipitate with limewater
Strength of acids and concentration of acids
Strong acids
A strong acid is an acid that is completely ionised in an aqueous solution
hydrochloric acid in the stomach helps to digest food is a strong acid.All the HCl molecules will comletely ionise in an aqueous solution
Weak acids
A weak acid that is only partially ionised in an aqueous solution
Citric acid, found in citrus fruits is a weak acid.Vinegar is another example of a weak acid.Only some CH3 COOH molecules will ionise in an aqueous solution
The strength of an acid depends on its degree of ionisation whereas its concentration is related to the number of acid molecules present in a given volume of water
A strong or weak acid can be dilute or concentrated in a solution as it depends on the number of acid molecules are present
Types of bases
Bases feel slippery and soapy and are used in many cleaning products
Weak bases are used as window cleaners
Strong bases are able to dissolve grease and protein and are used for cleaning drains and ovens
They must be handled with care to prevent the solution from reacting with the skin
A base is any metal oxide or hydroxide.They contain either the oxide ion or the hydroxide ion(OH-)
Most bases are insoluble in water
Eg of some bases are sodium oxide(Na2O), zinc oxide(ZnO),copper(ii) oxide( CuO),magnseium hydroxide(Mg(OH)2) and aluminium hydroxide(Al(OH)3)
Reaction of bases with acids
Base + acid->salt + water
For eh:copper oxide and dilute sulfuric acid react to form a neutral solution
copper(ii) oxide + dilute sulfuric acid ->copper(ii) sulfate + water
CuO(s) + H2SO4(aq)
Alkalis
Alkalis are bases that are soluble in water. Eg is sodium oxide
sodium oxide+water->sodium hydroxide
Na2O(s) + H2O(L)->2NaOH(aq)
Strong and weak alkalis
How strong or weak an alkali is dependent on the degree of ionisation
Strong soluble bases such as sodium hydroxide(NaOH) are fully ionised when dissolved in water.
Ammonia is a weak alkali since it is only partially ionised in water
NH3(g) + H2O(L)<->NH4+(aq)+OH-(aq)
Properties of alkalis
Alkalis taste bitter
They feel slippery and soapy
Alkalis dissolve in water to form solutions that conduct electricity
Alkalis turn red litmus paper blue
Alkalis react with acids
General equation for the reaction is: alkali + acid->salt + water
In a neutralisation reaction, the hydrogen ions from the acid,H+ and the hydroxide ions from the alkali,OH-, react to form water
Ionic equation for any neutrailisation reaction:H+(aq) + OH-(aq)->H2O(L)
Alkalis react with ammonium salts
Alkalis, when heated with ammonium salts, give off ammonia gas
General equation for the reaction is:Alkali + ammonium salt->salt + water + ammonia
For eg:When potassium hydroxide is heated with ammonium chloride, ammonia gas is produced
KOH(aq)+NH4Cl(s)->KCl(aq)+H2O(L)+NH3(g)
Ammonia gas can be recognised by its characteristic pungent smell.Ammonia gas can be tested with a piece of damp red litmus paper.AMmonia gas turns damp red litmus paper blue
How do we compare relative acidity and alkalinity
Indicators are coloured dyes.They change in colour when added to an acid or alkali
Universal indicator comes in the form of a pH paper or as a solution that contains a mixture of dyes.It gives different colours in solutions of different pH values
Testing the hydrogen ion concentration of aqueous solution
The hydrogen ion concentration in most solutions in the lab varies from 1mol/dm cube to 1x10 to the power of negative 14 mol/dm cube
To manage this wide range of concetration, a Danish scientist, S.P.L Sorensen proposed the pH scale.The nunbers on this scale usually range from 0 to 14.A solution with pH of 4 has 1000 times more H plus ions than a solution with pH 7.