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Week 3, Lesson 3. Chapter 13 – Introducing Acids & Bases. Acids. Acids are commonly used in our homes. Many foods contain acids to enhance flavour or as a preservative. The sour taste of some food substances is due to the presence of acid.

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acids
Acids
  • Acids are commonly used in our homes.
  • Many foods contain acids to enhance flavour or as a preservative.
  • The sour taste of some food substances is due to the presence of acid.
  • In industry solutions of acids are used extensively to produce a wide range of products, such as fertilisers, drugs, explosives and plastics.
  • Acids are also used to clean metal surfaces before use.
acids cont
Acids cont…
  • The three most commonly used acids in the lab are hydrochloric acid, sulfuric acid and nitric acid.
  • Acids can cause severe problems if misused.
  • Eg, acid rain, acid contamination.
properties of acids
Properties of Acids
  • Change the colour of some indicators.
  • Tend to be corrosive
  • Taste sour
  • React with bases
  • Have a relatively low pH.
bases
Bases
  • Acids react with bases.
  • In solution, bases sometimes taste bitter and have a slippery feel.
  • They react with some plant extracts to counteract the effect of acids.
  • If a base is continually added to a solution of an acid, the properties of the acid slowly disappear.
  • The same goes for if an acid is added to a basic solution.
  • The acid and base are said to have neutralised each other.
  • Bases are effective cleaners because they react with fats and oils to produce water-soluble soaps.
properties of bases
Properties of Bases
  • Turn litmus blue
  • Have a slippery feel
  • Are caustic
  • React with acids
  • Have a relatively high pH
safety with acids and bases
Safety with Acids and Bases
  • Acids and bases should be treated with caution and you should avoid these solutions coming in contact with your skin and eyes.
  • You should always wear safety goggles and lab coats.
  • Concentrated sulfuric acid is a viscous liquid and accidents can happen if water is added to the acid in order to produce dilute solutions.
  • The ionisation/hydrolysis of sulfuric acid is an energy-releasing reaction.
  • A common method of neutralising an acid spill is to add sodium hydrogen carbonate powder.
indicators
Indicators
  • One of the characteristic properties of acids and bases is their ability to change to colour of certain plant extracts.
  • Litmus is a dye obtained from lichen.
  • In the presence of acid, litmus turns red.
  • Such plant extracts are called indicators.
  • Indicators are often extracted from plant dyes and are themselves acids or bases.
  • They change from one colour in acid to another in basic solution.
  • Common indicators include methyl orange, phenolpthalein and litmus.
  • Universal indicator is a mixture of many indicators and changes through a range of colours to easily establish the pH of a solution.
  • The indicators that undergo a single colour change are also used for many analyses.
  • pH meters are often used in laboratories for more accurate determination of solution acidity and are not affected by coloured solutions.
reactions involving acids and bases
Reactions Involving Acids and Bases
  • Acids react with many metals particularly those found in the main groups of the periodic table, although they also react with several transition metals.
  • These reactions typically produce a solution of a metal salt and hydrogen gas.
  • Salts are compounds usually made up of a metal cation and a non-metal anion.
  • The salt produced will depend on the acid used in the reaction.
  • Acids also react with many compounds such as metal hydroxides and metal carbonates.
  • A salt is again produced with each of these, together with water.
  • In the case of metal carbonates, carbon dioxide is also formed.
general reaction types involving acids
General Reaction Types involving Acids
  • There are numerous ways in which acids and bases react.
  • It is possible to group some reactions together on the basis of the reactants involved and the products formed.
  • The following are six of the more common reaction types.
acid reactive metal salt hydrogen
Acid + Reactive Metal  Salt + Hydrogen
  • Reactive metals include Ca, Mg, K but not Cu, Ag or Au.
  • When dilute acids are added to main group metals, and some transition metals, bubbles of hydrogen gas are released, and a salt is formed.
  • For example, the reaction between dilute hydrochloric acid and zinc metal can be represented by the equation:

2HCl(aq) + Zn(s)  ZnCl2(aq) + H2(g)

c ont
Cont…
  • This reaction can also be represented by an ionic equation.
  • In an aqueous solution the hydrochloric acid is ionised and the zinc chloride is dissociated.
  • The equation can therefore be written as:

2H+(aq) + 2Cl-(aq) + Zn(s)  Zn2+(aq) + 2Cl-(aq) +H2(g)

However the chloride is the only spectator ion. The ionic equation is therefore:

2H+(aq) + Zn(s)  Zn2+(aq) + H2(g)

acid m e tal hydroxide salt water
Acid + Metal Hydroxide  Salt + Water
  • Metal hydroxides include NaOH, Ca(OH)2 and Mg(OH)2.
  • The hydroxide ions from metal hydroxides readily react with the H+ ion from acid.
  • The products are a salt and water.
  • For example, the reaction between solutions of sulfuric acid and sodium hydroxide can be represented as:

H2SO4(aq) + 2NaOH(aq)  Na2SO4(aq) + H2O(l)

slide15
Cont…
  • The sulfuric acid is ionised in solution and both sodium hydroxide and sodium sulfate are ionic, and therefore dissociate.
  • Water however is a covalent molecular substance that does not ionise to a significant extent.
  • So the equation becomes:

2H+(aq) + SO42-(aq) + 2Na+(aq) + 2OH-(aq) 2Na+(aq) + SO42-(aq) + 2H2O(l)

The ionic equation is therefore:

H+(aq) + OH-(aq)  H2O(l)

acid metal oxide salt water
Acid + Metal Oxide  Salt + Water
  • Metal oxides include Na2O, MgO, CaO and ZnO.
  • Metal oxides are usually basic since they contain the oxide ion.
  • Water soluble oxides tend to form the hydroxide ion.
  • The reaction between dilute nitric acid and solid calcium oxide can be represented by the equation:

2HNO3(aq) + CaO(s)  Ca(NO3)2(aq) + H2O(l)

slide17
Cont…
  • The calcium oxide is solid, so the ions are not dissociated. The nitric acid is ionised in solution and therefore dissociates.
  • The equation becomes:

2H+(aq) + 2NO3-(aq) + CaO(s)  Ca2+(aq) + 2NO3-(aq) + H2O(l)

The nitrate ions are the spectator ions so the ionic equation is:

2H+(aq) + CaO(s)  Ca2+(aq) + H2O(l)

acid metal carbonate salt water carbon dioxide
Acid + Metal Carbonate  Salt + Water + Carbon Dioxide
  • Metal carbonates include Na2CO3, MgCO3 and CaCO3.
  • Acids reacting with metal carbonates produce carbon dioxide gas with a salt and water.
  • For example the reaction between a solution of nitric acid and solid magnesium carbonate can be represented by the equation:

2HNO3(aq) + MgCO3(s)  Mg(NO3)2(aq) + H2O(l) + CO2(g)

The nitrate ions are the spectator ions so the ionic equation is:

2H+(aq) + MgCO3(s)  Mg2+(aq) + H2O(l) + CO2(g)

acid metal hydrogen carbonate salt water carbon dioxide
Acid + Metal Hydrogen Carbonate  Salt + Water + Carbon Dioxide
  • Metal hydrogen carbonates include NaHCO3, KHCO3 and Ca(HCO3)2.
  • Acids added to metal hydrogen carbonates (aka bicarbonates) produce a salt, water and carbon dioxide.
  • For example, the reaction between solutions of hydrochloric acid and sodium hydrogen carbonate can be represented by the equation:

HCl(aq) + NaHCO3(aq)  NaCl(aq) + H2O(l) + CO2(g)

The sodium and chloride are spectator ions in this reaction so the ionic equation is:

H+(aq) + HCO3-(aq)  H2O(l) + CO2(g)

acidic oxide non metal oxide base salt water
Acidic Oxide (non-metal oxide) + Base  Salt + Water
  • Acidic oxides include SO2, SO3, P4O10 and CO2.
  • When oxides are added to water they form acidic solution.
  • The reaction of these with bases produce a salt and water.
  • For example the reaction between carbon dioxide and a solution of calcium hydroxide can be represented by the equation:

CO2(aq) + Ca(OH)2(aq)  CaCO3(s) + H2O(l)

c ont1
Cont…
  • The table below lists some common acidic oxides and the anions they produce in the reaction.