Acids, bases and salts

Question 1

characteristic properties of acids as reactions with metals, bases, carbonates and effect on litmus and methyl orange

Answer 1

Neutralisation​ ​reactions:

• acid + metal → salt + hydrogen
• acid + base → salt + water
• acid + metal carbonate → salt + water + carbon dioxide

The​ ​salt​ ​produced​ ​depends​ ​on​ ​the​ ​acid​ ​used:
▪ Hydrochloric​ ​acid​ ​produces​ ​chlorides
▪ Nitric​ ​acid​ ​produces​ ​nitrates
▪ Sulfuric​ ​acid​ ​produces​ ​sulfates
o It​ ​also​ ​depends​ ​on​ ​the​ ​positive​ ​ions​ ​in​ ​the​ ​base,​ ​alkali​ ​or​ ​carbonate​ ​i.e. the​ ​metal
● Red​ ​litmus​ 
o Stays​ ​red​ ​in​ ​acidic
o Stays​ ​red​ ​in​ ​neutral 
o Turns​ ​blue​ ​in​ ​alkaline
● Blue​ ​litmus​
o Turns​ ​red​ ​in​ ​acidic
o Stays​ ​blue​ ​in​ ​neutral 
o Stays​ ​blue​ ​in​ ​alkaline
● Methyl​ ​orange​ ​
o Red​ ​in​ ​acidic
o Yellow​ ​in​ ​neutral 
o Yellow​ ​in​ ​alkaline

Question 2

acids and bases

Answer 2

-Protons​ ​are​ ​H​+​​ ​ions
-Acids​ ​are​ ​proton​ ​donors​ ​
-Bases​ ​are​ ​proton​ ​acceptors,​ ​therefore​ ​there​ ​is​ ​a
proton​ ​transfer​ ​from​ ​acids​ ​to​ ​bases

Question 3

characteristic properties of bases as reactions with acids and with ammonium salts and effect on litmus and methyl orange

Answer 3

● Acid​ ​+​ ​ammonia​ ​->​ ​ammonium​ ​salt
oE.g.​​ HCl ​​+​​ NH3​​​​ ->​​ NH4​C​l
● Effect​ ​would​ ​be​ ​going​ ​from​ ​alkaline​ ​to​ ​neutral​ ​(assuming​ ​that​ ​you​ ​start​ ​with​ ​the base​ ​or​ ​ammonia​ ​then​ ​add​ ​the​ ​acid)
o Methyl​ ​orange:​ ​stays​ ​yellow
o Red​ ​litmus:​ ​blue​ ​to​ ​red
o Blue​ ​litmus:​ ​stays​ ​blue

Question 4

weak and strong acids and bases

Answer 4

Acids​ ​release​ ​H​+​​ ​ions​ ​in​ ​aqueous​ ​solution
● Strong​ ​acid​ ​=​ ​completely​ ​dissociates​ ​to​ ​release​ ​H​+​​ ​ions​ ​in​ ​aqueous​ ​solution
o Hydrochloric,​ ​nitric​ ​and​ ​sulfuric​ ​acids
● Weak​ ​acid​ ​=​ ​partially​ ​dissociates​ ​to​ ​release​ ​H​+​​ ​ions​ ​in​ ​aqueous​ ​solution
o Ethanoic,​ ​citric​ ​and​ ​carbonic​ ​acids
● Stronger​ ​an​ ​acid,​ ​lower​ ​the​ ​pH​

bases​ ​release​ ​OH​-​​ ​ions​ ​in​ ​aqueous​ ​solution
● strong​ ​bases​ ​fully​ ​dissociate​ ​to​ ​release​ ​OH​-​​ ​ions​ ​in​ ​aqueous​ ​solution
● weak​ ​bases​ ​partially​ ​dissociate​ ​to​ ​release​ ​OH​-​ ions​ ​in​ ​aqueous​ ​solution
​​​ ● the​ ​stronger​ ​a​ ​base,​ ​the​ ​higher​ ​the​ ​pH

Question 5

eutrality and relative acidity and alkalinity in terms of pH measured using universal indicator paper

Answer 5

o pH​ ​7​ ​is​ ​neutral
o ​ ​pH​ ​7​ ​is​ ​alkaline
●H​+(​aq)​​+​​OH​-(​aq)​​->​​H2​O​(l)​​ is​​ the ​​Ionic ​​equation ​​of​​ any ​​neutralisation ​​reaction

Question 6

importance of controlling acidity in soil

Answer 6

• If​ ​the​ ​pH​ ​of​ ​soil​ ​is​ ​too​ ​low​,​ ​too​ ​acidic,​ ​this​ ​would​ ​mean​ ​that​ ​crops​ ​would​ ​be unable​ ​to​ ​grow​ ​in​ ​these​ ​acidic​ ​soils
• Farmers​ ​use​ ​lime​ ​(calcium​ ​oxide)​ ​to​ ​neutralise​ ​acid​ ​soils

Question 7

Classify oxides as either acidic or basic, related to metallic and non-metallic character

Answer 7

Many​ ​metals​ ​and​ ​non-metals​ ​react​ ​with​ ​oxygen​ ​in​ ​the​ ​air​ ​when​ ​they​ ​are​ ​heated to​ ​produce​ ​metal​ ​oxides​ ​and​ ​non-metal​ ​oxides
● The​ ​nature​ ​of​ ​these​ ​oxides​ ​is​ ​either​ ​acidic​ ​or​ ​basic
o E.g.​ ​MgO​ ​basic​ ​(metal​ ​oxide)
o E.g.​ ​CO2​ ​​ ​acidic​ ​(non-metal​ ​oxide)
o E.g.​ ​SO​2​​ ​acidic​ ​(non-metal​ ​oxide)

Question 8

classify other oxides as neutral or amphoteric

Answer 8

● Neutral​ ​oxides​
o These​ ​are​ ​non-metal​ ​oxides​ ​that​ ​neither​ ​neutralise​ ​acids​ ​or​ ​base
o E.g.​ ​H​2O​, CO,​ ​NO​
● Amphoteric​ ​oxides​
o Metal-oxides​ ​that​ ​neutralise​ ​both​ ​acid​ ​and​ ​bases​ ​to​ ​form​ ​a​ ​salt​ ​and​ ​water
o E.g.​ ​Al​2O​ ​3​​ ​and​ ​ZnO

Question 9

preparation, separation and purification of salts

Answer 9

Soluble salts
Method A: adding acid to a solid metal, base or carbonate
1.Warm acid, then ad excess Metal, Base or Carbonate.
2.Filter, to remove excess metal, base or carbonate out.
3.Carefully evaporate the solution out, to evaporate water out, when crystals start to appear stop heating
4.Allow solution to cool, crystals will form, filter crystals and wash with little distilled water and carefully dry with filter paper
-Preparation of pure, Hydrated Copper (II) Sulfate Crystals using Method A Acid = Dilute Sulfuric Acid Insoluble base = Copper (II) Oxide
Reaction:
-Copper (II) Oxide + Dilute Sulfuric Acid → Copper (II) Sulphate + Water
-CuO (s) + H2SO4 (aq) → CuSO4 (s) + H2O (l)

Question 10

Method B: reacting a dilute acid and alkali

Answer 10

1. Add alkali and few drops of indicator (phenolphtaleine or Methyl orange) into a conical flask using a burette.
2. Using a pipette add acid, noting the starting point
   - a pipette to accurately measure a certain volume of acid or alkali
3. Add acid slowly from pipette to conical flask until indicator changes colour.
4. Record final volume of acid, and calculate volume of acid added.
5. Repeat without indicator
6. Heat to partially evaporate, cooled to form crystalls. Then filtered off and washed with little distilled water and carefully dried with filter paper

Question 11

Preparing Insoluble Salts: PPT method

Answer 11

Solid salt being formed must be insoluble in water

1. Dissolve soluble salts in water and mix together using a stirring rod in a beaker
2. Filter to remove precipitate from mixture
3. Wash filtrate with water to remove traces of other solutions
4. Leave in an oven to dry

Preparation of Pure, Dry Lead (II) Sulfate Crystals using a precipitation reaction

• Soluble Salt 1 = Lead (II) Nitrate
• Soluble Salt 2 = Potassium Sulfate

Method:

1. Dissolve Lead (II) Nitrate and Potassium Sulfate in water and mix together using a stirring rod in a beaker
2. Filter to remove precipitate from mixture
3. Wash precipitate with water to remove traces of potassium nitrate solution
4. Leave in an oven to dry

Equation of reaction:

• Lead (II) Nitrate + Potassium Sulfate → Lead (II) Sulfate + Potassium Nitrate
• Pb(NO3)2 (aq) + K2SO4 (aq) → PbSO4 (s) + 2KNO3 (aq)

Question 12

Selecting method of preparation

Answer 12

When deciding the method of preparation, it is important to first know whether the salt being produced is soluble or insoluble

• If it is soluble then it can be prepared using either method (A or B) for preparing a soluble salt
• If it is insoluble then it must be prepared by using precipitation

Question 13

Identification of ions

Answer 13

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