Chapter 8: Acids and Bases

Question 1

Whatare acids?

Answer 1

Acids are substances that dissolve in water to produce hydrogen ions, H+, as the only positive ions.

Question 2

What are the chemical properties of pure acids?

Answer 2

*The properties are due to the presence of H+ in the aqueous solution.

Pure acids exist as simple, covalent molecules with all the electrons used in bonding. When water is added, molecules react with the water to form mobile charged ions (ionisation), this is shown by the electrical conductivity of acids. Thus pure acids do not confuct electricity, or exhibit any acidic physical/chemical properties.

Question 3

What are the chemical and physical properties of acids?

Answer 3

• Taste sour
• Corrosive when concentrated
• Conduct electricity (when aqueous/dissolved in water)
• Change colours of indicators (blue litmus to red)
• ph < 7

Question 4

List some common acids.

Answer 4

• Hydrochloric acid, HCl: Stomach acid, cleaning metals, maintenance of pools, household cleaning
• Nitric acid, HNO3: Manufacture of fertilisers, explosives, extraction of gold
• Sulfuric acid, H2SO4: Car batteries, manufacture of fertilisers, detergents, ‘pickling’ of steel or iron to remove rust

Question 5

What are acids able to react with?

Answer 5

Metals, carbonate salts and bases.

Question 6

How to test for the presence of acids?

Answer 6

Indicators or pH meter, positive reactions with metals, carbonate salts and bases (gas is produced, bubbling seen)

Question 7

Which metals can react with acids and why?

Answer 7

Only metals above [H] in the reactivity series can react with acids as a reactive metal can displace hydrogen from the acid to form a metal salt.

Question 8

What is the equation for the reaction between acids and metals?

Answer 8

acid (aq) + metal (s) -> metal salt (aq) + hydrogen (g)

Question 9

What are the conditions for a feasible reaction between an acid and metal?

Answer 9

It should produce a soluble metal salt. If an insoluble metal salt is produced, the reaction cannot proceed further due to layer of insoluble salt acting as a barrier to prevent acid reacting with the metal.

Question 10

What is the test for hydrogen gas?

Answer 10

Lighted splint extinguishes with a ‘pop’ sound - H2 is explosive and reacts with air to produce ‘pop’ sound, water vapour produced extinguishes the lighted splint.

2H2 (g) + O2 -> 2H2O (g)

Question 11

Why are group 1 metals unable to be reacted with acids?

Answer 11

Group 1 metals are too violent to be done safely in a normal lab environment.

Question 12

What are the observations in a reaction between Ca, Pb, and acid?

Answer 12

Pb reacts very slowly (unless warmed), with acid.
However only feasible with Pb is nitric acid, HNO3.
As reactions produce insoluble salts, it stops quickly as the layer of salt prevents acid reaction with metal.

Question 13

What are the observations seen when an acid and metal are reacted?

Answer 13

Metal seemingly dissolves (include speed depending on reactivity), clear, colourless solution produced, (include speed depending on reactivity) bubbling is seen (include reason for speed of bubbling due to reactivity), gas produced extinguishes lighted splint with a ‘pop’ sound.

Question 14

What colours are Fe2+ and Fe3+?

Answer 14

• Iron(II), Fe2+, is a green substance (pale green solution)
• Iron(III), Fe3+, is a reddish-brown/yellow substance

Question 15

What colour are copper solutions?

Answer 15

Blue solutions.

Question 16

What is the equation between acids and carbonate salts?

Answer 16

acid (aq) + carbonate (s/aq) -> salt (aq) + carbon dioxide (g) + water (l)

Question 17

What is the test for presence of carbon dioxide?

Answer 17

White precipitate is formed in limewater. Acid reacts with the carbonate salt to produce CO2 which passes through the delivery tube into limewater. Co2 gas is acidic, while limewater, Ca(OH)2 is an alkali/base, neutralisation occurs, white precipitate is formed as resultant salt.

Question 18

What are the polyatomic ions?

Answer 18

OH^-
NO3^-
SO4^2-
CO3^2-
PO4^3-
NH4^+

Question 19

What are some carbonates?

Answer 19

Carbonates are all metal carbonate salts, except ammonium carbonate, (NH4)2CO3 and group 1 metal carbonates are slightly alkaline in water

Question 20

What are the soluble carbonates and what colour and state are they?

Answer 20

SPA (sodium, potassium, ammonium) and group 1. All white crystals/clear and colourless solutions.

Question 21

What are the insoluble carbonates and what coloue and state are they?

Answer 21

White solid:
- Calcium carbonate, CaCO3
- Magnesium carbonate, MgCO3
- Barium carbonate, BaCO3
- Aluminium carbonate, Al2(CO3)3
- Zinc carbonate, ZnCO3
lead(II) carbonate, PbCO3

Other colours:
- Copper(II) carbonate, CuCO3 - green solid
- Silver carbonate, Ag2CO3 - yellow-grey solid

Question 22

What are the conditions of a feasible reaction between an acid and carbonate?

Answer 22

Produces a soluble salt. If an insoluble salt is produced, the reaction cannot proceed further as a layer of insoluble salt will act as a barrier to prevent the acid from reacting with the substance