Chemistry

Question 1

What type of ions are in tap water and what is their effect on the water

Answer 1

Calcium and magnesium ions make the water hard

Question 2

Describe the problems caused by hard water

Answer 2

Doesn’t easily form lather with soap, more soap is needed to produce lather
Reacts with soap to form a precipitate (scum)
Scum causes soap to be wasted
Temporary hardness can reduce the efficiency of kettles and heating systems because limescale (a solid containing calcium carbonate) is produced when the water is heated

Question 3

What are the two forms of hard water

Answer 3

temporary and permanent

Question 4

Describe how temporary hard water can be softened

Answer 4

Boiling
Temporary hard water contains dissolved hydrogen carbonate ions, HCO3–. When heated, these ions decompose to form carbonate ions, CO32–.
(The carbonate ions in the boiled water react with dissolved calcium and magnesium ions to form insoluble precipitates (calcium carbonate and magnesium carbonate).)

 add soap (solution)
 shake
 no lather / less than with soft water
 scum/ precipitate
 boiled sample
 after boiling precipitate / (lime)scale formed
 lather (immediately)

Question 5

Describe how permanent hard water can be softened

Answer 5

Boiling wont work
Permanent hard water contains dissolved sulfate ions, SO42–.which do not decompose as they don’t react with calcium and magnesium ions - so the water stays hard even when boiled.

An ion exchange resin
The resin beads have sodium ions attached to them. As the hard water passes through the column, the calcium and magnesium ions swap places with the sodium ions.
The calcium and magnesium ions are left attached to the beads, while the water leaving the column contains more sodium ions. The hard water is softened because it no longer contains calcium or magnesium ions. Some ion exchange resins use hydrogen ions instead of sodium ions.

 add soap (solution)
 shake
 no lather / less than with 
soft water
 scum/ precipitate
 boiled sample
 same results / boiling does not change
 becomes soft after ion exchange but not after boiling

Question 6

What are soluble salts prepared from?

Answer 6

an acid and an insoluble/soluble reactant

Question 7

How do you ensure all the acid is used when preparing a salt from an acid and an insoluble reactant?

Answer 7

add the excess of the reactant

Question 8

How do you remove the excess reactant from salt preparation from an acid and an insoluble reactant?

Answer 8

Filteration

Question 9

What is the product of a reaction between an acid and an insoluble reactant?

Answer 9

soluble salt, water and excess reactant

Question 10

How do you prepare pure salt from an acid and a soluble reactant

Answer 10

titration must be used to determine the exact amount of the soluble reactant that reacts with the acid to mix it in the correct proportions

• mix the same volume of alkali with the volume of acid
(determined from titration)
• pour solution into an evaporating basin
• {heat solution/leave the water to evaporate} until pure salt
crystals are left

Question 11

What is the product of a reaction between an acid and an soluble reactant?

Answer 11

soluble salt, water

Question 12

What are electrolytes?

Answer 12

ionic substances in the molten state/ dissolved in water

Question 13

How do ions move during electrolysis?

Answer 13

+ve cations= -ve cathode

-ve anions= +ve anode

Question 14

Whats oxidation and which electrode does it happen at?

Answer 14

the loss of electrons, at anode

Question 15

Whats reduction and which electrode does it happen at?

Answer 15

the gain of electrons, at cathode

Question 16

Write the half equation for the electrolysis of molten sodium chloride (NaCl)

Answer 16

Cathode= Na+ + e- = Na
Anode   = 2Cl-= Cl2 + 2e-

Question 17

Write the half equation for the electrolysis of molten lead bromide (PbBr2)

Answer 17

Cathode= Pb2+ + 2e- = Pb
Anode   = 2Br-= Br2 + 2e-

Question 18

Write the half equation for the electrolysis of the solution copper chloride (CuCl2)

Answer 18

Cathode= Cu2+ + 2e- = Cu
Anode   = 2Cl-= Cl2 + 2e-

Question 19

Write the half equation for the electrolysis of the solution copper sulfate (CuSO4)

Answer 19

Cathode= Cu2+ + 2e- = Cu
Anode   = 4OH-= 2h2O + O2 + 4e-

Question 20

Write the half equation for the electrolysis of the solution sodium sulfate (Na2SO4)

Answer 20

Cathode= 2H+ + 2e- = H2
Anode   = 4OH-= 2h2O + O2 + 4e-

Question 21

Write the half equation for the electrolysis of the solution sodium chloride (NaCl)

Answer 21

Cathode= 2H+ + 2e- = H2
Anode   = 2Cl-= Cl2 + 2e-