Salts and Electrolysis Lab

Ionic compounds• Made of • positive ions = cations (metal or

polyatomic ion) -AND-• negative ions = anions (nonmetal or

polyatomic ion)• Salts = ionic compounds• Greater the electronegativity difference the

more ionic – See table S for eletronegativities– Difference in electronegativities >1.7 = ionic

Hydrolysis = salts dissociate in water cations and anions (aqueous solution)

• Ex: NaCl + H2O Na+(aq) + Cl-(aq)

• Cations =• Na+

• Anions = • Cl-

• Note: what happens to the water – some salts react with water solutions of acids, bases, ions and salts.

1) What happens when you dissolve salts in water?

• They form ions in solution

Gypsum Springs, Axel Heiburg

Glacial melt flows through Gypsum Hill Gypsum Springs

CaSO4 = gypsum

2) What ions form when gypsum salts dissolve in water? CaSO4(s) + H2O ___Be sure to write the proper oxidation # that goes with each

• Ca+2(aq) = cations

• SO4-2(aq) = anions

Aqueous solutions = Electrolytes

• Electrolytes = ionic solutions that conduct electricity

• Add salt to water salt ions

• Salt ions increase conductivity of water

• How can we test this???

Construct a Voltaic Cell

(testing electrolytes)

Pre-lab Questions• Using Table J which metal is more active Mg or

Cu?• Mg• Mg and Cu act as electrodes (places where

electrons move to and from.) Metals like to lose electrons so electrons flow from more active metals to less active ones. Which way will electrons flow if we use Mg and Cu electrodes?

• From Mg to Cu• Which one will act as the anode?• Mg

Using table J

• Mg Fe• Zn Ag• Mn Sn• Al

Cu

Anode Cathode

Part 2: Electrolysis

• Add electricity to water water molecules split

• Overall reaction is:

2H2O(l) 2H2(g) + O2(g)

Laws of Thermodynamics (energy laws)

• 1st law = energy cannot be created or destroyed (just transformed from one type to another)

• 2nd law = at every energy transformation some energy is lost in the form of heat (less usable form of energy)

Set up your electrolysis apparatus

Follow lab procedures for comparing electrolytes