T1W8L1: salts & covalent bonding

• salts.
• some salts are different from others?!

salts §

• what is a salt
• salts are substances that form when a hydrogen acid gets replaced with a metal ion.

copper sulphate (example) §

• copper sulphate has two forms:
  • hydrated, and anhydrous
• CuSO4 . 7H2O (s)
  • hydrated salt, water is part of the crystal.
    • the water xH2O is called water of crystallisation
    • the water has weak attractions in particular to cations.
  • not ionic bonding, heat is enough to dehydrate the compound.
    • if that occurs, white powder of CuSO4 (s) and xH2O (g) which evaporates.
    • this is called anhydrous.
  • you can calculate mass of water compounds given mass of solution and mass of anhydrous salt. $m_1-m_2=m_3$
  • use $n=\frac{m}{M}$ since u should use moles as the unit in your calculation.

example question §

1. from the experiment results below, work out the formula of the hydrated salt.

   • mass of CaCl2 . xH2O = 6.573g

   • mass of CaCl2 = 3.333g

   • n = m/M

   • n(CaCl2) = 3.333g / (40.08 + 35.45 + 35.45)

   • => 3.333/(40.08 + 35.45 + 34.45) = 0.03003 moles (0.03003243828)

   • n(CaCl2.xH2O) = (6.573)/(16 + 16 + 1.008 + 40.08 + 35.45 + 35.45) = 0.04565 moles (0.04564963747)

   • n(xH2O) = (6.573-3.333)/(16 + 1.008 + 1.008) = 0.17984

   • 0.3003/0.3003 = 1 | 0.17984/0.03003 = 5.989 ~= 6

     	$CaCl$	$H_{2}O$
     mass	3.333	3.24
     Mr	110.98	18.016
     moles	0.03003	0.17984
     ratio	1	5.986

     	CoCl2	H2O
     mass	0.64	0.532
     Mr	129.83	18.016
     moles	0.00493	0.0294
     ratio	1	6

     	NiSO4	H2O
     mass	0.673	0.471
     Mr	154.75	18.016
     moles	0.004348949919	0.02614342806
     ratio	1	6.0114346099

covalent bonding §

• Cl2 H2O, HCl, CH3COOH, Co2, N2, O3
  • the following are all covalently bonded
  • shared electrons (called the bonding/shared pair)
  • long definition: there is electrostatic forces of attraction between the bonding pair/shared pair of electrons and nuclei of atoms at each side.
  • short definition: shared electrons between electrostatic forces of attractions.

combining power §

• the amount of hydrogen atoms required to complete the electron shell to achieve the stability of nearest noble gas.