PowerPoint Presentation
1. ions
2. valences
3. salts
1. ions
Inorganic compounds dissolved in water dissociate to a greater
or lesser extentAB A+ + B- with the formation of :negative charged
ions (anions) : B-positive charged ions (cations) : A+
The dissolved substance is called an electrolyte and facilitates
the flow of an electric current.
1. ions
Some acids, bases and/or salts are entirely dissociated even in
relatively concentrated solutions. They are called strong
electrolytes.
e.g.NaClNa+ + Cl-NaOHNa+ + OH-H2SO42H++ SO42-1. ions
Other substances are only partially dissociated into ions.They
are called weak electrolytes.
e.g.Ca3(PO4)23Ca2+ + 2PO43-CH3COOH CH3COO- + H+7. Conversion
calculations
2. valences
Definition: " The charge acquired by an atom when it gains or
loses electrons in a chemical (oxidation-reduction) reaction, while
acquiring the electron configuration of the nearest inert gas."
Note: The atoms either give up or accept electrons to make their
outer shell "full".
=> Summarized: charge of an atom2. valences
Valency can be thought of as the "combining power" of an element
(or group) in a chemical reaction.
All atoms or elements are neutral to begin with (they possess
the same number of positive charges as negative charges, equal
numbers of protons and electrons).
An element obtains a valency only when it reacts with another
substance.2. valences
Positive Valences: (oxidation numbers) are acquired by atoms
losing electrons, since they are losing negative charges.
Negative Valences: (oxidation numbers) are acquired by atoms
receiving electrons, since they are gaining negative charges.
2. valences
One (I)Two (II)Three (III)Four (IV)Five (V)Six (VI)Seven
(VII)ZeroMost common valence+-+-+-+-+-+-+-Element (generally one
valence, ox.
state)HNaKLiAgHFClBrICaMgBaZnSOAlNCSiCSiHeNeArKrXeRnOften more than
one valence, ox.
stateCuHgCuHgNiFeCrPbSnMnNiFeCrNPAsSbPbSnMnSNPAsSbSPolyatomic
ionsNH4SO4SO3CO3HPO4HPO3CrO4SiO3Cr2O7PO4PO3AsO4SiO43. salts
The presence of dissolved salts in water increases its
conductivity which also varies with temperature.
Conductivity is measured by the conductance of a water column
located between two metal electrodes of 1 cm in area, seperated by
a distance of 1 cm.
Conductivity is expressed in Siemens per cm 1 S/cm = 10 mS/cm =
106 S/cm
Conductivity = 1/Resistivity(ohms.cm)
e.g. 1000 mg NaCl/l = 2200 S/cm
3. salts
Examples of water soluble salts:NaClSodium chlorideNa2SO4Sodium
sulphateKClPotasium chlorideK2SO4Potasium sulphateFeCl3Ferric
chlorideNaNO3Sodium nitrate
Examples of partially water soluble saltsCa3(PO4)2Calcium
phosphateCaSO4Calcium sulphateFePO4Ferric phosphate4. ph
pH= -log[H+]
In pure water [H+] = [OH-] = 10-7 mol/l
An acid medium is a solution in which [H+] is greater than 10-7
mol/l (pH < 7)
An alkaline medium is one in which [H+] is less than 10-7 mol/l
(pH > 7)
The pH is measured by means of coloured indicators or by an
electrometric method (glass-electrode pH meter)
pH-scale ranges from pH 0 to pH 145. oxygen
Oxygen = O2 (MM:32)
D.O.= Dissolved Oxygen (mg O2/l)
Measurement: titrationelectrochemical with an oxygen meter with
an oxygen probe
Dissolved oxygen saturation in water at a pressure of 760 mm Hg
and 20C = 9.1 mg/l
6. Si-units
QuantityUnit Expression in other SI units
Units used with the SI or temporarily accepted
(T)NameSymbolNameSymbolValue in unitsLengthmetremSurface areasquare
metremarea1are=100 mVolumecubiq
metremlitrel1l=1dmTimesecondsminutemin1min=60shourh1h=60mindayd1d=24hVelocitymetre
per secondm.s-1Masskilogrammekgtonnet1t=10kgDensityKilogramme pr
cubic metreKg.m-Volume flow ratecubic metre per secondm.s-16.
Si-units
QuantityUnit Expression in other SI units
Units used with the SI or temporarily accepted
(T)NameSymbolNameSymbolValue in
unitsForcenewtonNKg.m.s-2PressurepascalPaN.m-Bar (T)bar1bar=105
PaAtmosphere (T)atm1atm=101325 PaAbsolute
viscositypascal-secondPa.sm-1.kg.s-2
EnergyjouleJN.mm.kg.s-2PowerwattWJ.s-1Resistivityohm-metre.mConductivitysiemens
per metreS.m-1Amount of substancemolemolMolar concentrationmole per
cubic metremol.m-37. Conversion calculations
To convert from ...ToMultiply by ...mg/l NH4+mg/l NH4+-N
0.776mg/l NH4+-Nmg/l NH4+1.288mg/l NO2-mg/l NO2--N0.3045mg/l
NO2--Nmg/l NO2-3.284mg/l NO3-mg/l NO3--N0.226mg/l NO3--Nmg/l
NO3-4.427mg/l PO43-mg/l PO43--P0.326mg/l PO43--Pmg/l PO43-3.067mg/l
CaCO3meq/l0.02meq/lmg/l CaCO350.0
