EDTA Flashcards
water hardness
amount of calcium and magnesium contained in water
low concentration of ions
soft water (corrosive)
high concentration of ions
hard water (hard water scales)
Mg and Ca in natural waters do what
regulate pH and reduces toxicity of metals that enter the water
ligand
a species that is an electron donor and binds to a metal (electron acceptor)
Ligands in EDTA
lone pairs on N and O
Metal-ligand complex
metal surrounded by the ligand of a compound
How must EDTA titrations occur?
in basic conditions
Each molecule of EDTA
binds to one metal ion
Indictors
organic dyes that form stable complexes with metal ions
What is special about these indicators?
their colour depends on the presence of free metal ions
Before titration
indicator will bind to the metal ions in solution (formation of EDTA)
During titration
EDTA reacts with free metal ions.
Nearing endpoint and after
EDTA release the metal ions from the INDICATOR to form metal-EDTA complexes
indicators used in experiment
calcon and hydroxynaphthol blue
what colour are the solutions at the beginning of titration?
red-pink
what colour are the solutions at the end of titration?
blue
what colour are the solutions at during titration?
purple
Why is a pH 10 buffer solution needed?
- EDTA needs to exist in its deprotonated form
- controls the binding strength of the indicator molecules to the metal ions
Why is NaOH needed?
To precipitate MgOH, leaving CaOH as the remaining molecule to titrate.
Total concentration of Ca and Mg ions
CtitrantVtitrant=CanalyteVanalyte
Binding affinity
a measure of how well two compounds bind together
How do you know which one has more binding affinity?
The molecule affected by the basic state will have a lower binding affinity than the other molecule
Common products EDTA is used in
Skin Care, Laundry Detergent
If a question asks to convert the waterhardness to mg/L
convert both Mg and Ca seperately and then combine together
