INDICATORS SALT HYDROLYSIS
LEWIS THEORY • an acid-base indicator is a weak acid which • an ionic salt is formed from the neutralisation reaction of an acid and base
• LEWIS ACID: an electron pair acceptor, electrophile dissociates to give an anion of a different colour
• LEWIS BASE: an electron pair donor, nucleophile •
•
the conjugate acids/bases are different colours
the colour of the indicator depends on the pH of the
int Mentalisatio Mt
+ <
pH CURVE solution • the ionic salt, MA, formed will dissociate in water
• s-shape curve • colour changes gradually over a pH range • HYDROLYSIS - splitting of a bond using water
• EQUIVALENCE POINT: midpoint of inflection • the pKa of an indicator = pH of its endpoint • the reaction of the salt will vary depending on the strength of the acid and
• pkA = pH at half equivalence —> the stage of the bases used in the neutralisation reaction
titration at which exactly half the amount of …. has been • the use of the different strengths of the acids and bases will directly influence
neutralised the type of salt hydrolysis and the pH of the final solution
pH curves can: • if the Ka is larger = solution will be acidic
• determine the pH of the acid by looking where the curve • if the Kb is larger = solution will be basic
starts on the axis • if Ka = Kb then the pH will be 7
• find the pH at the equivalence point •
• find volume of base at the equivalence point
• obtain the range of pH at the vertical section of the curve ACIDS & BASES FORMULAS SUMMARY
[Hg0t] pOH -logCOH]
BUFFERS pH=-log
=
STRONG ACID + STRONG BASE
.
WEAK BASE + STRONG ACID
·
PH polt
• is a solution which resists changes in pH when small amount of (OH-] 10
-
(H30 ] 10
+
·
·
= =
acid or base are added
(Hz0 ] kw/20H]
+ =
• used to keep the pH almost constant
·
• can consist of weak acid -conjugate base or weak base - ·
pH 14-pot
=
conjugate acid · kw = Ka kp
·
= 10-14
• Equilibrium is reestablished, ex ethanoate ate ions in the buffer 14
pku =
pka + pkp =
solution react with the added H+ to prevent the pH from
decreasing pKb -legkb
pKa -logka =
·
·
=
BUFFER REGION 10-plb
Kn
10-pha
=
Ka
·
• these are seen on a pH curve and represent the region where
=
WEAK ACID + STRONG BASE WEAK ACID + WEAK BASE
·
(BH
+
)(OH]
small addition in acid or base result in little change in the overall Het
<A k
·
=
·
Ka =
[B]
pH of the solution
↳ B +2 = BH
+
+ 04-
• ex;
+
↳ HAJA + H
+
LEWIS THEORY • an acid-base indicator is a weak acid which • an ionic salt is formed from the neutralisation reaction of an acid and base
• LEWIS ACID: an electron pair acceptor, electrophile dissociates to give an anion of a different colour
• LEWIS BASE: an electron pair donor, nucleophile •
•
the conjugate acids/bases are different colours
the colour of the indicator depends on the pH of the
int Mentalisatio Mt
+ <
pH CURVE solution • the ionic salt, MA, formed will dissociate in water
• s-shape curve • colour changes gradually over a pH range • HYDROLYSIS - splitting of a bond using water
• EQUIVALENCE POINT: midpoint of inflection • the pKa of an indicator = pH of its endpoint • the reaction of the salt will vary depending on the strength of the acid and
• pkA = pH at half equivalence —> the stage of the bases used in the neutralisation reaction
titration at which exactly half the amount of …. has been • the use of the different strengths of the acids and bases will directly influence
neutralised the type of salt hydrolysis and the pH of the final solution
pH curves can: • if the Ka is larger = solution will be acidic
• determine the pH of the acid by looking where the curve • if the Kb is larger = solution will be basic
starts on the axis • if Ka = Kb then the pH will be 7
• find the pH at the equivalence point •
• find volume of base at the equivalence point
• obtain the range of pH at the vertical section of the curve ACIDS & BASES FORMULAS SUMMARY
[Hg0t] pOH -logCOH]
BUFFERS pH=-log
=
STRONG ACID + STRONG BASE
.
WEAK BASE + STRONG ACID
·
PH polt
• is a solution which resists changes in pH when small amount of (OH-] 10
-
(H30 ] 10
+
·
·
= =
acid or base are added
(Hz0 ] kw/20H]
+ =
• used to keep the pH almost constant
·
• can consist of weak acid -conjugate base or weak base - ·
pH 14-pot
=
conjugate acid · kw = Ka kp
·
= 10-14
• Equilibrium is reestablished, ex ethanoate ate ions in the buffer 14
pku =
pka + pkp =
solution react with the added H+ to prevent the pH from
decreasing pKb -legkb
pKa -logka =
·
·
=
BUFFER REGION 10-plb
Kn
10-pha
=
Ka
·
• these are seen on a pH curve and represent the region where
=
WEAK ACID + STRONG BASE WEAK ACID + WEAK BASE
·
(BH
+
)(OH]
small addition in acid or base result in little change in the overall Het
<A k
·
=
·
Ka =
[B]
pH of the solution
↳ B +2 = BH
+
+ 04-
• ex;
+
↳ HAJA + H
+
