How to deduce Nature of Salt in Salt Hydrolysis
A salt can be acidic, neutral or alkaline.
We can deduce the nature of the salt from its constituent ions, namely:
1. ion formed from a weak acid will be a conjugate base, eg CH3COO- (from weak acid CH3COOH)
2. ion formed from a strong acid will be neutral, eg Cl- (from strong acid HCl)
3. ion formed from a weak base will be a conjugate acid, eg NH4+ (from weak base NH3)
4. ion formed from a strong base will be neutral, eg Na+ (from strong base NaOH)
This can be summarised as shown:
salt hydrolysis nature of ions summary
Next we can move on to deduce the nature of a salt.
Let's have some examples.
1. Sodium chloride NaCl is neutral
What we do is simply just deduce the nature of each constituent ion based on the acid or base that forms that ion.
salt hydrolysis sodium chloride neutral
Na+ is neutral since it is formed from strong base NaOH
Cl- is neutral since it is formed from strong acid HCl
Since both cation and anion are neutral, NaCl must be neutral.
2. Sodium ethanoate CH3COONa is alkaline
salt hydrolysis sodium ethanoate is alkaline
Na+ is neutral since it is formed from strong base NaOH.
CH3COO- is alkaline since it is the conjugate base of weak acid CH3COOH.
Since we have a conjugate base, CH3COO- will dissociate in water to give OH-, hence the salt is alkaline.
3. Ammonium chloride NH4Cl is acidic
salt hydrolysis ammonium chloride is acidic
Cl- is neutral since it is formed from strong acid HCl.
NH4+ is acidic since it is the conjugate acid of weak base NH3.
Since we have a conjugate acid, NH4+ will dissociate in water to give H+, hence the salt is acidic.
Watch this video to learn an easy way to understand salt hydrolysis, a concept that students often find confusing in Ionic Equilibria!
Topic: Ionic Equilibria, Physical Chemistry, A Level Chemistry, Singapore
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/salt-hydrolysis-how-to-deduce-nature-of-salt
Do check out the following for more video lessons:
Physical Chemistry Videos at https://chemistryguru.com.sg/a-level-physical-chemistry-video-lessons
A Level Chemistry Videos at https://chemistryguru.com.sg/a-level-chemistry-video-lessons
If you are looking for H2 Chemistry Tuition, do consider taking up my classes at Bishan. More info at https://chemistryguru.com.sg/
You can also find out more about my online classes at https://chemistryguru.com.sg/a-level-chemistry-tuition-online
Bronsted Acids and Bases: Types and Strength
According to Bronsted-Lowry theory of acids and bases,
- an acid is a proton, H3O+ or H+ donor
- a base is a proton, H3O+ or H+ acceptor
The strength of an acid or base is related to the extent of dissociation in solution:
- a strong acid or base is fully dissociated
- a weak acid or base is partially dissociated
So therefore we will have 4 possible types of acids and bases:
1. Weak Acid
2. Strong Acid
3. Weak Base
4. Strong Base
Also, each of these acids and bases will dissociate in solution to give different species.
1. Weak Acid Dissociation eg CH3COOH
bronsted theory weak acid CH3COOH dissociation
CH3COOH is a weak acid and dissociates partially in solution (as indicated with reversible arrow) to form H+ and CH3COO- ions.
Since this is a reversible process, CH3COO- can accept H+ to form back CH3COOH.
Therefore the nature of CH3COO- is basic and we call CH3COO- the conjugate base of CH3COOH.
2. Strong Acid Dissociation eg HCl
bronsted theory strong acid HCl dissociation
HCl is a strong acid and will dissociate fully (as indicated with full arrow) in solution to form H+ and Cl- ions.
Since this is an irreversible process, Cl- has no tendency to accept H+ and form back HCl.
Therefore the nature of Cl- is neutral.
3. Weak base dissociation eg NH3
bronsted theory weak base NH3 dissociation
NH3 is a weak base and dissociates partially in solution (as indicated with reversible arrow) to form OH- and NH4+ ions.
Since this is a reversible process, NH4+ can donate H+ to form back NH3.
Therefore the nature of NH4+ is acidic and we call NH4+ the conjugate acid of NH3.
4. Strong base dissociation eg NaOH
bronsted theory strong base NaOH dissociation
NaOH is a strong base and will dissociate fully (as indicated with full arrow) in solution to form OH- and Na+ ions.
Since this is an irreversible process, Na+ has no tendency to donate H+ and form back NaOH.
Therefore the nature of Na+ is neutral.
So in summary:
- weak acid will dissociate to give conjugate base
- weak base will dissociate to give conjugate acid
- strong acid will dissociate to give a neutral ion
- strong base will dissociate to give a neutral ion
bronsted theory dissociation summary
These concepts are fundamental and very important in Ionic Equilibria.
Check out this video lesson to learn more about acids and bases and their dissociation in solution!
Topic: Ionic Equilibria, Physical Chemistry, JC, H2, A Level Chemistry, Singapore
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/bronsted-acids-and-bases-types-and-strength
Do check out the following for more video lessons:
Physical Chemistry Videos at https://chemistryguru.com.sg/a-level-physical-chemistry-video-lessons
A Level Chemistry Videos at https://chemistryguru.com.sg/a-level-chemistry-video-lessons
If you are looking for H2 Chemistry Tuition, do consider taking up my classes at Bishan. More info at https://chemistryguru.com.sg/
Balance Redox Reaction via Half Eqn Method
Balancing Redox Equations via the Half-Equation Method can be done via the following systematic steps.
1. Balance Redox Equation in Acidic Medium
Let's have this reaction as an example:
balance redox reaction using half equation method example
We can determine which species is oxidised and reduced by comparing the oxidation number:
- Oxidation state of manganese decreases from +7 to +4 hence MnO4- is reduced
- Oxidation state of iodine increases from -1 to 0 hence I- is oxidised
We can then write down the half equations for oxidation and reduction:
balance redox reaction half equations
Next we need to balance each half equation.
For half equation in acidic medium, the steps are:
1. Balance elements oxidised or reduced
2. Balance oxygen using water
3. Balance hydrogen using H+
4. Balance charge using electron
So after applying these 4 steps for each half equation, we'll end up with these two balanced half equations:
balance redox reaction half equation balanced in acidic medium
Next we need to modify each half equation so that the number of electrons for both half equations are the same (lowest common multiple).
In this case the lowest common multiple is 6, so we need to multiply the reduction half equation by 2, and the oxidation half equation by 3.
We can then add the oxidation and reduction half equations together to get an overall redox equation in acidic medium.
balance redox reaction overall balanced in acidic medium
2. Balance Redox Equation in Alkaline Medium
If we want to balance the redox reaction in alkaline medium, an additional step is required which is to add OH- to neutralise the H+.
From the balanced redox equation in acidic medium that we have done previously, there are 8H+ on the left hand side of the equation.
Therefore we need to add 8OH- on the left side to neutralise the 8H+, forming 8H2O.
We also need to add 8OH- on the right side to keep the equation balanced.
Usually there will be H2O on both sides of the equation to cancel out.
This will give us the overall balanced redox equation in alkaline medium:
balance redox reaction balanced in alkaline medium
Watch this video tutorial to learn how to balance a redox equation step-by-step!
Topic: Redox Titrations, Physical Chemistry, JC, H2, A Level Chemistry, Singapore
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/balance-redox-reaction-via-half-eqn-method
Do check out the following for more video lessons:
Physical Chemistry Videos at https://chemistryguru.com.sg/a-level-physical-chemistry-video-lessons
A Level Chemistry Videos at https://chemistryguru.com.sg/a-level-chemistry-video-lessons
If you are looking for H2 Chemistry Tuition, do consider taking up my classes at Bishan. More info at https://chemistryguru.com.sg/
Compare Strength of 2 Acids with different pH
Comparing Strength of 2 Acids with different pH values by Maverick Puah the Chemistry Guru
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/compare-strength-of-2-acids-with-different-ph
Do check out the following for more video lessons:
Physical Chemistry Videos at https://chemistryguru.com.sg/a-level-physical-chemistry-video-lessons
A Level Chemistry Videos at https://chemistryguru.com.sg/a-level-chemistry-video-lessons
If you are looking for H2 Chemistry Tuition, do consider taking up my classes at Bishan. More info at https://chemistryguru.com.sg/
How to draw Amino Acids and Proteins
Learn how to draw Alpha Amino Acids and Primary structure of Proteins by Maverick Puah the Chemistry Guru.
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/how-to-draw-amino-acids-and-proteins
How to compare Basicity of Amines, Phenylamines and Amides
Learn how to compare Basicity for Amines, Phenylamines and Amides using Lewis Acid-Base Theory by Maverick Puah the Chemistry Guru
You can also view this at our website https://chemistryguru.com.sg/how-to-compare-basicity-of-organic-compounds
Alkene Mechanism: How to describe Electrophilic Addition Mechanism for Alkenes
Step-by-step tutorial to learn how to draw the Electrophilic Addition Mechanism of Alkene by Maverick Puah the Chemistry Guru
You can also view this video lesson with screenshots and detailed explanation at https://chemistryguru.com.sg/electrophilic-addition-mechanism-for-alkenes
Organic Chem Basicity: How to compare Basicity of Organic Compounds
Nitrogen Compounds can act as Lewis bases as there is a lone pair of electrons available on nitrogen for donation. How basic the nitrogen compound is depends on the availability of that lone pair.
Check out this video lesson to learn how to compare basicity for different Nitrogen Compounds in Organic Chemistry!
Topic: Nitrogen Compounds, Organic Chemistry, JC, H2, A Level Chemistry, Singapore
Making Chemistry Simpler
https://chemistryguru.com.sg/