pH is defined as the negative logarithm of H+ ion concentration. Hence the meaning of the name pH is justified as the power of hydrogen.
We know that all the acids and bases do not react with the same chemical compound at the same rate. Some react very vigorously, some moderately while others show no reaction. To determine the strength of acids and bases quantitatively, we use a universal indicator which shows different colours at different concentrations of hydrogen ions in solution. Generally, the value of pH of acids and bases are used to quantitatively determine their strength.
Table of Contents
pH Chemistry
A pH scale is a tool for measuring acids and bases. The scale ranges from 0-14. Litmus paper is an indicator used to tell if a substance is an acid or a base. The colour of the paper matches up with the numbers on the pH scale to indicate what kind of substance is being tested. For example, Vinegar is an acid and measures 2.4 on the pH scale.
A healthy pH balance plays a significant role in your overall well-being, and doctors and scientists usually agree on this. The pH level, or possible level of hydrogen in your body, is determined by the food and type of drink you consume. The pH is the concentration of the hydrogen ions. This calculation is based on a pH scale.
The pH scale is logarithmic and shows the solution’s concentration of hydrogen ions inversely. More specifically, the pH of the solution is the negative logarithm to the base 10 of its hydrogen ion concentration in moles per litre.
The pH scale can be traced to a series of standard solutions whose pH is defined by international agreement. By calculating the potential difference between a hydrogen electrode and a standard electrode such as the silver chloride electrode, primary pH standard values are calculated using a concentration cell with transference.
A glass electrode and pH metre, or colour-changing indicator, may be used to measure the pH of aqueous solutions.
pH Abbreviation
pH may be seen as an abbreviation of the power of hydrogen-or, more fully, the concentration of hydrogen ion in a liquid.
Mathematical definition of pH is a little less intuitive but more useful in general. It states that the pH equals the negative logarithmic value of the concentration of hydrogen ion (H+)
pH = -log [H+]
A water source ‘s pH value is a function of its acidity, or alkalinity.
The pH level is a function of the hydrogen atom activity, as the hydrogen activity is a reasonable indicator of the water’s acidity or alkalinity.
As seen below, the pH scale ranges from 0 to 14 when 7.0 is neutral. It is said that water with a low pH is acidic and that water with a high pH is basic, or alkaline.
Pure water should have a pH of 7.0 however, due to pollutants in the water, water supplies and precipitation appear to be slightly acidic.
In view of the defined scale, pH is a decided value, like the temperature. This means that the pH of water is not a physical parameter that can be measured either as a fixed, or in a quantity.
Rather, it’s a nearby number of 0 and 14 that characterizes how acidic or basic a body of water is in a logarithmic scale.
The smaller the amount, the more acidic the water will be. The higher the list, the more basic it is.
Why does a Water Source Change pH?
Surface water usually has a pH value of 6.5 to 8.5 and groundwater appears to have a pH of 6.0 to 8.5. The pH of a source of water can naturally vary. Some types of rock and soil, such as limestone, can more effectively neutralize acid than other rock and soil types, such as granite.
Or, when large numbers of plants grow in a lake or river, when they die and decompose, they release carbon dioxide. A weak carbonic acid is produced when the carbon dioxide interacts with the water; this can then cause the water body to decrease its pH.
With Increase in Temperature pH of Pure Water
As temperature increases, the degree of dissociation of water increases. Thus, the water dissociates to give more [H+], and hence its pH decreases. Temperature plays a significant role in pH measurements. As the temperature rises, molecular vibrations increase which results in the ability of water to ionize and form more hydrogen ions. As a result, the pH will drop.
pH decreases with an increase in temperature. In the case of pure water, there are always the same concentration of hydrogen ions and hydroxide ions and hence, the water is still neutral (even if its pH changes). At 100°C, a pH value of 6.14 is the new neutral point on the pH scale at this higher temperature.
pH of Acids and Bases
The pH of a solution varies from 0 to 14.
Solutions having a value of pH ranging from 0 to 7 on the pH scale are termed as acidic and the value of pH ranging from 7 to 14 on pH scale are known as basic solutions.
Solutions having the value of pH equal to 7 on pH scale are known as neutral solutions.
Solutions having the value of pH equal to 0 are known to be strongly acidic solutions. Further, the acidity decreases as the value of pH increases from 0 to 7 whereas, solutions with the value of pH equal to 14 are termed as strongly basic solutions.
The basicity decreases as the value of pH decreases from 14 to 7. The strength of acids and bases depends on the number of H+ and OH– ions produced. Acids furnishing more number of H+ ions are known to be strong acids and vice versa.
The degree of ionisation of acids and bases differs for different acids and bases. It helps in the determination of the strength of acids and bases. The strength of an acid depends on the concentration of hydronium ion (H3O+) too. With the help of the comparison between the concentration of hydronium ion and the hydroxyl ion, we can distinguish between acids and bases.
For acidic solution: [H3O+] > [OH–]
For neutral solution: [H3O+] = [OH–]
For basic solution: [H3O+] < [OH–]
Limitations of pH Scale
pH value of a solution does not instantaneously give us an idea of the relative strength of the solution.
pH is zero for 1N solution of strong acid.
pH is negative for concentrations 2N, 3N, ION of strong acids.
At higher concentrations, in place of pH Hammett acidity functions are used.
pH Scale
pH Scale
The concentration of hydronium ion is conveniently expressed on a logarithmic scale. This scale is known as pH scale. pH of acids and bases is defined as the negative logarithm (with base 10) of activity of hydrogen ion (H+).
How to Calculate pH?
The activity has no units and is defined in terms of H+ ion concentration,
Thus, the pH of an acidic solution of HNO3 (10–3 M) = 3, a basic solution of KOH having [OH–] =10–4M and [H3O+] =10–10 M will have a pH = 10. pH of acids is generally less than 7 whereas for bases it is greater than 7. At 298 K, ionic product of water, Kw can be given as:
Kw = [H3O+] [OH–] = 10–14
Taking the negative logarithm of RHS and LHS, we deduce
–log Kw = – log ([H3O+] [OH–])= – log 10–14
=>pKw= – log [H3O+] – log [OH–] = 14
=>pKw = pH + pOH = 14
The value of pKw controls the relative concentrations of hydrogen and hydroxyl ions as their product is always constant. pH of acids and bases can be roughly calculated with the help of pH scale while for accurate values we use pH meters.
pH Example Chart
pH Value and Nature of a Solution
If [H+] > 10-7, pH is less than 7 and the solution is acidic.
If [H+] = 10-7, pH is 7 and the solution is neutral.
If [H+] < 10-7, pH is more than 7 and the solution is basic.
Importance of pH
Only a narrow range of pH change can be sustained by a living organism, any further change in pH can make the living difficult. For example: in the case of acid rain, the pH of water is less than 7. As it flows into a river, it lowers the pH of river water which makes the survival of aquatic life difficult.
We know that our stomach contains hydrochloric acid which helps in the digestion of food. When the stomach produces too much of hydrochloric acid during indigestion, we feel a lot of pain and irritation. Hence, we generally use antacids or a mild base which increases the pH of the acidic stomach and thus decreases the pain.
Bacteria present in our mouth sometimes lower the pH of our mouth by producing acids through degradation of the food particle. Hence, we are instructed to clean our mouths with toothpaste (which is generally basic) to prevent their decay by maintaining the pH.
We experience a lot of pain in case of bee-sting as the bee injects the methanoic acid through its sting. Hence, we are generally advised to apply baking soda or other mild bases on the surface as it helps in maintaining the pH of the surface.
Points to Remember on pH Scale
pH of strong acid or base does not depend upon temperature.
pH of weak acid decreases with increase in temperature due to increase in ionization.
pH of weak base increases with increase in temperature due to increase in ionization or [OH-] ion concentration.
Frequently Asked Questions – FAQs
Q1
What is pH scale in chemistry?
The pH is a measure of the concentration of hydrogen ions, the acidity or alkalinity of a solution. The pH-scale is normally between 0 and 14. Aqueous solutions at 25 ° C with a pH of less than 7 are acidic and basic or alkaline solutions are those with a pH greater than 7.
Q2
What is the best pH for the human body?
For our blood and body tissues the optimum pH is about 7.2. (The use of saliva and urine test strips will show a much lower pH level due to the protein present in the solution. A healthy body saliva and urine tests should have a pH of 6.6 to 6.8 approximately.) Acidosis is a condition of excess acidity in the blood and body tissue.
Q3
What is pH full form?
PH stands for Hydrogen potentials. It refers to the concentration of the hydrogen ions in a solution. This is the indicator of a solution’s acidity or alkalinity. The pH value on a pH-scale varies from 0 to 14.
Q4
Is pH of water important?
PH is a function of the acid / basic water content. Water with more free hydrogen ions is acidic and water with more free hydroxyl ions is basic. Because pH in the water can be changed by chemicals, pH is a significant indicator of water that is chemically changing.
Q5
What happens if your pH is too high?
An increase in alkaline causes a rise in pH levels. When the acid levels are too high in the blood, it’s called acidosis. This is called alkalosis when the blood is too alkaline. A problem with the lungs is due to respiratory acidosis and alkalosis.
Q6
What causes high pH in water?
The cause of the unbalanced pH is the soil, bedrock, or other underlying composition from which the water source comes. High alkaline water is a consequence of rocky areas with a lot of calcareous. It contains compounds of carbonate, bicarbonate, and hydroxide that dissolve and migrate with the water, increasing its pH.
Q7
What is the pH of blood?
Humans have a typical pH range from 7.35 to 7.45. That means blood is of course very alkaline or normal. Your stomach acid, by contrast, has a pH of around 1.5 to 3.5. That makes it acidic.
Q8
Who discovered the pH?
Exactly 100 years ago, Carlsberg ‘s director of chemistry, Søren Sørensen, developed a vital diagnostic tool for measuring acidity, thus helping to detect digestive , respiratory and metabolic disorders. The invention of Sørensen was the pH scale.
Neeraj Anand, Param Anand
Er. Neeraj K.Anand is a freelance mentor and writer who specializes in Engineering & Science subjects. Neeraj Anand received a B.Tech degree in Electronics and Communication Engineering from N.I.T Warangal & M.Tech Post Graduation from IETE, New Delhi. He has over 30 years of teaching experience and serves as the Head of Department of ANAND CLASSES. He concentrated all his energy and experiences in academics and subsequently grew up as one of the best mentors in the country for students aspiring for success in competitive examinations.
In parallel, he started a Technical Publication "ANAND TECHNICAL PUBLISHERS" in 2002 and Educational Newspaper "NATIONAL EDUCATION NEWS" in 2014 at Jalandhar. Now he is a Director of leading publication "ANAND TECHNICAL PUBLISHERS", "ANAND CLASSES" and "NATIONAL EDUCATION NEWS".
He has published more than hundred books in the field of Physics, Mathematics, Computers and Information Technology. Besides this he has written many books to help students prepare for IIT-JEE and AIPMT entrance exams. He is an executive member of the IEEE (Institute of Electrical & Electronics Engineers. USA) and honorary member of many Indian scientific societies such as Institution of Electronics & Telecommunication Engineers, Aeronautical Society of India, Bioinformatics Institute of India, Institution of Engineers. He has got award from American Biographical Institute Board of International Research in the year 2005.
CBSE Class 11 Chemistry Syllabus is a vast which needs a clear understanding of the concepts and topics. Knowing CBSE Class 11 Chemistry syllabus helps students to understand the course structure of Chemistry.
Unit-wise CBSE Class 11 Syllabus for Chemistry
Below is a list of detailed information on each unit for Class 11 Students.
UNIT I – Some Basic Concepts of Chemistry
General Introduction: Importance and scope of Chemistry.
Nature of matter, laws of chemical combination, Dalton’s atomic theory: concept of elements, atoms and molecules.
Atomic and molecular masses, mole concept and molar mass, percentage composition, empirical and molecular formula, chemical reactions, stoichiometry and calculations based on stoichiometry.
UNIT II – Structure of Atom
Discovery of Electron, Proton and Neutron, atomic number, isotopes and isobars. Thomson’s model and its limitations. Rutherford’s model and its limitations, Bohr’s model and its limitations, concept of shells and subshells, dual nature of matter and light, de Broglie’s relationship, Heisenberg uncertainty principle, concept of orbitals, quantum numbers, shapes of s, p and d orbitals, rules for filling electrons in orbitals – Aufbau principle, Pauli’s exclusion principle and Hund’s rule, electronic configuration of atoms, stability of half-filled and completely filled orbitals.
UNIT III – Classification of Elements and Periodicity in Properties
Significance of classification, brief history of the development of periodic table, modern periodic law and the present form of periodic table, periodic trends in properties of elements -atomic radii, ionic radii, inert gas radii, Ionization enthalpy, electron gain enthalpy, electronegativity, valency. Nomenclature of elements with atomic number greater than 100.
UNIT IV – Chemical Bonding and Molecular Structure
Valence electrons, ionic bond, covalent bond, bond parameters, Lewis structure, polar character of covalent bond, covalent character of ionic bond, valence bond theory, resonance, geometry of covalent molecules, VSEPR theory, concept of hybridization, involving s, p and d orbitals and shapes of some simple molecules, molecular orbital theory of homonuclear diatomic molecules(qualitative idea only), Hydrogen bond.
UNIT V – Chemical Thermodynamics
Concepts of System and types of systems, surroundings, work, heat, energy, extensive and intensive properties, state functions. First law of thermodynamics – internal energy and enthalpy, measurement of U and H, Hess’s law of constant heat summation, enthalpy of bond dissociation, combustion, formation, atomization, sublimation, phase transition, ionization, solution and dilution. Second law of Thermodynamics (brief introduction) Introduction of entropy as a state function, Gibb’s energy change for spontaneous and nonspontaneous processes. Third law of thermodynamics (brief introduction).
UNIT VI – Equilibrium
Equilibrium in physical and chemical processes, dynamic nature of equilibrium, law of mass action, equilibrium constant, factors affecting equilibrium – Le Chatelier’s principle, ionic equilibrium- ionization of acids and bases, strong and weak electrolytes, degree of ionization, ionization of poly basic acids, acid strength, concept of pH, hydrolysis of salts (elementary idea), buffer solution, Henderson Equation, solubility product, common ion effect (with illustrative examples).
UNIT VII – Redox Reactions
Concept of oxidation and reduction, redox reactions, oxidation number, balancing redox reactions, in terms of loss and gain of electrons and change in oxidation number, applications of redox reactions.
UNIT VIII – Organic Chemistry: Some basic Principles and Techniques
General introduction, classification and IUPAC nomenclature of organic compounds. Electronic displacements in a covalent bond: inductive effect, electromeric effect, resonance and hyper conjugation. Homolytic and heterolytic fission of a covalent bond: free radicals, carbocations, carbanions, electrophiles and nucleophiles, types of organic reactions.
UNIT IX – Hydrocarbons
Classification of Hydrocarbons Aliphatic Hydrocarbons: Alkanes – Nomenclature, isomerism, conformation (ethane only), physical properties, chemical reactions. Alkenes – Nomenclature, structure of double bond (ethene), geometrical isomerism, physical properties, methods of preparation, chemical reactions: addition of hydrogen, halogen, water, hydrogen halides (Markovnikov’s addition and peroxide effect), ozonolysis, oxidation, mechanism of electrophilic addition. Alkynes – Nomenclature, structure of triple bond (ethyne), physical properties, methods of preparation, chemical reactions: acidic character of alkynes, addition reaction of – hydrogen, halogens, hydrogen halides and water.
Aromatic Hydrocarbons:
Introduction, IUPAC nomenclature, benzene: resonance, aromaticity, chemical properties: mechanism of electrophilic substitution. Nitration, sulphonation, halogenation, Friedel Craft’s alkylation and acylation, directive influence of functional group in monosubstituted benzene. Carcinogenicity and toxicity.
To know the CBSE Syllabus for all the classes from 1 to 12, visit the Syllabus page of CBSE. Meanwhile, to get the Practical Syllabus of Class 11 Chemistry, read on to find out more about the syllabus and related information in this page.
CBSE Class 11 Chemistry Practical Syllabus with Marking Scheme
In Chemistry subject, practical also plays a vital role in improving their academic scores in the subject. The overall weightage of Chemistry practical mentioned in the CBSE Class 11 Chemistry syllabus is 30 marks. So, students must try their best to score well in practicals along with theory. It will help in increasing their overall academic score.
CBSE Class 11 Chemistry Practical Syllabus
The experiments will be conducted under the supervision of subject teacher. CBSE Chemistry Practicals is for 30 marks. This contribute to the overall practical marks for the subject.
The table below consists of evaluation scheme of practical exams.
Evaluation Scheme
Marks
Volumetric Analysis
08
Salt Analysis
08
Content Based Experiment
06
Project Work
04
Class record and viva
04
Total
30
CBSE Syllabus for Class 11 Chemistry Practical
Micro-chemical methods are available for several of the practical experiments. Wherever possible such techniques should be used.
A. Basic Laboratory Techniques 1. Cutting glass tube and glass rod 2. Bending a glass tube 3. Drawing out a glass jet 4. Boring a cork
B. Characterization and Purification of Chemical Substances 1. Determination of melting point of an organic compound. 2. Determination of boiling point of an organic compound. 3. Crystallization of impure sample of any one of the following: Alum, Copper Sulphate, Benzoic Acid.
C. Experiments based on pH
1. Any one of the following experiments:
Determination of pH of some solutions obtained from fruit juices, solution of known and varied concentrations of acids, bases and salts using pH paper or universal indicator.
Comparing the pH of solutions of strong and weak acids of same concentration.
Study the pH change in the titration of a strong base using universal indicator.
2. Study the pH change by common-ion in case of weak acids and weak bases.
D. Chemical Equilibrium One of the following experiments:
1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of either of the ions. 2. Study the shift in equilibrium between [Co(H2O)6] 2+ and chloride ions by changing the concentration of either of the ions.
E. Quantitative Estimation i. Using a mechanical balance/electronic balance. ii. Preparation of standard solution of Oxalic acid. iii. Determination of strength of a given solution of Sodium hydroxide by titrating it against standard solution of Oxalic acid. iv. Preparation of standard solution of Sodium carbonate. v. Determination of strength of a given solution of hydrochloric acid by titrating it against standard Sodium Carbonatesolution.
F. Qualitative Analysis 1) Determination of one anion and one cation in a given salt Cations‐ Pb2+, Cu2+, As3+, Al3+, Fe3+, Mn2+, Ni2+, Zn2+, Co2+, Ca2+, Sr2+, Ba2+, Mg2+, NH4+ Anions – (CO3)2‐ , S2‐, NO2‐ , SO32‐, SO2‐ , NO ‐ , Cl‐ , Br‐, I‐, PO43‐ , C2O2‐ ,CH3COO‐ (Note: Insoluble salts excluded)
2) Detection of ‐ Nitrogen, Sulphur, Chlorine in organic compounds.
G) PROJECTS Scientific investigations involving laboratory testing and collecting information from other sources.
A few suggested projects are as follows:
Checking the bacterial contamination in drinking water by testing sulphide ion
Study of the methods of purification of water.
Testing the hardness, presence of Iron, Fluoride, Chloride, etc., depending upon the regional variation in drinking water and study of causes of presence of these ions above permissible limit (if any).
Investigation of the foaming capacity of different washing soaps and the effect of addition of Sodium carbonate on it.
Study the acidity of different samples of tea leaves.
Determination of the rate of evaporation of different liquids Study the effect of acids and bases on the tensile strength of fibres.
Study of acidity of fruit and vegetable juices.
Note: Any other investigatory project, which involves about 10 periods of work, can be chosen with theapproval of the teacher.
Practical Examination for Visually Impaired Students of Class 11
Below is a list of practicals for the visually impaired students.
A. List of apparatus for identification for assessment in practicals (All experiments) Beaker, tripod stand, wire gauze, glass rod, funnel, filter paper, Bunsen burner, test tube, test tube stand, dropper, test tube holder, ignition tube, china dish, tongs, standard flask, pipette, burette, conical flask, clamp stand, dropper, wash bottle • Odour detection in qualitative analysis • Procedure/Setup of the apparatus
B. List of Experiments A. Characterization and Purification of Chemical Substances 1. Crystallization of an impure sample of any one of the following: copper sulphate, benzoic acid B. Experiments based on pH 1. Determination of pH of some solutions obtained from fruit juices, solutions of known and varied concentrations of acids, bases and salts using pH paper 2. Comparing the pH of solutions of strong and weak acids of same concentration.
C. Chemical Equilibrium 1. Study the shift in equilibrium between ferric ions and thiocyanate ions by increasing/decreasing the concentration of eitherions. 2. Study the shift in equilibrium between [Co(H2O)6]2+ and chloride ions by changing the concentration of either of the ions.
D. Quantitative estimation 1. Preparation of standard solution of oxalic acid. 2. Determination of molarity of a given solution of sodium hydroxide by titrating it against standard solution of oxalic acid.
E. Qualitative Analysis 1. Determination of one anion and one cation in a given salt 2. Cations – NH+4 Anions – (CO3)2-, S2-, (SO3)2-, Cl-, CH3COO- (Note: insoluble salts excluded) 3. Detection of Nitrogen in the given organic compound. 4. Detection of Halogen in the given organic compound.
Note: The above practicals may be carried out in an experiential manner rather than recording observations.
We hope students must have found this information on CBSE Syllabus useful for their studying Chemistry. Learn Maths & Science in interactive and fun loving ways with ANAND CLASSES (A School Of Competitions) App/Tablet.
Frequently Asked Questions on CBSE Class 11 Chemistry Syllabus
Q1
How many units are in the CBSE Class 11 Chemistry Syllabus?
There are 9 units in the CBSE Class 11 Chemistry Syllabus. Students can access various study materials for the chapters mentioned in this article for free at ANAND CLASSES (A School Of Competitions).
Q2
What is the total marks for practicals examination as per the CBSE Class 11 Chemistry Syllabus?
The total marks for the practicals as per the CBSE Class 11 Chemistry Syllabus is 30. It includes volumetric analysis, content-based experiment, salt analysis, class record, project work and viva.
Q3
Which chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry?
The organic chemistry chapter carries more weightage as per the CBSE Syllabus for Class 11 Chemistry.
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