Find the Ph of a 0.26m Kclo3 Solution
What is pH Formula?
pH is a term that is derived from a German word, "Potenz". It means "Power". Its full form is symbolized with H and the full form of pH is written as "power of Hydrogen". The concept was discovered by Soren Sorensen who was a Danish chemist. He suggested that – It is an equation to have even a small amount of H + concentration in a solution.
pH is also defined as "the negative logarithm to base 10 of the activity (a H + ) of a hydrogen ion." A minimum quantity is measured in this scale that contains the least amount of H + ions with the help of a mathematical expression in which pH is equal to the negative of log 10 of H + or H 3 O + , where the concentration is expressed in moles/liters. The Scales have a neutral value that is 7. A value greater to it is acidic and lesser to it is basic.
- pH <7 – acidic solution
- pH> 7 – basic solution
- pH = 7 – neutral solution
Also check:
pH Formula in Chemistry
We can define pH in the given way:
pH = -loga H + = -log{[H + ]/ mol L -1 }
Or
pH = - log [H + ]
Or
pH = - log [H 3 O + ]
For example, if we want to write the pH of pure water, we can write it as:
pH= - log (10 -7 ) = 7
- The solutions which are acidic have a concentration of hydrogen ion [H + ]> 10 -7 M.
- In the case of basic solutions, the concentration of hydrogen ions, [H + ] < 10 -7 M.
pH value: Calculation of Ions
In case we are provided with the pH value, and we have to calculate the concentration of ion, then the equation we will use is:
[H + ] = 10 –pH
Also, there is a pOH scale-like the pH scale. In the case of the pOH scale, if pOH is negative of the logarithm, then
pOH = - log [OH - ]
Or
[OH - ]= 10 -pOH
Also check:
Calculating the pH of Water
In the case of a pure sample of water that is neutral (neither acidic nor basic), the H + ion concentration is:
[H + ] = 1.0 x 10 -7 moles/litre
So, the pH can be calculated as:
pH = - log [1.0 x 10 -7 ]
pH = -(-7)
So, the pH of water = 7
Ionic constant of Water
Water undergoes the process of self-ionization, hence it dissociates like:
So, if we consider the Law of Mass Action, the Equilibrium constant (K w ) is equal to:
K w = [H 3 O + ] [OH - ]/ [H 2 O]
The water is in excess amount & is also the solvent; the concentration can be estimated to be 1
Then, K w = [H 3 O + ] [OH - ]
So, if calculated at room temperature,
K w = 1.0 x 10 -14
So, we can say that, if in an aqueous solution:
[H 3 O + ] > [OH - ], pH < 7 (solution is acidic)
[H 3 O + ] < [OH - ], pH > 7 (solution is basic)
[H 3 O + ] = [OH - ], pH = 7 (solution is neutral)
Also check:
pH: Value Equation
If the acids are weak, they partially dissolve in an aqueous solution and also attain a state of equilibrium. Such equation of equilibrium is:
K a = [H 3 O + ]/ [A - ] HA
Here, [H 3 O + ] is Hydronium Concentration
[A - ] is conjugate base concentration
HA = weak acid concentration
If the bases are weak, they partially dissolve and also attain a state of equilibrium. Such equation of equilibrium and their partial dissociation is:
K b = [OH - ]/ [B + ] B
Here, [OH - ] is hydroxide Concentration
[B + ] is Ion
B is weak base concentration
Relation in pOH, pH & pK w
– log K w =pK w
–log K w =–log ([H3O+][OH - ])
–log K w = (–log [H3O+])+(–log[OH - ])
Thus, we have pK w =pH + pOH
As we already know,
K w =1.0×10 -14
So, pK w =14
Hence, pH +pOH = 14
pH: Acid and Base in Buffer Solution
Generally, solutions that consist of a weak acid or weak base and its a conjugate base or conjugate acid is known as buffer solution.
pH in Acid Buffer Solution
If we consider, an example of an acid dissociating in its aqueous solution. Acid HA dissociates and results in the formation of H + ion and its conjugate base A - . Then,
For such ionisation reaction, the equilibrium constant (K a ) is:
K a = [H + ] [A - ]/ [HA]
Taking the negative log & rearranging, we get,
-log ([HA]/[A -1 ]) – log K a = - log [H + ] .......(1)
So, pH= - log [H + ] & pK a = -log K a
So we can say,
pH= pK a + log ([A - ]/[HA]) which is also written as
pH= pK a + log ([salt]/[acid])
pOH in Basic Buffer Solution
If we consider an example of dissociation of the base in its aqueous solution, the reaction we get:
For such ionisation reaction, the equilibrium constant (K a ) is:
K b = [BH + ] [OH - ] / [B]
Taking the negative log & rearranging, we get,
-log ([B]/[BH + ]) – log K b = - log [OH - ] .......(1)
As we already know,
pOH = -log [OH - ]= -log [OH - ] & pK b = - log K b
So, pOH = pK b + log [BH + ]/ [B]), which can also be written aspOH = pK b + log ([salt]/[Base])
Also check:
Salt of Weak Acid & Strong Base
In the case of a strong base and weak acid, the acid will get fully neutralized and the conjugate base will be left. Hence, the pH will be greater than 7.
pH = ½ [pK w + pK a + log C] (pK w =7; K a = dissociation constant; C is concentration of salt formed)
Hence, pH = 7 + ½ [pK a + log C]
Salt of Strong Acid & Weak Base
In the case of strong acid and weak base, the base will get fully neutralized and the conjugate acid will be left. Hence, the pH will be less than 7.
pH = ½ [pK w – pK b - log C] (pK w =7; K b = dissociation constant; C is concentration of salt formed)
Hence, pH = 7 - ½ [pK b + log C]
Applications of pH as a Universal Indicator
- pH paper is used to determine the pH of any given solution. The pH paper is dipped in the solution. The value is then compared with the color which appears on the pH paper or strip with a color chart and pH value is obtained.
- The pH value is very important for industries like a pharmacy. The pH of medicines is checked as it is needed to be equal to the human body fluids pH. Otherwise, it will not react when consumed.
- A device known as a pH meter is used to check the précised pH value of a given solution. It has a connected pH electrode that is dipped in a solution and the pH meter shows the pH value (on a scale or digitally)
- Buffer solutions are made for maintaining the pH of a solution as in chemical reactions, the pH of equations needs to be in proper equilibrium.
Things to Remember
- The sub-topic "pH Formula" has been taken from Class 11 Chemistry Chapter 7 "Equilibrium ". Both subjective and objective type questions are likely to come from this portion.
- The amount of H + ion in a solution is measured by pH. pH can be calculated by K w = [H 3 O + ][OH - ].
- Buffer solutions are prepared to maintain the pH of a solution. The pH of a solution, if it is equal to 7 is considered neutral
- The pH of a solution, if greater than 7 is considered basic. The pH of a solution, if is less than 7 is considered acidic
- Examples of a few Acidic solutions are vinegar or lemon juice whereas examples of some basic solutions are milk of magnesia or ammonia.
- The acidic solution consists of low pH than alkaline or basic solutions.
Sample Questions
Ques: What will be the pH of HCl of 1.0 x10 -8 M solution? (3 marks)
Ans: 2H 2 O (l) ? H 3 O + (aq) + OH - (aq)
K w = [OH - ] [H 3 O + ] = 10 14
If x = [OH - ] = [H 3 O + ], then [H 3 O + ] concentration will be obtained
- From dissolved HCl ionisation
HCl + H 2 O ? H 3 O + + Cl -
- H 2 O ionisation
So, [ H 3 O + ]= 10 -8 + x
K w = (10 -8 +x) (x) = 10 -14
Or
x 2 + 10 -8 x – 10 14 = 0
[OH - ] = x= 9.5x 10 -8
Hence, pOH = 7.02
And pH = 6.98
Ques: A sample of soft drinks has a concentration of H + ion 3.8 x 10 -3 M. Calculate its pH. (2 marks)
Ans: pH = -log [3.8 x 10 -3 ]
= - {log [3.8] + log [10 -3 ]}
= - (0.58) + (-3.0)
= - (-2.42)
= 2.42
So, the pH of the soft drink is 2.42 and hence, it is an acidic solution.
Ques: If the concentration of Hydronium ion is 8.0 x 10 -8 M, calculate the pH of its solution. (2 marks)
Ans: Given, the concentration of Hydronium ion is 8.0 x 10 -8 M
pH = - log [H 3 O + ]
pH = - log [8.0 x 10 -8 ]
pH= 7.09
So, the pH of Hydronium ion solution is 7.09
Ques: What is the pH of a solution of 0.005M HBr? (2 marks)
Ans: Using the equation, pH = - log [H 3 O + ]
[H 3 O + ] = 5.5 x 10 -2 M
pH = - log [5.5 x 10 -2 ]
= 1.26
Hence, the pH of the solution is 1.26 and the solution is acidic in nature.
Ques: What do you mean by pH of an Acid? (2 marks)
Ans: pH is considered as the measurement of the amount of hydroxyl and hydrogen ions in water. The range of pH is 0-14, 7 is the neutral value. If pH is less than 7, the pH value inferred is acidic. If pH is greater than 7, the pH value inferred is basic.
Ques: How does one can calculate the pH & pOH? (2 marks)
Ans: The "p" in pH and pOH signifies "-log." The H or the OH in pH and pOH denote the concentration of either hydronium ions (H 3 O+) or hydroxide ions (OH-). Therefore, pH measures hydronium ion concentration, whereas pOH measures hydroxide ion concentration.
The pOH of a solution can be calculated by a formula: pOH =–log [OH - ]. Both pH & pOH are related as pH + pOH = 14
Ques: What will be the pH of 0.001M of HCl solution? (2 marks)
Ans: HCl is a very strong acid and hence, completely dissolves into water and dissociates in H + & Cl -
pH = - log [ H + ]
pH = -log [0.001]= 3
So, the pH of HCl solution is 3.
Ques: What is the pH of a formic acid solution of 5 x 10 -3 M? [K a (HCOOH) = 2 x 10 -4 ] (3 marks)
Ans: K a (HCOOH) = 2 x 10 -4 = 0.0002
C = 5 x 10 -3 = 0.005
Hence, [ H + ] 2 + K a [ H + ]- C K a = 0
Let [ H + ] = x
X 2 + (0.0002x)- (0.005) x (0.0002)= 0
X = [ H + ] = 0.0009
pH = - log 10 [H + ]
= - log (0.0004)
= 3.039
Ques: Explain what will be the pH value for a neutral solution? (2 marks)
Ans: The pH value of a neutral solution is 7. The pH of pure water is neutral. When chemicals will be mixed with water, they will either turn acidic (pH<7) or basic (pH>7). In a neutral solution, the consistency of the hydrogen ion remains equal to hydroxide ions.
Ques: Write the applications of pH as a universal indicator. (4 marks)
Ans: The applications of pH as a universal indicator are:
- pH paper is used to determine the pH of any given solution. The pH paper is dipped in the solution. The value is then compared with the color which appears on the pH paper or strip with a color chart and pH value is obtained.
- The pH value is very important for industries like a pharmacy. The pH of medicines is checked as it is needed to be equal to the human body fluids pH. Otherwise, it will not react when consumed.
- A device known as a pH meter is used to check the précised pH value of a given solution. It has a connected pH electrode that is dipped in a solution and the pH meter shows the pH value (on a scale or digitally)
- Buffer solutions are made for maintaining the pH of a solution as in chemical reactions, the pH of equations needs to be in proper equilibrium.
Find the Ph of a 0.26m Kclo3 Solution
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