The term pH means “Power of Hydrogen” or “Potential of Hydrogen” in chemistry. But simply pH level of water indicates the concentration of hydrogen ion in water.
pH Formula & pH Scale:
pH = -log[H+]
Based on hydrogen ion concentration pH scale is developed. pH scale ranges from 0 to 14. pH value 7 is considered as neutral water.
Water having a pH value between 0 to less than 7 is considered as a acidic water & from greater than 7 to 14 considered as basic or alkaline water.
Simple Table To Remember pH Scale:
pH
Nature of Water
7.0
Neutral
<7.0
Acidic
>7.0
Basic or Alkaline
pH Test:
It is accurately determined by pH Meter. However you can also check approximate pH value by pH indicator or pH test strips.
Nowadays, It’s very easy to test pH of water. All you need to do is simply purchase the pen type pH meter & dip it into the water sample.Display shows the pH of sample.
Remember, if pH of drinking water found within the range of 6.5-8.5. There is a no need to take any action. This range is recommended by EPA
pH Calculation:
Let’s take example & Calculate pH:
How to calculate the pH & hydrogen ion concentration of 0.1M Hydrochloric Acid?
Hydrochloric Acid(HCl) is strong acid. It is fully dissociate into H+ and Cl- ions.
Formula to calculate pH:
pH = -log[H+]
[H+] indicates the concentration. In our example it is 0.1M
pH = -log[0.1] =1
So, The pH of 0.1M Hydrochloric Acid is 1.
Formula to calculate Hydrogen ion(H+) concentration
H+ = 10 ^ -pH
H+ = 10 ^ (-0.1) = 0.1M
This is reverse calculation of pH.
Important Note:
You can easily calculate pH of all strong acid and bases by simply putting molar concentration value in above formula.
Therefore, Ka & Kb value requires in order to calculate pH of Weak Acid & Bases.
Here, Ka & Kb value represents weak acid & Weak base.
Remember that Ka & Kb values are very small because weak acid & bases are not completely ionized in water.
Let’s take another example & Calculate pH of Weak Acid:
How to calculate pH of 0.7M Acetic Acid? Ka value of acetic acid is 1.8 × 10^(-5)
Dissociation of acetic acid,
CH3COOH ↔ H+ + CH3COO-
Ka = [H+][CH3COO-] ÷ [CH3COOH]
put values in formula,
1.8 × 10^(-5) = [x] × [x] ÷ [0.7]
X2 = 1.8 × 10^(-5) × 0.7
X = √[0.7 × 0.00018] = 0.0112
0.0112 is the concentration of H+ ion in 0.7M acetic acid solution.
put this value in pH formula,
pH = -log[0.0112] = 1.95
So, The pH of 0.7M acetic acid is 1.95
In summary, pH level of water indicates the nature of water. Water having a very low or very high pH is a sign of contaminant present in water.
Alkalinity means acid neutralization capacity of water. When we add acid in water (adding H+ ions) water absorbs H+ ions without showing significant change in pH mainly it is due to carbonate, bicarbonate & hydroxide ion present in water or the mixture of two ions present in water. The possibility of OH– and HCO3– ions together is not possible since they combine together to form CO3-2 ions.
OH- + HCO3- ⇒ CO3-2 + H2O
Two types of Alkalinity present in water,
P-Alkalinity also called Phenolphthalein Alkalinity because Phenolphthalein indicator used for analysis
M-Alkalinity also called Methyl orange Alkalinity because Methyl orange indicator used for analysis
In alkalinity analysis different ions can be estimated separately by titration against standard acid solution, using selective indicators like phenolphthalein and methyl orange.
Below reaction occurs during analysis:
OH- + H+ ⇒ H2O
CO3-2 + H+ ⇒ HCO3-
HCO3- + H+ ⇒ H2O + CO2
The neutralization reaction up to phenolphthalein end point shows the completion of reactions (1) and (2) only.
The amount of acid used thus corresponds to complete neutralization of OH– plus half neutralization of CO32–.
The titration of water sample using methyl orange indicator marks the completion of the reactions (1), (2) and (3).
Based on above three reaction,
Alkalinity Relationship:
P-Alkalinity = Total Hydroxide + 1/2 Carbonate
M-Alkalinity = (Total Hydroxide + 1/2 Carbonate) +1/2 Carbonate + Total Bicarbonate
Alkalinity Summary Table
Ion
P = 0
P = 1/2M
P > 1/2M
P < 1/2M
P = M
OH-
0
0
2P-M
0
M
CO3-2
0
M
2(M-P)
2P
0
HCO3-
M
0
0
M-2P
0
1.Phenolphthalein alkalinity (P) = 0; that means the volume of acid used till the completion of reaction (1) and (2) is 0. This can only happen when both OH– and CO32– ions are not present in water. Alkalinity is present due to HCO3– ion only which can be determined using methyl orange indicator and called methyl orange alkalinity (M).
2. P = ½ M; indicates that only CO32– ions are present. Using phenolphthalein indicator neutralization reaches upto HCO3– but using methyl orange indicator the complete neutralization of HCO3– takes place.
3.P > ½M; implies OH– ions are also present along with CO32– ions. Upto phenolphthalein alkalinity OH– ions will be neutralized completely whereas CO32– will be neutralized upto HCO3– ion. But using methyl orange indicator HCO3– will be completely neutralized along with OH– and CO32–.
4.P < ½ M; indicates that beside CO32– ions HCO3– ions are also present. The volume of acid required for the neutralization upto phenolphthalein end point correspond half neutralization of CO32– (equation 2). Neutralization using methyl orange indicator corresponds to HCO3– obtained from CO32– and HCO3– originally present in the water sample
5.P = M; indicates only OH– ions are present.
Alkalinity of water is very important parameter in boiler water treatment program. Based on alkalinity analysis we can predict the presence of free caustic as mentioned in above table. Free caustic is responsible for caustic corrosion in boiler system.
Simple defination of hardness is the amount of calcium & magnesium ions present in water. It is divided in two parts carbonate or temporary hardness and non-carbonate or permanent hardness.
It is a major source of scale in water systems i.e.boiler water & cooling water systems. Softening is a popular method for removal of hardness from water.
Let us discuss both the types of water hardness in detail.
#1. Carbonate or Temporary Hardness
Carbonate and bicarbonate ions are responsible for this type of water hardness.It is also known as temporary hardness because it removes from water when we boil the water.
When we boil the water carbonate & bicarbonates ions are present in water decomposes & insoluble carbonate is reformed.Boiling the water causes the precipitation of calcium and magnesium carbonate so that, calcium and magnesium ions are remove from water.
Example: CaCO3, MgCO3, Ca(HCO3)2, Mg(HCO3)2
#2. Non-Carbonate or Permanent Hardness
Chloride and Sulfate (non-carbonate) ions are responsible for this type of water hardness.It is also known as permanent hardness because it isn’t remove from water by boiling it.
It is only remove from water either by softening or demineralization process.
Example: CaCl2, MgCl2, CaSO4, MgSO4
Water Hardness Scale:
As a general rule for classification of hardness, Water having hardness below 60 ppm is considered as soft water,61 ppm to 120 ppm as moderately hard; 121 ppm to 180 ppm as hard & above 181 ppm as very hard.
Water Hardness Measurement:
Analysis of Water harness divide in three parts namely total hardness,calcium hardness & magnesium hardness.
Total hardness is a sum of calcium & magnesium hardness.
Total hardness = Calcium Hardness + Magnesium Hardness
In order to determine total hardness ammonia buffer solution is added to the sample to maintain the pH of around 11. Then Eriochrome Black T indicator is added so the wine red color is developed in the sample.
After that titrate the sample against EDTA solution and sample color will change from wine red to blue. This is the end point of total hardness titration.
Determine the calcium hardness by titration sodium hydroxide solution is added to the sample to maintain pH & then murexide indicator is added. Sample color turns into pink & titrate the sample against EDTA solution this time sample color will change from pink to purple. This is the end point of calcium hardness test.
Magnesium hardness is the difference of total hardness & calcium harness value. It is determined by subtracting calcium hardness value from total hardness value.
Magnesium Hardness = Total Hardness – Calcium Hardness
Water Hardness Conversion:
In Conclusion, Water hardness is a major source of scale in water treatment system. It is very essential to remove it from water by selecting proper water treatment program.
Normality in chemistry is very important term & very useful to making reagents for analysis.
Unfortunately, many professional even experienced professionals don’t have the clear basics concept of normality.
I guarantee you after reading this article you have solid understanding about normality & its calculation.
Defination: Normality in chemistry means numbers of equivalents per liter of solution.It is denoted by symbol N.
Normality in chemistry defined by below formula:
Formula: Normality(N) = Numbers of equivalent(n) / Volume of Solution(L)
Another very important factor is how to calculate the equivalents of substance.You can easily calculate equivalent by dividing molecular weight by its valency.
Let’s take example and calculate numbers of equivalents of Hydrochloric Acid & Sulphuric Acid.
Formula: Molecular Wight(gm/mol) / Valency
What is valency in chemistry?
The “valency” or “valence” of an atom or molecule described as how may hydrogen atoms it can bond with. In our example,
Hydrochloric Acid – HCl have a one hydrogen atom so, the equivalents of Hydrochloric Acid is 36.46/1 = 36.46
Sulphuric Acid – H2SO4 have two hydrogen atoms so, the equivalents of Sulphuric Acid is 98/2 = 49
How to calculate normality of concentrated hydrochloric acid?
First, note down three things form packing label of solution:
Specific gravity
Specific gravity means the substance is how much heavier or lighter in compare to the water. It is unit less because it shows the comparison.
Assay Percentage
Assay indicates the purity of substance in percentage. To convert percentage in decimal simply divide assay by 100.
Equivalent weight
Assay indicates the purity of substance in percentage. To convert percentage in decimal simply divide assay by 100.
Use below formula to calculate normality of any commercially available liquid solution:
Normality = Specific gravity × Percentage of purity in decimal × 1000 ÷ Equivalent weight
If you see label of reagent bottle of hydrochloric acid you will get below three values:
Specific gravity – 1.18
Assay – 35.4 (convert it into decimal divided by 100. 35.4/100 =0.354)
Molecular Weight – 36.46 gm/mole (Calculate equivalent weight divided by its valency. valency of hydrochloric acid is 1. that means 36.46/1 =36.46)
Put the above values in formula,
Normality = 1.18 × 0.354 × 1000 ÷ 36.46 = 11.46 N
Important Note
If any substance or chemical have the same molecular weight & equivalent weight then Molarity & Normality of that substance or chemical will be the same
How to calculate normality of concentrated sulphuric acid?
If you see label of reagent bottle of sulphuric acid you will get below three values:
Specific gravity – 1.84
Assay – 98 (convert it into decimal divided by 100. 98/100 =0.98)
Molecular Weight – 98.08 gm/mole (Calculate equivalent weight divided by its valency. valency of sulphuric acid is 2. that means 98.08/2 =49.04)
Put the above values in formula,
Normality = 1.84 × 0.98 × 1000 ÷ 49.04 = 36.77 N
Normality Calculator For Concentrated Liquid Chemical
This is very handy tool for science student to make reagents for analysis. You can easily calculate normality of any concentrated acid or base liquid solution by using this normality calculator.
In conclusion, Normality or equivalent concentration of the solution indicates how many equivalent are present per liter of solution.
Molarity means numbers of moles of solute per liter of solution.It is denoted by symbol M. Based on this defination the molarity formula becomes as below:
Molarity(M) = Numbers of Moles of Solute(n) / Volume of Solution In Liter(L)———(1)
To understand molarity concept first you need to know what is mole & How to calculate it.
Mole = Weight of substance in gram / Molecular weight of the substance (gm/mol)——- (2)
Calculation of Numbers of Mole in Solution:
To calculate mole we take example of Sodium Hydroxide(NaOH). Suppose, we dissolve 40 gm of NaOH in one liter of solution then what is the numbers of mole present in this solution?
In our example we dissolve 40 gm of NaOH in one liter water that means weight of substance becomes 40 gm
Let’s put above values in molarity formula (2),
♦ Mole = Weight of substance in gram / Molecular weight of the substance (gm/mol)
Mole = 40/40 =1
Now, we have numbers of mole available with us & we also know the volume of solution so put both the values in formula(1),
♦ M = Moles of Solute(n)/ Volume of solution in liter(L) = 1/1 =1M
In conclusion, simplest definition of molarity is when we dissolve substance exactly the same weight as its molecular weight in one liter of water then the molarity of the solution becomes 1M .
Let’s take another example,
How to calculate Molarity of concentrated HCl?
Three things requires in order to calculate molarity of concentrated solution in our case it is concentrated Hydrochloric Acid(HCl):
Molecular Weight : 36.46 gm/mole
Specific Gravity : 1.18
Percentage of Purity : 35.4% (Convert into decimal divide it by 100. 35.4/100=0.354)
Please note that all of the above information you can find on packing lable of solution.
Important Note:
♦ Remember this molarity formula to calculate molarity of any commercially available liquid solution:
M = Specific gravity × Percentage of purity × 1000 ÷ Molecular Weight
Molarity Calculator For Concentrated Liquid Chemical
Molarity Calculator is very handy tool for science student to make reagents for analysis. You can easily calculate molarity of any concentrated acid or base liquid solution.
All you need to do is only enter the three values which is mentioned on label of reagent bottle.
Hope, This article will clear your concept about molarity formula & its calculations.
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