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Methods of expressing concentration

This document discusses different methods of expressing concentrations in solutions. It defines key terms like solution, standard solution, concentration, percent concentration, parts per million, parts per billion, molarity, normality, molality and formality. It provides formulas and examples to calculate the concentration values using these different methods for solutions like sodium hydroxide and hydrochloric acid. The key methods covered are percent concentration, parts per million, parts per billion, molarity, normality, molality and formality.

Education◦
Email: shah.sapan@rediffmail.com Method of Expressing Concentrations Sapan K. Shah Asst. Prof. Priyadarshini J. L. College of Pharmacy, Nagpur
Email: shah.sapan@rediffmail.com Concentration, Solution, Standard solution Percent concentration, parts per million, parts per billion Molecular and Equivalent Weight Molarity, Normality, Molality and Formality
1) Solution: It is homogenous mixture containing two or more solutes. In such mixture, solute is dissolved in another solute or solvent. 2) Standard Solution: It is a solution of known concentration. 3) Concentration: It represents how much of given substance is present in given solution. Generally, concept is limited to homogenous solutions, where it refers to the amount of solute in a substance.
 In all the techniques of quantitative analysis the use of solutions requires some basis for the expression of solution concentration. 1) Percent Concentration 2) Parts per million 3) Parts per billion 4) Molarity 5) Normality 6) Molality 7) Formality
1)Percent Concentration:  It refers to the amount of the solute per 100 parts of the solution. It can also be called as parts per hundred (pph).  It can be expressed by any of following four methods, a. 𝑷𝒆𝒓𝒄𝒆𝒏𝒕 𝒘/𝒘 = 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟎 b. 𝑷𝒆𝒓𝒄𝒆𝒏𝒕 𝒗/𝒗 = 𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟎 c. 𝑷𝒆𝒓𝒄𝒆𝒏𝒕 𝒘/𝒗 = 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟎 d. 𝑷𝒆𝒓𝒄𝒆𝒏𝒕 𝒗/𝒘 = 𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟎
2) Parts per million (ppm):  It is used to express the concentration of dilute solutions and is expressed as- ppm = 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟔 3) Parts per billion (ppb):  It is used to express the concentration of dilute solutions and is expressed as- ppb = 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑴𝒂𝒔𝒔 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿𝟏𝟎𝟗
Email: shah.sapan@rediffmail.com 4) Molarity Number of moles of solute (Substance) dissolved in one litre (1000 mL) of Solution is called as Molarity.  1 g in 1000 ml = 1 mol  Molarity is indicated by M  Molarity Examples 1-Molecular weight of NaOH (Sodium Hydroxide)= Atomic Weight of Na= 22.99 Atomic Weight of O= 16 Atomic Weight of H= 1 40 Number of moles of Solute M = ------------------------------------ 1000 mL of Solution
1M= 40 g of NaOH is Dissolved in 1000 mL of water (H2O) 0.1 M= 4 g of NaOH is Dissolved in 1000 mL of water (H2O) 0.01M= 0.4 g of NaOH is Dissolved in 1000 mL of water (H2O)  Molarity Examples 2-Molecular weight of HCl (Hydrochloric acid)= Atomic Weight of Cl = 35.5 Atomic Weight of H = 1 36.5 1M = 36.5 gm of HCl is Dissolved in 1000 mL of water (H2O) 0.1 M = 3.65 gm of HCl is Dissolved in 1000 mL of water (H2O) 0.01M = 0.365 gm of HCl is Dissolved in 1000 mL of water (H2O)
5) Normality Number of gram equivalent of solute (Substance) dissolved in one litre (1000 mL) of solution is called as Normality.  Normality is indicated by N  Normality Examples 1- Molecular weight of NaOH (Sodium Hydroxide)= Atomic Weight of Na = 22.99 Atomic Weight of O = 16 Atomic Weight of H = 1 40 Gram equivalent Weight of Solute Equivalent Weight = --------------------------------------------- No. of replaceable H + & OH-
1N = 40 g of NaOH is Dissolved in 1000 ml of water (H2O) 0.1N = 4 g of NaOH is Dissolved in 1000 ml of water (H2O) 0.01N = 0.4 g of NaOH is Dissolved in 1000 ml of water (H2O)
6) Molality A molal solution contains 1 mole of solute per one kilogram of solution ( 1 lit. of solvent) is called as Molality.  Molality is indicated by M  Molality Examples 1-Molecular weight of NaOH (Sodium Hydroxide)= Atomic Weight of Na = 22.99 Atomic Weight of O = 16 Atomic Weight of H = 1 40 Number of mol. Wt. of substance N = --------------------------------------- 1000 gm of Solution (1Kg)
1m = 40g of NaOH is dissolved in 1000g ofwater (H2O) 0.1m = 4 g of NaOH is dissolved in 1000g of water (H2O) 0.01m= 0.4 g of NaOH is Dissolved in 1000 g of water (H2O) 1.5m= 60g of NaOH is dissolved in 1000g of water (H2O)
7) Formal Concentration (Formality)  The concentration unit, formal, is similar to the more familiar molar concentration in that it is calculated as the number of moles of a substance in a liter of solution.  Formal concentrations arenotated with the symbol F  The formal Concentration(Formality) is applicable to the ionic substances.  Ex. We'll use calcium carbonate because it has a simple formula weight (100 g/mole). If one has 1 g CaCO3 in 1 L aqueous solution, the concentration of CaCO3, in formal, is... 1 g CaCO3/(100 g CaCO3/mole)/(1 L) = 0.01 F CaCO3 𝑭 = 𝑾𝒆𝒊𝒈𝒉𝒕 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒆 𝑽𝒐𝒍𝒖𝒎𝒆 𝒐𝒇 𝒔𝒐𝒍𝒖𝒕𝒊𝒐𝒏 𝑿 𝑭𝒐𝒓𝒎𝒖𝒍𝒂 𝒘𝒆𝒊𝒈𝒉𝒕
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