Explain the Normality in Physical Chemistry
What is the unit of normality? How do you calculate normality? What is normality in chemistry formula?
Chemistry
- asked 7 years ago
- M K L
2Answer
Normality is a rarely used expression which indicates the concentration of a solution. It is defined as the gram equivalent weight per liter of solution.
The reason normality is rarely used lies in the definition of gram equivalent weight. Gram equivalent weight is determined by the amount of an ion that reacts, which could change depending on the reaction. The fact that the gram equivalent weight is not a consistent amount creates confusion and leads scientists to use other concentration values.
Normality, when used, is typically done so in acid base reactions. Here, a more favorable calculation for normality is considered, where the normality of a solution is equal to the molarity multiplied by the number of equivalents.
Normality(N) = Molarity(M) x number of equivalents
- answered 7 years ago
- Community wiki
NORMALITY DEFINITION
Normality is a measure of concentration equal to the gram equivalent weight per liter of solution. Gram equivalent weight is the measure of the reactive capacity of a molecule. The solute's role in the reaction determines the solution's normality. Normality is also known as the equivalent concentration of a solution.
NORMALITY EQUATION
Normality (N) is the molar concentration ci divided by an equivalence factor feq:
N = ci / feq
Another common equation is normality (N) equal to the gram equivalent weight divided by liters of solution:
N = gram equivalent weight / liters of solution (often expressed in g/L)
or it may be the molarity multiplied by the number of equivalents:
N = molarity x equivalents
UNITS OF NORMALITY
The capital letter N is used to indicate concentration in terms of normality. It may also be expressed as eq/L (equivalent per liter) or meq/L (milliequivalent per liter of 0.001 N, typically reserved for medical reporting).
EXAMPLES OF NORMALITY
For acid reactions, a 1 M H2SO4 solution will have a normality (N) of 2 N because 2 moles of H+ ions are present per liter of solution.
For sulfide precipitation reactions, where the SO4- ion is the important part, the same 1 M H2SO4 solution will have a normality of 1 N.
EXAMPLE PROBLEM
Find the normality of 0.1 M H2SO4 (sulfuric acid) for the reaction:
H2SO4 + 2 NaOH → Na2SO4 + 2 H2O
According to the equation, 2 moles of H+ ions (2 equivalents) from sulfuric acid react with sodium hydroxide (NaOH) to form sodium sulfate (Na2SO4) and water. Using the equation:
N = molarity x equivalents
N = 0.1 x 2
N = 0.2 N
Don't be confused by the number of moles of sodium hydroxide and water in the equation.
Since you've been given the molarity of the acid, you don't need the additional information. All you need to figure out are how many moles of hydrogen ions are participating in the reaction. Since sulfuric acid is a strong acid, you know it completely dissociates into its ions.
POTENTIAL ISSUES USING N FOR CONCENTRATION
Although normality is a useful unit of concentration, it can't be used for all situations because its value depends on an equivalence factor that can change based on the type of chemical reaction of interest. As an example, a solution of magnesium chloride (MgCl2) may be 1 N for the Mg2+ ion, yet 2 N for the Cl- ion. While N is a good unit to know, it's not used as much as molarity or molality in actual labwork. It has value for acid-base titrations, precipitation reactions, and redox reactions. In acid-base reactions and precipitation reactions, 1/feq is an integer value. in redox reactions, 1/feqmay be a fraction.
- answered 7 years ago
- Community wiki
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