Definition of the Titration Formula
When scientists need to know the concentration of an unknown acidic solution, they use a process called titration. Titration requires scientists to add a standard basic solution to the unknown solution to provoke a chemical reaction. When the reaction occurs, an indicator in the unknown solution changes the solution's color to indicate the new pH level of the titrated solution.
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What Is the Titration Formula?
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Once scientists titrate the solution in question, they can then use a mathematical formula to figure out the pH level of the original solution, telling them how strong or weak an acid it is. In its simplest form, the titration formula is written:
n = M/V
where n is the moles of reactant, M is the concentration of the reactant, and V is the volume of the reactant.
Collecting Data While Titrating
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While performing the actual titration, scientists need to record certain data in order to determine the concentration of the acidic solution, including the volume of the solution being titrated, the standard solution used to neutralize it, the chemical make-up of both solutions and the concentration of the standard solution.
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Steps to Determine Concentration
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After titration, the scientist must first write out and balance the chemical equation for the reaction that just took place. This step is important, because the scientist must know the ratio of standard solution to unknown solution in order to determine the concentration of the unknown solution.
Once the equation is balanced, the scientist writes the titration formula and the values that are known. The scientist then calculates the moles of standard solution used, using the formula.
Next, the scientist finds the moles of the unknown solution by using the ratio of standard solution to unknown solution. For example, if there are 2 moles of the unknown solution for every mole of the standard solution, the scientist multiplies the moles of standard solution used by 2 to find this value.
Finally, the scientist solves the formula for M to determine the concentration of the unknown solution.
Example of Using Titration Formula
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Ausetute.com.au, a website for science teachers and students in Australia, provides an example of the titration formula:
During titration, 30 mL of .10 mL NaOH neutralizes an unknown concentration of 25 mL HCl.
First the scientist balances the equation for the chemical reaction: NaOH + HCl --> NaCl + H2O
Next, the scientist writes down known values for the formula M = n/V
NAOH : .10 mL = n/30 mL HCl: M = n/25 mLNext, the scientist solves the NaOH formula for n
.10 mL = 3/30 mL
Now the scientist refers back to the balanced equation. NaOH and HCl exist in a 1:1 ratio in this equation. So n(NaOH) = n (HCl). (If there was a 2 or other number in front of one of the reactants, the ratio would be different).
Therefore n(HCl) = 3
Finally, the scientist solves the HCl equation for M. M = 3/25 mL or .12 mL
Advanced Titration Formulas
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Scientists can also calculate the pH level of a titrated solution. This uses different formulae, depending upon the strength of the acid and base used in the titration. These formulae are complex, involving logarithms; scientists often use a pH calculator to assist in these calculations.
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References
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