4.2.10 Titration Calculations

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Titration calculations determine the concentration of an unknown acid or base in a solution. By using the volume of titrant (a solution of known concentration) required to neutralise a known volume of analyte (the solution being tested), you can calculate the unknown concentration.

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Worked Example: Calculating the Concentration of an Acid In this example, we'll calculate the concentration of hydrochloric acid (HCl) using data from a titration with sodium hydroxide (NaOH).

Given:

Volume of NaOH solution: 25.0 cm³
Concentration of NaOH solution: 0.100 mol/dm³
The volume of HCl solution: 20.00 cm³ Goal: Find the concentration of the hydrochloric acid solution.

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Step 1: Calculate the Amount of Sodium Hydroxide in Moles First, convert the volume of the sodium hydroxide solution from cm³ to dm³:

\ce{Volume of NaOH solution = \frac{25.0cm^3}{1000}​=0.0250 dm^3}

Use the formula:

Amount of solute in mol=Concentration in Concentration in mol/dm^3×Volume in dm^3

Substituting the values:

Amount of NaOH = $0.100×0.0250=0.00250 mol$

Step 2: Find the Amount of Hydrochloric Acid in Moles

Using the balanced chemical equation:

\ce{NaOH(aq) +HCl(aq)→NaCl(aq) +H2​O(l)}

The mole ratio of NaOH to HCl is 1:1. Therefore, the amount of HCl that reacted is the same as the amount of NaOH:

Amount of HCl = $0.00250 mol$

Step 3: Calculate the Concentration of Hydrochloric Acid in mol/dm³

Convert the volume of the hydrochloric acid solution from cm³ to dm³:

\ce{Volume of HCl solution = \frac{20.00cm^3}{1000}= 0.0200 dm^3}

Now, calculate the concentration using the formula:

\ce{Concentration mol/dm^3 = \frac{Amount of solute in mol}{Volume in dm^3}}

Substituting the values:

\ce{Volume of HCl= \frac{0.00250}{0.0200}=0.125 mol/ dm^3}

Step 4: Calculate the Concentration of Hydrochloric Acid in g/dm³

To find the concentration in g/dm³, use the relative formula mass (Mᵣ) of HCl:

\ce{M_r​ of HCl=1+35.5=36.5}

Now calculate the mass:

Mass=M_r​×Amount in mol

Mass of HCl=36.5×0.125=4.56

So, the concentration of hydrochloric acid in g/dm³ is:

Concentration=:highlight[4.56 g/dm^3]

Summary

In this titration example, we calculated the concentration of hydrochloric acid by following a systematic process:

Calculate the moles of the base used.
Determine the moles of acid that reacted, using the balanced equation.
Calculate the concentration of the acid in mol/dm³.
Convert the concentration to g/dm³ if required.

Titration Calculations Simplified Revision Notes for GCSE AQA Chemistry

4.2.10 Titration Calculations

Step 2: Find the Amount of Hydrochloric Acid in Moles

Step 3: Calculate the Concentration of Hydrochloric Acid in mol/dm³

Step 4: Calculate the Concentration of Hydrochloric Acid in g/dm³

Summary

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