chemical calculations part 3 titrations

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What is concentration?

The concentration of a solution is a measure of how much solute is dissolved per unit of solvent.

amount of solute is measured in moles

volume of solvent is measured in dm3

concentration is measured in mol dm-3.

concentration = amount of solute / volume of solvent

Volumes are often expressed in cm3, so a more useful equation includes a conversion from cm3 to dm3.

concentration = (no. moles × 1000) / volume

mol dm3 cm3

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Concentration, moles and volume

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Concentration calculations

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Standard solutions

A standard solution is a solution of known concentration.

Standard solutions are made by dissolving an accurately weighed mass of solid in a known volume of solvent using a volumetric flask.

The volumetric flask has a thin neck, which is marked with a line so it can be filled accurately to the correct capacity.

The standard solution can then be used to find the concentration of a second solution with which it reacts. This is known as volumetric analysis or titration.

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Preparing standard solutions

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A titration is a procedure used to identify the concentration of a solution by reacting it with a solution of known concentration and measuring the volume required for a complete reaction.

Once the number of moles for the solution is known, the concentration can be easily calculated.

The number of moles in the standard solution is calculated. Using a balanced equation for the reaction, the number of moles in the solution of unknown concentration can also be calculated.

What is a titration?

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Carrying out a titration

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Titration calculations examples

What is the concentration of an NaOH solution if 25.0 cm3 is neutralized by 23.4 cm3 0.998 mol dm-3 HCl solution?

3. Calculate no. moles of NaOH:

0.0234 moles HCl = 0.0234 moles NaOH

4. Calculate conc. of NaOH: = (0.0234 × 1000) / 25.0

conc. = (moles × 1000) / volume

= 0.936 mol dm-3

1. Calculate no. moles HCl:

moles = (conc. × volume) / 1000

= 0.0234= (0.998 × 23.4) / 1000

2. Determine ratio of NaOH to HCl:

NaOH + HCl NaCl + H2O

ratio NaOH:NaCl = 1:1

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Titration calculations

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More titration calculations