what is the explanation of titration between sodium carbonate and HCl using phenolphthalene giving a colourless colour
The reaction between sodium carbonate (Na2CO3) and hydrochloric acid (HCl) can be explained through titration. Titration is a technique used to determine the concentration of a substance in a solution by reacting it with another substance of known concentration.
In this particular case, phenolphthalein is used as an indicator for the titration. Phenolphthalein is a pH indicator that changes color depending on the pH of the solution. It is colorless in acidic solutions (pH < 7) and turns pink in basic solutions (pH > 8).
Here's how the titration between sodium carbonate and HCl using phenolphthalein indicator works:
1. Prepare a solution of sodium carbonate: Dissolve a known mass of sodium carbonate in distilled water to make a solution. The concentration of the solution is usually measured in terms of moles per liter (M).
2. Set up the titration apparatus: Prepare a burette filled with a standardized solution of hydrochloric acid (HCl). The concentration of HCl solution is known. Place the sodium carbonate solution in a flask and add a few drops of phenolphthalein indicator.
3. Perform the titration: Slowly add the HCl solution from the burette into the sodium carbonate solution while stirring. The phenolphthalein indicator will initially be colorless since sodium carbonate acts as a weak base and does not affect the pH significantly.
4. Observe the color change: Continue adding HCl solution until a faint pink color that lasts for at least 30 seconds appears. This indicates the endpoint of the titration. The pink color signifies that the solution has become acidic due to the excess HCl.
5. Record the volume of HCl used: Note the volume of HCl solution required to achieve the endpoint (i.e., the point where the pink color persists). This volume can be used to calculate the concentration of the sodium carbonate solution.
The chemical reaction occurring during the titration is as follows:
Na2CO3 + 2HCl -> 2NaCl + H2O + CO2
Hydrochloric acid reacts with sodium carbonate to produce sodium chloride, water, and carbon dioxide. The carbon dioxide gas bubbles out of the solution, leaving water and sodium chloride behind.
By using phenolphthalein as the indicator in this titration, we can visually observe when the solution reaches the endpoint and understand the reaction taking place.