A 25mL solution of nitric acid was placed in a flask and a few drops of phenolphthalein were added. Dilute sodium hydroxide was added until the indicator changed colour. It was found that 28mL of the alkali was used.
What colour was the solution in the flask at the start of the titration?
What colour did it turn to when the acid had been neutralized?
Was the alkali more concentrated or less concentrated then the acid?
To determine the solution's initial color, we need to understand the properties of nitric acid and phenolphthalein. Nitric acid is a strong acid that can dissociate completely in water, resulting in a clear, colorless solution. Phenolphthalein is an indicator commonly used in acid-base titrations, which is colorless in acidic solutions and turns pink in alkaline/basic solutions.
Therefore, when the nitric acid solution was initially prepared, the solution in the flask would have been colorless.
During the titration, sodium hydroxide (NaOH) was added until the indicator changed color. The indicator, phenolphthalein, turns pink in an alkaline/basic solution. This color change indicates the neutralization of the acid since the strong base reacts with the strong acid to form water and a salt.
So, after adding the dilute sodium hydroxide and neutralizing the nitric acid, the solution in the flask would have turned from colorless to pink.
To determine which solution was more concentrated, we compare the volumes used. In this case, 25 mL of the nitric acid solution required 28 mL of the sodium hydroxide solution to achieve neutralization. Since a smaller volume of the sodium hydroxide solution (28 mL) was used compared to the volume of the nitric acid solution (25 mL), it suggests that the alkali (sodium hydroxide) was more concentrated than the acid (nitric acid).
To determine the color of the solution at the start of the titration, we need to understand the role of phenolphthalein in acid-base titrations. Phenolphthalein is an indicator commonly used in acid-base titrations. It is colorless in acidic solutions and turns pink or magenta in basic solutions.
In this case, when a few drops of phenolphthalein were added to the 25mL solution of nitric acid, the solution would have remained colorless since nitric acid is an acidic solution.
During the titration process, dilute sodium hydroxide (NaOH) was added until the indicator changed color. The color change indicates that the acid has been neutralized. In the case of phenolphthalein, it turns from colorless to pink or magenta in a basic solution. Therefore, the solution in the flask turned from colorless to pink/magenta when the nitric acid was neutralized.
Now, to determine whether the alkali was more concentrated or less concentrated than the acid, we can compare the volumes used. In this case, 28mL of the alkali (NaOH) was used to neutralize the 25mL of nitric acid. Since the volume of the alkali used was greater than the volume of the acid, we can conclude that the alkali was less concentrated than the acid.
In summary:
1. At the start of the titration, the solution in the flask was colorless.
2. The color of the solution turned to pink/magenta when the acid (nitric acid) was neutralized.
3. The alkali (sodium hydroxide) used in the titration was less concentrated than the acid.