Titration of an Unknown Acid...
What effect on the molar mass of the unknown acid would each of the following have... Would it make the calculated molar mass high, low, or would it have no effect?
1. Adding 5 drops of phenolphthalein instead of 1 drop... Answer: No effect.
2. Using a standard NaOH solution that has been left unstoppered for several days... Answer: Low
3. Failing to remove an air bubble in the tip of the burety containing the NaOH soltuion prior to titration... Answer: High
4. Failing to rinse down the unknown acid solution from the inside walls of the flask near the end of the titration... Answer: Low
5. Placing the unknown acid in a wet container prior to weighing it... Answer: High
These look ok to me except for #2. Rethink that one. For a monoprotic acid,
mL x M x millimolar mass = grams.
1. Adding 5 drops of phenolphthalein instead of 1 drop... Answer: No effect.
Why did the chemist bring 5 drops of phenolphthalein to the titration? Because they wanted to make sure everyone saw the reaction! But don't worry, it won't affect the molar mass calculation.
2. Using a standard NaOH solution that has been left unstoppered for several days... Answer: Low
Why did the NaOH solution feel left out? Because it was unstoppered for several days! But don't worry, it might slightly affect the molar mass, but not by a high amount.
3. Failing to remove an air bubble in the tip of the burette containing the NaOH solution prior to titration... Answer: High
Why did the air bubble in the burette fail its audition? Because it wasn't a good actor, it just kept floating! But beware, it can have a high effect on the molar mass calculation.
4. Failing to rinse down the unknown acid solution from the inside walls of the flask near the end of the titration... Answer: Low
Why did the chemist fail to rinse the flask? Because they were in a hurry and couldn't handle the pressure! But no worries, it might slightly affect the molar mass calculation, but not by a high amount.
5. Placing the unknown acid in a wet container prior to weighing it... Answer: High
Why did the unknown acid enjoy taking baths? Because it loved being in a wet container! But be careful, it can have a high effect on the molar mass calculation, causing it to be higher than expected.
1. Adding 5 drops of phenolphthalein instead of 1 drop would have no effect on the molar mass of the unknown acid.
2. Using a standard NaOH solution that has been left unstoppered for several days would result in a low calculated molar mass of the unknown acid. This is because the NaOH solution can absorb moisture from the air, leading to a decrease in concentration and therefore a lower calculated molar mass.
3. Failing to remove an air bubble in the tip of the burette containing the NaOH solution prior to titration would result in a high calculated molar mass of the unknown acid. This is because the volume of NaOH solution delivered would be higher than the actual volume due to the presence of the air bubble, leading to a higher concentration and calculated molar mass.
4. Failing to rinse down the unknown acid solution from the inside walls of the flask near the end of the titration would result in a low calculated molar mass of the unknown acid. This is because some of the acid solution would remain on the walls of the flask, leading to a lower concentration and calculated molar mass.
5. Placing the unknown acid in a wet container prior to weighing it would result in a high calculated molar mass of the unknown acid. This is because the presence of moisture can add to the weight of the acid being measured, leading to a higher measured mass and therefore a higher calculated molar mass.
To determine the effect that each of the listed scenarios would have on the calculated molar mass of the unknown acid, we need to understand the principles of titration.
Titration is a technique used in chemistry to determine the concentration of a known compound by reacting it with a known concentration of another compound (titrant). In this case, we are titrating the unknown acid with a standard NaOH solution.
Here's how each scenario affects the calculated molar mass of the unknown acid:
1. Adding 5 drops of phenolphthalein instead of 1 drop: No effect.
Phenolphthalein is commonly used as an indicator in acid-base titrations. It changes color based on the pH of the solution. The number of drops used will not affect the molar mass calculation since it does not directly affect the reaction between the acid and the titrant.
2. Using a standard NaOH solution that has been left unstoppered for several days: Low.
When sodium hydroxide (NaOH) is exposed to air, it can react with carbon dioxide (CO2) from the atmosphere, forming sodium carbonate (Na2CO3). This reaction reduces the concentration of the NaOH solution. Consequently, the calculated molar mass of the acid will be lower than it should be due to the lower concentration of the sodium hydroxide solution.
3. Failing to remove an air bubble in the tip of the burette containing the NaOH solution prior to titration: High.
An air bubble in the burette would displace the volume of the NaOH solution. Since volume is a crucial factor in determining the concentration of the solution, failing to remove the air bubble would lead to a lower concentration of NaOH being measured. As a result, the calculated molar mass of the acid will be higher than it should be due to the lower concentration of the NaOH solution.
4. Failing to rinse down the unknown acid solution from the inside walls of the flask near the end of the titration: Low.
During the titration, the goal is to ensure that the acid and base are fully reacted. Failing to rinse down the inside walls of the flask would result in some of the unknown acid solution being left behind. This leftover solution would affect the acid's molar mass calculation, leading to a slightly lower value.
5. Placing the unknown acid in a wet container prior to weighing it: High.
Moisture can affect the mass of the substance being weighed since it adds additional mass. Wetting the container before adding the unknown acid would introduce extra moisture, which would be accounted for in the measured mass. This would result in a higher calculated molar mass of the acid.
In summary, adding more drops of phenolphthalein, failing to rinse down the flask, and using a NaOH solution that has been left unstoppered for several days would have a low effect on the calculated molar mass. On the other hand, failing to remove an air bubble in the burette and placing the unknown acid in a wet container would have a high effect on the calculated molar mass.