Question: Explain whether the technique errors will result in high or low experimental determination of the molar concentration of CH3COOH in vinegar.
1. A student uses the pipet bulb to blow the last bit of vinegar sample from the tip into the titration flask, after the pipet is drained.
2. A student fails to clean the pipet first, After delivering the vinegar sample, the student notices a drop of vinegar clinging to the inner surface of the pipet.
3. A student stops the titration when the pink persists throughout the solution for less than 10 seconds
after completing the titration, a student notices that buret is not clean. Droplets of NaOH solution are clinging to the inner surface of the buret.
Briefly explain why adding distilled water to the vinegar sample prior to the beginning titration does not affect the results of your determination of the molarity of CH3COOH in your vinegar sample.
1. A student uses the pipet bulb to blow the last bit of vinegar sample from the tip into the titration flask, after the pipet is drained.
2. A student fails to clean the pipet first, After delivering the vinegar sample, the student notices a drop of vinegar clinging to the inner surface of the pipet.
3. A student stops the titration when the pink persists throughout the solution for less than 10 seconds
after completing the titration, a student notices that buret is not clean. Droplets of NaOH solution are clinging to the inner surface of the buret.
Briefly explain why adding distilled water to the vinegar sample prior to the beginning titration does not affect the results of your determination of the molarity of CH3COOH in your vinegar sample.
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1. never blow out the excess volume after the pipet is drained. if you add 5ml acid to a known concentration of base and you blow out the last little bit of acid in the pipet, the volume is no longer 5ml but you calculate it from 5ml. the concentration of the acid will be higher than it actually is.
0.1mole NaOH x 0.025L = xmoles HAc x 0.005L = 0.5moles HAc.....this is based upon the measured volume of 5ml + the volume of extra HAc blown from the pipet. if that volume is as much as 1ml...
0.1mole OH- x 0.025L = xmoles HAc x 0.006L = 0.417moles HAc. the unknown volume cannot be accounted for and the calculated moles HAc will be higher than they actually are.
2. if you are adding vinegar to a pipet with vinegar already in it, this should not be a problem since the pipet has gradations to determine the volume of vinegar. if it bothers you, you can dry it better but this won't matter. if the liquid were NaOH, then you would have a problem
3. the equivalence point has yet to be met. this creates a 'false' endpoint. the volume of HAc added is a fraction less than what is actually required. since the pink color is showing up and then dissipating, your calculations will be higher than they actually are but you won't be off by much.
4. you can add as much volume of distilled water that you want to the vinegar. the moles of acid will not change, only the molarity. no matter how many moles one has of a substance. diluting it will NOT change the amount of moles present, only the molarity
0.1mole NaOH x 0.025L = xmoles HAc x 0.005L = 0.5moles HAc.....this is based upon the measured volume of 5ml + the volume of extra HAc blown from the pipet. if that volume is as much as 1ml...
0.1mole OH- x 0.025L = xmoles HAc x 0.006L = 0.417moles HAc. the unknown volume cannot be accounted for and the calculated moles HAc will be higher than they actually are.
2. if you are adding vinegar to a pipet with vinegar already in it, this should not be a problem since the pipet has gradations to determine the volume of vinegar. if it bothers you, you can dry it better but this won't matter. if the liquid were NaOH, then you would have a problem
3. the equivalence point has yet to be met. this creates a 'false' endpoint. the volume of HAc added is a fraction less than what is actually required. since the pink color is showing up and then dissipating, your calculations will be higher than they actually are but you won't be off by much.
4. you can add as much volume of distilled water that you want to the vinegar. the moles of acid will not change, only the molarity. no matter how many moles one has of a substance. diluting it will NOT change the amount of moles present, only the molarity