AQA AS Chemistry 2017 Paper 1 Titration MCQ Q16
25.0 cm3 samples of NaOH solution were taken by pipette from a beaker. These were then titrated with an aqueous solution of ethanoic acid. The concentration of ethanoic acid calculated from the experimental results was found to be lower than the actual value.
Which of these could explain the difference?
A Rinsing the pipette with distilled water before filling with NaOH
B Rinsing the burette with distilled water before filling with ethanoic acid
C Rinsing the walls of the conical flask with distilled water during the titration
D Rinsing the beaker with distilled water before filling with NaOH
[1 mark]
Could anyone please explain why the answer is B and explain why.
Which of these could explain the difference?
A Rinsing the pipette with distilled water before filling with NaOH
B Rinsing the burette with distilled water before filling with ethanoic acid
C Rinsing the walls of the conical flask with distilled water during the titration
D Rinsing the beaker with distilled water before filling with NaOH
[1 mark]
Could anyone please explain why the answer is B and explain why.
A Rinsing the pipette with distilled water before filling with NaOH
-This would dilute the NaOH. This has no effect on the moles of NaOH that must be neutralised by the ethanoic acid.
B Rinsing the burette with distilled water before filling with ethanoic acid
-This dilutes the ethanoic acid meaning a larger volume is required to neutralise the NaOH this increases the mean titre reading. The mean titre reading is then used to calculate concentration (moles/volume). As volume is larger the calculated concentration is smaller.
C Rinsing the walls of the conical flask with distilled water during the titration
-same reasoning as A
D Rinsing the beaker with distilled water before filling with NaOH
-same reasoning as A
-This would dilute the NaOH. This has no effect on the moles of NaOH that must be neutralised by the ethanoic acid.
B Rinsing the burette with distilled water before filling with ethanoic acid
-This dilutes the ethanoic acid meaning a larger volume is required to neutralise the NaOH this increases the mean titre reading. The mean titre reading is then used to calculate concentration (moles/volume). As volume is larger the calculated concentration is smaller.
C Rinsing the walls of the conical flask with distilled water during the titration
-same reasoning as A
D Rinsing the beaker with distilled water before filling with NaOH
-same reasoning as A
Original post by Hellllpppp
A Rinsing the pipette with distilled water before filling with NaOH
-This would dilute the NaOH. This has no effect on the moles of NaOH that must be neutralised by the ethanoic acid.
B Rinsing the burette with distilled water before filling with ethanoic acid
-This dilutes the ethanoic acid meaning a larger volume is required to neutralise the NaOH this increases the mean titre reading. The mean titre reading is then used to calculate concentration (moles/volume). As volume is larger the calculated concentration is smaller.
C Rinsing the walls of the conical flask with distilled water during the titration
-same reasoning as A
D Rinsing the beaker with distilled water before filling with NaOH
-same reasoning as A
-This would dilute the NaOH. This has no effect on the moles of NaOH that must be neutralised by the ethanoic acid.
B Rinsing the burette with distilled water before filling with ethanoic acid
-This dilutes the ethanoic acid meaning a larger volume is required to neutralise the NaOH this increases the mean titre reading. The mean titre reading is then used to calculate concentration (moles/volume). As volume is larger the calculated concentration is smaller.
C Rinsing the walls of the conical flask with distilled water during the titration
-same reasoning as A
D Rinsing the beaker with distilled water before filling with NaOH
-same reasoning as A
So diluting has no effect on moles because:
If you dilute volume increases and concentration decreases
Due to n = c x v it has no effect on moles?
Original post by xxccvc
So diluting has no effect on moles because:
If you dilute volume increases and concentration decreases
Due to n = c x v it has no effect on moles?
If you dilute volume increases and concentration decreases
Due to n = c x v it has no effect on moles?
Yeah moles of a specific element just represents the amount of atoms of that element so adding water doesn’t change that.
Original post by miac0328
why is the answer not C? this also adds water to the ethanoic acid and so why does this not also have the same effect?
Adding water to the conical flask would neither change the moles of NaOH in the flask nor change the concentration of ethanoic acid in the burette
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