# Shape of titration curve in vol (NaOH) vs vol (HCl)

1. Jan 23, 2011

In an experiment titration. The NaOH was added drop wise into HCl in a conical flask.
The number of drops of NaOH was recorded against the varied volume of HCl in the flask.
A graph was to be plotted of number of drops of NaOH on the y-aixs to Volume of HCl on the x-axis.

What would the shape of the graph looks like?
The students got straight lines and s-curves...

(OK it was not an accurate experiment but was used to test their other skills sets)

Many thanks

If the graph is pH vs volume added, then it is an S-curve, but now it is volume (number of drops) of NaOH (on y-axis) plotted against the volume of dil HCl... hence the confusion

Many thanks.

PS: I suspect a straight line as y = mx, as the number of moles for neutralisation should increase proportionally with the volume of acid...

2. Jan 23, 2011

### symbolipoint

In the experiement, "drops" of NaOH were added to the HCl solution; was volume of NaOH measured, or were just the drops counted?

That description is not reasonable. If you are adding drops of NaOH titrant to an initial volume of HCl solution, the volume of HCl solution is increasing, yes, but it is both being neutralized with the NaOH, and the total volume is increasing in the flask; in other words, the concentration of the HCl is descreasing.

The graph of pH as "y" with the volume of added NaOH as "x" would give a 'S' shape graph. The graph of volume of added NaOH versus the volume of HCl in the flask---- explain what you really mean! There is a volume of HCl SOLUTION in the flask until it is all neutralized with NaOH, beyond which no more HCl is in the flask. Do you really mean CONCENTRATION of solution in the flask? If so, then this would be a graph of a line.

3. Jan 24, 2011

### Staff: Mentor

pH measurement is not mentioned, so it doesn't sound to me like a titration curve. More like confirming simple and obvious stoichiometry.

4. Jan 25, 2011

Sorry - I mean the plot of the initial volume of HCl on x-axis and the number of drops of NaOH added. ie Not the total volume (NaOH + HCl).

Hence my reasoning is that we are plotting the number of moles required for neutralization.
So it should be a y = mx straight line. Am I correct?

[my experiment graph is straight line]

5. Jan 25, 2011

### symbolipoint

What is the use of making a plot of volume of NaOH titrant versus initial volume of HCl solution? This would be a line with zero slope (just horizontal line). What are you really trying to measure and graph? Moles of NaOH titrant versus volume of initial amount of HCl solution? Same kind of graph: horizontal line.

OR do you mean you measured amount of NaOH needed to neutralize DIFFERENT initial volumes of HCl solution? This kind of graph really would give you a line with a positive slope (going upward as you go from left to right along the x axis.)

6. Jan 25, 2011