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

In summary, the conversation is about an experiment in which titration was performed by adding NaOH dropwise into HCl in a conical flask, while recording the number of drops and varied volume of HCl. The students were asked to plot a graph of number of drops of NaOH on the y-axis against the volume of HCl on the x-axis. There was some confusion about the shape of the graph, with some thinking it would be a straight line while others believed it would be an S-curve. It was clarified that the graph would be a straight line with a positive slope passing through the origin, as the experiment was measuring the amount of NaOH needed to neutralize different initial volumes of HCl solution.
  • #1
matthew77ask
45
0
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


Additional Details
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...
 
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  • #2
In the experiement, "drops" of NaOH were added to the HCl solution; was volume of NaOH measured, or were just the drops counted?

The number of drops of NaOH was recorded against the varied volume of HCl in the flask.
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
pH measurement is not mentioned, so it doesn't sound to me like a titration curve. More like confirming simple and obvious stoichiometry.
 
  • #4
symbolipoint said:
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.

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
matthew77ask said:
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]

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
symbolipoint said:
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.)

I am very sorry for the lack of clarity in written english language.
Yes sir, this is what it means:
measured amount of NaOH needed to neutralize DIFFERENT initial volumes of HCl solution?

ah - many times, when we speak we can understand - but when we write - it has to be more specific !

many thanks - got your answer... straight line with positive slope passing thru (0,0)

Cheers!:smile:
 

1. What is a titration curve?

A titration curve is a graph that shows the change in pH or other relevant property of a solution as a titrant is added. In this case, the titrant is a strong acid (HCl) and the solution being titrated is a strong base (NaOH).

2. How does the shape of the titration curve in vol (NaOH) vs vol (HCl) differ for different acid-base combinations?

The shape of the titration curve can vary depending on the strength and concentration of the acid and base being used. For example, a weak acid and strong base titration curve will have a steep initial rise in pH, followed by a gradual increase until reaching the equivalence point. A strong acid and strong base titration curve will have a more gradual rise in pH, and the equivalence point will occur at a pH closer to 7.

3. What does the equivalence point on the titration curve represent?

The equivalence point on the titration curve represents the point at which the number of moles of acid and base are equal, and the solution is neutral. This is also known as the stoichiometric point, as it indicates that the reaction between the acid and base is complete.

4. How can the shape of the titration curve be used to determine the concentration of an unknown acid or base?

The shape of the titration curve can provide information about the concentration of an unknown acid or base. By measuring the volume of titrant required to reach the equivalence point and using the known concentration of the titrant, the concentration of the unknown solution can be calculated using the equation M1V1 = M2V2.

5. What factors can affect the shape of the titration curve?

The shape of the titration curve can be affected by several factors, including the strength and concentration of the acid and base, the nature of the acid-base reaction, and the presence of any additional reactants or products in the solution. Temperature and pressure can also have an impact on the shape of the titration curve.

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