Méthode des tangentes parallèles. Titrage Volume équivalent

e-profs - Physique Chimie

24 Oct 201901:17

Summary

TLDRThe video explains how to determine the equivalent volume and pH at equivalence using the parallel tangent method when titrating. It instructs to first plot two tangents parallel to each other on either side of the pH jump. To ensure the tangents are parallel, use a ruler and set square. Then draw perpendicular lines to find the midpoint of each tangent segment to plot the parallel line equidistant to both. This green line intersects the pH-metric curve at the equivalence point. Finally, read the graph to get the coordinates of the equivalence point - the equivalent volume on the x-axis and pH at equivalence on the y-axis.

Takeaways

😀 To determine the equivalent volume and pH at the equivalence point using the parallel tangent method, first plot two parallel tangents to the curve on either side of the pH jump.
👉🏻 To plot truly parallel lines, use a ruler and square to ensure they are equidistant.
📏 Plot perpendicular lines from the parallel tangents to mark the midpoint of each segment, then connect the midpoints to trace the parallel line equidistant to the tangents.
🔃 This green line intersects the pH-metric curve tracing at the equivalence point.
📊 Read the graph coordinates of the intersection point to find the equivalent volume on the X-axis and pH at equivalence on the Y-axis.
✏️ Practice this parallel tangent technique to master it!
🧪 The script outlines how to determine key titration information from a pH-metric curve tracing using parallel tangents.
🔬 Tangents are plotted on either side of the pH jump, then connected by a parallel line that marks the equivalence point.
📐 Proper tools like rulers and squares help plot accurate, parallel tangent lines.
🎓 Mastering this graphical analysis technique is important for titration experiments.

Q & A

What is the purpose of plotting two parallel tangents on either side of the pH jump in a titration curve?
-Plotting parallel tangents allows you to locate the equivalence point on the titration curve. The line equidistant between the tangents intersects the curve at the equivalence point.
How can you ensure that two tangents plotted on a titration curve are properly parallel?
-Use a ruler and protractor to carefully plot tangents that are parallel. Draw perpendicular lines to the tangents and find the midpoint of each perpendicular segment to plot the equidistant line.
What values can be determined from the equivalence point located using parallel tangents?
-The equivalence point allows determination of the equivalent volume on the x-axis and the pH at equivalence on the y-axis.
Why is there a pH jump at the equivalence point in a titration curve?
-The pH jumps because the equivalence point is where the stoichiometric ratio between acid and base is exactly reached, causing a sharp change in pH.
What reagents are typically used in an acid-base titration?
-A strong acid or base as the titrant, and a weak acid or base as the analyte. This creates the greatest pH change at the equivalence point.
What is the best way to accurately plot tangents on a hand-drawn titration curve?
-Use a straight edge ruler and protractor to carefully mark parallel lines. Plot perpendiculars and find midpoints to add the equidistant line.
Why is it better to choose tangents just before or after the pH jump?
-The curve is steepest right before and after the jump, making it easier to plot accurate parallel tangents.
What are some potential sources of error when using the parallel tangent method?
-Possible errors include inaccurate pH measurements, plotting errors when drawing tangents, and determining volumes by eye from the graph.
How can the parallel tangent method be applied to other types of titration curves?
-The method can be used on titration curves monitoring parameters besides pH, such as electrical conductivity. The same principles apply.
What is the main advantage of locating equivalence points using parallel tangents?
-It provides a graphical interpretation to easily visualize the stoichiometric point and determine key parameters like pH and volume.

Outlines

00:00

😊 Determining the Equivalent Volume and pH using the Parallel Tangent Method

This paragraph explains how to determine the equivalent volume and pH at equivalence using the parallel tangent method when performing a titration. It advises tracing two parallel tangents on either side of the pH jump on the curve, constructing perpendiculars to find the midpoint, and connecting the midpoints to trace the equivalence point. It then explains how to read off the equivalent volume on the x-axis and pH at equivalence on the y-axis.

Mindmap

Keywords

💡titrage

Titrage refers to the process of doing a titration, where a solution of known concentration is slowly added from a burette to a solution of unknown concentration in order to determine chemical equivalency. This is a key procedure discussed in the video script, as it allows determining the equivalence volume and pH.

💡volume équivalent

The equivalence volume refers to the volume of titrant solution required to reach the equivalence point. Identifying this volume on the graph allows determining one of the key parameters in a titration analysis. The script explains how to graphically determine the equivalence volume using the double tangent method.

💡pH à l'équivalence

The pH at the equivalence point indicates the pH value precisely when chemical equivalency is reached during a titration. Finding this pH value on the graph provides the second key parameter alongside the equivalence volume. The video script outlines using parallel tangents to determine the pH at equivalence.

💡tangentes parallèles

Parallel tangents refer to drawing two parallel tangent lines on either side of the pH jump in a titration curve graph. This graphical method allows accurately locating the equivalence point volume and pH, as explained step-by-step in the script.

💡saut de pH

The pH jump indicates the abrupt change in pH value near the equivalence point during a titration. Identifying this pH jump on the titration curve helps position the parallel tangents appropriately to find the equivalence volume and pH, a key technique presented in the script.

💡point équivalent

The equivalence point refers to the stage during a titration when chemically equivalent amounts of acid/base or oxidant/reductant have been mixed. The script explains how to use parallel tangents and locate this equivalence point graphically to determine volume and pH.

💡lecture graphique

Graphical reading means interpreting key parameters from a titration curve graph, rather than actual experimental measurements. As detailed in the script, once parallel tangents identify the equivalence point, its volume and pH value can be read directly off the graph axes.

💡technique

Technique here refers to the step-by-step method outlined in the video script for using parallel tangents to graphically determine equivalence volume and pH from a titration curve. Mastering this technique is presented as an important skill for viewers.

💡axes des abscisses

The x-axis refers to the horizontal axis on a graph that typically plots an independent input variable. As explained in the script, the x-axis on a titration curve represents added volume, allowing a graphical reading of the equivalence volume at the intersection with the parallel tangents.

💡axes des ordonnées

The y-axis refers to the vertical axis on a graph that plots a dependent output variable. For a titration curve, the y-axis tracks pH, enabling a graphical reading of the pH at equivalence from where the parallel tangents intersect the curve.

Highlights

To determine the equivalent volume and pH at equivalence using the parallel tangent method, you first need to plot two parallel tangents on either side of the pH jump.

You can choose to plot the first tangent just before or just after the pH jump.

To truly plot parallel lines, I recommend using a ruler and protractor.

Then plot two perpendiculars to the parallel tangents, and mark the midpoint of each line segment.

This makes it easy to plot the parallel line equidistant from the two tangents.

The green line intersects the pH-metric curve at the equivalence point.

Now just graphically determine the coordinates of the equivalence point.

The equivalent volume is on the x-axis, and the pH at equivalence is on the y-axis.

Practice this technique to master it!

Plot two parallel tangents on either side of the pH jump

Mark perpendiculars and midpoints to plot an equidistant line

The green equidistant line intersects at the equivalence point

Read coordinates to get volume equivalent and pH

Practice to master the parallel tangent method

Apply this titration analysis technique