As strong base (NaOH) is added to strong acid (HCl), why does the conductance decrease?

Fast-moving H⁺ ions are replaced by slower-moving Na⁺ ions

The reaction is endothermic, slowing ions down

What does the V-shaped minimum on the conductometric curve represent?

The equivalence point where only salt and water remain

The point of maximum acid concentration

The point of maximum base concentration

Why does the conductance shoot up rapidly after the equivalence point?

Excess OH⁻ ions are added, which have very high ionic mobility

The salt begins to conduct better

What is a major advantage of conductometric titration?

It can be used for highly colored or turbid solutions where visual indicators fail

It doesn't require any equipment

It works without any ions present

It is faster than using an indicator

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Conductometric Titration: Strong Acid vs. Strong Base — Curve & Notes PDF

Endpoint found by the V-shaped minimum in the conductance vs. volume graph
H⁺ has highest ionic mobility — initial conductance is very high
PQ falls: H⁺ replaced by slow-moving Na⁺ as neutralisation proceeds
Q (Equivalence Point): only NaCl + H₂O — minimum conductance
QR rises: excess OH⁻ added — second highest ionic mobility

Conductometric titration is a method in which the endpoint of a titration is determined by measuring the change in electrical conductance of the solution as titrant is gradually added.

Reaction Involved

HCl + NaOH → NaCl + H₂O

Both acid and base are strong electrolytes — they dissociate completely in water:

HCl → H⁺ + Cl⁻

NaOH → Na⁺ + OH⁻

Titration Curve

The curve is a plot of conductance (mS) on the Y-axis versus volume of NaOH added (mL) on the X-axis.

Four Stages of the Titration

A. Initial Stage — Point P (Before any NaOH is added)

The solution contains only HCl, fully dissociated into H⁺ and Cl⁻ ions.

H⁺ ions have the highest ionic mobility of all known ions (due to the Grotthuss/proton-hopping mechanism).

Therefore, conductance is very high at the start.

High H⁺ concentration → Very high conductance → Point P is the highest point on the descending line PQ.

B. Before the Equivalence Point — Line PQ (Adding NaOH drop by drop)

Each drop of NaOH adds Na⁺ and OH⁻.

The OH⁻ immediately neutralises H⁺:

H⁺ + OH⁻ → H₂O

Highly mobile H⁺ ions are being removed and replaced by less mobile Na⁺ ions.

Since Na⁺ has much lower mobility than H⁺, conductance drops steadily with each drop added.

Solution composition: Unreacted HCl + NaCl (salt)

Conductance falls sharply — the curve slopes downward from P to Q.

C. At the Equivalence Point — Point Q

All H⁺ ions have been neutralised.

The solution now contains only NaCl + H₂O — no excess acid or base.

Na⁺ and Cl⁻ are present, but both have moderate, equal mobilities.

This is the minimum conductance point of the entire curve.

Point Q = Equivalence Point = End Point of the Titration.

D. After the Equivalence Point — Line QR (Excess NaOH)

Further addition of NaOH beyond the endpoint means excess NaOH is now dissolving into the solution.

NaOH adds Na⁺ and OH⁻ ions.

OH⁻ ions have the second highest ionic mobility after H⁺.

Conductance rises sharply again.

Solution composition: NaCl + excess NaOH

Conductance rises steeply — the curve slopes upward from Q to R.

Summary Table

Stage	What is happening	Effect on Conductance
Initial (P)	Only HCl — high [H⁺]	Very High
PQ (Before EP)	H⁺ replaced by slow Na⁺	Steadily Decreasing
Q (Equivalence Point)	Only NaCl in solution	Minimum
QR (After EP)	Excess OH⁻ added	Sharply Increasing

Why This Method Is Better Than Indicators

Works even with coloured or turbid solutions where visual indicators fail.

The V-shaped curve gives a very sharp, unambiguous endpoint.

Can be done with any combination of strong/weak acids and bases.

Does not require the solution to be transparent.

Key Inferences

The sharp V-shape minimum at point Q is diagnostic of a Strong Acid vs. Strong Base conductometric titration.

The steep fall (PQ) is due to loss of H⁺ (highest mobility ion) and its replacement by Na⁺ (lower mobility).

The steep rise (QR) is due to addition of excess OH⁻ (second highest mobility ion).

No colour change needed — the endpoint is read directly from the graph's minimum.

Endpoint found by the V-shaped minimum in the conductance vs. volume graph
H⁺ has highest ionic mobility — initial conductance is very high
PQ falls: H⁺ replaced by slow-moving Na⁺ as neutralisation proceeds
Q (Equivalence Point): only NaCl + H₂O — minimum conductance
QR rises: excess OH⁻ added — second highest ionic mobility

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Conductometric Titration — Strong Acid vs. Strong Base (HCl vs. NaOH)

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About Conductometric Titration: Strong Acid vs. Strong Base — Curve & Notes PDF

Conductometric Titration: Strong Acid vs. Strong Base — Curve & Notes PDF is a fundamental concept in physical chemistry. Understanding the mechanisms, reaction conditions, and stereo-chemical outcomes is crucial for mastering organic chemistry. Our curated resources provide step-by-step visualizations to help you excel.