Does Temperature Have an Impact on pH?

The pH (pondus Hydrogenium) is a measure of the number of free hydrogen ions present in an aqueous solution and indicates whether it is acidic or basic.

The pH of a solution with a higher hydrogen ion concentration is lower, while the pH of a solution with a lower hydrogen ion concentration is higher.

In this post, we’ll look at whether or not ph changes as a result of temperature changes.

Is temperature a factor in ph? Yes, the pH of a solution is inversely related to its temperature. When a solution’s temperature rises, so do its molecular vibrations, resulting in ionisation and the creation of H+ ions. The presence of more H+ ions causes the behaviour to become more acidic. The pH value of the solution fluctuates as the temperature changes. As a result, as the temperature rises, the pH drops.

The activity and concentration of ions in a solution are affected by temperature, which is related to the pH of a solution. This is owing to a lower proclivity for hydrogen bond formation.

Temperature variations alter the molecular equilibrium of a solution, which affects the character of the solution.

The pH of a solution or material drops by 0.2 when the temperature is raised from 0°C to 10°C.

What effect does temperature have on the pH of the solutions? Let’s have a look at the science behind this.

Temperature and pH: What’s the Connection?

The principle of Le Chaterlier

This theory describes how variables such as temperature have an impact on a chemical solution that is in equilibrium.

Changes in temperature, pressure, volume, or concentration of a reactive system at equilibrium allow the system to change its state, nullifying the effect of stress, according to the concept.

This is accomplished through a shift in the equilibrium state as a sequence of opposing changes take place.

Exothermic or endothermic responses occur to offset temperature fluctuations and reverse stress-induced alterations.

The temperature, as stated in the statement, can impact the equilibrium state of a system as well as the pH of a solution.

If a temperature change is made to water, for example, the rise in temperature will force the equilibrium to drop the temperature, which will be accomplished through the absorption of additional heat.

This causes hydrogen ions and hydroxide ions to form, lowering the pH of the water.

Water is split into hydrogen and hydroxide ions during dissociation.

H20 (L) = H+ (aq) + OH- (aq)

How do pH electrodes function and what are they used for?

The electrodes are attached to a pair of probes on which a pH metre is built. A glass electrode and a reference electrode are the two electrodes. The electrode is a tiny tube connected by a cable to a pH metre.

The electrode is made up of silver and platinum wires in a specific fluid called 3M-fluid (3M Kalium Chlorine). The tiny membranes are extremely fragile.

When the electrode is submerged in a solution, the H+ and OH- ions travel through the membrane and into the electrode. At each end of the electrode, minor negative and positive charges are produced.

The pH of the solution being tested is determined by comparing the potentials of the glass electrode and the reference electrode. The density of H+ and OH- ions is determined by the charge potential.

The pH of the solution will be determined by this density, as seen on the pH metre. The charge potential in the electrode is affected by the temperature of the solution.

As a result, pH metres display the temperature of the solution. Any change in temperature causes the electrode sensitivity to increase. With an increase in electrode sensitivity, the electrode potential changes, and the pH changes as well.

The Nernst equation is a good example of this.

The equilibrium potential and equilibrium constants are calculated using the Nernst equation.

The voltage necessary to resist the net movement of an ion down a concentration gradient is calculated using this equation.

E(cell) = E° (cell) – RT/zF ln Q

E(cell) drops as T grows, according to the preceding equation.

How does pH alter as the temperature rises or falls?

The temperature has two significant effects on pH readings:

• By causing the pH metre or pH electrodes to malfunction.

Temperature has a significant impact on the pH values of aqueous solutions, resulting in inaccuracies in readings and pH measurements.

This occurs as a result of a change in the electrodes’ responsiveness to pH as a result of temperature changes.

It’s a predicted inaccuracy that can be remedied with a temperature-compensated pH metre. pH controllers can remedy problems caused by altering electrode responsiveness or sensitivity in response to temperature variations.

• By having an effect on the sample solution

The activity of the hydrogen ions rises and they move faster when the fluid to be tested for pH value is heated. With the increased mobility of ions, the voltage rises.

The activity of hydrogen ions reduces when the temperature of the solution is lowered, and their movement becomes slow.

As a result, the voltage drops. The pH metre displays a new pH value based on the detected potential.

Chemical activity causes temperature changes in the sample solution, which is why the temperature is monitored using ATC (Automatic Temperature Compensation) devices.

What effect does temperature have on pH electrodes?

Temperature impacts on the electrode can be divided into three categories.

• Effects of Electrode Slope

The electrode response and temperature changes have a continuous connection.

ATC systems can be used to track electrode behaviour as temperatures change.

• Effects of the Isothermal Point

Because the ATC system fails to perform when the pH electrodes are placed in two different temperatures, isothermal point shifts cause pH reading inaccuracies.

Calibration and sample measurement should be done at the same temperature to avoid this.

• Effects of Electrode Response Time

With a change in temperature, the resistance of membrane glass and the response time of the electrode alter.

As a result, some electrodes specify the working minimum and maximum temperature values for accurate pH results.

How can temperature-related mistakes in pH readings be avoided?

The use of a pH controller can reduce or eliminate pH reading mistakes caused by temperature variations.

The calibration (testing if the pH electrodes are accurately detecting the pH using voltage or potential) is done carefully to ensure that the pH readings are accurate.

The pH electrodes are calibrated by immersing them in buffer solutions (pH-controlled solutions) and adjusting them accordingly.

The use of pH metres with built-in thermometers eliminates the temperature element as a stumbling block to getting accurate readings.

The pH values that change owing to temperature fluctuations are corrected by these thermometer-assisted pH metres. ATC systems are built to take into consideration changes in the electrode.

• Automated temperature compensation pH electrodes:

This pH electrode features a temperature sensor on top of the electrode that is coupled to a pH controller.

Both the sensor and the controller work together to correct readings and avoid errors caused by temperature changes and electrode sensitivity.

• Manual temperature compensation pH controllers:

The laboratory worker must manually insert the solution’s temperature into the pH controller in this scenario.

The metre compensates for variations in electrode sensitivity by automatically correcting the pH readings.

What effect does temperature have on pH levels in various samples?

Every sample has a distinct relationship between temperature and pH. This is known as the temperature coefficient, which changes depending on the sample.

For example, a sample tested at 30°C might have a pH of 14, but the same sample tested at 80°C might have a slightly different value.

Temperature change has a greater impact on alkali or basic solutions than it does on acidic ones.

The chemical equilibrium moves towards the endothermic direction at high temperatures and towards the exothermic direction at low temperatures.

Simply said, as the temperature rises, the reaction absorbs more heat, and as the temperature decreases, the process creates more heat.

Is it true that when the temperature rises, pure water becomes acidic?

Because the concentration of hydrogen and hydroxide ions in pure water remains constant, a drop in pH values does not render it acidic.

The -OH ions rise at the same rate as the H+ ions, bringing the water’s overall nature into balance. This ensures that the pH of the water remains neutral regardless of changes in the pH levels.

When water is exposed to a high temperature of 100°C, the pH lowers to 6.14, which is neutral but somewhat lower than 7.

Water is made up of OH- and H3O+ ions, and its pH is represented as logc(H3O+).

The chemical equilibrium of water will alter when the temperature changes.

The concentrations of H3O+ and OH- in the water, on the other hand, stay constant. Water is amphoteric (behaves either as an acid or a basic) and undergoes autoionization.

Does Temperature Have an Impact on pH?

Temperature has two effects on sample pH: it affects the electrode or changes the nature of the samples. The majority of these side effects can be avoided by using pH metres with integrated ATC systems.

When working with temperature-variable samples, not all ATC systems are reliable. pH electrodes that are appropriate for the sample’s temperature should be used.

Read more: Is I2 a polar or nonpolar substance?

Misha Khatri
Misha Khatri is an emeritus professor in the University of Notre Dame's Department of Chemistry and Biochemistry. He graduated from Northern Illinois University with a BSc in Chemistry and Mathematics and a PhD in Physical Analytical Chemistry from the University of Utah.


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