The pH (pondus Hydrogenium) indicates the acidic or basic nature of a solution and is a measure of the number of free hydrogen ions present in an aqueous solution.
A solution with a higher hydrogen ion concentration has a lower pH and that which has a lower hydrogen ion concentration has a higher pH.
In this article, we are going to learn whether ph changes by the changing temperature or not.
So, does temperature affect ph? Yes, the pH is inversely proportional to the temperature of the solution. When the temperature of a solution rises, the molecular vibrations in the solution rise resulting in the ionization and formation of H+ ions. More H+ ions lead to more acidic behavior. Owing to temperature changes, the pH value of the solution changes. Thus, pH decreases on increasing the temperature.
The temperature affects the activity and concentration of ions in a solution which is related to the pH of a solution. . This happens due to a decreased tendency of hydrogen bond formation.
The molecular equilibrium of a solution undergoes changes in the state due to temperature changes thereby affecting the nature of the solution.
If we increase the temperature from 0°C to 10°C, the pH of a solution or a substance will drop by 0.2.
How do the pH values of the solutions change with varying temperatures? Let us understand the science behind this.
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Relationship between temperature and pH
Le Chaterlier’s principle
This principle explains how factors like temperature influence the chemical solution in equilibrium.
The principle says that changes in temperature, pressure, volume, or concentration of a reacting system at equilibrium allow the system to change its state in order to nullify the effect of stress.
This is achieved by a shift in the equilibrium state as it undergoes a series of opposing changes.
In order to counteract the temperature variation, exothermic or endothermic reactions occur and reverse the changes impacted by stress.
As mentioned in the statement, the temperature can have an influence on the equilibrium state of a system and it affects the pH of a solution.
For instance, if a temperature change is applied to water, the rise in temperature will cause the equilibrium to lower the temperature and that will occur by the absorption of additional heat.
This results in the formation of hydrogen ions and hydroxide ions which lower the pH of water.
The dissociation of water into hydrogen and hydroxide ions takes place.
H20 (L) = H+ (aq) + OH- (aq)
What are pH electrodes and how do they work?
A pH meter consists of a pair of probes to which the electrodes are attached. The two electrodes are –a glass electrode and a reference electrode. The electrode is a small tube that is tied to a pH meter using a cable.
The electrode consists of a special fluid called the 3M-fluid (3M Kalium Chlorine) that has silver and platinum wires. The small membranes are delicate.
When placed in a solution, the H+ and OH- ions pass into the electrode crossing the membrane. Slight negative and positive charges are created at each end of the electrode.
The potential of both the glass electrode and the reference electrode is used to determine the pH of the solution being tested. The charge potential will determine the H+ and OH- ion density.
This density will determine the pH of the solution which will appear on the pH meter. The temperature of the solution affects the charge potential in the electrode.
The pH meters, therefore, show the temperature of the solution. Any change in temperature leads to an increase in electrode sensitivity. With an increase in electrode sensitivity, there is a change in electrode potential, and thus the pH changes.
This can be exemplified using the Nernst equation.
The Nernst equation is used to determine the equilibrium potential and equilibrium constants.
The equation determines the voltage required to oppose the net movement of an ion down the concentration gradient.
E(cell) = E° (cell) – RT/zF ln Q
The above equation implies that E(cell) decreases as T increases.
How does pH change with the change in temperature?
The temperature affects the pH readings in mainly two ways:
• By impacting the pH meter or pH electrodes
The major effect of temperature on the pH values of aqueous solutions leads to errors in readings and pH measurements.
This happens due to a change in the response of electrodes to pH which happens as a result of variation in temperature.
It is a predictable error and can be corrected using a pH meter with temperature compensation. The errors from changing electrode response or sensitivity with respect to changes in temperature can be corrected using pH controllers.
• By impacting the sample solution
When the solution to be tested for pH value is heated, the activity of the hydrogen ions increases and they move faster. The voltage increases with the increased movement of ions.
When the temperature of the solution is brought down, the activity of hydrogen ions decreases, and their movement becomes slow.
This results in a drop in voltage. The measured potential gives a new pH value on the pH meter.
The temperature variations that occur in the sample solution are a result of chemical activity and thus the temperature is monitored using the ATC (Automatic Temperature Compensation) systems.
How does temperature affect the pH electrodes?
The effects of temperature on the electrode are categorized into three main types.
• Electrode Slope Effects
The relationship between the electrode response and temperature variation remains constant.
The electrode behavior with changing temperatures can be monitored using ATC systems.
• Isothermal Point Effects
Isothermal point changes produce errors in the pH readings as the ATC system fails to work when the pH electrodes are placed in two different temperatures.
This can be avoided by carrying out calibration and sample measurement at the same temperature.
• Electrode Response Time Effects
The resistance of membrane glass and the response time of the electrode changes with a change in temperature.
Thus, some electrodes mention the operating minimum and maximum temperature levels for proper results of pH value.
How to eliminate temperature-related errors in pH readings?
The errors in the pH readings due to temperature changes can be minimized or eliminated by using a pH controller.
For the pH readings to be accurate, the calibration ( checking if the pH electrodes are correctly determining the pH using voltage or potential) is carried out carefully.
The pH electrodes are calibrated by inserting them into buffer solutions ( solutions of known pH) and are adjusted according to the buffer solution.
The temperature factor that serves as a barrier while obtaining accurate readings is eliminated by employing pH meters that have built-in thermometers.
These thermometer-assisted pH meters work by correcting the pH values that alter due to temperature fluctuations. ATC systems are designed to account for changes that occur in the electrode.
• pH electrodes with automated temperature compensation:
This pH electrode is built with a temperature sensor placed on the top of the electrode which is connected to a pH controller.
Both the sensor and the controller work simultaneously to adjust the readings and avoid errors that occur due to temperature variation and electrode sensitivity.
• pH controllers with manual temperature compensation:
In this case, the laboratory technician has to manually enter the temperature of the solution into the pH controller.
The meter automatically corrects the pH readings for the variation in the electrode sensitivity.
What impact does temperature have on the pH of different samples?
There is a definite relationship between temperature and pH for every sample. This is called the temperature coefficient that varies for different samples.
For example, a sample tested at 30°C may have a pH of 14, and the same sample when tested after heating at 80°C may show a slight change in the value.
The effect of temperature variation is relatively higher in the case of alkali or basic solutions than in acidic solutions.
At high temperatures, the chemical equilibrium shifts towards the endothermic direction, and at low temperatures the equilibrium shifts towards the exothermic direction.
In easy words, when the temperature rises, the reaction absorbs more heat and when the temperature drops, the reaction produces more heat.
Does pure water become acidic with an increase in temperature?
A drop in the pH values of pure water does not make it acidic because in pure water the concentration of hydrogen and hydroxide ions remains constant.
There is an equal increase in the -OH ions as that of H+ ions which balance the overall nature of the water. This maintains the neutral pH of water regardless of changes in the pH levels.
The pH of water at room temperature is 7 and when it is subjected to a high temperature of 100°C, the pH drops to 6.14 which is neutral but slightly lower than 7.
Water consists of OH- and H3O+ ions whose pH will be denoted as log{c(H3O+)}.
With changes in temperature, the chemical equilibrium of water will also change.
However, the concentration of H3O+ and OH- in the water remain equal. Water undergoes autoionization and is amphoteric (behaves either as acid or a base) in nature.
Conclusion: Does Temperature Affect pH?
Temperature impacts the pH of samples in two ways, either by affecting the electrode or by changing the nature of samples. Most of these effects can be eliminated using pH meters with built-in ATC systems.
Not all ATC systems are reliable when working with temperature variant samples. Suitable pH electrodes for a particular temperature of the sample are to be employed.
FAQs
How does temperature affect pH measurement? ›
Temperature plays a key role in pH measurements. When temperature levels increase, the pH level drops. However, this does not mean that the sample becomes more acidic at higher temperatures. A solution is considered acidic only if there are more hydrogen ions than hydroxide ions.
Does temperature affect pH titration? ›A change in temperature will change the equilibrium constant which can affect titrations in shifting equilibria one direction or the other, adding sources of error in the titration process.
Why does pH decrease with temperature? ›An increase in temperature increases Kw [ more H and OH ions] and a decrease in temperature decreases Kw [less H and OH ions]. The neutral pH point depends on the Kw of water where both H and OH ions are equal in number.
Do pH meters adjust for temperature? ›A: ATC stands for Automatic Temperature Compensation. This means the meter measures pH and temperature at the same time, then automatically calculates to correct for differences (e.g. if one sample is 20°C and another is 23°C).
What is the relationship between temperature and pH? ›At 30°C, the pH drops to 6.92. This is not an error. Water dissociates into ions more at higher temperatures, leading to a higher concentration of hydrogen ions (or H3O+). A higher concentration of H3O+ ([H3O+]) results in lower pH, but it does not mean the sample has changed acidity.
What is the effect of temperature on the titration? ›The temperature dependence of the potentiometric titration curve of a polyelectrolyte was analyzed in terms of an interionic interaction of theory. The extensionthe macroion in solutions was found to decrease with increasing temperature, in conformity with the temperature variation of the viscosity.
What affects pH in titration? ›Below the equivalence point, the pH is a function of the amount of excess acid present. Above the equivalence point, the pH is a function of the amount of excess base present. The equivalence point for the titration of a strong acid with a strong base occurs when [OH–] exactly equals [H3O+] in the solution; pH = 7.0.
What can cause a pH probe to give inaccurate readings? ›Dirty or faulty electrodes can cause anything from slow response to a completely erroneous reading. For example, if a film remains on the pH sensor after cleaning, the resulting measurement error could be misinterpreted as a need for re-calibration.
Why is my pH meter reading unstable? ›If the electrode becomes contaminated, the meter readings may become inaccurate, erratic, or unstable. Clean the electrode by soaking it in electrode cleaning solution for 10 to 30 minutes. Rinse the electrode with water (deionized, reverse osmosis, or distilled water are recommended).
Does colder temperature affect pH? ›The auto-dissociation activity increases as temperature increases. As such, the temperature is very important in regards to pH measurements. As the pH value changes with the change in temperature, the new measured pH value is technically the true pH value.
Why is titration carried out in cold? ›
It should also be apparent that the titrations involving iodine must be made in cold solutions in order to minimize loss through evaporation. 2. Atmospheric oxidation of iodide ion in acidic solution. In acid solution, prompt titration of the liberated iodine is necessary in order to prevent oxidation.
Does temperature affect titratable acidity? ›Titratable acidity and juice pH Storage temperature significantly (p ≤ 0.05) influenced wild plum fruit TTA (Fig. 5) and juice pH (Fig. 6). As storage temperature increased from 0 to 15°C, fruit TTA and juice pH significantly (p ≤ 0.05) decreased (Fig.
Does titration require heat? ›As we know with an increase in temperature rate of reaction increases, Hence, we heat oxalic acid solution before starting of titration to increase the rate of decolourisation.
What is the biggest factor that affects pH? ›In short, environmental factors are the biggest contributor to water pH, whether high or low. When it comes to increasing drinking water alkalinity, various chemicals and pollutants are known to cause high pH levels.
What affects pH and temperature? ›*pH decreases with increase in temperature. But this does not mean that water becomes more acidic at higher temperatures. A solution is considered acidic if there is an excess of hydrogen ions over hydroxide ions.
Why does the pH of water decrease when temperature increases? ›When the temperature is increased, it increases the kinetic energy of the molecules. This tends to increase the ionization and more water is converted to H+ and OH− ions. Hence pH and pOH decreases on increasing the temperature.
Why does pH change when temperature is ignored? ›pH of any solution depend on the concentration of H+ ions in it. pH changes only very slightly with temperature . The change is so minute that it can be neglected.
What happens to pH when temperature decreases? ›If you decrease the temperature the opposite will happen: the pH level will increase very slightly.