pH handbook
100Pages

HELPFUL GUIDE FOR PRACTICAL APPLICATION AND USE

Welcome to SI Analytics! We express our core competence, namely the production of analytical instruments, with our company name SI Analytics. SI also stands for the main products of our company: sensors and instruments. As part of the history of SCHOTT® AG, SI Analytics has more than 75 years experience in glass technology and in the development of analytical equipment. As always, our products are manufactured in Mainz with a high level of innovation and quality. Our electrodes, titrators and capillary viscometers will continue to be the right tools in any location where expertise in...

We look forward to presenting the pH handbook to you! The previous publication "Interesting facts about pH measurement" has been restructured, made clearer and more engaging, and extra information has been added. The focus has been consciously put on linking general information with our lab findings and making this accessible to you in a practical format. Complemented by the reference to our range of products and with practical recommendations for use with specific applications, the pH primer is an indispensable accompaniment for everyday lab work. We at SI Analytics would be happy to work...

Index of technical terms Bibliography

pH handbook SECTION 1 BASIC CONCEPTS OF POTENTIOMETRY AND pH MEASUREMENT This section explains basic concepts and contexts. The pH value plays a significant role in many areas of daily life. For food, the association of certain properties such as taste (acid = fresh, neutral = bland, alkaline = inedible) and shelf life (the reproduction of harmful bacteria) depend on the pH value. Figure 1 contains a diagram showing various examples of the pH values of well-known, everyday items compared to an acid and a base. The natural acid level of the skin lies somewhere between pH 4.2 - 6.7, and plays...

1.1  Definition of acid and base Whether an aqueous solution reacts as an acid or a base depends on its hydrogen ion content. Even chemically pure, neutral water contains hydrogen ions, because some of the water molecules are always dissociated: HOH In chemical terms, the positive H+ ion, the "proton", is usually referred to as the "hydrogen ion". The negative OH- ion was previously known as the "hydroxyl ion", but now the term "hydroxide ion" is prescribed internationally. [1] Strictly speaking, the hydrogen ion in aqueous solution is not present as a free proton, but is hydrated by at...

pH handbook The ionic product of water changes with the temperature. This is because, like all equilibrium constants, the dissociation constant is also dependent on temperature. The ionic product of water at 0 °C for example is 0.11·10-14 [mol/l]2, but at 100 °C it is 54.0·10-14 [mol/l]2. Instead of 1·10-7mol/l at 25  °C, the concentration of hydrogen ions at 0  is therefore only °C 0.34 ·10-7 mol/l, but at 100 °C it is 7.4 · 10-7 mol/l. This temperature dependency must also be taken into account in measuring the pH. Acids and Bases Acids are substances which release hydrogen ions in...

The dissociation constants (KD) for the different stages of dissociation of a multivalent acid are often markedly different.  This  varying level of dissociation at the different stages plays an important role, for example in the use of phosphoric acid and phosphates in buffer solutions. Bases are substances which accept hydrogen ions. When bases are dissolved in water, they bind to some of the hydrogen ions from the dissociation of the water. Basic solutions therefore contain fewer hydrogen ions than neutral water. Accordingly, the concentration of hydroxyl ions in basic solutions is...

pH handbook If a salt like this, which has been formed from a strong acid and base is dissolved in water, the solution reacts neutrally. On the other hand, if the salt of a strong base and a weak acid, such as sodium carbonate (Na2CO3) is dissolved, the resulting solution is basic. If the salt of a strong acid and a weak base, such as ammonium chloride (NH4Cl) is dissolved, the resulting solution is acidic. Na2CO3+ H2O NH4Cl + H2O 1.2  Definition of pH value The concentration of hydrogen ions in an aqueous solution is a measure of how acidic or basic it is. Accordingly, a scale can be...

However, concentration is not used as the measure of acidity, but a logarithmic scale, the "pH value". The pH value is directly proportional to the negative log base 10 of the hydrogen ion concentration. (The term "pH" comes from Latin and is an acronym for "potentia hydrogenii" - the power of hydrogen.) pH ~ -lg [H+] In practice that means that a change in the concentration of hydrogen ions by a factor of 10 creates a change of 1.0 on the pH scale. Concentration and activity Dissolved ions exert electrical forces as charge carriers on the medium surrounding them. While the solution is...

pH handbook The pH values measured in practice relate to a series of standard buffer solutions created by the NBS (National Bureau of Standards) and adopted by the Deutsche Institut für Normung (DIN). Conventional pH values are therefore measured in comparison to the pH values of these standard buffer solutions. Provided that calibration and measurement is done carefully, this makes all pH values comparable, regardless of the probe or measuring equipment used to record them. In determining the pH value of aqueous solutions, the reciprocal influence of the ions must not be ignored. A...

The change in the dissociation of the acid with the temperature is so slight that it is not recorded in the pH measurement. On the other hand, the pH value of basic solutions is quite strongly temperature dependent. This is because in basic solutions the hydrogen ion activity is determined by the temperaturedependent ionic product, i.e. the auto-dissociation of water. The pH value of basic solutions generally decreases noticeably with increasing temperature (Fig. 3). pH value and temperature reading Comparing pH values without simultaneously stating the measuring temperatures is virtually...