pH and concentration: what’s the link?

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pH measures the concentration of hydrogen ions in a solution, with high pH being basic and low pH being acidic. pH and concentration are logarithmically related, allowing for easy calculations and predictions. Both are calculated similarly and affect the properties of a solution.

Perhaps the most important connection between pH and concentration is that pH is by its very nature a measure of the concentration of hydrogen ions in a given solution. Compounds with high pH values ​​are basic or alkaline, while those with lower values ​​are acidic. Readings range between zero and fourteen, with the average, seven, being pH neutral. The properties of acids and bases are determined by both the pH and the concentration of acid and base molecules in a solution. As such, the two concepts necessarily go hand in hand. It is difficult to talk about the pH of a given solution without some understanding of the concentration of the elements it contains, and knowing the concentration breakdown of some compound necessarily sheds light on its pH. Chemists and researchers typically calculate the two together.

Understanding pH in general
In general, pH is a measure of the concentration of hydrogen ions in a given solution. It has been widely suggested that the letters ‘p’ and ‘h’ stand for ‘hydrogen power’, although this is not firmly established in the scientific community. What is established, however, is the universal importance of pH; as a measure it is used in all kinds of chemical and mathematical applications and is important for a wide variety of processes, from food production to drug creation.

On a logarithmic scale
All solutions have a specific pH and are made with a solvent, usually water, and a solute, which dissolves easily in the chosen solvent. Using a logarithmic scale for pH helps keep the scale small while retaining the valuable information that the pH scale represents. One connection between pH and hydrogen ion concentration is that together they allow for the use of a logarithmic scale. The lower the pH, the more concentrated the hydrogen ions are, because pH measures the negative log of hydrogen ion concentration, meaning that 0.1 ion concentration is one on the pH scale and 0.001 is three.

Another way to think of this is that pH and concentration become linearly related by a factor of ten, and pH changes by a factor of one as the hydrogen ion concentration changes by a factor of ten. The normal relationship is said to be exponential, and this connection helps avoid tedious equations involving higher levels of mathematics. This automatically changes the curved relationship to a linear relationship where simple math applies. The straight line can make predictions, relationships between different concentrations, and calculations easy to see.

Calculation similarities
Another connection between pH and concentration is that both are calculated similarly. Solution concentration measures the amount of a certain atom or molecule present relative to the entire solution. pH is a special measure of concentration that looks at how many hydrogen ions are in a solution compared to everything else. Most other concentration calculations do not use the pH scale. Many use a unit called molarity, which is the amount of atoms or molecules available per liter of solvent.

How does it change the gradients
Together, pH and concentration bring about predictable changes to the properties of a given acidic or basic solution. This can be demonstrated by heating to boiling both a solvent dissolved in a solute, such as salt water, and a pure solvent. The temperature at which a solution begins to boil will be different, so the liquid-to-gas transformation properties are changed by increasing the solute concentration. Similarly, it is possible to increase the boiling point or decrease the freezing point of a solution. For example, adding a small amount of bicarbonate salt does this to water by increasing the base salt concentration and raising the pH number.




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