pH & Acidity/Alkalinity

An important quality control indicator is pH, which is important in both raw materials and midstage products. Joe checks the pH of raw materials or product samples daily before sending them off to the next stage. Besides modifying the pH of samples, it is also important that Joe does calibration checks on his pH meters by using standard buffer solutions (which, the pH is known) with a pH usually between 4 and 7. A pH meter is an essential piece of equipment in Joe's lab, and it is used to check the pH. I was so shocked when I heard him say that he uses a pH meter! I couldn't believe that a professional like him actually used equipment similar to what I use in my simple school labs. I guess there are a lot more similarities than I thought there would be.

Sodium hydroxide and hydrochloric acid are also common substances used by Joe to make adjustments to the pH. Therefore, they are known as pH buffers. Of course, NaOH is used to make the sample more basic, and HCl is used to make it more acidic. This is something that I am familiar with, as these are also two common chemicals we use in the lab. These two compounds are used to adjust the pH because they are strong bases and strong acids, and dissociate 100% in water, in order to maximize the amount of pH change. When a strong acid is used, hydronium ions (H3O + (aq)) are formed since the acid donates a proton to water, and the high levels of H3O+ cause the solution to be more acidic. When a strong base is used, many hydroxide ions will be formed in solution, thus raising the pH.

Above is an illustration of sulphuric acid, a strong acid, forming a hydronium ion.

pH is important in the field of quality control, because there are specific, optimal ranges that the pH of specific products have to fall under. It's almost like how an enzyme works (but not quite)! When we were first introduced to the concepts of pH, acid, and base, we learned the approximate pH ranges of products, such as cleaning products (soap, detergent, etc.) having to be basic, and other commercial products like shampoo having to be slightly acidic. Well, this seemingly simple information is actually vital to Joe's field. I also learned that most cleaning products are basic because dirt often has a surface layer of carboxylic acid groups, and when placed in a basic solution (which they are soluble in due to the carboxylic acid's polar nature), they are netrualized to produce a carboxylic acid salt and water (something that I learned in organic chemistry!). Then the dirt is suspended into the water and is removed from the surface being cleaned.

Examples of netrualization of carboxylic acids with a strong base is shown above.