Question

(1) a. Typical household cleaners (ex.drain cleaner) has a higher pH than soup. Why is that?

b. One interesting note is that bleach has a lower measured pH than given based on its color. Why is that? (Hint: What is bleached used for?)

Answer 1

1)

The cleaning chemical”s pH value can have a direct effect on cleaning effectiveness. Each detergent formulation has maximum effectiveness at a specific pH value. For example, an acid solution is needed to remove metal oxide, such as rust, and an alkaline solution may be needed to clean a heavily soiled, solution-dyed olefin carpet in a rental unit.

A close-to-neutral pH is needed to clean wool, silk or stain resistant fibers.

Most cleaning chemicals are alkaline in nature, since hydrolysis (saponification), chelation and dispersion of soils typically occurs most effectively at alkaline pH levels.

Other factors, such as time, agitation and temperature play essential roles in the cleaning process. Although more detergency is achieved with longer times, more agitation and higher temperatures, this should be balanced against the damage these higher factors will do to the carpet or fiber.

The higher the pH level, the more corrosive the cleaner and the more damage it will do to pH sensitive fibers and dyes; hot temperatures employed in steam cleaning, together with higher alkalinity, makes it even worse.

Alkaline cleaners work best when soil can be hydrolyzed, such as kitchen grease containing natural oils and fats, natural greases, body oils and some proteins.

How fast can an alkaline cleaner damage a fiber? For dyes, the damage can be instantaneous and generally not reversible; the same is true with stain resistant fibers. With indicator-type dyes, the change may be reversible; for the fibers themselves, such as protein or silk, the damage will be slower, but corrective action must be taken immediately.

Oriental hand-knotted wool carpet undergoes harsh treatment during the washing and finishing in the manufacturing process, where luster is attained by use of caustic soda and bleach in the presence of a mineral acid. So there is no room for error as the carpet or rug may have gained the sheen, but as a result has become very fragile.

2)

Considering example of Chlorine here.

Chlorine is available as compressed elemental gas, sodium hypochlorite solution (NaOCl) or solid calcium hypochlorite (Ca(OCl)2). All forms of chlorine, when applied to water, form hypochlorous acid (HOCl). Gaseous chlorine acidifies the water and reduces the alkalinity, whereas the liquid and solid forms of chlorine increase the pH and the alkalinity at the application point. The pH of the water will affect the dominating chlorine species such that HOCl dominates at lower pH, while the hypochlorite ion (OCl-) dominates at higher pH. Of the two species, HOCl is the stronger oxidant. Therefore, chlorine is more effective as an oxidant and a disinfectant at lower pH. Both forms, HOCl and OCl-, are referred to as free chlorine.