Exercise 14 Micro Lab: Hand Washing

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1

Transient microorganisms

Temporary microorganisms removed before you begin a laboratory session as they may contaminate your cultures

2

Resident microorganisms

Long term flora that generally inhabit hair follicles and sebaceous glands of your skin and remain after thoroughly washing, scrubbing, and disinfecting your hands

3

Detergent

Any cleansing solution, including soap that can be used to remove bacteria embedded in fats and oils

4

Saponification

Process whereby a soap is formed when fats are heated in the presence of a base such as sodium hydroxide. The sodium salt (Na + RCOO-) of the acid (RCOO-) is the "soap."

5

Why don't we just use water to wash our hands?

While water can remove dirt, it is ineffective in eliminating bacteria suspended in fats, hydrocarbon chains, and other water-insoluble substances.

6

How does soap clean?

Each soap molecule has a long hydrocarbon chain (R) attached to a negatively charged carboxylate ion (COO-) and its associated sodium (Na+) ion.

In greasy, bacteria laden water, the hydrocarbon end of the soap molecule is soluble in oils and the carboxylate end is soluble in water. A chemical link forms between oil and water as the oily ends of the molecules dissolve together. Greasy oil is combined with water and can be carried away in the liquid.

7

Why is soap not an effective cleansing agent when used with hard water?

When soap is used with hard water, magnesium and calcium salts react with soapy oil droplets forming a lighter than water scum that adheres with grease and bacteria to whatever is being washed.

8

Hard water

water containing mineral salts