A sanitation engineer in Portland, Maine sends a water sample to your lab, and wants to know if there are lactose-fermenting microbes in the sample (their presence would indicate contamination with human waste). How might you determine if these microbes are present or not from this mixed-microbe specimen?

See the answer below

Explanation:

The first thing would be to isolate the bacteria in the water sample using appropriate isolation methods. After obtaining a pure culture of each isolate, a lactose broth fermentation test is then used to check for the isolates that are able to ferment lactose.

A sterile lactose broth containing an indicator (preferably, phenol red) is placed in different sterile test tubes and the pure culture of each isolate is aseptically introduced into each test tube. The test tubes are then incubated for 18 to 24 hours at 35 to 37 .

A change in the color of the indicator from red to yellow will give an indication of lactose fermentation by the organisms.

given:

mass of na = 115 g

excess cl2

to determine:

mass of nacl produced

explanation:

given reaction is-

2na(s) + cl2(g) → 2nacl(s)

since cl2 is in excess, na will be the limiting reagent

as per the reaction stoichiometry na: nacl = 1: 1

i.e. moles of na reacted = moles of nacl formed

now, # moles of na = mass of na/atomic mass

                                  = 115 g/23 g.mol-1 = 5 moles

therefore, moles of nacl = 5

molar mass of nacl = 58 g/mol

mass of nacl = 5 moles * 58 g.mol-1 = 290 g

ans: amount of nacl produced = 290 g

that tool would be a compass