Final answer:
Striking back in a Bunsen burner results in a green flame and loud noises due to ignition within the burner and presence of metal ions or impurities. It indicates incomplete combustion, which can happen with an inadequate oxygen supply.
Step-by-step explanation:
When a Bunsen burner using methane as fuel has its air hole fully opened, striking back can occur, noted by the appearance of a green flame and the production of loud noises. This happens due to the gas-air mixture igniting within the burner tube rather than at the nozzle, which creates a loud humming or whistling as the mixture burns at a higher pressure.
The green color of the flame could be due to the presence of specific metal ions or impurities in the mixture that emit green light when they are heated. It is also possible that the striking back causes a reduction in temperature on the burner, leading to incomplete combustion and the formation of diatomic carbon (C2), which emits a greenish glow.
Complete combustion typically produces a clean, blue flame and occurs when methane reacts with an adequate supply of oxygen, forming carbon dioxide and water. Incomplete combustion can result in a sooty, luminous flame and is a result of insufficient oxygen, leading to the production of carbon monoxide and water instead of carbon dioxide.