Briefly describe how a potentiometric pHmeter works. (Hint: Describe how the pH meter measures the amount of H+ or OH- ions in a
sample)
ii. Describe how an organic pH indicator works. (illustrate using chemical equations and
mathematical expressions)
ii. Describe how an organic pH indicator works. (illustrate using chemical equations and
mathematical expressions)
1 answer:
Answer:
Indicators show changes in the pH of a solution
Explanation:
A pH meter is an instrument that measures the hydrogen-ion activity in aqueous solutions, indicating the acidity or alkalinity of the solution expressed as pH .The pH meter measures the difference in electrical potential between a pH electrode and a reference electrode, hence the pH meter is sometimes referred to as a potentiometric pH meter. Potentiometric pH meters measure the voltage between two electrodes and display the result converted into the corresponding pH value. The instrument comprises of a simple electronic amplifier and a pair of electrodes, or alternatively a combination electrode, and some form of display calibrated in pH units. It usually has a glass electrode and a reference electrode, or a combination electrode. The electrodes, or probes, are inserted into the solution to be tested.
Organic indicators are chemical species that change their colour in response to changes in the pH of the solution. This implies that the anionic and protonated forms of the indicator possess different colours. Hence the colour changes in acidic, basic and neutral solutions. The images attached indicate the colour changes in phenolphthalein and methyl orange in acidic and basic media accordingly.
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The organic product formed when 1−hexyne is treated with H₂O, H₂SO₄, and HgSO₄ will be 2-hexanone (structure attached).
This reaction is an example of an oxymercuration reaction of the organic product 1−hexyne.
Oxymercuration is shown in three steps to the right. The nucleophilic double bond attacks the mercury ion, releasing an acetoxy group. The mercury ion's electron pair attacks carbon on the double bond, generating a positive-charged mercuronium ion. Mercury's dxz and 6s orbitals give electrons to the double bond's lowest unoccupied molecular orbitals.
In the second stage, the nucleophilic H₂O attacks the highly modified carbon, freeing its mercury-bonding electrons. Electrons neutralize mercury ions by collapsing. Water molecules have positive-charged oxygen.
In the third stage, the negatively charged acetoxy ion released in the first step attacks the hydrogen of the water group, generating the waste product HOAc. The two electrons in the oxygen-hydrogen link collapse into oxygen, neutralizing its charge and forming alcohol.
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