An aqueous solution contains 0.30 M hypochlorous acid. One Liter of this solution could be converted into a buffer by the addition of: (Assume that the volume remains constant as each substance is added.) 0.31 mol KClO 0.30 mol KBr 0.15 mol HCl 0.074 mol Ca(OH)2 0.31 mol HCl

Explanation:

Every buffer system comprises of a weak acid or a base and its salt. The pH of the resultant buffer is calculated by the Henderson-Hassel Bach equation as pH = pKa + log ([Salt]/[Acid]). Thus, a hypochlorous acid buffer should also contain a salt of hypochlorous acid, which among given is potassium hypochlorite (KClO). Potassium perchlorate on the other hand does not function as a buffer, as the counter ion by perchloric acid is not present, preventing common ion effect from arising for the perchlorate anion.

Nitric acid and sodium hydroxide are strong acid and base. Hence, they will not undergo partial ionization required for equilibrium adjustment necessary in a buffer. In a buffer, the partial ionization of the parent acid or base is essential as it is that factor that helps the buffer maintain pH during acid or base addition by simply increasing or decreasing the parent acid/base's ionization depending upon the excess quantity of proton of hydroxyl ions present. Such a reversible dissociation however is not possible in strong acids and bases rendering them useless as buffer components.

Therefore, among the given chemicals, 0.31mol KClO can be added to a liter of 0.3M HClO to afford a buffer.

a mercury barometer is a device that uses the physical properties of mercury in a tube to measure barometric pressure. mercury barometers are used for : -

1. measurement of atmospheric pressure  

2. determining the altitude of a place

3. weather forecasting

4. calibration and checking of aneroid barometers

5. application in fluid mechanics

6. measurement of pressure in aircrafts

7. surface weather analysis

8. preparation of barographs

9. usage in physical sciences like physics, astronomy & chemistry

10. preparation of aircraft altimeters

characteristics of mercury barometer : -

1.used to define and measure atmospheric pressure.

2.on the average at sea level the column of mercury rises to a height of about 760 mm.

3.this quantity is equal to 1 atmosphere.

4.it is also known as standard atmospheric pressure.

5.a barometer in which the weight of a column of mercury in a glass tube with a sealed top is balanced against that of the atmosphere pressing on an exposed cistern of mercury at the base of the mercury column, the height of the column varying with atmospheric pressure.