Ammonia Flashcards
Joseph priestly??
prepared ammonia by heating slaked lime. he called it alkaline air.
Claude Berthelot??
studied chemical properties of the gas
Davy??
established basic composition
lab prep of ammonia (using ammonium salts)
ammonium salt (NH4Cl) with an alkali (Ca(OH)2) , releasing CaCl2, H20 and NH3.
why is NH4NO3 not used in lab prep
explosive and decomposes
how and why is ammonia collected
downward displacement of air
1. lighter than air
2. highly soluble in water
why is more weight of alkali used in prep using ammonium salts
to counteract the loss by sublimation of NH4Cl on heating in solid state
why is Ca(OH)2 used in lab prep
cheap and not deliquescent
why is flask kept inclined in lab prep
so that water vapour may not trickle down and crack the hot flask
drying agent used for ammonia
quicklime
V.D of ammonia
8.5
lab prep of ammonia(metal nitrides)
Mg3N2 with warm water, releasing Mg(OH)2 and NH3
precaution of lab prep using metal nitrides
thistle funnel should dip below level of water
why is lab prep using metal nitride rarely used?
nitrides are expensive
what is the process of manufacture of ammonia called?
Haber’s process
Haber’s process
Nitrogen and hydrogen combine in a ratio of 1:3. 2 vols of ammonia is released.
conditions of haber’s process
reversible, exothermic(22,400 cals), decrease in volume
temp: 450-500 degrees
pressure: 200-900 atmos.
catalyst: Fe/Mo
precaution in haber’s process
CO, CO2, H2S poisons the catalyst, so mixture must be free of them
how is ammonia in haber’s process condensed
mixture of NH3, and residual nitrogen and hydrogen is allowed to expand suddenly under high pressure, through a small nozzle into a region of low pressure.
how is nitrogen of haber’s process obtained?
fractional distillation of air
Le Chatelier’s principle
if a reaction is exothermic, it is favoured by lowering the temperature
methods of seperation of ammonia from uncombined nitrogen and hydrogen in haber’s process
- liquefaction- it condenses at -33 degrees, at 8 atmos. p
- dissolving in water- 1 vol. of water dissolves 702 vols. of ammonia, at 20 degrees and 1 atmos. p
physical properties of ammonia
colourless, strong pungent odour, slight alkaline taste
non poisonous, affects respiratory system
freezing point and boiling point of ammonia
freezes: -77.7 degrees
boils: -33.5 degrees
chemical properties of ammonia
neither combustible, nor a supporter of combustion
burns in oxygen and undergoes catalytic oxidation
when is ammonia neutral to dry litmus
perfectly dry ammonia OR ammonia in liquefied form
what is liquor ammonia
an aqueous solution of ammonia in water. it is prepared by dissolving ammonia gas in water using funnel arrangement
why is ammonia basic?
aqueous solution of ammonia is alkaline and acts as a weak base, since it undergoes partial dissociation in aq. soln. to give hydroxyl ions in low concentration
what happens when excess ammonia is passed through aqueous salt solutions
it precipitates hydroxides of metals from the solution of their salts
why is ammonium hydroxide used in qualitative analysis for identifying positive cations
it reacts with metallic salt solutions to give insoluble precipitates of respective metallic hydroxides. precipitates vary in colour and solubility in excess NH4OH
reducing nature of ammonia
reduces metallic oxides and chlorine
what happens when ammonia reacts with excess chlorine
HCl is formed, along with explosive yellow liquid Nitrogen Trichloride
how to prepare nitrogen from unstable ammonium nitrite
first prepare NH4NO2 by mixing NH4Cl with NaNO2. The ammonium nitrite decomposes into water and nitrogen
nessler’s reagent
potassium mercuric iodide (turns pale brown in ammonia; brown precipitate is formed in excess)
industrial uses of ammonia
source of hydrogen and nitric acid, explosives, urea, dyes and drugs, baking soda, washing soda, artificial silk, fertilizers
uses of liquor ammonia
- emulsifies and dissolves fats, grease, removes oil stains
- cleans windows and porcelain
uses of liquid ammonia
used as refrigerant, since
1. highly volatile and high latent heat of evaporation
2. easily liquefies under pressure, at low temperatures
therefore, when liquid ammonia evaporates, it absorbs a lot of heat from the surroundings and reduces the temperature
