PREPARATION & COLLECTION OF NON-METAL COMPOUNDS UNLESS YOU TRY TO DO SOMETHING BEYOND WHAT YOU HAVE ALREADY MASTERED, YOU WILL NEVER GROW. RALPH WALSO EMERSON Ch19. J.C. Rowe Windsor University School of Medicine

 Downward displacement of water  Upward delivery  Downward delivery  Collecting 5 important gases (table) Collection of gases

Downward displacement of water  Downward displacement of water Suitable for collecting gases which are insoluble in water. e.g. hydrogen, oxygen, carbon dioxide.  Not suitable for hydrogen chloride gas and ammonia gas which are very soluble in water

Collection of a gas by the displacement of water

Upward delivery  A gas which is less dense than air can be collected by upwards delivery.  Ex: ammonia & hydrogen  A gas jar (inverted) is connected by a tube to the flask which is giving off the gas

Downward delivery  A gas which is more dense than air can be collected by downward delivery.  Ex: carbon dioxide, chlorine, hydrogen chloride & sulfur dioxide.  A gas jar (upward) is connected by a tube to the flask which is giving off the gas.

Downward vs. Upward collections  Downward delivery :  Gas jar is upward  Gas is more dense than air.  Upward delivery:  Gas jar is inverted (downward)  Gas is less dense than air.

 You need to know how to collect gases produced in reactions by upward & downward delivery, over water using a gas syringe.  You need to be able to explain the method of collection if you are given information about the density & solubility of the gas concerned.

Collecting 5 important gases HydrogenOxygenCarbon dioxide AmmoniaChlorine less dense than air? yes Upward delivery yes denser than air? slightlyyes Downward delivery yes Solubility in water? very lowlow very highmoderate over wateryes

 Ammonia, NH3  Carbon dioxide, CO2  Chlorine, Cl2  Hydrogen, H2  Nitrogen, NO2  Oxygen, O2  Sulphur dioxide, SO2 Laboratory preparation of gases

Ammonia, NH 3  Ammonia gas can be produced in laboratory by heating an ammonium salt (ammonium chloride) with a strong alkali (sodium hydroxide). NH 4 Cl (s) + NaOH (aq) ……. NH 3 (g) + NaCl (aq) + H 2 O (l)  Identification of gas Ammonia turns damp red litmus blue; & in the presence of HCl gas white fumes of ammonium chloride are formed.

Carbon dioxide, CO 2  Reacting any carbonate with any acid forms carbon dioxide; For example calcium carbonate & hydrochloric acid : CaCO 3 + 2HCl ……….. CaCl 2 + CO 2 + H 2 O  Identification of gas Carbon dioxide turns lime water “milky”

Chlorine, Cl 2  Chlorine is formed by oxidation of concentrated hydrochloric acid using either manganese dioxide or potassium permanganate as the oxidising agent. MnO 2 + 4HCl …… MnCl 2 + Cl 2 + H 2 0 2KMnO HCl ……. 2KCl + 5Cl 2 +2MnCl H 2 O  Identification of the gas. Chlorine is a pale green gas, which turns moist blue litmus paper red & then bleaches it.

Hydrogen, H 2  Any reactive metal (a meta above hydrogen in the reactivity series) will displace hydrogen from a dilute acid except for nitric acid.  Zn (s)+ HCl (aq) …………. ZnCl 2 (aq) + H 2 (g)  Identification of the gas. Hydrogen gives a “popping” sound when mixed with oxygen & ignited.

Nitrogen dioxide, NO 2  Nitrogen dioxide is formed during the decom- position of metal nitrates on heating: 2Pb(NO 3 ) 2 (s) …… 2PbO (s)+ 4NO2 (g) + O2 (g)  Sodium nitrate & potassium nitrate are exceptions as they produce the corresponding nitrite & oxygen gas instead. 2NaNO 3 (s) ………. 2NaNO 2 (s)+ O 2 (g)  Identification of the gas. Nitrogen dioxide is a brown gas, which turns moist blue litmus red but does not bleach it.

Oxygen, O 2  Oxygen is produced by the decomposition of hydrogen peroxide (H 2 O 2 ). Hydrogen peroxide naturally decomposes slowly to form oxygen & water on exposure to light. 2 H 2 O 2 (l) ……….. 2 H 2 O (l) + O 2 (g)  Identification of gas. Oxygen relights a glowing splint.

Sulphur dioxide, SO 2  Sulphur dioxide is formed by gently heating a sulphite salt or hydrogen sulphite with dilute hydrochloric acid or sulphuric acid: Na 2 SO 3 (s) + 2HCl (aq) ……. 2NaCl (aq) + SO 2 (g) + H 2 O (l) Na 2 SO 3 + H 2 SO 4 (aq) ……. Na 2 SO 4 (aq) + SO2 (g) + H2O (l)  Identification of gas. When sulphur dioxide is bubbled through acidified potassium dichromate, the color of the solution changes from orange to green.

A natural law regulates the advance of science. Where only observation can be made, the growth of knowledge creeps; where laboratory experiments can be carried on, knowledge leaps forward. Michael Faraday