Laboratory Preparation of Hydrogen Gas

Laboratory Preparation of Hydrogen Gas

In the laboratory method, hydrogen gas is prepared by reaction of Zinc granules with dil. Sulphuric Acid (H2SO4) or dil hydrochloric acid (HCl)
Zn   +    dil H2SO4 ­­­­­­­­­­­­­­ ———> ZnSO4   +    H2  
Zn   +    dil HCl—­­­­­­­­­­­­­­—->  ZnCl2   +    H2  
Hydrogen can also be produced by the reaction of zinc metal with dil aqueous alkali. 
Zn   +    2NaOH ­­­­­­­­­­­­­­  —–—-> Na2ZnO2   +    H2  

The procedure of Laboratory Preparation of Hydrogen Gas

To prepare Hydrogen gas in laboratory granulated zinc is taken in a round bottom flask/conical flask and diluted acidic solution is poured with the help of thistle funnel. Zinc metal reacts with acid and produces hydrogen gas. The produce hydrogen gas displaces the water by forming bubbles at other end and collected into an inverted jar by downward displacement of water.

Important Point To Be Noted:-

  1. Granulated Zinc is used in this method because it provides the more surface area for the reaction and also contains copper as an impurity which acts as a catalyst in the reaction
  2. Pure Zinc is not used for the preparation of H2 gas because pure zinc is nonporous and not provide a sufficient surface area, hence the rate of reaction of pure Zinc with dil. H2SO4 is relatively slow,
  3. Conc. H2SO4 is also not used because it will produce Sulphur dioxide (SO2) gas instead of H2.
  4. Also the on increasing concentration the rate of reaction may increases too rapidly which can cause a risk of over pressurization and explosion. Rapid production of hydrogen gas bubbles could splash the concentration acid onto the chemist working nearby or sensitive equipment. Hence safety always a concern while working in the laboratory dealing with chemicals and their reaction

Why Nitric acid (HNO3) is not used in the laboratory preparation of Hydrogen (H2) gas
Nitric acid (HNO3) is the strong oxidizing agent, hence it converts the hydrogen gas in water by oxidation. Whereas dilute HCl and dilute H2SO4 are not able to oxidize the Hydrogen gas into water, Therefore dil Hydrochloric acid and dil Sulphuric acid preferred over Nitric acid for the preparation of hydrogen gas in the laboratory

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Precaution When Preparing Hydrogen Gas

While handling hydrogen gas one should be very careful because hydrogen is colorless, orderless, and flammable gas with a high flammable range of 4 % to 75 % in the presence of air.
Hydrogen (H2) is a colorless, odorless, flammable gas that is compressed to high pressure. Even High-pressure leaks can ignite spontaneously and this becomes more hazardous as Hydrogen burn with a colorless flame. These Safety precautions that should be taken when using Hydrogen are deliberated as below.

Safety Precautions for Hydrogen Handling

1.    A person working with hydrogen gas should be first train about its risk and behaviour. Therefore he can understand the importance of safety precautions to taken while handling Hydrogen gas.
2.    MSDS (Material Safety Data Sheets) of Hydrogen with user manual must be available at designated place so anyone can access it.
3.     Safe Work Practice should be follow meticulously.
4.     The initial few bubbles of H2 gas contain air mixed and should not be collected because air mixed with hydrogen may cause an explosive mixture.
5.    Hydrogen gas is flammable, hence a flame should not bring near it.
6.    Always wear proper Personnel Protective Equipment(PPE) such as Safety Google, Mask, Safety gloves etc. 

Safety Precautions for Hydrogen Gas Cylinder

1. Always Select and use the truthful and adequate regulator connector for fitting. Incorrect installed connector can cause hazard.
2. Before fitting the regulator must check and ensure that the Compressed Gas Association (CGA) number is accurate.
3.    CGA 350 is the standard connector for Hydrogen gas cylinder
4.    Don’t use the regulator which is already used for other gas.
5.    Never work on a system which is pressurized or over pressurized.
6.    Leak test of the connection should be performed
7.    If a leak is detected, immediately close the cylinder valve.
8.    Before filling gas in the cylinder it should be purge and purging should be completed in safe manner carefully.

          Handling and Storage of Hydrogen GasCylinder

  1. Always stored the cylinder in proper ventilation space.
  2. Hydrogen gas cylinder must be separated from oxidizers by adequate distance (at least 20-21 feet)
  3. The use of delegated gas cabinet is safe for the storage of hydrogen gas cylinder.
  4. The temperature of storage area should be high. Gas cylinder should be store where temperature is below 500C, it should not be exceed 520C (125° F)
  5. When a cylinder is not in use, properly closed the valve.
  6. If racks are used for storage then adjust the racks in such way that cylinders are secured tightly

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