Non-metals: Hydrogen and Oxygen · 8 min read
Hydrogen: preparation and properties
Listen to this lesson
A calm voice reads the lesson aloud
Tap any word for its meaning, or to have that part explained further.
Introduction to Hydrogen
Hydrogen is the very first element in the periodic table. It is the lightest gas known to man. Think of a balloon filled with hydrogen; it will fly up faster than anything else because it is much lighter than the air around us.
Simply put, it is a basic gas that does not have any smell or color and burns very easily.
Laboratory Preparation of Hydrogen
In the school lab, we get hydrogen by reacting a metal like zinc with a dilute acid like hydrochloric acid (HCl). This is like putting a piece of iron in a strong cleaning liquid and watching bubbles come out.
1. Put some pieces of granulated zinc in a flask.
2. Pour dilute hydrochloric acid through a thistle funnel.
3. The reaction starts and hydrogen gas is released as bubbles.
4. We collect the gas over water because hydrogen does not dissolve in water.
The chemical equation for this reaction is: Zn + 2HCl -> ZnCl2 + H2.
Industrial Production of Hydrogen
In big factories, hydrogen is made using the Bosch process. They pass steam (hot water vapor) over red-hot coke (a form of coal). It is like pouring water on a very hot charcoal fire to get gas.
C + H2O -> CO + H2 (This mixture is called water gas).
Physical Properties of Hydrogen
It is the lightest substance known.
It is not soluble in water (it does not mix with water).
It has no color, no smell, and no taste.
Chemical Properties of Hydrogen
Hydrogen is very friendly with oxygen. If you bring a lighted match near a tube of hydrogen, it burns with a pop sound. This is a standard test for hydrogen in the lab.
When it burns in air, it reacts with oxygen to form water: 2H2 + O2 -> 2H2O.
Hydrogen also acts as a reducing agent. This means it can steal oxygen away from metal oxides. For example, if you pass hydrogen over hot black copper(II) oxide, it turns back to brown copper metal: CuO + H2 -> Cu + H2O.
Worked Example on Gas Calculations
Calculate the volume of hydrogen gas produced at s.t.p. when 6.5g of Zinc reacts with excess HCl. (Zn = 65, Molar volume at s.t.p. = 22.4 dm3).
1. Write the equation: Zn + 2HCl -> ZnCl2 + H2.
2. Find the moles of Zinc: Moles = mass / molar mass = 6.5 / 65 = 0.1 moles.
3. Use the mole ratio: 1 mole of Zn gives 1 mole of H2. So, 0.1 moles of Zn gives 0.1 moles of H2.
4. Convert to volume: Volume = moles x 22.4 = 0.1 x 22.4 = 2.24 dm3.
Key points
- •Hydrogen is the lightest gas and is less dense than air.
- •It is prepared in the lab using zinc and dilute HCl.
- •The Bosch process is the industrial method for making hydrogen.
- •A pop sound is the characteristic test for hydrogen gas.
- •Hydrogen is a powerful reducing agent for metal oxides.