Addition of hydrogen
Unsaturated becomes saturated.
A double bond opens
Ethene, C₂H₄, has a double bond between its carbon atoms. Hydrogen gas is passed over it in the presence of a nickel or palladium catalyst.
What kind of hydrocarbon do you expect to form?
What this lesson covers
The idea
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.
A double bond opens
Ethene, C₂H₄, has a double bond between its carbon atoms. Hydrogen gas is passed over it in the presence of a nickel or palladium catalyst.
What kind of hydrocarbon do you expect to form?
- A saturated hydrocarbon
- A hydrocarbon with a triple bond
- A compound with no hydrogen
Ethene takes up hydrogen
Press Next step. A teacher does such reactions in the lab.
Hydrogen adds across the double bond
Two hydrogen atoms add on, and the carbon-carbon double bond becomes a single bond.
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.
Notes
Unsaturated hydrocarbons add hydrogen in the presence of catalysts such as palladium or nickel to give saturated hydrocarbons.
Check yourself
What do unsaturated hydrocarbons add in this reaction?
Which metals are named as catalysts for adding hydrogen?
What kind of hydrocarbon forms when ethene adds hydrogen?
Ethene is C₂H₄ and it adds one molecule of hydrogen, H₂. How many hydrogen atoms does the product have?
Answer: 6
4 + 2 = 6 hydrogen atoms, so the product is C₂H₆, ethane.
- Oxygen. Adding oxygen is oxidation. Unsaturated hydrocarbons add hydrogen in this reaction.
- Water. Removing water is dehydration. Unsaturated hydrocarbons add hydrogen in this reaction.
- Hydrogen — correct. Yes!
- Palladium or nickel — correct. Yes!
- Sodium or iron. The catalysts the book names for adding hydrogen are palladium or nickel.
- Copper or silver. The book names palladium or nickel as the catalysts.
- An unsaturated hydrocarbon with a triple bond. Adding hydrogen removes the double bond. The product has only single bonds between carbon atoms.
- A saturated hydrocarbon, ethane — correct. Yes!
- Another alkene. Ethane, the product, has only single bonds, so it is not an alkene.