4 original questions from New Regents. The worksheet, answer key, and browser practice are free.

Download worksheet PDFDownload worked answer keyPractice these questions online
Redrawing Carbon Bonds After Hydrogen Addition 4 questions

Redrawing Carbon Bonds After Hydrogen Addition

Base your answers on the information provided and your knowledge of chemistry. Use the 2025 Chemistry Reference Tables as needed.

A simulation models a reaction between ethene and hydrogen. Each circle is an atom and each line is a bond. The separate pair of hydrogen atoms on the left is one H2 molecule. The model contains all the atoms before and after the reaction.

Before, two carbon atoms have a double bond and each carbon is attached to two hydrogen atoms. A separate H–H molecule is below. After, the two carbons have a single bond and each carbon is attached to three hydrogen atoms.
Atom connections before and after the reaction.
Open full-size figure

Question 1

Count the carbon and hydrogen atoms on both sides. Include the separate molecule on the left.

Write your answer and work on the printable worksheet, or answer online.

Question 2

Which change to the carbon bonds is shown in the diagram?

  1. The carbon-carbon bond changes from double to single.
  2. The carbon-carbon bond changes from single to triple.
  3. The two carbons become separate, unbonded atoms.
  4. Each carbon loses one attached hydrogen.

A detector checks the product after the separate H2 molecule has disappeared. It reports that each carbon has three attached hydrogen atoms. A student copies the product with those six hydrogens but keeps a double carbon-carbon bond.

Question 3

Explain why the student’s drawing gives the wrong number of shared electron pairs around each carbon. Describe the correction that keeps all six hydrogens.

Write your answer and work on the printable worksheet, or answer online.

Question 4

In a later trial the detector still reports a separate H₂ molecule as well as some product. Explain why the original before-and-after atom counts would not reveal this incomplete reaction.

Write your answer and work on the printable worksheet, or answer online.

Answer this set online →

2025 Chemistry Reference Tables · Browse Chemistry worksheets