chemistry question

Question

1.Measure 10 cm3 of ethyl ethanoate into an insulated 50 cm3 breaker. Record its temperature.
2.Add to this 10 cm3 of trichloromethane and mix well. Record the highest temperature of the liquid.
using either one liquid in excess. Form the temperature change estimate the strength of hydrogen bond formed between molecules of ethyl ethanoate and trichloromethane

Explain why it does not matter which liquid is used in excess?

Answer 1

The O atom in C=O group of ethyl ethanoate molecule (CH3COOCH2CH3) forms hydrogen bond with H atom in trichloromethane molecule (CHCl3).

Each O atom can form 2 hydrogen bonds (because it has 2 lone pairs), and each H atom can form 1 hydrogen bond (use the region opposite to the covalent bond because this region is rather bare of electron cloud).

Case 1 : Ethyl ethanoate is in excess
Obviously, it would be assumed that all CHCl3 form hydrogen bonds. Since each CHCl3 molecule can form 1 hydrogen bond, Number of moles of hydrogen bonds = Number of moles of CHCl3 molecules.

Case 2 : Trichloromethane is in excess
It would be assumed that all CH3COOCH2CH3 molecule form hydrogen bonds. Since each CH3COOCH2CH3 molecule, Number of moles of hydrogen bonds = 2 X Number of moles of CH3COOCH2CH3 molecules.