Presentation by Andreas Schleicher Tackling the School Absenteeism Crisis 30 ...
Hydrogen bonding
1. Hydrogen Bonding 8.4 Water (Prelim) 8.4.2 The wide distribution and importance of water on Earth is a consequence of its molecular structure and hydrogen bonding
2. Syllabus Points Stage 6 preliminary unit on Water. describe hydrogen bonding between molecules plan and perform an investigation to identify and describe the effect of anti-freeze or salt on the boiling point of water
4. What is a Hydrogen Bond? Hydrogen bonds are the attractive force between the hydrogen attached to an electronegative atom of one molecule and an electronegative atom of a different molecule. Hydrogen (H) needs to be attached to a highly electronegative Oxygen (O), Fluoride (F), Nitrogen (N) atom.
5. Why are O, F & N so attractive?? In each of these molecules note: 1. A hydrogen atom! 2. the hydrogen is attached directly to one of the most electronegative elements, causing the hydrogen to acquire a significant amount of positive charge. 3. Each of the elements to which the hydrogen is attached is not only significantly negative, but also has at least one "active" lone pair. In these interactions, a hydrogen atom is the donor, and the respective electronegative atom is the acceptor of the bond. Electronegativity Values F (4.0) O (3.5) N(3.0)
6. Hydrogen Bonding in Water Water could be considered as the "perfect" hydrogen bonded system. Each Oygen (O) has 2 lone pairs of electrons therefore, 4 Hydrogen bonds (H-bonds) can be formed. Hydrogen-bonding network formed in liquid water is responsible for many of the essential and unique properties of water. Ice forms a crystalline lattice, held together by a multitude of H-bonds
7. Hydrogen Bonding in molecules the hydrogen is partially positive and attracted to the partially negative charge on the nitrogen. Nitrogen has only one lone pair, thus, only one hydrogen bond can be made to each nitrogen.
10. Experiment Plan and perform an investigation to identify and describe the effect of anti-freeze (ethylene glycol) or salt on the boiling point of water. In today’s experiment, we will be concentrating on the effect of ethylene glycol on the boiling point of water.
11. How would you plan this experiment? Plan and perform an investigation to identify and describe the effect of anti-freeze (ethylene glycol) or salt on the boiling point of water. Structure for ethylene glycol.
12. How would you plan this experiment? The boiling point of water is 100°C (high due to hydrogen bonding) So to see the effect of ethylene glycol on water, we can make a 50-50 mixture and test the boiling point to see whether it increases or decreases the b.p.
13. What safety steps need to be taken? Ethylene glycol is harmful when swallowed and should not be breathed in. Appropriate disposal of ethylene glycol is required as it is not environmentally friendly. Other safety steps due to equipment used for prac, goggles, tongs, lab coat, gloves, tie up loose hair.
14. What is your hypothesis? Due to the 2 glycol groups attached on either side of the ethylene glycol, water molecules will create more hydrogen bonding with the glycol groups. This should ultimately increase the b.p. Of the mixture of water and ethylene glycol.
16. What can be concluded? More hydrogen bonding occurred between the water molecule and the ethylene glycol , hence more energy was required to break the bonds and that is why the b.p. F the mixture increased by an average of 4-5°
