1.7 Water Flashcards
What elements is water made from?
- Hydrogen + oxygen.
How do one atom of oxygen and two atoms of hydrogen combine?
- Sharing electrons in a covalent bond.
What is a covalent bond?
- Relatively strong chemical link between two atoms in which e- are shared between them.
What type of molecule is water?
- A polar molecule.
What is a polar molecule?
- Molecule that contains weak positive charges (δ+) and weak negative charges (δ-).
How is water a polar molecule?
- Unequal distribution of electrical charge.
- Large nucleus of oxygen draws e- from smaller hydrogen nuclei.
- Oxygen is slightly negative.
- Hydrogen is slightly positive.
What type of bonds does water have?
- Hydrogen bonds.
What are hydrogen bonds?
- Relatively weak link between two atoms in which a weakly negative atom attracts another weakly positive atom.
What do hydrogen bonds cause?
- Cohesion.
What is cohesion?
- Force by which hydrogen bonds hold polar molecules together, or to a charged surface.
What substances can water act as a solvent for due to its polar nature?
- Ionic substances.
- Carbon-containing organic molecules w ionised groups.
What are examples of ionic substances that dissolve in water?
- Sodium chloride (Na+, Cl-).
- All ions become surrounded by shell of oriented water molecules.
What are examples of carbon-containing organic molecules w ionised groups that dissolve inwater?
- Carboxyl group (-COO -) and ammino group (-NH3 +).
- Soluble organic molecules such as sugars, dissolve in water due to the formation of hydrogen bonds w their slightly charged hydroxyl groups (-OH -).
Why are dissolved substances more reactive than when in the undissolved solid state?
- When dissolved solute molecules are free to move around in the water (the solvent) so more chemically reactive.
What does hydrophilic mean?
- Refers to substances that will mix w water.
What does hydrophobic mean?
- Refers to substances that will not mix w water.
Does water have a high or low specific heat capacity?
- High.
Why does water have a high specific heat capacity?
- Heat is needed to break the hydrogen bonds between water molecules.
What is the benefit of water having a high specific heat capacity?
- Temp of aquatic environment change slower than air temp.
- More stable temp than terrestrial environments.
Compared with other liquids what does water have strong properties of?
- Cohesion and adhesion.
What is cohesion and what is it caused by?
- Force by which charged molecules stick together.
- Hydrogen bonds break and reform w other surrounding water molecules.
What does cohesion cause in water?
- Surface tension.
How is surface tension caused?
- Outermost molecules of water form hydrogen bonds w water molecules below them.
- High surface tension.
Why is water incompressible?
- Much less distance between molecules.
- Intermolecular force of hydrogen bonds aid this.
At what temp does water reach its maximum density?
- 4°C.
Why does ice float on water and how does this help aquatic life survive freezing temps??
- Ice less dense than cold water around it.
- Floating layer insulates water below.
- Means that lakes rarely freeze solid, meaning that aquatic life can survive freezing temps.
How do the molecular structures of water and ice differ?
- Water - Arranged more irregularly than ice + closer together but w almost as many hydrogen bonds as ice.
- Ice - Regular tetrahedron + spaced more widely apart.
