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level: 2.2 Water

Questions and Answers List

level questions: 2.2 Water

QuestionAnswer
Why are the electrons in H2O not shared equally?because oxygen has a higher electronegativity = attracts the electrons more strongly electrons orbit closer to the oxygen atom = polarity =permanent dipole
why is water polar?because of the slight charge difference across the different poles oxygen is slightly negative hydrogen atoms are slightly positive
What does the charge difference allow water to do?form weak polar associations with other polar molecules slightly negative attracts the slightly positive poles of other molecules vice versa
When does a hydrogen bond form?when the slightly positive hydrogen from H2O is attracted to a slightly negative F, O, N atom of another molecule
Why are hydrogen bonds stronger than other polar associations?because of the high electronegativity of F, O and N
How does water bond with other water molecules?between a + hydrogen and a - oxygen of two molecules
What gives water its special properties?the intermolecular bonding between water molecules
Why can water absorb so much heat before changing state?because of extensive hydrogen bonding between water molecules H-bonds need to be broken = needs heat energy
What are the 3 properties of water?thermal properties - water can absorb a lot of heat before changing state because breaking the hydrogen bonds is needed cohesive / adhesive properties - water sticks to other water molecules (cohesion) and charged substances (adhesion) Solvent properties - water dissolves polar and ionic substances = competing polar associations to draw materials apart
Why is water a good place for living organisms?temperature changes slowly = maintenance of constant conditions
Comparing Methane (CH4) with waterH20 weight = 18 dalton CH4 weight = 16 dalton both have tetrahedral orbital forms but water is bent because of unbonded electron pairs
What is sweating?evaporation of water to cool down
How does sweating work? (4)change of water from liquid = vapour needs energy energy comes from the skin's surface when its hot when water evaporates skin is cooled because water has a high SHC = absorbs a lot of thermal energy before evaporating water - highly effective coolant
What are the cohesive properties of water?same molecules stick together forms hydrogen bonds w other water molecules
What are the adhesive properties of water?different molecules stick together by forming intermolecular associations with polar and charged molecules
How does the cohesive properties explain surface tension?hydrogen bonding between water molecules helps the liquid to resist low levels of external force makes the water dense enough for small organisms to move along its surface
How does the adhesive properties explain the capillary action?attraction to charged or polar surfaces makes water to flow against gravity = capillary action needed for water to be transported up plant stems by transpiration
Why can water dissolve so many substances?can dissolve any substance that has charged particles (ions) or electronegative atoms (polarity) because the polar attraction of a large amount of water molecules = weaken intramolecular forces (ionic) = disassociation
How does hydration occur?slightly charged regions of the hydrogen atoms and the oxygen atoms surround atoms with an opposing charge = forms dispersive hydration shells
what does hydrophilic mean?substances that freely associate and readily dissolve in water all polar molecules and ions
What does hydrophobic mean?substances that don't dfeely associate or dissolve in water large non polar molecules (fats and oils)
What are water soluble substances that travel in our body?Sodium chloride (NaCl): ionic transported in blood Oxygen: small amounts are soluble in water transported in haemoglobin in red blood cells Glucose: hydroxyl groups (-OH) associates with water so it travels in the blood Amino Acids: transported in an ionized state (either amine or carboxyl group is charged)
What are water insoluble substances that travel in our body?lipids (fats and cholesterol): non polar and hydrophobic so it does not dissolve in water form complexes with proteins (lipoproteins) = to go through bloodstream hydrophilic parts of proteins, cholesterol and phospholipids shield internal hydrophobic parts