Water as a solvent & Water “quality”

Water Quality topics Water-the universal solvent Dissolved Oxygen Turbidity Acid/base Nitrates Phosphates

1) The amazing “polar” water molecule

1) Water is polar – has a charge Water is neutral But because the O atom is larger than the H atoms – electrons spend more of their time nearer the oxygen This gives water a slight overall charge called polarity + -

1) Being polar causes weak “hydrogen Bonding” Polarity allows bonding Hydrogen bonds are very weak 1/20th as strong as covalent bonds. They last for fractions of a second Continuously break and reform Polarity really does allow bonding They are hydrogen bonds and they are very weak They last for fractions of a second Continuously break and reform

1) Hydrogen bonding

1) Water has “surface tension” due to waters stickiness (hydrogen bonding)

1) Water – being polar cannot dissolve things well unless they have charges like it has. Does oil dissolve in water? Does gasoline dissolve in water? Does oil dissolve in gasoline? Polar dissolves polar (like dissolves like) Gasoline and Oil do not have “polar” ends to stick to the water molecules, so they can’t carry them around well. NO NO YES

2) Non–polar covalents can dissolve,… but not well… important example OXYGEN – all life needs it! Oxygen gas: O2(meaning two O bonded) It is THIS oxygen fish need, NOT the oxygen from the H2O!!! (test question!!) O2 is NOT polar, so very little will dissolve A constant “tug of war” means that for split seconds there are charges, just enough for water to cling on to a few of the gas molecules … but not much.

2) Things that effect how much oxygen is dissolved in the water Wind and water movement More water movement = more O2 gets in Amount of things living in the water Plants provide O2, Animals use it up. Temperature Cold water can dissolve more oxygen than hot water, just like your soda with carbonation this is opposite than solids dissolving.

2)Comparative solubilities in 100ml of water at room temp: 100ml of water can dissolve over 200g of sugar!!! (hot dissolves MORE) 100ml of water can dissolve over 50g of salt (NaCl)! (heat dissolves MORE) 100ml of water can dissolve only 0.00091g of Oxygen gas! (Heat dissovles LESS) To say again: all living things on this planet need oxygen gas! (NOT the O from H2O)…. To say the least… Oxygen is NOT abundant in water…

3) Turbidity: Secchi disk: Turbidity is a measure of the “cloudiness” of water. It is measured by a “Secchi disk” a white and black disk and you record the depth it disappears.

3) Things that do and do not influence turbidity Things that DON’T influence turbidity, these things are “invisible” when dissolved. - Salt, Sugar or any dissolved stuff! Things that DO – things that are “suspended” - Dirt stirred up - Fish waste (any waste) - Tiny plants (algae/plankton!!!!!)

Water is “NEUTRAL”,which only means amount of H = amount of OH (phet demo)

4) The pH Scale Ranges from 0 – 14 As the scale the H+ 0  6 (Acidic) 7 (Neutral) 8  14 (Basic) As the scale the H+ Base = higher concentration of OH- (NaOH) Acid = higher concentration of H+ (HCl)

4) 2 ways of becoming “acidic” Acidic is when the balance is tipped to the H’s side. How might we do this? Dissolve something with H+’s in it Or, put something in that will “take out” the OH-!!!!

4) 2 ways of becoming “basic” Basic is when the balance is tipped to the OH’s side. How might we do this? Dissolve something with OH-’s in it Or, put something in that will “take out” the H+!!!! (negative IONS love to take out H+ , like CO32- or HCO31-)

5) NUTRIENTS required by all livings things : nutrients = fertilizers Nitrogen and Phosphorous

5) Nitrogen Nitrogen in nature exist as: a) Nitrogen gas (N2) = completely harmless, very abundant AND USELESS to most living things b) Nitrate (NO31-) = Poisonous to animals but very good for Plants! c) Nitrite (NO21-) = EXTREMELY poisonous to animals, and useless to plants, but bacteria convert it to Nitrate, then plants can use it. d) Ammonium (NH4) and Ammonia (NH3) = fish waste. Ammonia is toxic to fish so in aquariums we keep pH ….

6) Phosphates – another fertilizer! PO43- is a well used ion. is the back bone of DNA & RNA for all living things ATP (Adenosine tri PHOSPHATE) is the energy carrying molecule of the cell in all living things Phosphate is the most LIMITING of all nutrients in the aquatic environment (normally) Meaning – life in water is limited (in general) by the availability of Phosphate! Or, there are other nutrients that are not ever used up because all the Phosphate is already used up

6) Phosphates: natural cycle Phosphates are so limiting that the best source of them is 1) dead decaying material it had DNA with PHOSPHATE!!! 2) Poop from animals… we normally eat more phosphate than we need..

6) Lucky for the plant life! X2 Not only is waste full of phosphates… Phosphates are common in soaps!!!

Soap molecules and how they work Soap molecules have half that bonds to oils, half that bonds with water… Provides a “place for water to grab hold of!

Soaps molecules have 2 parts: water connecting and oil connecting

Now… some things interfere with soaps (hard vs soft water) (We will explore hard vs soft water in greater detail soon but for now…we’ll keep it simple) HARD water has a lot of metal ions dissolved, Calcium ions , Magnesium ions, etc These cause soap to not work SOFT water does not have metals dissolved soaps work really well in soft water

Phosphates PHOSPHATE Phosphate is added to soaps to capture the Calcium and Magnesium that might be there. (Calcium ions will interfere with the soap, but Calcium phosphate is a harmless compound that does not interfere!) So, if you want soaps to work in hard water areas…. You add phosphates (look at ingredients of your dish soaps!) CALCIUM PHOSPHATE Ca2+

So, phosphates good right? Not so fast….

New word “eutrophication”

Phosphate summary: Naturally, phosphates are pretty limited. They are recycled in the environment by decomposition of living things If you ADD phosphates, you increase plant life A LOT!!! (this is not always a good thing, actually it’s kind of bad most of the time Soaps are an addition, non natural source of Phosphate that we put in the environment. Adding phosphate to water will cause “Eutrophication” Algae & plants to grow a lot Water will be come more turbid If too much light is blocked out, or at night with no sun, algae and plants help use up all the oxygen, causing a lot of problems