Water: Factors Affecting Solubility PDF

WONDERFUL WATER!!! 1 Water: Solutions SOLUTIONS: HOMOGENOUS mixtures of two or more components. SOLUTION components may be liquids, gases or solids. State of State of State of Example...

WONDERFUL WATER!!! 1 Water: Solutions SOLUTIONS: HOMOGENOUS mixtures of two or more components. SOLUTION components may be liquids, gases or solids. State of State of State of Example Solution Solute Solvent Air, natural gas Gas Gas Gas Vodka, antifreeze Liquid Liquid Liquid Brass Solid Solid Solid Carbonated water (soda) Liquid Gas Liquid Seawater, sugar solution Liquid Solid Liquid Hydrogen in platinum Solid Gas Solid 2 Water: Solutions SOLVENT: dissolving medium (and usually major component) in a solution. Other substances are incorporated into or mixed into SOLVENT. SOLUTE: the substance being dissolved (i.e., mixed) in a solution. SOLUTION: a HOMOGENOUS mixture of of ALL solutes AND solvent. In this course, deal with solutions whose SOLVENT is water (surface waters, seawaters and groundwaters are all solutions). AQUEOUS SOLUTION: solution in which solvent is H2O. WATER is a very common solvent. AQUEOUS SOLUTION: solution in which solvent is H2O. 3 Water: Solutions Important to know whether a specific SOLUTE dissolves/mixes with a particular SOLVENT (e.g., water). To predict whether a solute will dissolve (i.e., mix) in water, must consider SOLUTE properties and environmental conditions. SOLUBILITY: Ability of a SOLUTE to dissolve/mix with a given SOLVENT. e.g., Sodium chloride (i.e., NaCl or table salt) is VERY soluble in water. Three major factors affecting SOLUBILITY include: Sodium chloride (i.e., NaCl or table salt) is VERY soluble in water and 1. SOLUTE molecule structure/polarity helps pasta taste great! 2. Temperature 3. Pressure 4 Water: Factors Affecting Solubility Molecule structure/polarity affects SOLUBILITY. Can form solutions when SOLUTE and SOLVENT both POLAR or both NON-POLAR. Since water is POLAR, it dissolves POLAR SOLUTES (e.g., sugars) and solutes made of ions (e.g., salts). NOTE: Salt crystals which dissolve in water are made up of positive metal ions (e.g., sodium, Na+) and negative In dissolving a sodium chloride (NaCl) crystal, water non-metal ions (e.g., chloride, Cl- or carbonate, CO32-). molecules surround the negative chloride ions (Cl-) and the positive sodium ions (Na+) Molecular structure determines molecule POLARITY. Therefore, structure MUST affect SOLUBILITY. Let’s consider some examples. 5 Water: Factors Affecting Solubility Molecule structure/polarity affects SOLUBILITY. Vitamin A: Non-polar (fat soluble) C-H bonds can be considered to be non-polar! Fats and oils are primarily made up of C-H bonds! As we can see from Vitamin A structure below, consists mostly of non-polar C-H bonds. Fat also made largely of non-polar hydrocarbon chains. Vitamin A is soluble in fats but not in polar solvents like water. Only 1 polar O-H bond VITAMIN A 6 Water: Factors Affecting Solubility Molecule structure/polarity affects SOLUBILITY. Several polar O-H bonds Vitamin C: Polar (water soluble) C-H bonds considered non-polar but O-H bonds very polar! As we can see from Vitamin C structure at right, have five polar O-H bonds! Therefore, we can form Vitamin C solution in VITAMIN C water! Fun Fact: Vitamin C is also called ascorbic acid. 7 Water: Factors Affecting Solubility Following substances are ALL soluble in (mix with) water and are all POLAR. ETHANOL, an alcohol METHYLAMINE (note GLUCOSE, a sugar (note polar O-H bond) polar N-H bond) (note polar O-H bonds) POLAR SOLUTES (that dissolve in water) are referred to as “HYDROPHILIC”. HYDROPHILIC MOLECULES are “attracted to water” and dissolve in it. 8 Water: Factors Affecting Solubility Following compounds are insoluble (don’t mix) in water and are for the most part NON-POLAR. OCTANE, important CYCLOPENTANE BENZENE (non-polar component in gasoline (non-polar C-H and C-C C-H and C=C bonds) (non-polar C-H and C-C bonds) bonds) NON-POLAR SOLUTES are referred to as “HYDROPHOBIC” as water prefers to interact with itself than it does with them. HYDROPHOBIC MOLECULES are NOT “attracted to water” and do NOT dissolve/mix in it. 9 Water: Factors Affecting Solubility Things not always obvious though. For example: LARGER NON-POLAR SMALLER NON-POLAR BENZENE PORTION POLAR –COOH PORTION POLAR –COOH BENZOIC ACID ACETIC ACID (i.e., vinegar) NOT SOLUBLE IN WATER (since C-C, SOLUBLE IN WATER C=C, and C-H bonds NON-POLAR Both benzoic acid and acetic acid have the same “carboxylic acid” (-COOH) group, which is POLAR and helps a molecule dissolve in water. However, benzoic acid also has a larger NON-POLAR benzene portion and is therefore not soluble. 10 Water: Factors Affecting Solubility Soaps are made up of FATTY ACID molecules. Fatty acids are composed of: 1. a HYDROPHILIC head (polar -COOH carboxylic acid group) 2. a HYDROPHOBIC tail (non-polar hydrocarbon chain, referred to as a HYDROCARBON) POLAR –COOH NON-POLAR HYDROCARBON TAIL HEAD FATTY ACID: Consists of an acid (-COOH) head and a fat (HYDROCARBON) tail. 11 Water: Factors Affecting Solubility Soaps are made up of FATTY ACIDS. FATTY ACIDS align themselves to: 1. maximize hydrogen bonding between hydrophilic (-COOH) heads and water. 2. maximize interactions between hydrophobic tails (keep all the HYDROCARBON tails together). Form what is known as MICELLES. WATER WATER POLAR –COOH HYDROPHOBIC HEADS INTERACT HYDROCARBON WITH WATER INTERIOR WATER WATER MICELLE MICELLE 12 Water: Factors Affecting Solubility Overall, HYDROPHILIC MOLECULES are molecules whose interactions with water are more favorable than their interactions with non-polar substances such as HYDROCARBONS made up primarily of C-C and C-H bonds. The opposite is true for HYDROPHOBIC MOLECULES. Why? After an oil spill, oil (made up of C-C and C-H bonds) floats on the water and does not mix. Interactions between water and non-polar (HYDROPHOBIC) molecules not as strong as water-water or water-polar solute interactions. On other hand, water interacts as favorably with polar Sadly, aquatic animals are (HYDROPHILIC) molecules as it does with itself. often covered in Thus, structure definitely affects solubility! waterproof oil that attracts the oil from the spill. 13 Water: Factors Affecting Solubility TEMPERATURE: important factor in dissolving solids, liquids & gases in water. Assuming water is your solvent, how do you think solubility of a solid in water is affected by changes in temperature? Will more be able to dissolve/mix in? Or less? 14 Water: Factors Affecting Solubility TEMPERATURE: important factor in dissolving solids, liquids & gases in water. Assuming water is your solvent, how do you think solubility of a solid in water is affected by changes in temperature? Will more be able to dissolve/mix in? Or less? Solubility of solids in water often INCREASES with increasing temperature, However, solubility of some solids in water DECREASES with increasing temperature! e.g., solubility of Na2SO4 (sodium sulfate) and Ce2(SO4)3 (cerium sulfate) in water decreases with increasing temperature. Overall, only way to determine impact of temperature on solubility of a solid is to examine it experimentally! 15 Water: Factors Affecting Solubility Impact of temperature on the solubility of various solids in water can be seen at the right. Predicting temperature effect on solubility is very difficult. Often, solubility of solids in water INCREASES with INCREASING temperature. However, this is NOT always the case. 16 Water: Factors Affecting Solubility Solubility of GASES in water is easier to predict than that of solids. In general, can say that solubility of gases in water DECREASES with INCREASING temperature. Can see this in figure at the right. e.g., less oxygen will dissolve in warm water than cold water. 17 Water: Factors Affecting Solubility MAKE IT REAL!!! In general, solubility/mixing of gases in water DECREASES with INCREASING temperature. Trout need well oxygenated water and live in colder water with higher oxygen concentrations. Carp can handle lower oxygen concentrations and can live in warm ponds. BROOK TROUT in clear stream COMMON CARP in pond 18 Water: Factors Affecting Solubility PRESSURE: Important when dissolving gaseous (i.e., gas) solutes e.g., dissolving oxygen or carbon dioxide in water. PRESSURE (in other words the amount) of a gas above water’s surface determines frequency of collisions between gas and water’s surface PRESSURE (or amount of a gas) above water’s surface directly impacts amount of gas in aqueous solution and how fast gas dissolves in water. As amount of CO2 above our oceans increases due to human activities, amount of CO2 entering oceans also increases! 19 Water: Factors Affecting Solubility PRESSURE: Important when dissolving gaseous (i.e., gas) solutes Increasing PRESSURE or amount of a gas above the water, increases amount of that gas dissolved in water (since have more collisions between gas and water surface). e.g., as amount of CO2 above our oceans increases due to human activities, amount of CO2 entering oceans also increases! As amount of CO2 above our oceans increases due to human activities, amount of CO2 entering oceans also increases! 20 Water: Factors Affecting Solubility As mentioned, increasing PRESSURE or amount of a gas above water increases amount of that gas dissolved in water (since have more collisions between gas and water surface). This scientific fact is behind one of biggest environmental threats currently facing our planet: ACIDIFICATION OF OCEANS! As amount of CO2 above oceans increases, ocean’s pH decreases (i.e., oceans become more acidic). As amount of CO2 above our oceans increases, ocean’s pH decreases (i.e., oceans become more acidic). But what exactly is pH? And how does it affect the ocean’s creatures? 21 Water: The pH Scale pH: pH is a measure of how ACIDIC or BASIC a solution is pH SCALE: a range of pH values that generally goes from 0 to 14. ACIDS: when dissolved/mixed with water, aqueous solution will have a pH < 7. In other words: ACIDIC solution is one with a pH < 7. Examples of acids: hydrochloric acid (HCl) in your stomach, lemon juice, vinegar, etc… 22 Water: The pH Scale pH: pH is a measure of how ACIDIC or BASIC a solution is pH SCALE: a range of pH values that generally goes from 0 to 14. BASES: when dissolved/mixed with water, aqueous solution will have a pH > 7. In other words: BASIC solution is one with a pH > 7 Examples of bases: sodium hydroxide (NaOH) in your drain cleaner, soap, etc… 23 Water: The pH Scale pH: pH is a measure of how ACIDIC or BASIC a solution is pH SCALE: a range of pH values that generally goes from 0 to 14. Water is said to be NEUTRAL. A solution is NEUTRAL if pH = 7. NOTE: In reality, most of the water we encounter does NOT have a pH of 7! 24 Water: The pH Scale What exactly is pH? 25 Water: The pH Scale What exactly is pH? p = -log Therefore, pH = -log[H+], where [H+] is the concentration or amount of H+ e.g., if [H+] increases, pH decreases (acids decrease the pH of an aqueous solution) if [H+] decreases, pH increases (bases increase the pH of an aqueous solution) 26 Water: The pH Scale pH = -log[H+] Since working with a “log” scale: Each time decrease pH by 1 pH unit (e.g., 2 to 1): 10X MORE ACIDIC i.e., Concentration/amount of H+ increased by 10X! Since working with a “log” scale: Each time increase pH by 1 pH unit (e.g., from 8 to 9): 10X MORE BASIC i.e., Concentration/amount of H+ decreased by 10X! 27 Water: The pH Scale pH = -log[H+] Below can see pH values and corresponding [H+]. pH ACIDIC BASIC [H+] NEUTRAL 28 Water: The pH Scale Immediately see advantage of pH scale! Can work with simple numbers and not “ridiculous” concentrations with all those zeros. AGAIN: since working with a “log” scale: Each time decrease pH by 1 pH unit (e.g., 2 to 1): 10X MORE ACIDIC i.e., Concentration of H+ increased by 10X! Each time increase pH by 1 pH unit (e.g., from 8 to 9): 10X MORE BASIC i.e., Concentration of H+ decreased by 10X! 29 VOTE FOR SCIENCE! 30  VOTE FOR SCIENCE! Can you determine whether following are ACIDIC, BASIC or NEUTRAL? Lemon juice. A solution of HCl. A solution of NaOH. Pure water. Soap. Vinegar. Seawater. Milk. 31  VOTE FOR SCIENCE! Can you determine whether following are ACIDIC, BASIC or NEUTRAL? Lemon juice. ACIDIC A solution of HCl. ACIDIC A solution of NaOH. BASIC Pure water. NEUTRAL Soap. BASIC Vinegar. ACIDIC Seawater. SLIGHTLY BASIC Milk. SLIGHTLY ACIDIC 32 Thank you for listening!!! Fun videos to watch in preparing for next lecture: Excellent video covering GROUNDWATER basics: https://www.youtube.com/watch?v=oNWAerr_xEE AQUIFERS explained: https://www.youtube.com/watch?v=g7R0yLX0V9E 33