Chemistry 1 st class Water Resources department

1. Chemistry1st classWater Resources department By: IsraaMurtadha Hameed Israa Murtadha Hameed

2. Chemistryof solutions 3rd lecture By: IsraaMurtadha Hameed Israa Murtadha Hameed

3. Types of Homogeneous Mixtures There are basically three types of homogeneous mixtures. This means that the components of the mixtures are evenly dispersed throughout the volume of the mixture. Solutions: contain particles in the range of tenths of nanometers (nm) to several nm. A nanometer is 10-9 meters. They are transparent and, though they may be colored, do not separate on standing. Colloids:such as homogenized milk and fog, contain particles in the range of hundreds of nanometers. Although they are often murky or opaque to light, they do not separate on standing. Suspensions : are heterogeneous, non-uniform mixtures with particles so large they can be separated by use of filters or semi-permeable membranes Israa Murtadha Hameed

4. Solution Nomenclature It is important when discussing solutions that one use the agreed upon terminology that describes the constituents of a solution. Listed below are three very important definitions in solution chemistry. Solution A homogeneous mixture of molecules or ions. SolventThe medium in which the molecules or ions are dissolved. Solute Any substance dissolved in a solvent. Israa Murtadha Hameed

5. Although we will deal entirely with liquid solutions in this chapter, it should be noted that solutions do exist in all of the three states of matter. The following table shows examples of solutions in liquid, gaseous, and solid states of matter. Israa Murtadha Hameed

6. Solutions of Different States of Matter Israa Murtadha Hameed

7. Solution Properties As you may have already noticed, chemistry, like other sciences, can be viewed as a systematic way of observing a component or system of nature. These observations are then recorded, agreed upon, and set down as the properties of that component or system. Listed following are the properties of solutions that you will need to understand the chemistry of solutions. Israa Murtadha Hameed

8. Solution Properties Solubility: Solubility is the measure of how much of a solute will dissolve in a given amount of solvent. When solubility is measured in g/100 ml the 100 ml is the given amount. It has been agreed upon among chemists to measure and record solubilities in this manner using this specific unit. For example, common table salt (NaCl), has a solubility in water of 39.5 g/100 ml. You could prove this to yourself by measuring out 100 ml of water into a clear glass. Measure out 50 grams of table salt and try to get all of the salt into solution in the 100 ml of water. The table following lists solubilities of common substances in water at 20°C. Israa Murtadha Hameed

9. Solubilities in Water at 20°C Israa Murtadha Hameed

10. Solution Properties 2. Saturation: Saturation is that state of a solution where the amount of solute added to the solvent has exceeded the solubility of that solute. When excess solute is added to a solvent, that solute will not go into solution. It is common to stir a solution to get solutes into solution. When excess solute is added in this manner, the solution will appear turbid at first due to suspended solutes but will turn clear when the excess solute settles to bottom of the container. Israa Murtadha Hameed

11. Solution Properties 3. Supersaturation Supersaturationis the state of a solution when more solute is in solution than the solubility would allow for due to special circumstances. A sealed bottle of soda is a solution that is supersaturated with carbon dioxide (CO2) due to the high pressure inside the bottle. When the bottle cap is removed the pressure rapidly decreases releasing the excess CO2 to the atmosphere. Israa Murtadha Hameed

12. Solution Properties 4. Miscibility Miscibility is the property of liquids to combine with one another in all proportions to form homogeneous solutions. In a manner of speaking miscibility is unbounded solubility. In table (Solubilities in Water at 20°C), I showed the solubilities of some ionic compounds and a sugar. Had I included acetic acid I would have listed the solubility as miscible since it will combine with water at all proportions. At a range of 4% to 8% acetic acid in water the solution is commonly referred to as vinegar Israa Murtadha Hameed

13. Concentration is the measure of the amount of solute actually dissolved in a solvent. If you were to return to the experiment of adding 50 g of NaCl to 100 ml of water, under ideal conditions (pure water at 1 atm pressure and 20°C) the concentration of the NaCl in the water would be 39.5 g/100 ml. This is due to the limit of the solubility of NaCl in water. Staying within the SI system the 39.5 g/100 ml solubility of NaCl in water could be written in other terms of concentration. The 39.5 g/100 ml could be expressed as 395 g/L, 395 g/kg, 395,000 mg/kg, 395,000 ppm, and 6.76 moles/L. Israa Murtadha Hameed

14. Concentration's units Molarityis the measure of the concentration of a solute in a solvent expressed in terms of the number of moles of that solute in one liter of the solvent. Symbols and Terms of Molarity It is important to become familiar with the different symbols and terms used to express molarity. The symbol for molarity is the upper case letter M. However, there are a few different ways you may hear or see molarity expressed. Israa Murtadha Hameed

15. Symbols and Terms of Molarity It is important to become familiar with the different symbols and terms used to express molarity. The symbol for molarity is the upper case letter M. However, there are a few different ways you may hear or see molarity expressed. Here are some examples of the way a solution that contains 1.5 × 10-2 moles of NaCl in one liter of water may be expressed: The solution is 1.5 × 10-2 M in NaCl. The solution has 1.5 × 10-2 moles/liter NaCl. This is a 1.5 × 10-2 molar solution of NaCl. Just remember that they all mean the number of moles of solute per liter of solvent. Israa Murtadha Hameed

16. Molarity Calculations Calculating molarity is a critical skill for many scientific disciplines. Climate scientists will use molarity calculations to estimate the load of carbon being deposited to the Earth’s atmosphere. Pharmaceutical chemists definitely use molarity calculations to determine the correct amounts of the various constituents of a drug product. A nurse could use molarity calculations to determine correct dosage regimens of medicines. The following exercises may seem a bit extensive. It is a way of stressing how important these calculations are. Molarity calculations are also essential to the calculation of pH. Israa Murtadha Hameed

17. Exercises Exercise 1: What is the molarity of Cl- in a 1 L solution of water containing 3 moles of NaCl? Here the molar ratio of Cl- to NaCl is taken directly from the chemical formula Israa Murtadha Hameed

18. Exercises Exercise 2: What is the molarity of OH- in a 1.5 L solution of water that contains 4 moles of Ca(OH)2? Here the chemical formula shows that there are 2 moles OH- for 1 mole of Ca(OH)2. Israa Murtadha Hameed

19. Exercises Exercise 3: What is the molarity of Na+ in a 0.75 L solution containing 0.35 g of NaBr? Once again the molar ratio of Na+ to NaBr comes directly from the chemical formula Israa Murtadha Hameed

20. Mole Fractions The Concept of Mole Fraction Now that we know about both moles and molarity we can embrace the concept of mole fraction. A mole fraction can be expressed for either the solute or the solvent. Mole fraction is expressed as a fraction without units. Israa Murtadha Hameed

21. Mole Fractions If a certain amount of salt (NaCl) is added to a certain volume of pure water (H2O), you should be able to calculate to mole fraction of Na+ ions in that solution. You will need to calculate the number of moles of Na+ ions, Cl- ions, and water molecules that exist in that solution. Then the number of moles of Na+ ions divided by the number of moles of all other constituents in that solution is the mole fraction of Na+ ions in that solution. Israa Murtadha Hameed

22. Exercises Exercise 1 What is the mole fraction of Na+ ions in a 1 liter solution of pure water that is 0.1 molar in NaCl? Pure water has a density of 1kg/liter. Now that we have calculated the number of moles we need to calculate the number of moles Na+ and Cl- ions Since Na+ and Cl- exist in an equal molar ratio in NaCl there are also be 0.1 moles of Cl- in NaCl.Therefore in the solution there is a total of 55.56 + 0.1 + 0.1 = 55.76 of moles of all constituents. The mole fraction of Na+ ions in the solution is 0.1/ 55.76 or 1/557.6. Israa Murtadha Hameed

23. Exercises Exercise 2: What is the mole fraction of Cl- in a 1 liter solution of pure water that has a 1 × 10-2 molar concentration of CaCl2? From Exercise 1 we see that 1 liter of water contains 55.56 moles of water. If there are 0.02 moles of Cl- in the solution the 1 to 2 molar ratio of Ca2+ to Cl- means there are 0.01 moles of Ca2+ in the solution. So there are a total of 55.56 + 0.02 + 0.01 = 55.59 moles of all constituents in the solution. The Cl- mole fraction is 0.02/55.59 = 1/2795. Israa Murtadha Hameed

24. Any Questions? Israa Murtadha Hameed