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Solution Chemistry

Solution Chemistry. Vocabulary Refresher: A solution can be defined as a homogeneous mixture of two or more substances in a single phase. Solutions consist of a solute(s) and a solvent .

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Solution Chemistry

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  1. Solution Chemistry Vocabulary Refresher: A solution can be defined as a homogeneous mixture of two or more substances in a single phase. Solutions consist of a solute(s) and a solvent. The solvent is the dissolving medium in a solution. It causes the solute to dissolve. It is what does the dissolving. The solute is the dissolved substance in a solution. It’s what gets dissolved. If something is capable of being dissolved, it is said to be soluble.

  2. If two liquids dissolve together, like alcohol and water, they are said to be miscible. If not, then they are characterized as immiscible. i.e. oil and water.

  3. We are going to focus on aqueous solutions. Solutes can be classified in many ways; one way is according to their ability to conduct electricity when in solution. Electrical current is the flow of electrons; thus electricity is moving charges. Solutions of ionic compounds can conduct electricity, and are classified as electrolytes. The ions that are dissolved can move and flow. An electrolyte is a substance that dissolves in water to give a solution that conducts an electric current.

  4. Solutions of strong electrolytes conduct electricity well. • The solutes of these solutions typically have broken down into their ions, and thus there are many ions to conduct the electricity. • Solutions of weak electrolytes will conduct electricity slightly. The solutes of these solutions typically have only partlybroken down into their ions; having few ions to conduct the current. • A non-electrolyte is a substance that dissolves in water to give a solution that does not conduct an electric current. • A solution of a non-electrolyte will not conduct electricity. These solutes remain in their molecular form with no ions present in the solution.

  5. How does a solution conduct electricity? First you need two electrodes and a source of electricity. Electrodes are electrical conductors (copper, zinc, carbon) partially immersed in a solution and connected to a source of electricity. The positive electrode is called the anode, while the negative electrode is the cathode. The ions within the solution serve as carriers of electricity. An anion is a negatively charged ion, whereas a cation is a positively charged ion.

  6. How do I make a solution? First of all that depends on what the solute and solvent are. Will the solute dissolve in your solvent? If so, how much of it will dissolve? What affects the rate of dissolution (rate of dissolving)? • shaken or stirred • particles are made smaller • temperature is increased Why?

  7. In order for a solvent to dissolve a solute, the solvent molecules must come in contact with the solute. Stirring moves “fresh” solvent molecules next to the solute. Solvent particles are brought into contact more with solute particles. Fresh molecules????? Here is more theory to explain what is going on at the molecular level. Let’s use H2O for example. Water is known as the universal solvent, because many things will dissolve in it. Why?

  8. Well, it’s polar. It has an unequal sharing of electrons in its bonds. This coupled with its bent shape create “poles” within the molecule. The oxygen atom takes on a partial negative charge, whereas the hydrogen atoms have a partial positive charge. d- This creates a polar molecule with dipole forces. O H – O – H H H d+ d+

  9. The forces causing an ionic solid to dissolve in water are called ion-dipole forces; the attraction of water dipoles for cations and anions. The attractions of water dipoles for ions pull the ions out of the crystalline lattice and into the aqueous solution. The extent to which an ionic solid dissolves in water is determined largely by the competition between the inter-ionic attractions that hold ions in a crystal and the ion-dipole attractions that pull them into solution. • The breaking part of compounds into the ions that created them is called dissociation.

  10. The breaking part of compounds into the ions that created them is called dissociation. NaCl(s) dissociates into 1 Na+1(aq) and 1 Cl-(aq) CaCl2(s) dissociates into 1 Ca2+(aq) and 2 Cl-(aq) • The process of dissolving a solute with a solvent is called solvation. The process of dissolving a solute with water as the solvent is called hydration. NaCl(s) Na1+(aq) + Cl-(aq) CaCl2(s) Ca2+(aq) + 2 Cl-(aq)

  11. H bonds Formula unit

  12. So, agitating a solution will increase the rate of dissolution. Increasing the surface area of the solute will also rapidly increase the rate of dissolution. More surface area = more points of contact between the solute and solvent. Lastly, heating always increases the rate of dissolution of solids in liquids. Higher temperatures make the molecules of the solvent move around faster and contact the solute harder and more often.

  13. How much can I dissolve??? Increased temperature increases the rate at which a solid dissolves. The rate at which a substance dissolves does not alter the substances solubility. We can’t predict whether it will increase the amount of solid that dissolves. We must read it from a graph of experimental data. The solubility of a substance is the amount of that substance required to form a saturated solution with a specific amount of solvent at a specified temperature.

  14. For solids in liquids, as the temperature rises, solubilities also tend to increase. About 95% of all ionic compounds have aqueous solubilities that increase significantly with increasing temperature. Most of the remainder have solubilities that change little with temperature. A very few have solubilities that decrease with increasing temperature For gases in a liquid, as the temperature rises, the solubilitiesdecrease. Gas molecules can escape from the solution. For the gases in a liquid – as the pressure goes up, the solubility goes up.

  15. Pressure effects??? Changing the pressure doesn’t affect the amount of solid or liquid that dissolves. They are incompressible. Gases on the other hand, can be affected by pressure. The dissolved gas reaches an equilibrium with the gas above the liquid

  16. Henry’s Law The effect of pressure on the solubility of a gas is known as Henry’s law. The gas is at equilibrium with the dissolved gas in this solution. The equilibrium is dynamic. If you increase the pressure the gas molecules dissolve faster. The equilibrium is disturbed. The system reaches a new equilibrium with more gas dissolved. This is an illustration of Henry’s Law.

  17. Effervescence is the rapid escape of a gas from a liquid in which it is dissolved.

  18. What does it mean if a solution is saturated? A saturated solution is one that contains the maximum amount of dissolved solute. It will not dissolve any more solute under the existing conditions.

  19. An unsaturated solution is a solution that contains less solute than a saturated solution under the existing conditions. It will dissolve more solute (until the saturation point is reached) under the existing conditions.

  20. A supersaturated solution in one that temporarily contains more dissolved solute than a saturated solution contains under the same conditions. A supersaturated solution is created when a warm, saturated solution is allowed to cool without the precipitation of the excess solute. The addition of more solute will disrupt the solution and cause it to crystallize.

  21. Molarity Most chemical reactions take place in solution. Substances enter into chemical reactions according to certain molar ratios. We already know how to go from mass to moles, but volumes of solutions are more convenient to measure than their masses. So we need the concentration of the solutions. Concentration is a measure of the amount of solute dissolved in a certain amount of solvent.

  22. There are several methods of expressing the concentration of a solution. • Qualitatively solutions are termed either: • A concentrated solution contains a relatively large amount of solute as compared to the solvent. • A dilute solution contains a relatively small concentration of solute as compared to the solvent. These expressions are not very precise and can have many numerical equivalencies. To be more specific, chemists express concentrations quantitatively. dilute concentrated or

  23. These expressions are not very precise and can have many numerical equivalencies. To be more specific, chemists express concentrations quantitatively. • Molarity is the amount of solute (in moles) divided by the volume of solution (in liters). • Molalityis the amount of solute (in moles) divided by the mass of of solvent(in kilograms). • Percent by mass is the amount of solute (in grams) multiplied by 100% and divided by the amount of solution (in grams) • Percent by volume is the volume of solute (in liters) multiplied by 100% and divided by the volume of solution (in liters). • Mass/Volume percent is the amount of solute (in grams) multiplied by 100% and divided by the volume of solution (in liters).

  24. The most often used method in chemistry is MOLARITY (M). Molarity is defined as the moles of dissolved substance (solute) per volume of solution expressed in cubic decimeters (dm3) and liters (L).

  25. As chemists we express concentration in terms of molarity because we measure solutions by volume. Yet, we need to count the number of particles of the solution. A 0.372 M solution of Ba(NO3)2 contains 0.372 moles of Ba(NO3)2 in 1 dm3 of solution. One mole of sodium chloride, is 58.44 grams. If 58.44 grams of NaCl are dissolved in enough water (water is typically the solvent) to make 1 cubic decimeter of solution, the solution is a 1Msolution of NaCl. Similarly, if 2 moles of NaCl (116.88 g) are dissolved in enough water to make 1 dm3 of solution, the solution is a 2Msolution.

  26. Fifty (50) mL and 500 mL of a 2 M solution will have the SAME CONCENTRATION. The total numberof particles changes, but the concentration does not change. Recall: 1 mL = 1 cm3 1 dm3 = 1 L 1000 mL = 1L 1 dm3 = 1000 cm3

  27. 3 Basic formats FIND THE MOLARITY (M): UNITS: moles/Lormoles/dm3 EXAMPLE: Given: 2.50 x 102 cm3 solution and 9.46 g cesium bromide. Wanted: What is the molarity (M)? 0.178 mole/dm3CsBr • = 0.178 M CsBr

  28. Example: Calculate the Molarity of a solution with 34.6 g of NaCl dissolved in 125 mL of solution. = 4.74 mole/L NaCl • = 4.74 M NaCl

  29. FIND THE MASS OF SUBSTANCE NEEDED: The volume of solution is given, and the key is to use the MOLARITY as a conversion factor!!!! 6 M solution of NaCl means: 6 moles of NaClin every 1 L of solution 6 moles of NaCl= 1 L of solution EXAMPLE: Make a 0.133 M manganese (II) selenate solution with a final volume of 500. cm3. What is the formula for manganese (II) selenate? Use the Molarity as a Conversion Factor!!!! MnSeO4

  30. FIND THE MASS OF SUBSTANCE NEEDED: EXAMPLE: Make a 0.133 M manganese (II) selenate solution with a final volume of 500. cm3. Start the problem with the given (not the Molarity) We want to use the Molarity as a conversion factor. What are the units for Molarity? 0.133 M MnSeO4 = What should we convert the given into in order to use Molarity as a conversion factor?

  31. FIND THE MASS OF SUBSTANCE NEEDED: EXAMPLE: Make a 0.133 M manganese (II) selenate solution with a final volume of 500. cm3. • = 13.2 g MnSeO4 We will dissolve 13.2 g of manganese (II) selenate in enough water to make 500. cm3 of solution.

  32. Example: How many grams of CaCl2 are needed to make 625 mL of a 2.0 M solution? • = 140 g CaCl2 We will dissolve 140 g of calcium chloride in enough water to make 625mL of solution.

  33. Now let’s c if u can do it… Example: 10.3 g of KCl are dissolved in a small amount of water then diluted to 250 mL. What is the molarity? • = 0.55 M KCl Example: How many grams of glucose are needed to make 125 mL of a 0.50 M C6H12O6 solution? • = 11 g C6H12O6

  34. FIND THE VOLUME OF SOLUTION NEEDED: The mass of solute is given, and the key is to use the MOLARITY as a conversion factor!!!! EXAMPLE:To what volume should 5.0 g of KCl be diluted in order to prepare a 0.25 M solution? • = 0.27 L KCl What should we convert the given into in order to use Molarity as a conversion factor?

  35. Calculating Ion Concentrations In Solution Bracket symbols, [ ], are used to represent molar concentrations of ions or molecules in solution. Given 0.010 M Na2SO4 : • 2 Na1+ ions are formed in solution; therefore the concentration of Na1+ is 0.020M. • 1 SO42- ion is formed in solution; therefore the concentration of SO42- is 0.010M.

  36. Example: What would the concentration be if you used 27 g of CaCl2 to make 500. mL of solution? • = 0.4865741575 M CaCl2 • = 0.49 M CaCl2 What is the concentration of each ion? • = 0.49 M [Ca2+] • = 0.97 M [Cl1-]

  37. Example: Calculate the concentration of a solution made by dissolving 45.6 g of Fe2(SO4)3 to 475 mL. What is the concentration of each ion? • = 0.240 M Fe2(SO4)3 • = 0.480 M [Fe+3] • = 0.720 M [SO4-2]

  38. Molarity by Dilution Acids are usually acquired from the chemical suppliers in a highly concentrated solution. A solution for which a precise concentration is known is called a standardsolution. The following are standard solutions of concentrated acids. HCl 12 M HNO3 15.8 M H2SO4 18 M

  39. A lab that we are going to do requires a more dilute (less concentrated) solution. How can we make a solution with a lower Molarity? Add H2O How much water? M1V1= M2V2 M1= initial Molarity V1= initial volume M2= final Molarity V2= final volume

  40. EXAMPLE: Our next lab requires 1.0 M HCl. We need 3.0 L of HCl for the entire class. How much concentrated HCl is needed to prepare the solution? (Assume HCl is 12 M concentrated.) M1V1= M2V2 M1= 12 M HCl M2= 1.0 M HCl V2= 3.0 L V1= ??? M1V1= M2V2 • = 0.25 L KCl • = 250 mLKCl

  41. EXAMPLE: How much H2O should 250. mL of 12.0 M HCl be added in order to produce a 1.00 M solution? M1V1= M2V2 M1= 12.0 M HCl M2= 1.00 M HCl V2= ??? V1= 250. mL M1V1= M2V2 • This is NOT • the answer • V2 = 3000 mLKCl

  42. EXAMPLE: How much H2O should 250. mL of 12.0 M HCl be added in order to produce a 1.0 M solution? • This is NOT • the answer • V2 = 3000 mLKCl What does V2 represent? Are we looking for V2? How do we find the amount of water that was added? • V2 = 3000 mLKCl • V1 = 250 mLKCl • VH2O = 2750 mLKCl

  43. Arrhenius Concept of Acids and Bases • Arrhenius acid • a substance that, when dissolved in water, increases the concentration of hydronium ion, H3O+(aq). • Chemists often use the notation H+(aq) for the H3O+(aq) ion, and call it the hydrogen ion. • Remember, however, that the aqueous hydrogen ion is actually chemically bonded to water, that is, H3O+. • Arrhenius base • a substance that, when dissolved in water, increases the concentration of hydroxide ion, OH-(aq). • The Arrhenius concept limits bases to compounds that contain a hydroxide ion.

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