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Definition: SOLUTION

Definition: SOLUTION. A system in which one or more substances are homogenously mixed or dissolved in another substance. In other words: two chemicals mixed together completely. Can result in a solid, liquid, or gas. What are some examples?. Shampoo Soft drinks Air Gasoline steel.

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Definition: SOLUTION

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  1. Definition: SOLUTION • A system in which one or more substances are homogenously mixed or dissolved in another substance. • In other words: two chemicals mixed together completely. • Can result in a solid, liquid, or gas

  2. What are some examples? • Shampoo • Soft drinks • Air • Gasoline • steel

  3. What do you need to make a solution? • Example: Kool-aid, basically sugar water • 1) solute—part being dissolved (sugar) • 2) solvent—part doing dissolving (water) + =

  4. A True Solution 5 Properties of True Solutions • 1) mixture is homogenous and the ratios of solvent to solute can be varied. • In Kool-aid example, more or less sugar could be added to make the solution more or less concentrated.

  5. A True Solution Properties • 2) The dissolved solute is molecular or ionic in size. • The sugar in the packet dissolves into separate sugar molecules

  6. A True Solution Properties • 3) It is either colorless or transparent (not cloudy)

  7. A True Solution • Properties • 4) The solute is uniformly distributed and doesn’t settle out over time. • After an hour, the solution should still look the same. No chunks at the bottom or top…think of hot chocolate when it sits for a while

  8. A True Solution • Properties • 5) The solute can be separated from the solvent by physical means (evaporation, filtration, boiling, etc) • Recall the first lab where we boiled salt water, after the water evaporated, the salt was left at the bottom.

  9. Dissolving • How do substances dissolve?

  10. Diffusion • Molecules travel from areas of high concentration to areas of low concentration. • Solubility describes how likely one substance will dissolve in another.

  11. Solubility • Amount of solute that can dissolve in the solvent. • Solubility varies with temperature.

  12. 4 ways to make a solute dissolve faster? • (1)INCREASE THE TEMPERATURE • for liquids, this causes the solvent molecules to move faster and bump into the solute particles more often and harder, breaking them apart faster. • (2) AGITATION OR STIRRING • this physically helps the solute particles diffuse by distributing them to all parts of the solvent. • (3)BREAK IT DOWN • The smaller the particle, the faster it dissolves

  13. How can I make a solute dissolve faster? • (4) CONCENTRATION • The closer you get to the saturation point, the slower the dissolving occurs • The solute dissolves quickly at first because there is a lot of area to dissolve into • As more of the solute dissolves, the area shrinks and dissolving slows down.

  14. What Affects a Substance’s Solubility? • Question: When making Jell-o, why do the directions tell you to pour the packet into hot water and then cool it? Why can’t you just pour it in cold water and then drink it right away?

  15. What 3 factors affect the Solubility of substances? • (1) Temperature • For LIQUIDS: • More solute can be dissolved if you use warm solvents. • Why? • The KMT of course

  16. Which one would dissolve more salt? 100 C 50 C How much more would the first cup dissolve?

  17. Solubility Curves • Can use a graph to represent solubility • Y-axis = grams of solute per 100g H2O • X-axis = temperature • Different substances will have different curves on the graph.

  18. What’s happening with HCl, NH3, and SO2 (dotted lines)

  19. Solubility of Gases • The solubility of gases decreases with increasing temperatures. • Can you think of a situation where this principle is illustrated? (hint: many of you have one at lunch time) SODA

  20. SODA • Cold soda is more fizzy because more gas is dissolved in the soda. • Why does soda become flat as it warms to room temperature? (remember the KMT) • As the soda becomes warm, the gas molecules begin to move faster and evaporate out of the soda.

  21. (2) Solubility & Pressure Changes in pressure have the largest effect on gases dissolved in liquids. • Pressure and solubility vary directly. • As the pressure increases, the solubility increases.

  22. Back to the Soda • Why does a can of soda fizz when it’s opened? • Canned at high pressures. • When it’s opened, the pressure inside is reduced to the atmospheric pressure, and the excess dissolved CO2 bubbles out of the sol’n.

  23. (3) The Nature of the Solute and the Solvent • Explain why water and oil do not mix? • Like dissolves like • Polar substances dissolve in other polar substances and nonpolar dissolve in nonpolar. • Oil is nonpolar and water is polar.

  24. Nonpolar vs. Polar • When nonpolar substances dissolve in one another, they simply mix. • When polar substances dissolve, electrical reactions pull apart the molecules.

  25. Saturated, Unsaturated, & Supersaturated Sol’ns • SATURATED • Holds the maximum amount of solute in the dissolved state • No more solute can be added and still dissolve. • UNSATURATED • More solute could be added and still dissolve. • SUPERSATURATED • Holds more solute than the max. • Very unstable and have to be prepared in a special way.

  26. Supersaturated Solutions • Hand/foot warmer packs used for cold weather are examples. • Activated when they are crushed • The heat generated is a result of the supersaturated solution coming out of supersaturation. This reaction is exothermic. • Cold packs work the same way but are endothermic reactions.

  27. Will a solution made by adding 2.5g of CuSO4 to 10g of H2O be saturated or unsaturated at 20°C? • Use the curve on slides • Find the solubility of CuSO4 at 20° • It is 21g per 100g H2O • This is equivalent to 2.1g CuSO4 per 10g H2O • Since 2.5 is greater than 2.1, the sol’n will be saturated. How much will be undissolved? • .4g

  28. You Try • Will a sol’n made by adding 9.0g NH4Cl to 20g of H2O be saturated or unsaturated at 50°C? • unsaturated

  29. Solution Concentration • Equations to learn • (1) Molarity • (2) Dilution

  30. Molarity • Molarity describes a solution’s concentration by telling you how many moles of solute exist in one liter of solution. (symbol is a capital M) • M = moles L A 6 M HCl solution contains 6 moles of HCl for every Liter of solution. What does a 5.7 M solution contain? 5.7 moles of HCl for every Liter of solution.

  31. Dilutions Sometimes the available solution might be to concentrated for our purposes; therefore we must dilute the solution. In other words, we reduce the concentration of our solution. To find out how much solvent we must add to reduce the concentration, we use the following formula: M1V1 = M2V2 where M=molarity

  32. Dilution 100mL water 6 moles NaCl 200mL water 6 moles NaCl

  33. The moles are the same in each glass • Because they contain the same amount of moles, we can use: • M1V1 = M2V2 M=molarity or • C1V1 = C2V2 C=concentration

  34. Examples • Calculate the molarity of a solution prepared by diluting 125 mL of 0.400 M K2Cr2O7 with 875 mL of water. • (125)(.400) = (1000) M2 • .05 M

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