CHEM 1311 Lecture Notes - Lecture 12: Supersaturation, Intermolecular Force, Exothermic Process

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26 Apr 2018

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Chapter 13: Physical Properties of Solutions

Focus of this section: Energy changes w/ solution

formation

Concentration Units

Colligative Properties

Types of Solutions:

Review:

• Solution: a homogeneous mixture

• Solute: the component that is dissolved in solvent

-- usually in smaller amount

• Solvent: medium into which solutes are mixed

-- usually in greater amount (usually liquid)

• solubility: amount (mass) of solute that forms saturated

solution with given mass of solvent at specific

temp

• saturated solution: contains as much solute as can be

dissolved (at specific temp)

• unsaturated solution: can dissolve more solute

• supersaturated solution: contains more solute than is

actually stable at given temp

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= formed by cooling saturated solution from a higher

temperature (solutes typically more soluble at

higher temperatures)

“Molecular” View of Solution Process:

• Intermolecular forces important in formation of a solution

-- disruption of solute-solute interactions

-- disruption of solvent-solvent interactions

-- formation of solute-solvent interactions (solute

solvated by solvent)

unsaturated

supersaturated

saturated

heat

supersaturated

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ΔH1 = disruption of solute-solute

ΔH2 = disruption of solvent-solvent

ΔH3 = formation of solute-solvent

ΔHsoln = enthalpy of solution = heat of solution

ΔHsoln > 0 (endothermic) if ΔH3 < ΔH1 + ΔH2

ΔHsoln < 0 (exothermic) if ΔH3 > ΔH1 + ΔH2

• solutions of gases in liquids:

-- ΔHsoln usually < 0 (exothermic)

= don’t need to break solute-solute interactions,

so ΔH1 ~ 0

• Solubility of solute in a solvent can be predicted:

“like dissolves like” (in terms of IM forces)

-- the more similar the IM forces (solvent vs solute),

the more likely the solute will dissolve

321soln HHHH Δ+Δ+Δ=Δ

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Document Summary

Review: solution: a homogeneous mixture, solute: the component that is dissolved in solvent. - usually in smaller amount: solvent: medium into which solutes are mixed. = formed by cooling saturated solution from a higher temperature (solutes typically more soluble at higher temperatures) saturated supersaturated unsaturated. Molecular view of solution process: intermolecular forces important in formation of a solution supersaturated heat supersaturated. - formation of solute-solvent interactions (solute solvated by solvent) Hsoln = enthalpy of solution = heat of solution. 3 soln: solutions of gases in liquids: Hsoln > 0 (endothermic) if h3 < h1 + h2. Hsoln < 0 (exothermic) if h3 > h1 + h2. = don"t need to break solute-solute interactions: solubility of solute in a solvent can be predicted: so h1 ~ 0. Like dissolves like (in terms of im forces) - the more similar the im forces (solvent vs solute), the more likely the solute will dissolve. = ccl4 dissolves in benzene (c6h6) (both nonpolar)

Related Questions

HERE IS HOW THIS IS GOING TO WORK! IF YOU ANSWER THE QUESTIONS IWILL GIVE YOU THE 3K POINTS + MORE AFTER I REPOST IT.

2. The amount of heat involved in the synthesis of 1 mole of acompound from its elements, with all substances in their standardstates at 25*C, is called _________.

3. What is a valid unit for specific heat?

4. Use Hess's Law to find the heat of reaction in the examplebelow.

N2O4 (g) ----> 2NO2 (g)

Given that:

N2O4 (g) ----> N2 (g) + 2O2 (g) (Delta H =-9.7kJ)

2NO2 (g) ----> 2O2(g) + N2(g) ( Delta H= -67.7kJ)

5. Use Hess's Law to find the heat of reaction in the examplebelow. (Example doesn't exist btw.)

6. (Delta H) for the formation of rust (Fe2O3) is -826 kJ/mol. Howmuch energy is involved in the formation of 5 grams ofrust?

7. How many kilocalories of heat are required to raise thetemperature of 50g of aluminum from -5*C to 35*C? (Specific heat ofAluminum = 0.21 cal/g*C)

8.Calculate the (Delta H) for this reaction:

Zn(s) + Cu (2+ ion)(aq) ---> Zn(2+) + Cu(s)

(Delta H) for Cu(2+) = +64.4 kJ/Mol; (Delta H) for Zn(2+) = -152.4kJ/mol

9. The following equation shows the reaction that occurs whennitroglycerine explodes.

4C3H5O9N3 ----> 12CO2 + 6N2 + O2 +10H2O + 1725 Kcal

Is this reaction exothermic , endothermic, a combustion reaction ,or a combination reaction?

10. What does it mean for ammonia, (NH3) to have a (Delta H f) =-46 kJ/mol?

(for example: Define heat of formation. What does a negative heatof formation mean? what do the units of kJ/mol mean?)

11. What is the maximum amount of KCl that can dissolve in 500g ofwater?

(solubility of KCl is 34 g/ 100g of water at 20*C)

12.List the ways(operations) that can help make a substancedissolve faster in a solvent?

13. If a crystal added to an aqueous solution causes many particlesto come out of solution, the original solution was (saturate,unsaturated, supersaturated).

14. What is the number of moles of solute in 165 mL of a 0.82 Msolution?

15. What mass of NaCl is needed to make 350 mL of a 1.00 Msolution?

16. Colligative properties depend upon...

17. If one mole of each of these solutes in added to the sameamount of water, which solution has the highest boiling point?(glucose, aluminum sulfate, magnesium acetate, copper (I)chloride)

18. When an acid reacts with a base, what compounds areformed?

19. If the [H+] in a solution is 1x10^(-13) mol/L, what is the[OH-]?

20. If the [OH-] = 1x10^-6 mol/L, what is the pH of thesolution?

21. For a solution to be considered acidic what must be thehydrogen-ion concentration?

22. Which of the following represents a Bronsted-Lowry conjugateacid-base pair?

a) SO3(2-) and SO2 b) CO3(2-) and CO c) H3O and H2 d) NH4(+) and NH3

23. With solutions of "strong" acids and "strong" bases, the word"strong" refers to ...

24. What are the products of Al(OH)3 + H2CO3?

25.What is the concentration of hydrochloric acid if 5.0 mL of acidis neutralized by 30.0 mL of 2.00M sodium hydroxide.

26. At equilibrium, what is the rate of production of reactantscompared with the rate of production of products?

27. What is the equilibrium constant for the following reaction2SO3 ---> 2SO2 + O2

28. How does an increase in pressure affect the following reaction?2SO3 (g) --> 2SO2(g) +O2(g)

29.What stresses would shift the reaction to the right?

2SO3(g) ==> 2SO2(g) + O2(g)

30. The Keq of a reaction 4.9 x 10^(-7). Are products or reactantsfavored at equilibrium?

31. In which of these systems is the entropy decreasing?

a) air escaping from a tire b) snow melting c) a gas condensing d) salt dissolving inwater

32. If an atom is reduced in a redox reaction, what must occur toanother atom in the system?

33. Identify the oxidizing agent in the following reaction: 2Na + S---> Na2S

34. What are transferred in an oxidation -reductionreaction?

35. Give the oxidation number for each atom in KMnO4.

36. Which atom has a change in oxidation number of +4 in thefollowing reaction?

K2Cr2O7 + H2O + S ----> KOH + Cr2O3 +SO2

37. What is the oxidation number of sulfur in each of the following:

a. SO3 c.SO2(2-)

b. Na2SO4 d. S2O4 (2-)

38.Fe(3+) ----> Fe represents oxidation, reduction, orhydrolysis?

39. When the half reactions Br2+ 2e- -----> 2Br- and Na---->e- + Na(+) are combined the balanced redox equation is_____________________ ( WRITE the BALANCED REDOX eq)

40. To balance the oxygen and hydrogen for a redox reaction thattakes place in basic solution, it is necessary to use whichsubstance?

41. What particle completes this nuclear equation? 55/25 Mn + 2/1 H====> _____ +2 1/0 n

42. The half-life of tungsten-182 (182/74 W) is 1.1x10^(17) years.How long would it take for a 376.2 kg sample to decay until only123.0 grams remain?

43. After 3 days, the quantity of certain radioisotope is reducedfrom 13.6 grams to 1.9 grams. Calculate the half-life of theisotope.

44. What is the name of the compound having the formulaC8H18.

45. What is the name of the following compound:

CH3---CH2----CH---CH2--C

I \

CH3 OH

46. What is an isomer? Give an isomer of hexane (C6H14) and drawit's structure.

47. What is the name of the hydrocarbons with double covalentbonds?

48. Draw the stucture for 3-methylbutanoic acid.

49. Draw the structure for methylbenzene?

50. What is the name of the following compound:

CH3----C-----CH3

CH3

silverclam911

Seperation lab: Will rate question

Separation lab - will choose best answer

Seperation lab: will choose best answer

Separation of a Mixture Laboratory

In this experiment we will separate the different components of a mixture made up of sand (SiO2) and sodium chloride (NaCl, commonly known as salt). Both of these compounds are solid white crystals, so it is difficult to tell them apart with the naked eye. However, each component exhibits different physical properties that can be used to separate one from the other. There are several physical separation techniques that can be used to determine the percent composition of the original mixture.

Materials & Apparatus:

Sand/salt mixture provided in your Lab Kit

2 - Erlenmeyer Flasks

Scale

Water

Graduated Cylinder

Background:

It is important to know how to separate mixtures because many reactions carried out in the laboratory produce mixtures of different compounds. It is often necessary to separate the components of these mixtures, which can be done using several techniques. We will explore a few of these techniques: sublimation, filtration, evaporation and decantation.

Sublimation is the process of a substance passing from the solid to the gaseous state without first passing through the liquid state. Not all substances possess this characteristic. In fact, most substances to NOT sublime under normal conditions, but must be placed under low pressure and low temperature. Ammonium chloride (NH4Cl) and iodine (I2) are both substances that do sublime under normal conditions.

Filtration is the process used to separate the components of a mixture of solid substances that differ in solubility in a certain solvent. You can separate a mixture of solid substances by adding a liquid to the original mixture in which only some of the components of the mixture will dissolve. The resulting mixture, which contains both the dissolved and undissolved substances, is then poured through a filter paper--a porous paper that allows liquids to pass through while retaining any solids. The liquid that has passed through the filter paper is called the filtrate; the solid on the paper is the residue.

Evaporation can also be used to separate the solvent from the solution. A solution can be slowly heated in an Erlenmeyer flask, and the solute will remain after the solvent has evaporated.

Decantation is the process of separating a liquid from a solid (sediment) by gently pouring the liquid from the solid so as not to disturb the solid.

For this experiment, a practical plan is as follows: First combine the solid mixture of the two compounds, sodium chloride (NaCl) and sand (SiO2), with water. This will dissolve the sodium chloride. The sand will not dissolve into the water. We will "filter" the entire mixture, which allows the water in which the sodium chloride is dissolved to pass through, but not the sand. We will now have separated the sodium chloride and the sand. Then, we must evaporate off the water so that we weigh only the two original solids and not the water we added.

Procedure:

(NOTE: Do NOT dispose of any part of your lab until you are 100% positive you do not need it again. It is good practice to keep all parts of your lab until you are finished.)

Record the letter (A, B, C, or D) of your mixture (on the bag contents label) on the line above Data Table 1 below.

Obtain an Erlenmeyer flask [label it 1] and weigh and record the mass.

Add the entire contents of your unknown mixture bag to the flask and weigh and record the mass of the Erlenmeyer flask and the mixture.

Add 10 mL of water (preferably distilled) to the solid in the Erlenmeyer flask [Erlenmeyer flask 1] and stir gently for 5 minutes.

Weigh a new clean, dry Erlenmeyer flask [Erlenmeyer flask 2].

Decant the liquid from Erlenmeyer flask 1 into Erlenmeyer flask 2. This may work better if you place a utensil against the lip of the pouring flask to encourage a slow steady stream of liquid into the second flask.

Add another 10 mL of water to the solid in Erlenmeyer flask 1, stir for 1-2 minutes, and decant this liquid into the Erlenmeyer flask 2 as before.

Repeat with still another 10 mL of water. This process extracts (dissolves) the soluble sodium chloride from the insoluble sand.

Allow the two flasks to dry. Let them dry until the sand appears dry and freely moves when you shake the Erlenmeyer flask a little and the sodium chloride looks dry.

To speed up the process, you can heat the flasks slowly over a burner set on low on your stove top or in the oven (set at 125-200ËF). I would suggest heating it on top of another pan (NOT nonstick coated) Use a low setting and watch closely as you donât want it to boil over.

Allow the Erlenmeyer flasks to cool to room temperature (if they were heated) and weigh the Erlenmeyer flasks and their contents separately. Record their masses in the appropriate sections of the table.

To ensure that there is no water remaining, heat for another 5-10 minutes oven or 1-2 minutes on the stove. Allow to cool to room temperature and reweigh the Erlenmeyer flask. If it is within 0.3 g of your initial weighing you can stop. If the second weighing is not within 0.3 g of your initial weighing, reheat again, cool, and reweigh. The difference between this mass and the mass of the empty Erlenmeyer flask is the mass of NaCl.

Unknown Mixture Label (A, B, C, or D) ___________

Data Table 1

Measure or calculate and record the following (in grams):
mass of the empty Erlenmeyer flask 1:
mass of the Erlenmeyer flask 1 plus the mixture sample:
mass of the mixture sample:
mass of the Erlenmeyer flask 1 and the remaining contents after drying of sand:
mass of Erlenmeyer flask 1 and dry sand (2nd weighing)
Subtract (a) from (e) to obtain the mass of sand in the sample:
Measure or calculate and record the following (in grams):
mass of an empty Erlenmeyer flask 2:
mass of Erlenmeyer flask 2 and dry NaCl (1st weighing)
mass of Erlenmeyer flask 2 and dry NaCl (2nd weighing)
mass of Erlenmeyer flask 2 and dry NaCl (3rd weighing) if necessary
measured mass of dry NaCl:

Assignment Questions (all work must be shown for all calculations):

Using the results of your lab, complete all the questions below.

Upload one picture that is representative of your experiment with this report to the appropriate D2L Brightspace Assignments folder.

Complete Data Table 1 located in the Procedure. Make sure to include all your work for all the calculations performed.

The amount of sodium chloride in the original mixture may also be determined indirectly by subtracting the SiO2 mass from the initial sample mass. Calculate the expected mass of NaCl using this method.

Calculate the percent difference of NaCl (Note: This is not % Error, but it is a similar calculation. This is an error calculation that checks precision between the results of the two methods from the following equation: (Note: the unit for this calculation is â% differenceâ)

% difference=measured mass-mass by subtractionmass by subtraction x 100

What is the mass percent of each component in your mixture: SiO2, and NaCl? (Note: the units for this calculation are â% SiO2â and â% NaClâ)

mass percent=mass of componenttotal mass of sample x 100

Error Analysis: Was your % difference from Assignment Question 4 within 10%? Why or why not? Did your two mass percentages in Assignment Question 5 add up to 100%? Why or why not? What were your biggest sources of error in this experiment? What would you do differently if you were to repeat this experiment? Explain.

What type of properties (physical or chemical) are we using to separate the mixture in this laboratory. Explain your answer.

A mixture is found to contain 0.69 g SiO2, 1.05 g of cellulose, and 2.17 g of calcium carbonate. What is the mass percentage of SiO2 in this mixture?

Assume you have a mixture of NH4Cl, sand, and salt and access to a regular chemistry laboratory. How would you separate the three?Write out what your procedure would be in numbered steps. Please research the answer to this question and properly cite your source. It is alright to research using the internet. However, Wikipedia, Yahoo Answers, Ask.com, and other non-scientific sources cannot be used.

CHEM 1311 Lecture Notes - Lecture 12: Supersaturation, Intermolecular Force, Exothermic Process

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