cdo ap chemistry unit 7 part 2 problem set solutions schs

SCHS AP Chemistry Unit 7 Part 2 Solutions

CDO AP Chemistry Unit 7 Part 2 Problem Set Solutions

Pre Unit

1. Write equations for the dissociation in water of each of the following electrolytes. a. MgI

2

b. KClO4

c. Rb

2CO

3

d. Sc2(SO

4)3

2. Write a net ionic equation for each of the following reactions. a. A piece of copper is dropped into a container of water.

b. Liquid bromine is added to a container of sodium iodide crystals.

c. An aluminum strip is immersed in a solution of silver nitrate.

d. Fluorine gas is bubbled into a solution of aluminum chloride.



e. Silver nitrate + potassium chromate

f. Zinc acetate + cesium hydroxide

g. Ammonium sulfide + lead (II) nitrate

h. Ammonium sulfate and potassium hydroxide are mixed together.

i. Cobalt (II) chloride is combined with silver nitrate

j. Solid calcium carbonate is reacted with sulfuric acid



Video 6 3. Considering the energetic of solute-solute, solvent-solvent, and solute-solvent interactions,

a. Explain why NaCl dissolves in water but not in benzene (C6H6) NaCl and water are both polar. The ion-dipole formation between water and the NaCl is strong enough to overcome the lattice structure of the salt. Benzene is non polar and water is polar the dispersion IMF is not a strong enough attraction to water to overcome the Hbond that water has

b. What factors cause a cation to be strongly hydrated?

Strength of the ion-dipole interaction 4. Indicate the type of solute-solvent interaction that should be most important in each of the

following solutions. a. CCl4 in benzene(C6H6)

Both Non-polar - dispersion

b. Methanol (CH3OH) in water

Both polar – H-bond

c. KBr in water

Polar ionic compound and polar water – ion-dipole

d. HCl in acetonitrile (CH3CN)

Both polar – dipole/diple (HCl can ionize so ion-dipole)

5. Indicate the type of solute-solvent interaction in each of the following solutions, and rank

the solutions from weakest to strongest solute-solvent interaction. a. KCl in water

Ion-dipole b. CH2Cl2 in benzene (C6H6)

Dispersion – dipole/dipole c. Methanol (CH3OH) in water

H-bonding Dispersion < H-Bonding < Ion-Dipole



6. Explain how solutes can be separated through paper chromatography based on intermolecular forces. In paper chromatography a piece of paper with the substance to be separated is place in a solvent. The solvent (mobile phase) travels up the paper (stationary phase) carrying solute particle with it. The way the solute is separated is based on the solute’s attraction to the paper and to the solvent. If the solute has a strong attraction to the solvent the solute will travel further up the paper if it has a weak attraction to the solvent it will be lower on the paper. The paper is cellulose with -OH so it has non polar and polar portions of the paper.

7. Fractional distillation was used to isolate an unknown volatile substance that had contaminated the well water at a rural property. a. Is the boiling point of the unknown substance greater than, less than or equal to 100 oC

at 1.0 atm? Justify your answer. <100oC. In order for it to be separated from the water its vapor pressure must be greater the waters vapor pressure under the same conditions. A substance boils when the vapor pressure = the atmospheric pressure. The bp of the contaminate must be lower than the water or it cannot be separated by fractional distillation

b. What can be said about the relative strengths of intermolecular attraction among and between the contaminant and water? The strength of attraction between water molecules must be greater than the attraction between the water and the contaminant this is why the vapor pressure is greater and the bp lower

8. In the enthalpy of solution calculation which energy term for dissolving an ionic solid would correspond to the lattice energy? Which energy terms in this equation are always exothermic?

Separation of the ionic crystal lattice solute particles (solvation). Formation of the solution

9. The enthalpy of solution of KBr in water is about +198 KJ/mol. Nevertheless, the solubility of KBr in water is relatively high. Why does the solution process occur even though it is endothermic?

Increase in disorder lowers the energy so the solute can dissolve



Video 7 10. Draw one representation that shows the intermolecular interactions between NH3 and

water and another that shows the intermolecular interactions between SbH3 and water. Use your representations to help explain why NH3 has a higher solubility in water than SbH3.

11. Explain why CH3OH is miscible in water whereas CH3(CH2)6OH is not. CH3OH is polar where water is polar and can form Hbonds with water so miscible; CH3(CH2)6OH is mostly non polar and water will be more attracted to itself than to CH3(CH2)6OH so won’t be miscible in water

12. Which of the compounds below is most soluble in water? Justify your answer.

HOCH2CH2OH or CH3CH2OH

Both have the same nonpolar portion however HOCH2CH2OH can form 2 hbonds with water where CH3CH2OH can only form one, this is why HOCH2CH2OH is more soluble

13. Potassium bromide is least soluble in which of the two liquids from each set below? Justify

your choice. a. H2O or CH4 – methane is non polar, ionic compounds are soluble in polar solvents

b. CH3OH or CH3CH2OH – its soluble in both because they are both polar, however it is more soluble of methanol, since it has a shorter nonpolar portion

c. NH3 or Br2 – bromine is nonpolar, ionic compounds are soluble in polar solvent

14. Describe the process for making a saturated solution of sugar and water.

Keep temperature constant and add sugar to water until the sugar no longer dissolves and some remains on the botton



15. Describe the process for making a supersaturated solution of sugar and water.

Make a saturated solution then heat the solution so the sugar that remained on the bottom dissolves

16. You are given a supersaturated solution of sugar and water, and are told to turn it into a

saturated solution. How would you go about doing this? Add a few seed crystals to get recrystallization to occur

17. The following questions refer to the solubility curve below. Suppose you have four beakers containing equal volumes of water. You then add one type of salt to each beaker until the solutions become saturated.

a. Which of the four saturated solutions above would produce the greatest mass of precipitate when cooled from 90oC to 60oC? KClO3

b. The molality of which solution would increase by the greatest degree when it cooled

from 20oC to 0oC? Ce2(SO4)3 – more will go in solution when cooled

c. Which saturated solution has the highest molality?

KNO3

18. These questions refer to the solubility curve in questions 17. a. Will adding 50 g of NaCl to 100 g of distilled water at 60oC produce a saturated or an

unsaturated solution? Saturated



b. Will adding 20 g of KClO3 to 100 g of distilled water at 75oC produce a saturated or an unsaturated solution? Unsaturatured

19. You are given a dry mixture containing 60 g of KNO3(s) and 60 g KClO3(s) and are asked to

produce as much KClO3(s) as possible. Solve this problem using fractional crystallization and the solubility curve from question 17.

Heat water to 100oC and add the mixture to the water, both will dissolve. Cool the mixture to 50oC so that the KNO3 will precipitate and the KClO3 will stay in solution. (See curves) The KNO3 can then be filtered gravimetrically

Video 8

20. In the following images, a single unit represents one mole of a particle and the boxes represent one liter containers. Circle the illustration that provides the best representation a 4 M solution of NaCl. The first one, shows the NaCl as 4 ions not as molecules

21. A 9.98 g sample of glucose, C6H12O6, is dissolved in enough water to produce a 1395 mL solution. What is the molarity of the solution?

22. How many grams of MgSO4 . 9H2O are needed to prepare 125 mL of 0.200 M magnesium

sulfate?



23. 251 mL of 0.45 M HCl is added to 455 mL water. What is the molarity of the final solution? (Assume the volumes are additive).

24. How many milliliters of 0.250 M KMnO4 are needed to deliver 0.00450 moles of KMnO4 in a titration?

25. A 5.75 g sample of KOH is dissolved in 425 mL of water. Find the molality of the solution.

26. 200 mL of 2.0 M copper (I) nitrate is mixed with 150 mL of 2.5 M sodium hydroxide. The mixture produces a precipitate.

a. Identify the precipitate



b. What is the limiting reactant? Justify your answer

c. What is the maximum mass of precipitate that can be formed in this reaction?

d. What is the percent yield if 31 g of precipitate is formed in the reaction?

e. The percentage yield increases when the temperature of the solution is reduced. Explain why this is. The reaction must be exothermic because decreasing the temperature would cause more products to be produced. (you don’t know this yet

cdo ap chemistry unit 7 part 2 problem set solutions schs

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