Examples of tasks with their solutions

 

1. What occurs with erythrocytes at 310⁰ K in 2% solution of glucose(ρ = 1,006                                                 

Data:                                                              Solution:               g/ml).

T = 310⁰K                    P_osm = C(X)·R·T;

ω(C₆H₁₂O₆) = 2%             10·ρ(solution) · ω%(X)

ρ = 1,006 g/m           P_osm = ——————————·R·T;

M(C₆H₁₂O₆) =180g/M                        M(X)

P_osm -?                              1)   10·1,006·2

                                     P_osm = ————— · 8,31·310 = 287,951(kPa)

                                                      180

                                          2) P_osm (glucose) < P_osm(blood)

                               Consequently, in this solution hemolysis occurs.

                                                                             The answer: hemolysis.

 

2. Calculate the vapor pressure of solution, containing 34,2 g of sucrose

C₁₂H₂₂O₁₁ in 180 g of water at 30⁰C if vapor pressure of water equals

0,42·10⁵ Pa at the same temperature.

Data:                                                              Solution:

M(C₁₂H₂₂O₁₁) =34,2 g    1) n = ν(C₁₂H₂₂O₁₁) = 34,2/342 = 0,1 Mole

m(H₂O) = 180 g              2) N = ν(H₂O) = 180/ 18 = 10 Mole

 P_o = 4,2·10⁴ Pa               3) P_o· n   4,2·10⁴· 0,1

                                     P= ——— = ————— = 4,16·10⁴ Pa

 P-?                                N+n        10+0,1

M(C₁₂H₂₂O₁₁) =342 g/M                 

 M(H₂O) = 180 g/M               

                                                   The answer: 4,16·10⁴ Pa

 

3. Determine the molecular weight of the substance if vapor pressure above the    solution of 21 g of the substance in 400 g of acetone is equal to 21854,4 Pa. Vapor pressure of acetone (CH₃)CO equals 23939,35 Pa at the same temperature.

Data:                                                              Solution:

m(substance) =21 g        1) N= ν(CH₃)CO = 400/58 = 6,9

m(CH₃)CO) = 400 g       2)     P_o –P    n

    P₁= 21854,4 Pa                     ——— = ———

    P₀ =23939,35 Pa                       P₀     n+N

                         23939,35 – 21854,4      n

        M(sub) -?             ————————— = ———

M(CH₃)CO) = 58 g/Mol            23939,35          n + 6,9

                              2084,95   n

                          ———— = ———;    n = 0,658

                           23939,35   n + 6,9

3)M(sub) = 21/0,658 = 32(g/Mole)

                                                      The answer: 32g/Mole

 

4. Determine the freezing and boiling temperatures of solution, containing 1 g of   nitrobezene in 10 g of benzene. E(C₆H₆) = 2,57⁰, K(C₆H₆) = 5,1⁰. The boiling point of pure benzene equals 80,2 ⁰C, and freezing -5,4⁰C.

Data:                                            Solution:

       m(C₆H₅NO₂) =1 g        1)                m(X)

       K(C₆H₆) = 5,1⁰.                   b(X) = —————— ∙1000

       E(C₆H₆) = 2,57⁰                                         M(X)∙m(solvent)

t_b = 80,2⁰C                   2) b(C₆H₅NO₂) = 1 ∙1000/123∙10 = 0,813 (M/kg)

t_f = 5,4⁰C                     3) ∆t_f = K ∙b(X),  ∆t_b = E∙b(X)

                                         ∆t_f = 5,1∙0,813 = 4,15⁰   ∆t_b = 2,51∙0,813 =2,09⁰

        t_b(solution) -?      4) t_b = 80,2 + 2,09 = 82,29⁰C

        t_f(solution) -?         t_f = 5,4 –4,15 = 1,25⁰C                   

   M(C₆H₅NO₂) =123 g/M                   Тhe answer: 82,29⁰C, 1,25⁰C

 

5. Determine the molecular weight of solute if 4 g of substance are dissolved in 110 g of ethanol C₂H₅OH, and the solution boils at 78,62⁰C, if E(C₂H₅OH)=1,22⁰. Boiling point of ethanol is 73,3⁰C.

Data:                                                              Solution:

m(substance) =4 g              1)Δt_b=78,62 – 78,3 = 0,32⁰

m(C₂H₅OH) = 110 g           2)                                E m(X)

           E (C₂H₅OH) =1,22⁰             Δt_b = E ^. b (x) = ———————∙1000

                                                               M(X)∙m(solvent)

   t=78,3⁰C                                            E∙1000         1,22∙1000

M(sub) -?                            M(sub) = —————— = ———— =138,64

                                                          Δt_b∙m(C₂H₅OH) 0,32∙110

                                                                                                                                           

The answer: 138,64 g/Mole.

Question and tasks:

1. What physico-chemical properties are called colligative? List.

2. What does the quantitative expression of colligative properties depend on?

3. What membranes are called semipermeable? Give the examples of materials with the properties of semipermeability.

4. What pressure is called osmotic? What apparatus are applied for determination of osmotic pressure?

5. What factors does the osmotic pressure depend on? Express this dependence.

6. In what cases do the electrolyte solutions have the same osmotic pressure at the same temperature? How are these solutions called?

7. What solution is called a) hipertensive, compared with the other one              b) hipotonic? In the direction of which of them must the osmosis go?

8. Formulate and give the mathematical expression of the Raoult’s law.

9. What two consequences of Raoult’s law do you know?

10. When do liquids boil (crystallize)?

11. What constants are called ebullioscopic and cryoscopic? Do they depend on nature of solute, solvent?

12. Is it right that all one-molal aqueous solutions of nonelectrolytes a) boil at 100,52⁰C b) freeze at –1,86⁰C, prove the answer.

13. What is called the isotonic coefficient (i)? What is physical meaning of i?            What are the methods of experimental determinations?

 14.How are dissociation degree and isotonic coefficient connected with each other?

15. How are the molecular weights of solutes determined using their colligative properties. Give the formulas for the calculations.

16. Determine the osmotic pressure of solution in 1 L of which 18,4 g of glycerin (C₃H₈O₃) are contained at 0⁰C. The answer: 4,54∙10⁵ Pa.

17. Calculate the osmotic pressure of solution in 5 L of which 171g of sucrose C₁₂H₂₂O₁₁ are contained at 25⁰ C. The answer: 2,477∙10⁵ Pa.

18. 400 ml of solution contain 2 g of solute at 27⁰C. The osmotic pressure of the solution is 1,216∙10⁵ Pa. Determine the molecular weight of the solute.                                                              The answer:102,5 g/M.

19. Sucrose solution (C₁₂H₂₂O₁₁) at 0⁰C possesses the osmotic pressure as 7,1∙10⁵ Pa. How many grams of sucrose do the 250 ml of this solution contain?                                                                 The answer: 18g.

20. How many grams of ethanol should we dissolve in 500 ml of water to get the osmotic pressure of this solution 4,052∙10⁵ Pa at 20⁰ C.                                                                                  The answer: 3,8g.

21. The osmotic pressure of solution whose volume is 5L at 27⁰C is 1,2∙10⁵ Pa. What is the molarity of this solution? The answer: 0,053 M/L.

22. How many grams of ethanol must 1 L of solution contain to get the osmotic pressure the same as for formaldegid solution containing in 1L 4,5 g formaldegid CH₂O at the same temperature. The answer: 6,9 g.

23. 200 ml of solution contain 1 g of solute and have the osmotic pressure 7,1∙10⁵ Pa at 20⁰. Determine the molecular weight of the solute.                                                     The answer: 283 m/L.

24. Determine the molecular weight of the solute if the solution, containing in

0,5 L 6 g of solute at 17⁰C possesses the osmotic pressure 4,82∙10⁵ Pa.                                                                       The answer: 62 g/M.

25. Calculate the osmotic pressure of solution in 1L of which 0,2 M of nonelectrolyte are contained: a) at 0⁰C b) at 18⁰ C.      The answer: 4,54∙10⁵ Pa; 4,84∙10⁵ Pa.

26. Determine if 3% aqueous solutions of sucrose C₁₂H₂₂O₁₁ and glucerine C₃H₈O₃ will be isotonic at the same temperature or not. Take the densities of solutions as 1 g/ml. The answer: they won’t.

27. The osmotic pressure of solution, whose volume is 3L at 100⁰C equals             1,2∙10⁵ Pa. What is the molarity of this solution?                                                                                        The answer: 0,05 M/L.

 28. Calculate the osmotic pressure of 20% aqueous solution of glucose (ρ = 1,08 g/ml) at 310⁰K applying for intravenous invasions when pulmonary happens. What kind of solution will it be compared with blood, if P_osm of blood equals 740-780 kPa?                           The answer: 3091,3 kPa, solution will be hypertensive.

29. Calculate the osmotic pressure of 0,01 M potassium chloride solution at 310 K, if isotonic coefficient equals 1,96. What kind of solution will it be if compared with blood plasma. The answer:50,5 kPa, hypotonic.

30. Calculate the vapor pressure of 30% aqueous solution of carbamaide CO(NH₂)₂ at 50⁰ C. The water vapor pressure at this temperature equals 12,33 kPa.

 

                             Class 6

      Topic: The summary on the topic: Valumetric analyses (1hour).

       Test on the topics “Solutions”, “Volumetric analyses” (2hours)

                 Test card sample:

 

1. Up to what volume should we dilute 500 ml of 20% (by mass) solution of NaCl (ρ = 1,152 g/ml) to prepare 4,5% solution (ρ = 1,029 g/ml).

                                                                          The answer: up to 2,49 L.

2. What do the concentration of hydrogen ions and pH of formic acid solution (HCOOH) equal, if α = 0,003 K_a = 1,8·10^-4?                                                       The answer: 6·10^-3; 2,22.

3 As a result of the dissolving of 13,0 g of nonelectrolyte in 400 g of diethylether the boiling temperature increases by 0,453 K. Determine the molecular weight of solute E(ether) = 2,02. The answer: 145.

4 Determine the titre and normality of KMnO₄ solution if 20 ml of KMnO₄ solution are consumed for titration of Na₂C₂O₄- sample whose mass is equal to 0,0165 g.                                             The answer: 0,00367 g/ml, 0,0116 Mol/L

 

                    

Class 7