Questions and tasks for self-control.

1. What does it mean “the solution”?

2. What approximate ways of concentration expressions exist? List, give the brief characteristic of each one.

3. What exact ways of concentration expressions do you know? List them.

4. What does it mean the ”mass fraction”?

5. Give the differences between percentage and mass fraction.

6. What does it mean “the molarity”.

7. What does it mean “the equivalent”, “factor of equivalent”, “molar mass of equivalent”. Give the examples of their determinations.

8. What does it mean “the normality”.

9. Explain the term “titre of solution”.

10. What algebraic relationship exists between C(X) and w(X); C(1/Z X) and C(X), C(1/Z X) and ω(x)?

11. What algebraic relationship exists between C(1/Z X) and t(X)?

12.  How many moles of FeSO₄· 7H₂O must we add to 100 ml of water to prepare 10% solution of FeSO₄? The answer: 1,45 mol.

13. To 250 g of 10% acid solution 500g of the solution of the same acid with unknown mass fraction are added and 25% solution is obtained. Determine mass fraction of acid in added solution. The answer: 32,3%.

14. 125 ml of hydrogen chloride (n.c.) are dissolved in 500 ml of water. Determine the mass fraction of HCl in obtained solution. The answer: 29%.

15. In what volume of 1 M H₂SO₄ solution 4,9 g of H₂SO₄ are contained? The answer: 50 ml.

16. How many (ml) of 20% HCl solution with density of 1,098 g/ml are required to prepare 1 L of 2 M solution?  The answer: 332,4 ml.

17. How many (ml) of 0,5 N BaCl₂ solution can we prepare from 24,4 g of BaCl₂·2 H₂O? The answer: 400 ml.

18. Calculate normality and titre of H₃PO₄ in 13% solution whose density is 1,07 g/ml. This solution is destined for complete reacting. The answer: 4,25 N; 0,139100g/ml.

19. In which mass of ether must we dissolve 3,04 g of aniline C₆H₅NH₂ to obtain the solution with molality 0,3 mol/kg. The answer: 225 ml.

20. What volume of 3N solution must be added to 900 ml of 0,5 N solution of the same substance to obtain the concentration equal to 1 N?The answer: 225 ml.

    21 For the reaction with solution, contained 0,498 g of Na₂B₄O₇·10H₂O are consumed 25,2 ml of HCl solution. Calculate the normality of HCl solution. The answer: 0,103 N.

Sample of test card on the topic “concentration units”

1. Solve for percentage of the solution, obtained by mixing of 100 ml of 30% sodium chloride solution (ρ = 1,20 g/ml) and 100 ml of 5% sodium chloride solution (ρ = 1,04 g/ml). 

             a) 18,39                     b) 20,60                   c) 41,20

2. Molar mass of equivalent for H₃PO₄ in reaction of NaH₂PO₄ formation is      equal to (in g/mol)

            a) 49                      b) 73,5                        c) 98

3. Factor of equivalence of salt in reaction:                                                                 Al₂(SO₄) + 8 NaOH = 2 Na[Al(OH)₄] +3Na₂SO₄ is equal to

            a) 1/8                      b) 1/6                        c) ¼

4. What weighed sample of Na₂CO₃ (in g) must we take to prepare 2 L of 2N solution used in reaction of full ion-exchange?

            a) 53                   b) 212                        c) 159

5.  Solve for molarity of 96% H₂SO₄  solution (ρ = 1,84 g/ml)

             a) 16                  b) 18                      c) 20

The answers to tasks of card sample

Number of question          1             2          3           4           5

Code of answer                 a              b          a           b           b

 

Laboratory work

 

Preparation of solution with given concentration by dilution of

Concentrated solution

 

Fulfillment of the work

Take the task from your teacher - to prepare from concentrated solution the certain volume of solution with less concentration.

 Calculate, how many (ml) of initial solution are required to prepare solution with given concentration. Then find the water volume required to obtain this solution. Find the solution density using the table. Show your calculations to teacher.

 After check prepare given solution by mixing obtained volumes of initial solution and water. To prepare solution with certain concentration use: measured flask, measured cilinder, pipette with help of which carry the determined volume of liquid over into the measured flask to our solution till the mark and mix. Addition of the water is carried on quickly at the beginning and closer to mark, below 1-2 sm from the mark, by drops. Estimation of liquid level in measured flask and measured cilinder is carried on by low meniscus. Mixing of the solution in the flask is carried on by shake and rotation.

Prepared solution have to be given out to the labassistent.

 

Example of calculation:

 It is required to prepare 50 ml of 0,05 N Na₂CO₃ solution from 0,2 M Na₂CO₃ solution if f_eq(Na₂CO₃) = ½.

Calculation:

 ν₂(1/2 Na₂CO₃)= C₂(1/2 Na₂CO₃)·V(s-n 2) =0,05·0,05 = 0,0025 (Mol)

ν(Na₂CO₃)=1/2ν₂(1/2 Na₂CO₃)=1/2 ·0,0025 = 0,0012(mol)

      ν(Na₂CO₃)    0,00125

V(s-n 1) = ————— = ———— =0,00625L or 6,25 ml of 0,2 M solution.

      C(Na₂CO₃)     0,2

 

Class 2