SOLUTIONS
Mixtures
Mixtures are made by mixing two or more different pure substances. Mixtures do not have a fixed composition. Mixtures with different combinations have different properties.
         Types of Mixtures
Homogeneous mixtures: Have single phase and same properties throughout.
Ex: air, tea, salty water, sugar and water…

*Homogeneous mixtures are called SOLUTIONS.

Heterogeneous mixtures: Have phases with different properties.
Ex: soup, chalk and water, gasoline and water…
There are two types of heterogeneous mixtures:
-emulsion: liquid + liquid ex: oil-water
-suspension: solid + liquid ex: sand-water

A solution has two parts:

Solute: minor part of the solution: the substance that is dissolved in the solution by a solvent.

Solvent: major part of the solution: the substance in which solute is dissolved.

Aqueous Solution: The solution in which water is used as a solvent.

Solubility of Substances in Water
 Solubility is the maximum quantity of a solute dissolved in a solvent under specified conditions.

• Solubility of solids generally increases by increasing temperature.
• Solubility of gases generally increases by decreasing temperature and increasing pressure.
• Rate of dissolution of a substance increases by stirring or increasing temperature and surface area.

 According to their solubility’s in water, substances can be classified into three groups;

1. Soluble(almost completely soluble): Table salt and sugar
2. Slightly soluble : Oxygen and nitrogen
3. Insoluble (almost completely insoluble) : silver, gold

NO3-

CH3COO-

Cl-

OH-

I-

SO42-

CO32-

Br-

S2-

SO32-

PO43-

SiO32-

NH4+

S

S

S

S

S

S

S

S

S

S

S

U

K+

S

S

S

S

S

S

S

S

S

S

S

S

Na+

S

S

S

S

S

S

S

S

S

S

S

S

Ba2+

S

S

S

S

S

I

I

S

U

SS

I

I

Ca2+

S

S

S

SS

S

SS

I

S

U

SS

I

I

Mg2+

S

S

S

I

S

S

I

S

U

SS

I

I

Al3+

S

S

S

I

S

S

U

S

U

U

I

I

Zn2+

S

S

S

I

S

S

I

S

I

SS

I

I

Fe2+

S

S

S

I

S

S

I

S

I

SS

I

I

Fe3+

S

S

S

I

U

S

U

S

I

U

I

I

Cu2+

S

S

S

I

U

S

U

U

I

U

I

I

Ag+

S

S

I

U

I

SS

I

I

I

SS

I

U

Hg2+

S

S

S

U

I

S

U

SS

I

U

I

U

H+

S

S

S

U

S

S

S

S

S

S

S

I

Cr3+

S

S

S

I

S

S

U

S

U

U

I

I

Pb2+

S

S

SS

I

I

I

I

SS

I

I

I

I

 

Types of Solutions
1. Saturated Solutions: The solutions in which no more solute can be dissolved are called saturated solutions.
2. Unsaturated Solutions: A solution which does not contain the maximum amount of solute than it can dissolve is said to be unsaturated. When more solute is added to an unsaturated solution, it dissolves.
According to the amount of solute in a solution, solutions are classified in two groups: concentrated and dilute.
3. Dilute: If the amount of dissolved solute is less in comparison to the amount of solution, the solution is called dilute.
4. Concentrated: If a solution contains relatively large amount of dissolved solute, the solution is said to be concentrated.

PERCENT CONCENTRATION
The mass of solute dissolved in 100 g of solution is called the percentage concentration of the solution.

Examples:

1. A 250g of solution contains 50g of sodium chloride. Calculate the mass percentage of NaCl in this solution.
2. Calculate the mass percentage of sugar in a solution that is prepared by 25g of sugar and 225g of water.
3. A 150g of sodium sulfate (Na2SO4) solution contains 15% salt by mass. Calculate the mass of sodium sulfate that is found in this solution.
4. A 30% sulfuric acid solution was found to contain 60g sulfuric acid. Determine the mass of this solution.
5. A 2liters nitric acid solution has a density of 1.12g/ml. Determine the mass percentage of nitric acid if the mass of nitric acid in this solution is 448g.
6. A 200g solution contains 10% sodium carbonate by mass. Calculate the mass percentage after addition of 50g of sodium carbonate to this solution.
7. A 300 g 20% nitric acid solution was heated and the volume of evaporated water was found to be 100ml. Calculate the final mass percentage of nitric acid.
8. At 25°C 36g of table salt can be dissolved in 100g of water. Calculate the mass percentage of table salt in such a solution.
9. A 400g solution contains 20% potassium nitrate by mass. Determine the new mass percentage after addition of 100g of water.
10. A 200g 10% and a 300g 20% glucose solution were mixed. Calculate the mass percentage of the final solution.
11. What would be the final mass percentage of nitric acid if you mix a 80ml 96% nitric acid solution(d:1.5g/ml) with a 60ml 48% nitric acid solution(d:1.3g/ml).
12. What volume of 38% hydrochloric acid solution (d:1.19g/ml) should be used to prepare a 5% 1L hydrochloric acid solution?
13. You have two sugar solutions containing 10% and 25% sugar by mass. How can you prepare a 20% 300g of solution out these two solutions?
14. Through a 1L 10% ammonia solution (d:0.96g/ml) 11.2L of ammonia was passed at STP. Calculate the new mass percentage of ammonia in the final solution.
15. 50g, 5% sodium carbonate solution was added to a 200g saturated sodium carbonate solution. (The solubility of sodium carbonate in water is 21.5g in 100g water.) Calculate the mass percentage of sodium carbonate in the final solution.
16. Calculate the mass percentage of CuSO4.5H2O in a solution that is prepared by addition of 25g of cupper nitrate penta hydrate to 75g of water.
17. Calculate the mass of Glaubert’s salt, Na2SO4.10H2O that should be used to prepare 500g of 10% sodium sulfate solution.
18. What mass of Glaubert’s salt should be added to a 200g 8% sodium sulfate solution to make the final mass percentage 20%?
19. Solubility of KCl at 70°C and 30°C are 30.2g and 10.1g in 100g of water. What mass of KCl would crystallize if the temperature of a 150g saturated solution was decreased from 70°C to 30°C.?

 

MOLARITY

Molarity is the most common concentration unit. It is generally used in calculations dealing with volumetric stoichiometry. Molarity can be defined as the mole number of solute dissolved per liter of solution. The abbreviation for molarity is M. The unit of molarity is mol/L or M (read as molar).

1. A water sample taken from a lake contains 3.8 g of sodium chloride (NaCl) in one liter of solution. Find the molarity of sodium chloride in the sample.
2. A 5.6 g sample of potassium hydroxide is dissolved in enough water to obtain 100mL of solution. What is the molar concentration of the resulting solution?
3. How many grams of potassium permanganate (KMn04) should be dissolved in water to prepare 100mL of 0.25 M solution?
4. How many grams of sodium hydroxide are needed to prepare 500 mL of 0.2 M solution?
5. Suppose that you are given a concentrated solution of HCI which is known to be 36.5% HCI by mass. If the density of the solution equals 1.2 g/mL, what is the molarity of the solution?
6. What is the molarity of the solution that is 63% nitric acid (HN03) by mass? (The density of the solution is 1.4 g/mL)
7. What is the molarity of a solution obtained by mixing 200 mL of 0.3 M ammonium nitrate solution with 400 mL of 0.6 M ammonium nitrate solution?
8. How many mililiters of 3 M and 1.5 M sulfuric acid solutions should be mixed in order to prepare 600 mL of 2 M sulfuric acid solution?

 

ELECTROLYTIC DISSOCIATION

A liquid that conducts electricity as a result of the presence of positive or negative ions is called an electrolyte.
For a solution to conduct electricity the solution has to contain ions. Therefore electrolytes are molten ionic compounds or solutions containing ions.

HCl(ag) ® H+ + Cl-

NaCl(s) ® Na+ + Cl-

Ca(NO3)2® Ca2+ + 2NO3-
This process is called dissociation or ionization. Salts, acids and bases can act as electrolyte.
Ex:HF, HNO3, KI, CaSO4, BaCl2, NaOH, Mg(NO3)2

Substances whose water solutions or molten forms do not conduct electricity are called non-electrolytes. They dissolve but do not produce ions in water.

C12H22O11(s) ® C12H22O11 (aq)
                                                           Sugar
Ex: Decide if the following compounds are electrolyte or non-electrolyte: table salt, tap water, distilled water, alcohol, NaOH, CaCl2, BaO, H3PO4
(Distilled water, alcohol, BaO are non-electrolytes.)

• Diprotic acids and bases are ionize in water in two step

 

1st step:         H2SO4  ® H+ + HSO41-
2nd step:     + HSO41- ® H+ + SO42-   
                     H2SO4® 2H+ + SO42-  

 1st step:      Ba(OH)2 ® BaOH+ + OH-
2nd step:   + BaOH+   ® Ba2+ + OH-       

• Acidic and basic salts are formed from incomplete neutralization of acids with bases. Solution of these salts contains H+ and OH- ions in addition to metal and acidic remnant ions.

 

 2NaOH + H2SO4 ®  NaHSO4 + H2O
                              sodium hydro sulfate
                                              (ACIDIC SALT)

 1st step:      NaHSO4 ® Na+ + HSO4-
 2nd step:     HSO4-      ® H+ + SO42-

  Ba(OH)2 + HCl ® BaOHCl + H2O
                            Barium hydroxyl chloride
                                          (BASIC SALT)

1st step:    BaOHCl ® BaOH+ + Cl-
2nd step:   BaOH+   ® Ba2+ + OH-

Ex: Write the equations for the dissociation of the following species: LiOH, H2CO3, Na2SO4, Ca(OH)2, KHSO3, Ba(NO3)2, Al2(SO4)3, K3PO4, Mg(HCO3)2

Ex: Calculate the number of chlorine ions those are found in 20% 267g AlCl3 solution.

Quiz:
1. Write the equations for the dissociation of the following compounds: HNO3, H2SO3, AlCl3, LiOH, NaHCO3
2. Calculate the number of sulfate ions those are found in 200g 34.2% aluminum sulfate solution.

FRACTION NUMBER of DISSOCIATION (a)

All electrolytes do not dissociate completely. The electrolytes those ionize completely are called strong electrolytes and ones those ionize partially are called weak electrolytes. The amount of dissociation of a substance can be understood by ``a`` which is called fractional number of dissociation.

a = n/N      where n is equal to number of dissociated particles and N is equal to total number of particles.
     

• For strong electrolytes a »1. Because they ionize almost completely. Most of the salts, HBr, HCl, HNO3, H2SO4, HMnO4, HClO4, KOH, NaOH, Ba(OH)2, are examples for strong electrolytes.

• For weak electrolytes a << 1. Because they ionize partially. H2CO3, H2S, HNO2, H2SO3, Ca(OH)2 are examples for weak electrolytes. In their water solutions, there are some molecules too.

 

• For non-electrolytes a = 0

Ex: 4.48L of HF was passed through water. Calculate the number of moles of hydrogen ions in the media.
Ex: Some HF was passed through water and the amount of F- was found to be 0.75 moles. Determine the volume of used HF.

Reactions in Solutions

When solutions are mixed, a reaction may take place between the ions present in solutions. The reaction takes place only in case of;

• formation of a precipitate
• formation of a gas
• formation of a weaker electrolyte

Example1:
Molecular formula:  Na2SO4 + Ba(NO3)2 ® BaSO4¯ + 2NaNO3

Ionic equation      :  2Na+ + SO42- + Ba2+ 2NO3- ® BaSO4¯ + 2Na+ + 2NO3-

Net ionic eqn       :  Ba2+ + SO42- ® BaSO4¯

As you see Na+ and NO3- ions do not take part in net ionic equation reaction, such ions are called spectator ions.

Example2:
Molecular formula:  2HCl + Na2CO3 ® (H2CO3) H2O + CO2­ + NaCl

Ionic equation      :  2H+  +  2Cl-  +  2Na+  +  CO32- ® H2O  +  CO2­  + 2Na+  +  2Cl-

Net ionic eqn       :  2H+ + CO32- ®  H2O + CO2­ 

Spectator ions     : Na+ and Cl-
Example3:
Molecular formula:  Na2CO3 + 2HNO3 ® H2O + CO2­ + NaNO3

Ionic equation      :  2Na+ + CO32- + 2H+ + 2NO3-® H2O + CO2­  + 2Na+ + 2NO3-

Net ionic eqn       :  2H+ + CO32- ®  H2O + CO2­ 

Spectator ions     : Na+ and NO3-

 

 

Ex: Complete and balance the following molecular reactions. Write the ionic and net ionic equations for each reaction.

• ZnCl2 + K2S à
• 2HBr + K2SO4 à 2KBr + H2SO4
• KOH + H3PO4 à
• Zn + HCl à
• Cu + AgNO3 à
• 2KOH + H2SO4  ® K2SO4 + 2H2O
• 2NaNO3 + K2SO4 ® Na2SO4 + 2KNO3
• CuSO4 + KOH ® Cu(OH)2¯ + K2SO4

Ex: Below are some pairs of compounds. Decide if these pairs are would react with another one or not.

• CaCl2 and Na2CO3
• H2SO4 and Ba(OH)2
• Na2SO4 and KNO3
• BaCl2 and NaOH
• MgCl2 and NaOH
• HNO3 and K2CO3

• 2HBr + K2SO4 à 2KBr + H2SO4

Ionic equation: 2H+ + 2Br- + 2K+ + SO42- à 2K+ + 2Br- + 2H+ +SO42-
Net ionic equation: no reaction
Spectator ions: H+-Br--K+-SO42-

• CuSO4 + 2KOH ® Cu(OH)2 + K2SO4

Ionic equation: Cu2+ + SO42- + 2K+ + 2OH- à Cu(OH)2 + 2K+ + SO42-
Net ionic equation: Cu2+ + 2OH- à Cu(OH)2
Spectator ions: K+-SO42-