Answers and solutions to odd-numbered exercises are in appendia 1. Why is water

Question

Answers and solutions to odd-numbered exercises are in appendia 1. Why is water considered polar? 2. List some physical properties of water attibuted to hydrogen bonding. 3. Complete and balance the equations of the reactions leading to the formation of insoluble calcium and magnesium bicarbonates that cause hard water 4. Soap is either sodium or potassium stearate which reacts with calcium and magnesium bicarbonates forming insoluble compounds, e.g, a bathtub ring. Write a complete equation to express 5. List the various ways hard water can be softened. 6. With the help of a chemical equation, show how magnesium and calcium bicarbonates can be decomposed by heating. 7. Use an equation to show how hard water caused by magnesium and calcium sulfate can be softened with sodium carbonate (washing soda). 8. Show how hardness containing Ca and Mg can be removed with borax (Na, B,O,) 9. With equations, show how sulftur can become an acid in rain water.

Explanation / Answer

1. Water is called as "Polar" molecule because it has the uneven distribution of electron density. It has one side which is positively charged and another side negatively charged. The negative charges are towards hydrogen atoms whereas positive charges are towards oxygen atoms.

2. Physical properties of water attributed due to hydrogen bonding are

a. Water has high polar density

b. The lower density of Ice.

c. Water has a very high heat of evaporation

d. Surface Tension

e. Vapor Pressure.

3. Hard water is the water which has charges of Calcium and Magnesium.So when hard water is heated, Ca2+ ions react with bicarbonate(HCO3-) it forms insoluble Calcium Carbonate(CaCO3)

Ca2+ + 2HCO3-   ---> CaCO3 + H2O + CO2.

4. Ca2+ + RCOONa(Soap) -----> RCOOCa( Calcium salt) + 2Na+

     Mg2+ +RCOONa (Soap) ----> RCOOMg (Magnesium salt) + 2Na+

5. Hard water can be softened by following ways

a. Ion exchange water softener.

b. Shower head water filters

c. Reverse Osmosis

d. Water filter pitchers

6. Ca(HCO3)2 -------> CaCO3 +H2O+CO2

   Mg(HCO3)2 ------> MgCO3 + H2O+CO2

7. Na2CO3(Sodium sulphate) + CaSO4(Calcium Sulfate) ----> Na2SO4(sodium sulfate) + CaCO3(calcium carbonate)

   Na2CO3(Sodium sulphate) + MgSO4(Magnesium sulfate) ---> Na2SO4(sodium sulfate) + MgCO3(Magnesium carbonate)

8. Na2B4O7 .10H2O + Mg2+ ---> MgB4 O7 + NaOH

     Na2B4O7 .10H2O + Ca2+ ---> CaB4 O7 + NaOH

9. S + O2 ---> SO2 Fossil fuels burnt emit sulphur di oxide

    2SO2 + O2 ---> 2SO3 Sulphurdioxide reacts with atmosphere gives sulphate ion

   SO3 +H2O ---> H2SO4 which is nothing but ACID RAIN

10. N2 + O2 ---> 2NO

     NO + H2O ---> HNO3 Nitric acid is formed

11. Volume of solute = (Concentration of solution x Volume of solution) / 100.

12. Percent by mass =( Mass of solute x 100) / volume of solution

                                 = ( 10 x 100) / 100

                                  = 10%

13. 2.5mg/ml diphenhydramine HCL will be present

14. Molarity is nothing but the ratio of moles of solute per liters of solution

     a. Concentration of molarity = 6/5 = 1.2mol/L

15. Molarity = 0.75/ 1 = 0.75mol/L

16. Molarity is nothing but the ratio of moles of solute per liters of solution

     a. 3 molal solutions is made by dissolving 3 moles(40x3 = 120g) of NaOH in 1000g of water

       So for 500g of water it will be 60g of NaOH

       Total mass of solution = 500+60 = 560g

     

       

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