Observatory Workbook p57-60 Moles, Stoichiometry

Observatory Workbook p34 (#6 to 9) Electrolytes and pH

Observatory Workbook p36 to 38 (several topics)

To the authors and publisher of Observatory: I am not violating copyright laws! If you look at the solutions, youll see that they are entirely my own. The method of solving stoichiometry problems is standard and radically different from whats in the teacher's manual.

p57               N2 + 3 H2 2 NH3

5.       a)       6 moles NH3 (1 N2/2 NH3) = 3 moles N2

                    6 moles NH3 (3 H2/2 NH3) = 9 moles H2

b)              2 moles NH3 (1 N2/2 NH3) = 1 moles N2 = 28 g

2 moles NH3 (3 H2/2 NH3) = 3 moles H2

3 moles H2 (2g /mole) = 6.0 g

c)               10 g N2 ( mole/28 g) = 0.357 moles N2

0.357 moles N2(2 NH3/1 N2/) = 0.714 moles NH3

0.714 moles NH3(17g/mole) = 12.1 g

d)              150 g NH3 ( mole/17 g) = 8.82 moles NH3

8.82 moles NH3 (3 H2/2 NH3) = 13.235 moles H2

6.                 a)       122 g H2O(moles/18g) = 6.78 moles H2O

                              6.78 moles H2O (1 O2 /2 H2O) =  3.39 moles O2

                    b)       6.78 moles H2O (2 H2 /2 H2O) =  6.78 moles H2

7.                 50 g Fe2O3 ( moles/159.5 g)= 0.313 moles Fe2O3

0.313 moles Fe2O3 (4 Fe/ 2 Fe2O3 ) = 0.6269 moles Fe

0.6269 moles Fe (55.8 g/mole) = 34.98 g

 8.                a)         0.012 moles

                    b)         1:1 ratio, so 0.012 moles of HCl

9.             a)       0.017 moles

                 b)       0.017 moles Mg(OH)2 ( 2 HCl/1 Mg(OH)2) = 0.034 moles HCl

10.                    1 g of Mg(OH)2 neutralizes more HCl than 1 g of NaHCO3(see #8 and 9)

11.                     a)       1000 g C7H6O3 (mole/138 g) = 7.246 moles C7H6O3

7.246 moles C7H6O3 ( C4H6O3/ 2 C7H6O3 ) = 3.623 moles C4H6O3

3.623 moles C4H6O3 ( 102 g/mole) = 369.6 g C4H6O3

b)       7.246 moles C7H6O3 (2 C9H8O4 / 2 C7H6O3) = 7.246 moles moles C9H8O4

7.246 moles moles C9H8O4 ( 180 g/mole) = 1304 g C9H8O4

p34 (#6 to 9)

6.               10-2/10-5 = 1000 times more acidic

7.               10000 = 104, so go up 4 units to pH = 10. As you go up on the scale it gets more basic.

8.               a) basic

b) bases

c) a strong electrolyte

d)   it is a strong electrolyte from looking at the bright light, and from the colour, it is an acid.

p36 to 38

6.

a)                                      diphosphorus pentoxide

b)                                      lithium hydride

c)                                      CaF2 (should be calcium fluoride)

d)                                      Magnesium sulphate

e)                                      CCl4

f)                                       Sodium phosphate(do not use tri!) Na3PO4

g)                                      Calcium chloride

h)                                      AgNO3

6. Use n = CV

5000

0.425

0.04

255

0.0002 ppm

7. They are showing 10-10, so the pH is 10.

a) true

b) false; you need two or more non-metals

c) false; there are rules based on type of bonding

d) false; dissociation has to do with whether or not ions are formed

e) false; it's based on H+ concentration

9. The weak electrolyte is either A or B. Use a stronger bulb(50W or 100W), and the weak electrolyte will not be able to create a bright glow.

10. 500 g CaSO4(mole/136 g) = 3.67 moles

C = n/V = 3.67 moles/1.2 L = 3.1 moles/L

11. A molecule of N2 is more stable because through sharing with another N atom it fills the second shell.

In so doing thee bonds form within te molecule. The N atom has a valence of 5 and the ability to pull in more electrons

12. Convert molecules to moles by dividing by 6.02 X1023. You'll get about 5 moles.

Then C = n/V =5 moles/0.600L = 8.3 moles/L

13. 0.0069 moles/L

14. Get moles from molecules(see #12)= 2 moles.

n = CV

2 = 4V

V = 0.5 L

15. AgCl Ag+ + Cl-

Ca(OH)2 Ca+2 + 2 OH-

HCH2CO2 H+ + CH2CO2

HCl H+ + Cl-

NaCl Na+ + Cl-

NaOH Na+ + OH-