Soutions to January Review #2

1.         A

2.         C         Notice the balanced equation is 2 H2O--> 2H2 + O2, so we need two separate hydrogen molecules, and only one connected oxygen molecule.

3.         C

4.         C         436 only           N2 + 3H2 --> 2NH3, so 2(14) + 3(2[1]) = 34 g

5.         C

6.         D

7.         A

8.         D         436 only           2(1) + 1 + 4(1) = 7 moles. If they had asked for atoms you have had to multiply by Avogadro's number = 6.02 X 1023.

9.         D         436 only

10.       D         436 only           2[2(1) + 16] = 36 g

11.       B          436 only           440g/ [44g/mole] = 10 moles.

12.       D         436 only           3 X 6.02 X 1023 = 1.81 X 1024  .

13.       C         436 only           153g/[2(27)+3(16) g/mole] = 1.5 moles Al2O3. From ratio we see that 2(1.5) = 3.0 moles of Al are needed. So 3.0 moles (27.0g/mole ) = 81 g.

14.       D         436 only           From the ration, (6/2)(3)moles = 9 moles of oxygen will form. 9 X 6.02 X 1023 = 5.4 X 1024  molecules of oxygen.

15.       B          436 only           First we need a balanced equation:        4 Fe + 3 O2 -->2 Fe2O3.

1.00 kg = 1000g of Fe2O3 = 1000g / [160g/mole] = 6.25 moles. From the ratio we obtain (3/2)(6.25)= 9.375 moles of oxygen

16.       B          436 only           50 g CaCO3 / ( 100 g/mole) = 0.50 moles. Ratio is 1: 1, so we will get 0.50 moles of water. 0.50 moles of water(18g/mole) = 9.0 g

17.       D         436 only           100 g NaOH / ( 40 g/mole) = 2.5 moles. Ratio is 1: 1, so we will get 2.5 moles of sodium chloride( there was a typo-error). 2.5 moles NaCl(58.5 g/mole) = 146.25 g

18.       D         436 only           219 g HCl / (36.5 g/mole) = 6.0 moles HCl. Ratio reveals that only (1/2) (6) = 3.0 moles of hydrogen are made.

19.       B                      Note that 2.0 mg/L = only 0.002 g/ L.

20.       A

21.       B

22.       A                     120g / (100ml + 300 mL) = 0.3 g/mL

23.       C                     C1V1 = C2V2                1x = 3(0.2) = 0.6 L

24.       D         436 only           0.5 moles/(0.050 L) = 10 moles/L

25.       436 only                       2.5 moles X 6.02 X 1023molecules/mole= 1.5 X 1024  molecules.

26.       436 only                       2.5 moles X 6.02 X 1023molecules/mole(10 H atoms/molecule) = 1.5 X 1025 atoms.

27.       C1V1 = C2V2

20x = 12(0.050 L)

x = 0.030L = 30 mL. Pipette 30 mL and transfer into a 50 mL flask. Add water and dilute to the mark, and mix.

28.       2HCl  + Mg(OH)2 --> MgCl2 + 2 H2O

29.       436 only + O2 --> 2CuO

10.0  g / [63.5 g/mole] = 0.157 moles of Cu

Ratio is 2:1, so we will get only (1/2) 0.157 moles of oxygen reacting = 0.079 moles.

0.079 moles(32 g/mole) = 2.5 g.

30.       This is the same diagram as the one in your notes. Note how the hydrogens in the water molecule that attack the negative ions(Cl-1) in the crystal, whereas the oxygen attacks the positive ions.

31.       Na+1 is forced into accepting electrons at the cathode. Chloride (Cl-1) returns them to the circuit at the anode.

32.       Differences:

 Electrolytes Non electrolytes Chemical Properties Forms ions. React quickly as in neutralization and precipitation reactions Do not form ions in solution React slowly Physical Properties Conduct electricity; Don't conduct