1) The law of conservation of matter states that in a chemical reaction matter is neither created nor destroyed.

2) Scientific law summarizes what has been learned by carful observations of nature.

3) "Using up" and "trowing away" expressions are misleade because logically you would that matter is lost cince you are getting rid of it, yet matter is neither created nor destroyed.

4) a) Reaction - Sn: 1 H:1 F:1
        Product - Sn:1 H:2 F:2
        NOT BALENCED
    b) Reaction - Si: 1 0:2 C:1
        Product- Ai: 1 O: 1 C: 2
        NOT BALANCED
    c) Reaction- Al: 1 O: 3 H: 6 Cl: 3
        Products- Al: 1 O: 3 H: 6 Cl: 3
        BALANCED

5) a) 3
    b) 2
    c) 1

6) a) 1, 3, 1, 3
    b) 1, 1, 1, 1
    c) 4, 3, 2
 
7) a) 1, 3, 2, 3
    b) 2, 10, 16, 18

8) a) Yes.
     Reactants: Na- 2 S- 1 O- 4 K- 2 Cl- 1
     Product side: Na- 2 S- 1 O- 4 K- 2 Cl- 1
     b) No when balancing equations the subscripts remain the same but the coefficients are altered to balance the equation
    c) 1 Na2SO4 + 2 KCl -> NaCl + 1 K2SO4

9) About 2,000,000 years