A good answer should contain the following:
1. The equation isn't balanced because there aren't equal numbers of hydrogen or chlorine atoms on both sides of the equation. To correct this, a coefficient of 2 must be placed in front of HCl on the left-hand side of the equation.
Zn+2HCl→ZnCl2+H2
Zn and 2HCl are the reactants; ZnCl2 and H2 are the products. This is a substitution reaction because a free element (Zn) replaces another element (H) in a compound.
2. This is a balanced equation because the same types of atoms and the same numbers of each atom are present on both sides of the equation. 8 S atoms are found on both sides of the equation, and 48 F atoms are found on both sides of the equation. S8 and 24F2 are the reactants; 8SF6 is the product. This is a combination reaction because two substances (S8 and 24F2) undergo a chemical union to form a more complex substance (8SF6).
S8+24F2→8SF6
3. In ferric oxide (Fe3O4), there are 3 atoms of iron (Fe) and 4 atoms of oxygen (O). From the Periodic Table of Elements, we know that the atomic mass of iron is 55.8457 and the atomic mass of oxygen is 15.9994.
Fe3 = 55.8457 × 3 = 167.5371
O4 = 15.9994 × 4 = 63.9976
167.5371 + 63.9976 = 231.5347 (231.535 rounded)
Therefore, the molecular mass of ferric oxide is 231.535.
4. The percentage composition of chlorine in CaCl2 is derived as follows:
The molecular mass of the entire compound is:
Ca = 40.078 × 1 = 40.078
Cl2 = 35.4527 × 2 = 70.9054
40.078 + 70.9054 = 110.9834 (110.983 rounded)
The atomic mass of each element (or its multiple) is divided by the molecular mass of the compound:
Ca = 40.078 ÷ 110.983 = 0.361
Cl2 = 70.9054 ÷ 110.983 = 0.639
Multiplying each by 100 will turn these into percents. Therefore, the percentage composition of chlorine is 63.9%.
5. i. a, c, f, h
ii. e
iii. b, d, g, i
iv. i
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