Question

1. In the reaction C5H8 + ______ O2 --> 8H2O + 5CO2, what coefficient should be placed in front of O2 to balance the reaction?

a. 5
b. 8
c. 9
d. no coefficient is needed

2. How does the law of conservation of mass apply to this reaction: C2H4 + O2 --> 2H2O + 2CO2?

a. Each element needs to be balanced.
b. The equation needs to be balanced. There are fewer oxygen atons in the equation than hydrogen or carbon.
c. Only the oxygen needs to be balanced. There are equal numbers of hydrogen and carbon.
d. The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation

3. How does the law of conservation of mass apply to this reaction: Mg + HCl --> H2 + MgCl2?

a. The law of conservation of mass has already been applied. There is an equal number of each element on both sides of the equation.
b. Only the hydrogen needs to be balanced. There are equal amount of magnesium and chlorine.
c. Hydrogen and chlorine need to be balanced. There is an equal amount of magnesium on each side.
d. The equation needs to be balanced. There are a few hydrogen atoms in the equation than magnesium or chlorine.

4. Which of these is an example of a solution?

a. oil and vinegar in a salad dressing jar
b. a glass of water with ice in it
c. sugar stirred in tea
d. sand stirred in water

Answer 1

I have just taken the test, and can confirm the answer to the last question, 4, is in fact C, sugar stirred in tea.

Answer 2

1) C
Oxygen on left = oxygen on right
Oxygen on right = 8 + 5 * 2 = 18
Oxygen on left = 2x
2x = 18; x = 9

2) C
Carbon on left = Carbon on right = 2
Hydrogen on left = Hydrogen on right = 4
Oxygen on left = 2 ≠ Oxygen on right = 6

3) C
Same method as previous part

4) C