Question

1. which ion is the conjugate base of \\(\text{h}_2\text{po}_4^-\\)\\ after losing one \\(\text{h}^+\\)?

a. \\(\text{h}_3\text{po}_4\\)
b. \\(\text{hpo}_4^{2-}\\)
c. \\(\text{po}_4^{3-}\\)
d. \\(\text{oh}^-\\)

1. what is the coefficient of \\(\text{o}_2\\) when \\(\text{c}_3\text{h}_8 + \text{o}_2 \

ightarrow \text{co}_2 + \text{h}_2\text{o}\\) is balanced?
a. 3
b. 4
c. 5

Explanation:

Identify conjugate base of H2PO4-

A conjugate base is formed when an acid loses a proton \((\text{H}^+)\).
Subtracting one \(\text{H}^+\) from \(\text{H}_2\text{PO}_4^-\):

$$ \text{H}_2\text{PO}_4^- ightarrow \text{H}^+ + \text{HPO}_4^{2-} $$

The resulting ion is \(\text{HPO}_4^{2-}\).

Balance the combustion equation

Write the unbalanced chemical equation:

$$ \text{C}_3\text{H}_8 + \text{O}_2 ightarrow \text{CO}_2 + \text{H}_2\text{O} $$

Balance carbon atoms first:

$$ \text{C}_3\text{H}_8 + \text{O}_2 ightarrow 3\text{CO}_2 + \text{H}_2\text{O} $$

Balance hydrogen atoms next:

$$ \text{C}_3\text{H}_8 + \text{O}_2 ightarrow 3\text{CO}_2 + 4\text{H}_2\text{O} $$

Count oxygen atoms on the right side:

$$ (3 \times 2) + (4 \times 1) = 10 \text{ oxygen atoms} $$

Balance oxygen atoms on the left side:

$$ \text{C}_3\text{H}_8 + 5\text{O}_2 ightarrow 3\text{CO}_2 + 4\text{H}_2\text{O} $$

The coefficient of \(\text{O}_2\) is 5.

Answer:

Question 8

• A. H3PO4
• B. HPO4^2- (Correct answer)
• C. PO4^3-
• D. OH-

Question 9

• A. 3
• B. 4
• C. 5 (Correct answer)