Extra Credit 6

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Q15.1.X

Most barium compounds are very poisonous; however, barium sulfate is often administered internally as an aid in the X-ray examination of the lower intestinal tract. This use of BaSO₄ is possible because of its low solubility. Calculate the molar solubility of BaSO₄ and the mass of barium present in 1.00 L of water saturated with BaSO₄.

Answer:

$$K_{sp(BaSO_4)} = 1.1 \times 10^{-10}$$

$$K_{sp(BaSO_4)} = [Ba^{2+}][SO_4^{2-}] $$

$$Solubility = [Ba^{2+}] = [SO_4^{2-}] = \sqrt{K_{sp}}$$

$$Solubility = \sqrt {1.1 \times 10^{-10}} = 1.05 \times 10^{-5} M$$

solubility is typically in terms of maximum mass, not max concenration...

Q16.2.13

Write the balanced chemical equation for the combustion of methane, CH₄(g), to give carbon dioxide and water vapor. Explain why it is difficult to predict whether ΔS is positive or negative for this chemical reaction.

Answer:

$$ CH_4(g) + 2O_2(g) \longrightarrow CO_2(g) + 2H_2O(l) $$

The reactants are three gas molecules, but the reactants are one gas molecule and two liquid molecules. Because $\Delta S_{gas}$ > $\Delta S_{liquid}$, it is hard to determine the $\Delta S_{rxn} $.

Q5.3.21

A pint of premium ice cream can contain 1100 Calories. What mass of fat, in grams and pounds, must be produced in the body to store an extra 1.1 × 10³ Calories if the average number of Calories for fat is 9.1 Calories/g?

Answer:

$$ m_{fat} = 1100 Calories \div 9.1 Calories/g = 120.9 g$$

Q10.1.16

Silane (SiH₄), phosphine (PH₃), and hydrogen sulfide (H₂S) melt at −185 °C, −133 °C, and −85 °C, respectively. What does this suggest about the polar character and intermolecular attractions of the three compounds?

Answer:

Boiling point is a bulk property reflecting strength of intermolecular forces, the higher the boiling point, the greater the intermolecular forces. $\ce {SiH4}$ has the weakest intermolecular forces, $\ce {H2S}$ has the strongest intermolecular forces. The result may not suggest the polar character directly from boiling point.

Q14.1.12

State which of the following species are amphiprotic and write chemical equations illustrating the amphiprotic character of these species:

H₂O
$\ce{H2PO4-}$
S²⁻
$\ce{CO3^2-}$
$\ce{HSO4-}$

Answer:

a. It is amphiprotic.

$$ H_2O + H^+ \rightleftharpoons H_3O^+ $$

$$ H_2O \rightleftharpoons H^+ + OH^- $$

b. It is amphiprotic. $$ H_2PO_4^- + H^+ \rightleftharpoons H_3PO_4$$

$$ H_2PO_4^- \rightleftharpoons H^+ + HPO_4^{2-}$$

c. It is not amphiprotic.

d. It is not amphiprotic.

e. It is amphiprotic. $$HSO_4^- + H^+ \rightleftharpoons H_2SO_4$$

$$HSO_4^- \rightleftharpoons SO_4^{2-} + H^+ $$

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Q15.1.X

Q16.2.13

Q5.3.21

Q10.1.16

Q14.1.12