23. high levels of phosphorus are not toxic, but can cause digestive problems. the allowable drinking water concentration is 0.05 ppm. what is the maximum mass of phosphorus that could be present in a 250 ml glass of tap water?
24. is a 1% solution of table salt, nacl(aq), more concentrated, less concentrated, or at the same concentration as a 1% solution of sugar, c₁₂h₂₂o₁₁(aq)? explain.
25. bones and teeth consist mostly of a compound called hydroxyapatite, ca₅(po₄)₃(oh). this compound contains po₄³⁻ and oh⁻ ions.
(a) do you expect hydroxyapatite will be an acid or a base?
(b) i...

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Accepted Answer

### Question 23 Solution:
# Explanation:
## Step1: Recall ppm definition (mass/mass or mass/volume, assume water density 1 g/mL)
ppm (parts per million) for dilute aqueous solutions can be approximated as $\frac{\text{mass of solute (g)}}{\text{mass of solution (g)}} \times 10^6$. For water, density $= 1\space g/mL$, so $250\space mL$ water has mass $m_{\text{solution}} = 250\space g$ (since $d=\frac{m}{V}\Rightarrow m = d\times V = 1\space g/mL\times250\space mL = 250\space g$).

## Step2: Use ppm formula to solve for $m_{\text{phosphorus}}$
Given ppm $= 0.05=\frac{m_{\text{phosphorus}}}{m_{\text{solution}}}\times10^6$. Rearranging: $m_{\text{phosphorus}}=\frac{\text{ppm}\times m_{\text{solution}}}{10^6}$. Substitute ppm $= 0.05$, $m_{\text{solution}} = 250\space g$:
$m_{\text{phosphorus}}=\frac{0.05\times250}{10^6}\space g$

## Step3: Calculate the mass
$0.05\times250 = 12.5$, so $m_{\text{phosphorus}}=\frac{12.5}{10^6}\space g = 1.25\times10^{-5}\space g = 12.5\space \mu g$ (since $1\space g = 10^6\space \mu g$)

# Answer:
The maximum mass of phosphorus is $1.25\times10^{-5}\space g$ (or $12.5\space \mu g$).

### Question 24 Solution:
# Brief Explanations:
A 1% solution means $1\space g$ solute per $99\space g$ solvent (or $100\space g$ solution). Molar mass of $NaCl$ is $\approx58.44\space g/mol$, molar mass of $C_{12}H_{22}O_{11}$ (sugar) is $\approx342.3\space g/mol$. For 1% solutions:
- Moles of $NaCl$ in 100g solution: $n_{NaCl}=\frac{1\space g}{58.44\space g/mol}\approx0.0171\space mol$
- Moles of sugar: $n_{\text{sugar}}=\frac{1\space g}{342.3\space g/mol}\approx0.00292\space mol$

Molarity ($M=\frac{n}{V}$): since both solutions have ~100g (≈100mL) volume, $V$ is similar. Higher moles mean higher molarity (concentration). $NaCl$ has more moles per 100g solution, so 1% $NaCl$ is more concentrated than 1% sugar.

# Answer:
A 1% $NaCl_{(aq)}$ solution is more concentrated than a 1% sugar ($C_{12}H_{22}O_{11(aq)}$) solution because $NaCl$ has a lower molar mass than sugar, so 1g of $NaCl$ contains more moles than 1g of sugar. For the same mass - percent (1%), the $NaCl$ solution has a higher molarity (more moles of solute per unit volume).

### Question 25(a) Solution:
# Brief Explanations:
Hydroxyapatite is $Ca_{5}(PO_4)_3(OH)$. It contains $PO_4^{3 - }$ (phosphate, a conjugate base of weak acid $H_3PO_4$) and $OH^-$ (hydroxide, a strong base - derived ion). When dissolved, $OH^-$ increases $[OH^-]$, and $PO_4^{3 - }$ hydrolyzes: $PO_4^{3 - }+H_2O
ightleftharpoons HPO_4^{2 - }+OH^-$, producing more $OH^-$. Thus, the solution will be basic (pH > 7).

# Answer:
Hydroxyapatite is expected to be a base. The compound contains $OH^-$ ions (which increase $[OH^-]$ directly) and $PO_4^{3 - }$ ions, which hydrolyze in water to produce $OH^-$ ions ($PO_4^{3 - }+H_2O
ightleftharpoons HPO_4^{2 - }+OH^-$). Both processes increase the hydroxide ion concentration, making the solution basic.

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Question

Explanation:

Question 23 Solution:

Step1: Recall ppm definition (mass/mass or mass/volume, assume water density 1 g/mL)

Step2: Use ppm formula to solve for \(m_{\text{phosphorus}}\)

Step3: Calculate the mass

Answer:

Question 24 Solution: