1. Problem: Convert 270 mg/dL of Ca$^{2+}$ to mEq/L. Step 1: Convert mg/dL to mg/L. $$270\ \text{mg/dL} = 270 \times 10 = 2700 \ \text{mg/L}$$ Step 2: Convert mg/L to moles per liter (M). Molecular weight (MW) of Ca = 40 g/mol = 40000 mg/mol. $$\text{moles/L} = \frac{2700}{40000} = 0.0675 \ \text{mol/L}$$ Step 3: Calculate mEq/L using valence. Valence of Ca$^{2+} = 2$. $$\text{mEq/L} = 0.0675 \times 2 \times 1000 = 135 \ \text{mEq/L}$$ 2. Problem: Find mass of MgCO$_3$ needed for 650 mL of 0.65% solution. Step 1: Understand % solution as grams per 100 mL. $$0.65\% = 0.65 \ \text{g per } 100 \ \text{mL}$$ Step 2: Calculate grams for 650 mL. $$\text{grams} = 0.65 \times \frac{650}{100} = 4.225 \ \text{g}$$ 3. Problem: Prepare 1000 mL of 3.5 M NaF solution. Step 1: Calculate moles required. $$3.5 \ \text{mol/L} \times 1 \ \text{L} = 3.5 \ \text{mol}$$ Step 2: Calculate mass to weigh. MW of NaF = Na(23) + F(19) = 42 g/mol. $$\text{mass} = 3.5 \times 42 = 147 \ \text{g}$$ 4. Problem: Convert 10 mg/dL of Cl to mmol/L. Step 1: Convert mg/dL to mg/L. $$10\ \text{mg/dL} = 10 \times 10 = 100 \ \text{mg/L}$$ Step 2: Calculate mmol/L. MW of Cl = 35.5 g/mol = 35500 mg/mol. $$\text{mmol/L} = \frac{100}{35.5} = 2.82 \ \text{mmol/L}$$ 5. Problem: Find molality of solution with 25 g MgCl$_2$ in 600 g water. Step 1: Convert mass of solute to moles. MW MgCl$_2$ = 24 + 2*35.5 = 95 g/mol. $$\text{moles} = \frac{25}{95} = 0.2632 \ \text{mol}$$ Step 2: Convert solvent mass from grams to kilograms. $$600 \ \text{g} = 0.6 \ \text{kg}$$ Step 3: Calculate molality. $$\text{molality} = \frac{0.2632}{0.6} = 0.4387 \ \text{mol/kg}$$ Final answers: 1. 135 mEq/L Ca$^{2+}$ 2. 4.225 g MgCO$_3$ 3. 147 g NaF 4. 2.82 mmol/L Cl 5. 0.439 mol/kg (molal) MgCl$_2$