Chapter 19: Problem 43
A human body contains approximately \(5 \mathrm{~L}\) of blood. A bipolar disorder patient receives \(2.0 \mathrm{~g}\) lithium carbonate as a daily dose. Calculate the concentration of \(\mathrm{Li}^{+}(\mathrm{mmol} / \mathrm{L})\) that this dosage provides.
Short Answer
Expert verified
The concentration of \(\text{Li}^+\) ions is \(10.8 \, \text{mmol/L}\).
Step by step solution
01
Identify the Molecular Weight of Lithium Carbonate
Lithium carbonate has the chemical formula \(\text{Li}_2\text{CO}_3\). Calculate the molecular weight: \(\text{Li} = 7 \text{ g/mol}\), \(\text{C} = 12 \text{ g/mol}\), \(\text{O} = 16 \text{ g/mol}\). Therefore, the molecular weight is \(2 \times 7 + 12 + 3 \times 16 = 74 \text{ g/mol}\).
02
Determine Moles of Lithium Carbonate Administered
Find the number of moles of lithium carbonate in the daily dose: \(\text{mass} = 2.0 \text{ g}\), \(\text{molar mass} = 74 \text{ g/mol}\). Use the formula \(\text{moles} = \frac{\text{mass}}{\text{molar mass}}\). Hence, \(2.0 \text{ g} \div 74 \text{ g/mol} = 0.027 \, \text{mol}\).
03
Calculate Moles of Lithium Ions
Since lithium carbonate contains 2 lithium ions per molecule, the moles of \(\text{Li}^+\) ions is double the moles of \(\text{Li}_2\text{CO}_3\): \(0.027 \, \text{mol} \times 2 = 0.054 \, \text{mol of Li}^+\).
04
Convert Moles to Millimoles
Convert moles of \(\text{Li}^+\) to millimoles: \(0.054 \,\text{mol} = 54 \,\text{mmol of Li}^+\) (as 1 mol = 1000 mmol).
05
Calculate Concentration of Lithium Ions
Calculate the concentration of \(\text{Li}^+\) in the blood: \(\text{conc} = \frac{\text{mmol of Li}^+}{\text{volume of blood in L}} = \frac{54 \,\text{mmol}}{5 \,\text{L}} = 10.8 \,\text{mmol/L}\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Molecular Weight Calculation
Molecular weight, also known as molar mass, is a calculation of the total mass of one mole of a molecule. It is crucial in converting between the mass of a substance and the number of moles. To determine the molecular weight of a compound, you must know the atomic weights of each element involved. These are usually listed on the periodic table.
- Step 1: Identify the chemical formula: For lithium carbonate, it's \(\text{Li}_2\text{CO}_3\).
- Step 2: Determine atomic weights: Lithium (\(\text{Li}\)) is 7 g/mol, Carbon (\(\text{C}\)) is 12 g/mol, Oxygen (\(\text{O}\)) is 16 g/mol.
- Step 3: Calculate the molecular weight: Add up the atomic weights in accordance with the formula.
- For \(\text{Li}_2\text{CO}_3\): \(2 \times 7 + 12 + 3 \times 16 = 74\) g/mol.
Molarity Calculation
Molarity is a way to express the concentration of a solute in a solution. It is particularly useful in chemistry to quantify the amount of a substance dissolved in a liquid.Molarity is calculated as the number of moles of solute divided by the liters of solution. The formula is:\[\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}\]Here’s how you can apply it for lithium carbonate:
- Once the moles of lithium carbonate are known (in this case, 0.027 moles), you convert it to the moles of lithium ions.
- Since each molecule of lithium carbonate provides two lithium ions, multiply the moles by 2.
- Next, convert moles to millimoles (1 mole equals 1000 millimoles) for ease of calculation with blood volume.
- The molarity is then the number of millimoles of \(\text{Li}^{+}\) divided by the total blood volume in liters.
- Using 5 liters of blood, the concentration is \(\frac{54 \, \text{mmol}}{5 \, \text{L}} = 10.8 \, \text{mmol/L}\).
Lithium Carbonate in Medicine
Lithium carbonate is commonly used in medicine, particularly in the treatment of mood disorders such as bipolar disorder. It functions to stabilize mood swings, thus playing a crucial role in mental health care.
Some significant features of lithium carbonate in medical use:
- Lithium works by affecting the flow of sodium through nerve and muscle cells in the body, influencing mood regulation.
- Patients are prescribed specific dosages, often based on weight and blood volume, to ensure therapeutic efficiency while avoiding toxicity.
- Regular monitoring of blood lithium levels is crucial to prevent side effects which can be caused by exceeding therapeutic levels.
- It is essential for dosages to be accurate, harnessing concepts like molecular weight and molarity to guide medication administration.