12.0 g NaHSO4 (MM: 120.1 g/mol) is dissolved in water to make a 2.00 L solution. What is the molarity of the resulting NaHSO4 solution?
The Correct Answer and Explanation is:
To calculate the molarity of the NaHSO₄ solution, we use the molarity formula: Molarity (M)=moles of soluteliters of solution\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{liters of solution}}
Step 1: Calculate moles of NaHSO₄
Given:
- Mass of NaHSO₄ = 12.0 g
- Molar mass (MM) of NaHSO₄ = 120.1 g/mol
Moles of NaHSO₄=12.0 g120.1 g/mol≈0.0999 mol\text{Moles of NaHSO₄} = \frac{12.0\ \text{g}}{120.1\ \text{g/mol}} \approx 0.0999\ \text{mol}
Step 2: Use volume of solution
Given:
- Volume of solution = 2.00 L
Step 3: Plug into the molarity formula
Molarity=0.0999 mol2.00 L=0.04995 mol/L\text{Molarity} = \frac{0.0999\ \text{mol}}{2.00\ \text{L}} = 0.04995\ \text{mol/L} Final Answer:0.0500 M (rounded to 3 significant figures)\text{Final Answer:} \boxed{0.0500\ \text{M}} \ (\text{rounded to 3 significant figures})
Explanation
Molarity is a common way to express the concentration of a solution in chemistry. It tells us how many moles of solute are present in each liter of solution. In this case, sodium bisulfate (NaHSO₄) is the solute, and water is the solvent.
First, to determine the number of moles of NaHSO₄, we use its molar mass, which is the mass of one mole of the compound. This is calculated by summing the atomic masses of its constituent elements: sodium (Na), hydrogen (H), sulfur (S), and oxygen (O). This gives a molar mass of 120.1 g/mol. By dividing the given mass of NaHSO₄ (12.0 g) by its molar mass, we find the number of moles, which is approximately 0.0999 mol.
Next, since the solute is dissolved in enough water to make 2.00 liters of solution, we divide the number of moles by this volume to find the molarity. This gives a value of approximately 0.04995 mol/L. Following standard rules of significant figures (based on the 3 significant figures in the given values), we round the answer to 0.0500 M.
This result tells us that for every liter of this solution, there are 0.0500 moles of NaHSO₄ dissolved. Knowing the molarity is essential in chemical reactions and lab work, especially when dealing with acids and bases, where exact concentrations determine reaction rates and product yields.
