If a student weighs out 0.514 g of KHP and titrates it with sodium hydroxide solution, what is the molarity of the sodium hydroxide solution if it takes 35.01 mL of it to titrate the KΗΡ?
The correct answer and explanation is :
To determine the molarity of the sodium hydroxide (NaOH) solution, we need to use the concept of stoichiometry and the neutralization reaction between potassium hydrogen phthalate (KHP) and sodium hydroxide. The reaction between KHP (C8H5KO4) and NaOH is as follows: KHC8H4O4(aq)+NaOH(aq)→NaKC8H4O4(aq)+H2O(l)KHC_8H_4O_4(aq) + NaOH(aq) \rightarrow NaKC_8H_4O_4(aq) + H_2O(l)
This reaction shows a 1:1 molar ratio between KHP and NaOH. In other words, one mole of KHP reacts with one mole of NaOH.
Given data:
- Mass of KHP: 0.514 g
- Volume of NaOH used: 35.01 mL = 0.03501 L (conversion from mL to L)
- Molar mass of KHP (C8H5KO4): 204.23 g/mol
Steps to solve:
- Calculate the moles of KHP: The number of moles of KHP is calculated using its molar mass: Moles of KHP=Mass of KHPMolar mass of KHP=0.514 g204.23 g/mol=0.00252 mol\text{Moles of KHP} = \frac{\text{Mass of KHP}}{\text{Molar mass of KHP}} = \frac{0.514 \, \text{g}}{204.23 \, \text{g/mol}} = 0.00252 \, \text{mol}
- Use the mole ratio to find moles of NaOH: From the balanced equation, the mole ratio of KHP to NaOH is 1:1, meaning that the moles of NaOH are equal to the moles of KHP: Moles of NaOH=0.00252 mol\text{Moles of NaOH} = 0.00252 \, \text{mol}
- Calculate the molarity of NaOH: Molarity is defined as moles of solute per liter of solution. The formula is: Molarity=Moles of NaOHVolume of NaOH in liters=0.00252 mol0.03501 L=0.0720 MMolarity = \frac{\text{Moles of NaOH}}{\text{Volume of NaOH in liters}} = \frac{0.00252 \, \text{mol}}{0.03501 \, \text{L}} = 0.0720 \, \text{M}
Conclusion:
The molarity of the sodium hydroxide solution is 0.0720 M.
Explanation:
In this titration, KHP is used because it is a primary standard that reacts with NaOH in a 1:1 molar ratio. By knowing the mass of KHP and using its molar mass, we can calculate the number of moles of KHP. Since the reaction between KHP and NaOH is a 1:1 ratio, the moles of NaOH required for the titration are equal to the moles of KHP. Dividing the moles of NaOH by the volume of NaOH used gives the molarity of the NaOH solution.