Calculate the mass of potassium hydrogen phthalate, KHC8H4O4 (MM is 204.2 g/mol) needed to react completely with 20 mL of 0.1 M NaOH solution.
The correct answer and explanation is :
Answer:
To find the mass of potassium hydrogen phthalate (KHP) needed to react with 20 mL of 0.1 M NaOH, we use stoichiometry.
Step 1: Write the balanced reaction
KHP (KHC₈H₄O₄) is a monoprotic acid; it donates one proton:
$$
\text{KHC}_8\text{H}_4\text{O}_4 + \text{NaOH} \rightarrow \text{KNaC}_8\text{H}_4\text{O}_4 + \text{H}_2\text{O}
$$
This shows a 1:1 molar ratio between KHP and NaOH.
Step 2: Calculate moles of NaOH
$$
\text{Moles of NaOH} = Molarity \times Volume (L) = 0.1\ \text{mol/L} \times 0.020\ \text{L} = 0.002\ \text{mol}
$$
Step 3: Use 1:1 ratio to find moles of KHP
$$
\text{Moles of KHP} = 0.002\ \text{mol}
$$
Step 4: Calculate mass of KHP
$$
\text{Mass} = \text{Moles} \times \text{Molar Mass} = 0.002\ \text{mol} \times 204.2\ \text{g/mol} = \boxed{0.4084\ \text{g}}
$$
Explanation (300 words)
Potassium hydrogen phthalate (KHC₈H₄O₄), commonly known as KHP, is a solid, acidic compound often used as a primary standard in acid-base titrations because of its high purity and stable molecular weight. In this case, KHP is being used to neutralize a sodium hydroxide (NaOH) solution, allowing precise determination of the amount of base present or required.
To find out how much KHP is required to react with a known amount of NaOH, we first write the balanced chemical equation. Since KHP contains one acidic hydrogen, it reacts with NaOH in a 1:1 molar ratio. This is key to determining how many moles of KHP are needed.
Given 20 mL (or 0.020 L) of a 0.1 M NaOH solution, we calculate the moles of NaOH using the formula:
$$
\text{moles} = M \times V = 0.1\ \text{mol/L} \times 0.020\ \text{L} = 0.002\ \text{mol}
$$
Because of the 1:1 ratio, 0.002 mol of KHP are required to completely react with the NaOH. The mass of KHP can be found by multiplying these moles by its molar mass, which is 204.2 g/mol:
$$
\text{Mass} = 0.002 \times 204.2 = 0.4084\ \text{g}
$$
Therefore, 0.4084 grams of KHP are required to exactly neutralize 20 mL of 0.1 M NaOH. This calculation is essential in standardizing NaOH solutions accurately in laboratory settings. Would you like a visual diagram of this reaction and calculation?