Question

The concentration of a certain sodium hydroxide solution was determined by using the solution to titrate a sample of potassium hydrogen phthalate (abbreviated as KHP). KHP is an acid with one acidic hydrogen and a molar mass of \(204.22 \mathrm{~g} / \mathrm{mol}\). In the titration, \(34.67 \mathrm{~mL}\) of the sodium hydroxide solution was required to react with \(0.1082 \mathrm{~g}\) KHP. Calculate the molarity of the sodium hydroxide.

Short answer

The molarity of the sodium hydroxide solution can be calculated using the following steps: 1. Calculate the moles of KHP: \(moles\,of\,KHP = \frac{0.1082\,g}{204.22\,\frac{g}{mol}}\) 2. Determine the moles of NaOH using stoichiometry: Moles of NaOH = Moles of KHP 3. Calculate the molarity of NaOH: Molarity of NaOH = \(\frac{moles\,of\,NaOH}{0.03467\,L}\) After solving these equations, the molarity of the sodium hydroxide solution is found.

Step-by-step solution

Calculate moles of KHP

To find the moles of KHP, we will use the mass of KHP and its molar mass. The formula to calculate moles is: Number of moles = (mass of substance) / (molar mass of substance) Given mass of KHP = 0.1082g Molar mass of KHP = 204.22g/mol Let's calculate the moles of KHP: \(Number\,of\,moles\,of\,KHP = \frac{0.1082\,g}{204.22\,\frac{g}{mol}} \)

Calculate moles of NaOH using stoichiometry

For every mole of KHP, one mole of NaOH is required since the reaction between KHP and NaOH is 1:1. Thus, the moles of NaOH are equal to the moles of KHP. Moles of NaOH = Moles of KHP

Calculate the molarity of NaOH

Now that we have the moles of NaOH, we can find the molarity of the sodium hydroxide solution. To calculate the molarity, we will use the formula: Molarity = (moles of solute) / (volume of solution in liters) Given volume of NaOH solution = 34.67mL First, convert the given volume of NaOH solution in mL to liters: Volume in liters = \(34.67\frac{mL}{1000\,\frac{mL}{L}}\) Now, calculate the molarity of NaOH: Molarity of NaOH = \(\frac{moles\,of\,NaOH}{Volume\,of\,NaOH\,solution\,in\,liters}\)

Key concepts

Understanding Molarity

In chemistry, understanding concentrations is crucial when working with solutions. Molarity is one of the most common units of concentration, providing the number of moles of solute per liter of solution.

• Definition: Molarity (M) is calculated using the formula:\[\text{Molarity (M)} = \frac{\text{moles of solute}}{\text{volume of solution in liters}}\]

Molarity is specifically useful when you need to know the exact amount of a substance present in a given volume of liquid. This type of measurement is crucial for accurate chemical reactions, such as titrations, where precise concentrations are required.
When performing a titration, like in the original exercise, calculating molarity helps determine the concentration of the titrant solution after measuring how much of it was required to reach the endpoint of the reaction.

Exploring Sodium Hydroxide in Titrations

Sodium hydroxide (NaOH) is a commonly used strong base in titrations. It reacts readily with many substances due to its strong alkaline nature, making it an excellent titrant in acid-base titrations.

• Properties: Sodium hydroxide's strength comes from its ability to completely dissociate in water, releasing hydroxide ions \((OH^-)\).
• Reactivity: In titrations involving acids, NaOH reacts in a predictable 1:1 mole ratio, especially with monoprotic acids like KHP (potassium hydrogen phthalate).

In our problem, sodium hydroxide serves as the titrant. The known volume and resulting molarity of NaOH provide a means to backtrack and determine the original concentration of the base used. This allows chemists to control reactions precisely, ensuring the desired outcome.

Role of Potassium Hydrogen Phthalate

Potassium hydrogen phthalate (KHP) is a solid, monoprotic acid that serves as a primary standard in acid-base titrations. Its stable and non-hygroscopic nature enables precise, reliable reactions.

• Characteristics: With a single acidic hydrogen, KHP reacts with bases like NaOH in a straightforward 1:1 stoichiometry.
• Usage: KHP is used to standardize the concentration of strong bases, since a known amount of KHP can be used to accurately calculate the molarity of the base solution.
• Molar Mass: The molar mass of 204.22 g/mol makes calculation straightforward, using weight and stoichiometry in titration.

In our solution, we use KHP to find out the concentration of NaOH by calculating the moles of KHP and using them to determine the necessary moles of NaOH. This procedure underscores the importance of careful weighing and knowledge of molar relationships in quantitative chemical analyses.