Question

The total acidity in water samples can be determined by neutralization with standard sodium hydroxide solution. What is the total concentration of hydrogen ion, \(\mathrm{H}^{+},\) present in a water sample if \(100 .\) mL of the sample requires \(7.2 \mathrm{mL}\) of \(2.5 \times 10^{-3} \mathrm{M} \mathrm{NaOH}\) to be neutralized?

Short answer

The total concentration of hydrogen ions (H+) in the water sample is \(1.8 \times 10^{-4}\) M.

Step-by-step solution

Write the neutralization reaction equation

First, we need to write down the reaction between the water sample (containing unknown concentration of H+) and the sodium hydroxide (NaOH). The reaction between an acidic solution and sodium hydroxide can be represented as follows: \(H^{+} (aq) + OH^{-}(aq) \rightarrow H_2O (l)\) This means that one mole of H+ reacts with one mole of OH- to form one mole of water.

Calculate the moles of NaOH used

Since we know the volume (7.2 mL) and concentration (2.5 x 10^{-3} M) of NaOH used, we can now find the moles of NaOH using the following formula: moles = volume (L) × concentration (M) Converting the volume of NaOH to liters: \(7.2\:mL \times \frac{1\:L}{1000\:mL} = 0.0072\:L\) Now, calculating the moles of NaOH: moles (NaOH) = 0.0072 L × 2.5 × 10^{-3} M = 1.8 × 10^{-5} moles

Equate the moles of H+ to the moles of NaOH

Since the ratio of H+ to OH- in the reaction is 1:1, the moles of H+ in the water sample must be equal to the moles of NaOH used for neutralization. moles (H+) = 1.8 × 10^{-5} moles

Calculate the concentration of H+ in the water sample

We can now find the concentration of H+ ions in the water sample by using the following formula: concentration (H+) = moles (H+) / volume (L) First, we will convert the volume of the water sample to liters: \(100\:mL \times \frac{1\:L}{1000\:mL} = 0.1\:L\) Now, calculating the concentration of H+ ions in the water sample: concentration (H+) = \(\frac{1.8 \times 10^{-5}\:moles}{0.1\:L}\) concentration (H+) = 1.8 × 10^{-4} M

Final Answer

The total concentration of hydrogen ions (H+) in the water sample is 1.8 × 10^{-4} M.

Key concepts

Neutralization Reaction

A neutralization reaction is a chemical process in which an acid and a base react to form water and a salt. This reaction involves the combination of hydrogen ions (H⁺) from the acid and hydroxide ions (OH⁻) from the base. The general form of this reaction can be written as: \[ H^+ (aq) + OH^- (aq) \rightarrow H_2O (l) \] This formula demonstrates that one mole of hydrogen ions reacts with one mole of hydroxide ions to produce a mole of water. The process is crucial in determining the acidity of a substance, such as in our water sample exercise. In this context, sodium hydroxide (NaOH) is used as the base, and the amount required to neutralize the acid in a water sample reflects the concentration of hydrogen ions in that sample. Understanding neutralization helps us analyze substances in various fields such as chemical manufacturing, environmental science, and pharmaceuticals.

• Neutralization reactions are used in titrations to determine concentrations.
• They are essential for applications like wastewater treatment to ensure pH balance.

Sodium Hydroxide

Sodium hydroxide, often referred to as lye or caustic soda, is a strong base extensively used in neutralization reactions. Its chemical formula is \( NaOH \). When dissolved in water, it dissociates into sodium ions (Na⁺) and hydroxide ions (OH⁻). These hydroxide ions are key participants in neutralization reactions. The ability of sodium hydroxide to react with acids like the hydrogen ions in our water sample makes it invaluable for determining acidity levels. In the exercise, we used a known concentration of sodium hydroxide to find how much is needed to neutralize the acidic solution completely. This procedure relies on the precise measurement of both the base’s volume and concentration.

• Sodium hydroxide is often employed in the manufacturing of paper, textiles, and soap.
• In laboratories, it's used to test the acidity or alkalinity of substances.
• It must be handled with care due to its corrosive nature.

Hydrogen Ion Concentration

The hydrogen ion concentration in a solution indicates its acidity. In our exercise, measuring this concentration involves using sodium hydroxide to neutralize the sample. The reaction between hydrogen ions (H⁺) and hydroxide ions (OH⁻) helps us calculate the exact concentration of hydrogen ions. To determine hydrogen ion concentration, we first measure the amount of sodium hydroxide needed to neutralize the sample and convert these measurements into moles. This involves simple volumetric calculations using the neutralization equation, since the moles of H⁺ are equal to the moles of OH⁻ in our exercise.
Knowing the concentration of hydrogen ions in the water sample allows us to understand its acidity level. The term pH is often used to represent this acidity on a logarithmic scale, where lower pH values indicate higher acidity due to higher H⁺ concentration.

• Acidity is essential for various biochemical processes, including digestion.
• pH meters are used to measure the hydrogen ion concentration accurately in laboratories.
• Maintaining proper pH levels is critical for the ecological balance in aquatic environments.