Chemistry Chapter on Water Ionization and pH

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Questions and Answers

What is the calculated mass of chlorine (mg Cl) for Trial 2?

30.1989 mg

31.3179 mg

32.0000 mg

31.8291 mg (correct)

Which formula is used to calculate the % Cl in a sample?

%Cl = mg Cl / mg sample × 100 (correct)

%Cl = mg sample / mg Cl × 100

%Cl = mg sample × 100 / mg Cl

%Cl = mg NaCl / mg sample × 100

Which value represents the average percentage of Cl from the trials?

62.28%

58.45%

61.77%

60.83% (correct)

Using dimensional analysis, what is the first step in calculating mg of Cl?

Calculate moles of NaCl from AgNO3 concentration. Signup and view all the answers

If the formula mass of NaCl is 58.44 g/mol, what is the direct relationship between mg Cl and mg NaCl in the calculations?

mg Cl is proportional to mg NaCl based on their molecular weights. Signup and view all the answers

What is the purpose of standardizing a silver nitrate solution in precipitation titration?

To calculate the chloride concentration in a sample Signup and view all the answers

Which of the following compounds is known to form a precipitate when reacting with potassium iodide?

Lead nitrate Signup and view all the answers

In a precipitation reaction, what determines which compound will precipitate?

The solubility rules of ionic compounds Signup and view all the answers

What is the end product of the reaction between sodium carbonate and calcium chloride?

Sodium chloride and calcium carbonate Signup and view all the answers

Which of the following ions does NOT follow the common solubility guidelines for ionic compounds?

Carbonate (CO3^2-) Signup and view all the answers

Which of the following statements is true regarding precipitation reactions?

They result in the formation of an insoluble product. Signup and view all the answers

In the Mohr method, which ion is primarily measured to determine chloride concentration?

Chloride ion (Cl-) Signup and view all the answers

What type of reaction occurs when two ionic compounds are mixed and produce a solid precipitate?

Double displacement reaction Signup and view all the answers

What factor primarily influences the pH at the post-equivalence point in a titration?

Concentration of excess titrant Signup and view all the answers

What is the primary purpose of standardizing a standard solution?

To ascertain the concentration of a standard solution Signup and view all the answers

In the example calculation for trial 1, what is the correct volume of NaOH used based on the given weight of KHP?

40.00 mL Signup and view all the answers

What unit conversion is necessary to calculate the molarity of NaOH during the standardization process?

Weight in grams to moles Signup and view all the answers

What is a vital outcome of proper dimensional analysis during calculations?

Ensuring that units cancel out correctly Signup and view all the answers

What is the value of the ion-product constant for water, $K_w$, at 25°C?

$1.0 imes 10^{-14}$ Signup and view all the answers

Which of the following correctly represents the average molarity of the NaOH standard solution based on the trials?

0.1012 M Signup and view all the answers

How do you calculate pOH from the hydroxide ion concentration?

$pOH = -log [OH-]$ Signup and view all the answers

In the calculation for determining the volume of NaOH needed, what is the role of KHP?

It serves as a primary standard Signup and view all the answers

Given that $[H_3O+] = 3.4 imes 10^{-4} M$, what is the concentration of hydroxide ions, $[OH-]$, in the solution?

$2.9 imes 10^{-11} M$ Signup and view all the answers

What must be calculated alongside the volume of NaOH used to determine the concentration of acetic acid in vinegar?

The molarity of acetic acid Signup and view all the answers

What is the pH of a solution that is 0.100 M in HCl?

1.00 Signup and view all the answers

At the equivalence point of a titration of HCl with NaOH, what is the primary factor determining the pH?

The dissociation of water Signup and view all the answers

What relationship holds true for pH and pOH at 25°C?

$pH + pOH = 14.00$ Signup and view all the answers

What is the effect of adding 10.0 mL of 0.200 M NaOH to 50.0 mL of 0.100 M HCl on the resulting concentration of HCl?

It decreases the concentration of HCl. Signup and view all the answers

What is the pH of a solution after adding 30 mL of NaOH to 50 mL of 0.100 M HCl?

12.10 Signup and view all the answers

At what point during the titration of a strong acid with a strong base is the pH equal to 7?

At the equivalence point Signup and view all the answers

How is the concentration of hydroxide ions related to the amount of excess NaOH added past the equivalence point?

It increases as more NaOH is added. Signup and view all the answers

What volume of NaOH is needed to completely neutralize 50.0 mL of 0.100 M acetic acid?

25 mL Signup and view all the answers

What is the hydroxonium ion concentration after adding 30 mL of NaOH to the original acid solution?

$8.00 imes 10^{-13} M$ Signup and view all the answers

What happens to the pH as you approach the equivalence point in a titration of a weak acid with a strong base?

pH increases gradually. Signup and view all the answers

What is the $K_a$ expression for acetic acid during its dissociation in water?

$K_a = rac{[H_3O^+][CH_3COO^-]}{[CH_3COOH]}$ Signup and view all the answers

In the titration of a strong base with a weak acid like acetic acid, what can be expected once the equivalence point is surpassed?

The pH will continue to rise sharply. Signup and view all the answers

Study Notes

Water Auto-Ionization

Water molecules undergo a reversible reaction to form hydronium (H3O+H_3O^+H3O+) and hydroxide (OH−OH^-OH−) ions.
The equilibrium expression for this process is Kw=[H3O+][OH−]K_w = [H_3O^+][OH-]Kw=[H3O+][OH−], where KwK_wKw is the ion-product constant for water.
At 25°C, Kw=1.0×10−14K_w = 1.0 × 10^{-14}Kw=1.0×10−14.
In pure water, [H3O+]=[OH−]=1.0×10−7[H_3O^+]=[OH^-]=1.0 × 10^{-7}[H3O+]=[OH−]=1.0×10−7 M.

pH, pOH, and pKw

pH is the negative logarithm of the hydronium ion concentration: pH=−log[H3O+]pH = -log[H_3O^+]pH=−log[H3O+].
Similarly, pOH is the negative logarithm of the hydroxide ion concentration: pOH=−log[OH−]pOH = -log[OH-]pOH=−log[OH−].
The relationship between pH, pOH, and pKw is: pH+pOH=pKw=14.00pH + pOH = pK_w = 14.00pH+pOH=pKw=14.00.

Sample Exercise: Calculating [OH-] and pH

A solution with [H3O+]=3.4×10−4M[H_3O^+]=3.4 × 10^{-4} M[H3O+]=3.4×10−4M is acidic because its pH is less than 7.
The [OH−][OH^-][OH−] can be calculated using the KwK_wKw expression: [OH−]=1.0×10−14[H3O+][OH-]=\frac{1.0 × 10^{-14}}{[H_3O^+]}[OH−]=[H3O+]1.0×10−14.

Titration of Strong Acids and Strong Bases

The reaction between a strong acid and a strong base is a neutralization reaction: H3O+(aq)+OH−(aq)→2H2O(l)H_3O^+(aq) + OH^-(aq) \rightarrow 2H_2O(l)H3O+(aq)+OH−(aq)→2H2O(l).
The equivalence point is reached when the moles of acid and base are equal.
The volume of titrant needed to reach the equivalence point can be calculated using the equation: Ma×Va=Mb×VbM_a \times V_a = M_b \times V_bMa×Va=Mb×Vb.
Before the equivalence point, the pH is determined by the excess acid concentration.
At the equivalence point, the pH is 7.00.
After the equivalence point, the pH is determined by the excess base concentration.

Titration Curve of a Strong Acid with a Strong Base

The titration curve of a strong acid with a strong base shows a steep rise near the equivalence point.
The pH at the equivalence point is 7.00.

Titration of a Weak Acid with a Strong Base

The reaction between a weak acid and a strong base produces the conjugate base of the weak acid.
The pH is calculated using the KaK_aKa expression for the weak acid.
The equivalence point is reached when the moles of acid and base are equal.
The pH at the equivalence point is greater than 7.00.

Experiment 3: Determination of Acetic Acid Content in Vinegar

The concentration of acetic acid in vinegar can be determined by titrating it with a standardized NaOH solution.
The standardization of NaOH solution involves titrating it with a primary standard (KHP).
The data from the titration is used to calculate the concentration of acetic acid in the vinegar sample using stoichiometry and dimensional analysis.
The volume of NaOH needed to reach the equivalence point is calculated using the equation: molCH3COOH=molNaOHmol CH_3COOH = mol NaOHmolCH3COOH=molNaOH.
The titration curve of a weak acid with a strong base shows a gradual rise near the equivalence point.

Precipitation Titration

A precipitation titration is based on the reaction between two ionic compounds to form an insoluble precipitate.
The equivalence point is reached when the stoichiometric amount of titrant has been added to react with the analyte.
The Mohr method is used to determine the chloride concentration using a standard solution of silver nitrate.
The concentration of chloride in the sample can be calculated in terms of mg/L and % NaCl using dimensional analysis.

Solubility

The solubility of a substance is the amount of the substance that can be dissolved in a given quantity of solvent at a given temperature.
The solubility guidelines for common ionic compounds can be used to predict which compounds are soluble or insoluble in water.
The solubility of a compound is affected by several factors, including temperature and the presence of other ions in the solution.

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Description

This quiz covers the auto-ionization of water, the concepts of pH and pOH, and their relationships. It also includes calculations for hydronium and hydroxide concentrations, as well as the titration of strong acids and bases. Test your understanding of these fundamental chemistry concepts.