Chapter 15: Problem 67
Obtain the \(\mathrm{pH}\) corresponding to the following hydronium-ion concentrations. a. \(1.0 \times 10^{-8} M\) b. \(5.0 \times 10^{-12} M\) c. \(7.5 \times 10^{-3} M\) d. \(6.35 \times 10^{-9} M\)
Short Answer
Expert verified
a. 8; b. 11.3; c. 2.12; d. 8.20
Step by step solution
01
Understand the relationship between pH and hydronium-ion concentration
The pH of a solution is a measure of how acidic or basic it is. The pH is calculated using the negative logarithm (base 10) of the hydronium-ion ([H_3O^+]) concentration. The formula is:\[\text{pH} = -\log_{10}([H_3O^+])\]
02
Calculate pH for each concentration
Use the formula from Step 1 to calculate the pH for each given hydronium-ion concentration.
03
Step 3a: Calculate pH for 1.0 × 10^{-8} M
For concentration \([H_3O^+] = 1.0 \times 10^{-8} \text{ M}\), calculate:\[\text{pH} = -\log_{10}(1.0 \times 10^{-8}) = 8\]
04
Step 3b: Calculate pH for 5.0 × 10^{-12} M
For concentration \([H_3O^+] = 5.0 \times 10^{-12} \text{ M}\), calculate:\[\text{pH} = -\log_{10}(5.0 \times 10^{-12}) = 11.3\]
05
Step 3c: Calculate pH for 7.5 × 10^{-3} M
For concentration \([H_3O^+] = 7.5 \times 10^{-3} \text{ M}\), calculate:\[\text{pH} = -\log_{10}(7.5 \times 10^{-3}) \approx 2.12\]
06
Step 3d: Calculate pH for 6.35 × 10^{-9} M
For concentration \([H_3O^+] = 6.35 \times 10^{-9} \text{ M}\), calculate:\[\text{pH} = -\log_{10}(6.35 \times 10^{-9}) \approx 8.20\]
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
Hydronium-ion concentration
Hydronium ions, represented as \([H_3O^+]\), are crucial in determining the acidity of a solution. When an acid dissolves in water, it donates a proton \((H^+)\) to a water molecule, creating the hydronium ion. The concentration of these ions indicates the acidic strength of the solution:
Understanding hydronium-ion concentration helps bridge the gap between acid strength and pH, allowing us to see whether a solution leans towards being acidic or basic.
- Higher hydronium-ion concentration means stronger acidity.
- Lower concentration implies weaker acidity.
Understanding hydronium-ion concentration helps bridge the gap between acid strength and pH, allowing us to see whether a solution leans towards being acidic or basic.
Acidic and basic solutions
Acidity and basicity are key properties of solutions defined by their \( ext{pH}\) values. The term "pH" means "potential of hydrogen" and represents how acidic or basic a solution is:
- An acidic solution has a \( ext{pH}\) less than 7. This indicates a higher concentration of hydronium ions.
- A basic (or alkaline) solution has a \( ext{pH}\) greater than 7. This signifies higher hydroxide ion concentrations than hydronium ions.
- A neutral solution, such as pure water, exhibits a \( ext{pH}\) of exactly 7, where hydronium and hydroxide ion concentrations are equal.
Logarithms in chemistry
Logarithms, powerful mathematical tools, are crucial in chemistry for simplifying calculations that involve concentrations, like \( ext{pH}\). The logarithmic scale allows us to express very large or very small numbers in a compact form.
The \( ext{pH}\) calculation uses the base-10 logarithm due to its capacity to easily express the changes in hydronium-ion concentrations:
Mastering logarithms enriches one's ability to communicate effectively about chemical properties and reactions, especially in exercises involving pH calculations.
The \( ext{pH}\) calculation uses the base-10 logarithm due to its capacity to easily express the changes in hydronium-ion concentrations:
- The formula \( ext{pH} = -\log_{10}([H_3O^+])\) takes the logarithm of the hydronium concentration, making it simpler to grasp.
- The negative sign flips the scale to ensure higher \([H_3O^+]\) leads to lower \( ext{pH}\).
Mastering logarithms enriches one's ability to communicate effectively about chemical properties and reactions, especially in exercises involving pH calculations.