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Refer to the definition of pH in Example 5 to solve Exercises \(69-73\). Find the \(\mathrm{pH}\) of a solution with \(\left[\mathrm{H}^{+}\right]=4 \times 10^{-5}\).

Short Answer

Expert verified
The pH of the solution with [H+] = \(4 \times 10^{-5}\) is approximately 4.40.

Step by step solution

01

Understand the pH Definition

The pH of a solution is defined by the formula \( \mathrm{pH} = -\log [\mathrm{H}^{+}]\), where [H+] is the concentration of hydrogen ions in the solution.
02

Substitute the Given Value

Substitute the given equation with [H+] = \(4 \times 10^{-5}\). So, the calculation becomes: \(\mathrm{pH} = -\log (4 \times 10^{-5})\).
03

Simplify the Calculation

Simplify the calculation. First, apply the logarithm rules. The logarithm of a product is the sum of the logarithms, so we can simplify as follows: \(\mathrm{pH} = -(\log 4 + \log 10^{-5})\). The \(\log 10^{-5}\) is simply \(-5\), based on the definition of logarithms. Therefore, this becomes: \(\mathrm{pH} = -(\log 4 - 5)\).
04

Compute the Value

Now compute \(-(\log 4 - 5)\), which is approximately 4.40. Thus, the pH of the given solution is roughly 4.40.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Logarithms
Logarithms are a powerful mathematical tool that simplifies multiplication and division into addition and subtraction. When dealing with logarithms, you often face expressions like \( \log(ab) = \log a + \log b \). This property allows us to break complex calculations into simpler parts. When we say 'log' in science, we usually mean the base 10 logarithm, commonly written as \( \log \). In the context of our exercise, we're using logarithms to find the pH of a solution. Here, the main step involves using the fact that the logarithm of a power of ten, like \( 10^{-5} \), is simply the exponent, -5. That's because \( \log 10^{-5} = -5 \). This makes it easy to handle very small or very large numbers, like ion concentrations, which is why logarithms are common in chemistry.
Hydrogen Ion Concentration
Hydrogen ion concentration in a solution determines its acidity, and it's commonly expressed in terms of molarity, \( [\text{H}^+] \). A basic concept is that more hydrogen ions mean a more acidic solution, and fewer ions mean a more basic or alkaline solution. In scientific notation, hydrogen ion concentrations are often written as powers of ten, such as \( 4 \times 10^{-5} \). This expresses very small numbers in an easily understandable format. The pH scale, which ranges generally from 0 to 14, provides a way to express these concentrations in a compact, practical manner. A low pH indicates high acidity, while a high pH indicates basicity. This is why understanding \([\text{H}^+]\) is crucial when calculating the pH.
Chemistry
Chemistry is the study of matter, its properties, and the changes it undergoes. One of the key aspects of chemistry is the interaction of atoms and molecules, which often involves chemical reactions and changes in the state of matter. For solutions, understanding chemistry involves knowing how substances interact and dissolve in a solvent, typically water. The pH scale plays a pivotal role in chemistry by helping chemists understand how acidic or basic a solution is, especially when working with reactions sensitive to these conditions. The concept of pH, which stands for 'potential of hydrogen,' is one of the central concepts in chemistry. It helps to understand the equilibrium of acids and bases in solutions, which is critical in fields ranging from biochemistry to environmental science. This is why chemistry lessons often start with basic pH calculations, like calculating the pH from hydrogen ion concentration, to build a strong foundation for more complex chemical equations.

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Most popular questions from this chapter

Evaluate the given quantity by referring to the function \(f\) given in the following table. $$\begin{array}{cc}x & f(x) \\\\-2 & 1 \\\\-1 & 2 \\\0 & 0 \\\1 & -1 \\\2 & -2\end{array}$$ $$f^{-1}\left(f^{-1}(-2)\right)$$

The cost of removing chemicals from drinking water depends on how much of the chemical can safcly be left behind in the water. The following table lists the annual removal costs for arsenic in terms of the concentration of arsenic in the drinking water. (Source: Environmental Protection Agency) $$\begin{array}{|c|c|}\hline\text { Arsenic Concentration } & \text { Annual Cost } \\\\\text { (micrograms per liter) } & \text { (millions of dollars) } \\\\\hline 3 & 645 \\\5 & 379 \\\10 & 166 \\\20 & 65\\\ \hline\end{array}$$ (a) Interpret the data in the table. What is the relation between the amount of arsenic left behind in the removal process and the annual cost? (One microgram is equal to \(10^{-6}\) gram.) (b) Make a scatter plot of the data and find the exponential function of the form \(C(x)=C a^{*}\) that best fits the data. Here, \(x\) is the arscnic concentration. (c) Why must \(a\) be less than 1 in your model? (d) Using your model, what is the annual cost to obtain an arsenic concentration of 12 micrograms per liter? (e) It would be best to have the smallest possible amount of arsenic in the drinking water, but the cost may be prohibitive. Use your model to calculate the annual cost of processing such that the concentration of arsenic is only 2 micrograms per liter of water. Interpret your result.

Evaluate the expression to four decimal places using a calculator. $$2 \log \frac{1}{5}$$

Applications In this set of exercises, you will use inverse functions to study real-world problems. Find a function that converts \(x\) gallons into quarts. Find its inverse and explain what it does.

The 1960 earthquake in Chile registered 9.5 on the Richter scale. Find the energy \(E\) (in Ergs) released by using the following model, which relates the energy in Ergs to the magnitude \(R\) of an earthquake. (Source: National Earthquake Information Center, U.S. Geological Survey) $$\log E=11.4+(1.5) R$$

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