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pH Scale — Reading Comprehension

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This comprehensive science passage introduces middle school students to the pH scale, a critical scientific tool for measuring the acidity or alkalinity of substances. Aligned with NGSS standard MS-PS1-2, the text explains the mechanisms behind the 0-14 pH scale, defines key terms like acidic, basic, and neutral, and provides real-world examples such as stomach acid, blood, and bleach. The passage explores why pH matters in biological, environmental, and technological contexts while connecting to broader scientific principles. Included are a glossary, differentiated reading versions, Spanish translations, and a variety of engaging activities such as multiple-choice quizzes, writing prompts, and graphic organizers. All resources are designed for grades 6-8 and include audio integration to support diverse learners.

CONTENT PREVIEW

pH-scale-1 — The pH Scale: Measuring Acidity and Alkalinity

The pH scale is an essential scientific tool that allows us to measure how acidic or basic a substance is. Scientists use the pH scale to better understand and control chemical reactions, monitor environmental health, and study biological processes. The scale ranges from 0 to 14, with each number representing a different level of acidity or alkalinity. Understanding the pH of substances helps us answer important questions, such as why certain foods taste sour or why our bodies need to maintain a stable internal environment.

How the pH Scale Works

The pH scale is based on the concentration of hydrogen ions (H⁺) in a solution. Substances with a high concentration of hydrogen ions have a low pH and are called acids. Acids have a pH less than 7. Substances with a low concentration of hydrogen ions have a high pH and are called bases or alkaline. Bases have a pH greater than 7. A substance with a pH of exactly 7 is considered neutral. For example, pure water is neutral. The pH scale is logarithmic, which means that each step on the scale represents a tenfold change in hydrogen ion concentration. This means a substance with a pH of 4 is ten times more acidic than one with a pH of 5.

Examples and Applications of the pH Scale

Many familiar substances have different pH values. For instance, stomach acid has a pH of about 2, making it very acidic. Human blood has a pH around 7.4, which is slightly basic and necessary for proper body function. Household bleach is highly basic, with a pH near 13. Scientists and health professionals often measure pH using indicators, such as litmus paper or digital meters. These tools change color or display a number to show the pH of a substance. Monitoring pH is crucial in fields like medicine, agriculture, and environmental science. For example, farmers test soil pH to ensure crops grow well, and doctors monitor blood pH to diagnose health conditions.

Interactions and Broader Implications

The pH scale connects to many scientific principles and real-world systems. Changes in pH can affect chemical reactions, the health of living organisms, and the safety of environments. For example, when rainwater becomes more acidic due to pollution, it can harm plants, animals, and buildings—a phenomenon called acid rain. In our bodies, even small changes in blood pH can disrupt vital processes, so mechanisms like breathing and kidney function help keep it balanced. Understanding pH also helps engineers design better cleaning products and water treatment systems. The study of pH demonstrates how chemistry, biology, and environmental science are interconnected.

In summary, the pH scale is a powerful way to measure and compare acidity and alkalinity in many contexts. By knowing pH values, scientists can predict reactions, protect health, and solve real-world problems. The ability to test and interpret pH is a foundational skill in science that supports our understanding of both natural and human-made systems.

Interesting Fact: The word "pH" comes from the German term "potenz Hydrogen," which means "power of hydrogen."

What does the pH scale measure?

How acidic or basic a substance isThe temperature of a substanceThe color of a substanceHow much energy a substance has

Which pH value is considered neutral?

07142

What is the pH of human blood?

About 2Exactly 7Around 7.4Close to 13

What does it mean if a substance has a pH of 13?

It is acidicIt is neutralIt is basic/alkalineIt is not measurable

What is an indicator in the context of pH?

A machine that heats substancesA material that changes color to show pHA scale that shows weightA device that measures temperature

What is the main difference between acids and bases as explained in the passage?

Acids have higher pH and more hydrogen ionsBases have higher pH and fewer hydrogen ionsAcids have lower pH and fewer hydrogen ionsBases and acids have the same pH

Why do doctors care about blood pH?

It helps diagnose health conditionsIt shows how much oxygen is in the bloodIt makes the blood redIt helps keep the blood warm

If rainwater becomes more acidic, what can happen?

It can harm plants and buildingsIt can make the sky turn greenIt can cool the environmentIt helps crops grow better

True or False: The pH scale is logarithmic, so each number change means a tenfold change in hydrogen ion concentration.

TrueFalse

True or False: Pure water is considered an acid.

TrueFalse