What Is The pH Scale | Acids, Bases & Alkalis | Chemistry | FuseSchool

FuseSchool - Global Education

30 May 201603:11

Summary

TLDRThis educational video explores the pH scale and the use of indicators to determine the acidity or alkalinity of substances. It explains how litmus paper, either red or blue, changes color in response to acids or alkalis, but cannot quantify the pH level. The video then introduces the universal indicator, a mixture of dyes that can indicate the pH value of a solution across the full 0 to 14 scale. It also touches on the use of a pH meter for more precise measurements. Examples of various substances' pH levels, such as stomach acid, milk, and seawater, are provided to illustrate the concept.

Takeaways

🔬 The pH scale is a measure of how acidic or alkaline a substance is, ranging from 0 (extremely acidic) to 14 (extremely alkaline), with 7 being neutral.
🌈 Indicators are substances that change color in the presence of acids or alkalis, helping to identify their properties.
🍂 Litmus paper, derived from lichens, is a simple indicator that turns red in acids and blue in alkalis.
📄 Red litmus paper changes color to blue in alkaline conditions, while blue litmus paper changes to red in acidic conditions.
🚫 Litmus paper cannot provide the degree of acidity or alkalinity; it only indicates the presence of an acid or alkali.
🌈 Universal indicator is a more complex mixture that can show the pH value of a solution through various color changes.
🔍 The pH scale is used to measure the exact level of acidity or alkalinity, with substances like stomach acid being very acidic (pH 2) and bleach being very alkaline (pH 13).
🌊 Examples of substances with specific pH levels include acid rain (around 5.5), milk (neutral at 7), and seawater (slightly alkaline).
🔬 Universal indicator is called 'universal' because it can indicate the entire pH spectrum, unlike some other indicators with limited color changes.
📊 For even more precise pH measurements, a pH meter can be used, providing readings accurate to two decimal places.

Q & A

What is an indicator and how does it help in determining the acidity or alkalinity of a substance?
-An indicator is a substance that changes color in the presence of acids or alkalis, helping to identify whether a substance is acidic, neutral, or alkaline.
What are the two forms in which litmus paper is available, and what is its source?
-Litmus paper is available in two forms: liquid and paper, with the paper form being easier and more reliable. It is sourced from lichens, which have been used for centuries to dye cloth.
How does red litmus paper react to alkaline conditions, and what color does it change to?
-Red litmus paper changes color from red to blue under alkaline conditions.
What is the color change of blue litmus paper under acidic conditions?
-Blue litmus paper changes color from blue to red under acidic conditions.
What is the pH scale and what does it measure?
-The pH scale is a scale from 0 to 14 that measures the acidity or alkalinity of a solution, with 0 being extremely acidic, 7 neutral, and 14 extremely alkaline.
What is a universal indicator and how does it differ from litmus paper?
-A universal indicator is a mixture of different indicators or dyes that can show many color changes, indicating the pH value of a solution. It differs from litmus paper in that it provides a more detailed indication of where on the pH scale a solution lies.
What is the pH of stomach acid, and how does it compare to the pH of acid rain?
-Stomach acid has a pH of about 2, which is stronger than acid rain, which has a pH of about 5.5.
Why is a universal indicator called 'universal'?
-A universal indicator is called 'universal' because it can indicate the entire pH spectrum, providing a detailed view of a solution's acidity or alkalinity.
How can one get more accurate pH measurements than what is provided by a universal indicator?
-One can use a pH meter for more accurate measurements, which can provide readings to two decimal places of the pH scale.
What is the pH range for acids, neutral substances, and alkalis according to the script?
-Acids are from 0 to 6, neutral is 7, and alkalis are from 8 to 14 on the pH scale.
What is the pH of milk, and how does it relate to the concept of neutrality?
-Milk has a pH of 7, which is considered neutral, neither acidic nor alkaline.

Outlines

00:00

🔬 Understanding pH Scale and Indicators

This video segment introduces viewers to the pH scale, which is a measure of how acidic or alkaline a substance is. It explains that indicators, like litmus paper, can be used to determine if a substance is acidic or alkaline. Litmus paper is red in acids and blue in alkalis, and it is made from lichens, which have been used for centuries to dye cloth. The segment also mentions that while litmus paper can indicate the presence of an acid or alkali, it does not provide information about the degree of acidity or alkalinity. To measure this, one can use the pH scale or a universal indicator. The pH scale ranges from 0 (extremely acidic) to 14 (extremely alkaline), with 7 being neutral. Examples given include stomach acid at pH 2, milk at pH 7, and bleach at pH 13. The video also touches on the use of a universal indicator, which can show the pH value of a solution through various color changes, and the use of a pH meter for more precise measurements.

Mindmap

Keywords

💡pH scale

The pH scale is a logarithmic scale used to specify the acidity or alkalinity of a solution. It ranges from 0 to 14, with 7 being neutral. In the video, the pH scale is introduced as a method to quantify how acidic or alkaline a substance is, beyond just identifying it as such. For example, stomach acid is mentioned as having a pH of about 2, indicating it is a strong acid.

💡Indicators

Indicators are substances that change color in response to the acidity or alkalinity of a solution. They are used to visually determine the pH of a substance. The video explains that indicators like litmus paper show different colors in acidic or alkaline conditions, which is crucial for understanding the basic properties of substances.

💡Litmus paper

Litmus paper is a type of indicator that changes color based on the pH of a solution. It is made from lichens and is used in both liquid and paper forms. In the video, red and blue litmus papers are discussed, where red litmus paper turns blue in alkaline conditions and blue litmus paper turns red in acidic conditions, serving as a simple test for pH.

💡Acidic

A substance is considered acidic if it has a pH value less than 7. The video mentions that indicators like litmus paper can be used to identify if a substance is acidic. An example given is that red litmus paper remains red in acidic conditions, indicating the presence of an acid.

💡Alkaline

Alkaline substances have a pH value greater than 7. The video explains that alkaline solutions turn blue litmus paper red and can be identified using indicators. The concept is further illustrated by stating that soapy water and bleach are examples of strong alkalis.

💡Neutral

A neutral substance has a pH of exactly 7, meaning it is neither acidic nor alkaline. The video uses milk as an example of a neutral substance, highlighting the importance of neutrality in various contexts.

💡Universal indicator

A universal indicator is a mixture of indicators that can show a wide range of color changes, thereby indicating the pH value of a solution more precisely than simple indicators like litmus paper. The video explains that universal indicators can indicate the entire pH spectrum, providing a more detailed understanding of a solution's acidity or alkalinity.

💡Acid rain

Acid rain is mentioned in the video as an example of a naturally occurring acidic substance, with a pH of about 5.5. It is formed when sulfur dioxide and nitrogen oxides in the atmosphere react with water, and it serves as an example of how the pH scale can be applied to environmental phenomena.

💡Seawater

Seawater is described in the video as being slightly alkaline, with a pH typically around 8.1. This example illustrates how the pH scale can be used to characterize the酸碱性质 of natural bodies of water.

💡pH meter

A pH meter is a device that provides precise measurements of the pH of a solution, with readings that can be as specific as 0.01 pH units. The video mentions pH meters as a tool for obtaining more accurate pH measurements than what can be achieved with indicators like litmus paper or universal indicators.

💡Stomach acid

Stomach acid is used in the video as an example of a strong acid, with a pH of about 2. This example is important for understanding the role of acids in biological systems and how the pH scale can be used to describe their strength.

Highlights

The pH scale and indicators are discussed to determine if a substance is acidic, neutral, or alkaline.

Indicators show different colors in acidic or alkaline conditions.

Litmus paper is a simple indicator made from lichens, used to determine if a substance is acidic or alkaline.

Litmus paper comes in red and blue forms, with red indicating alkalis and blue indicating acids.

Red litmus paper turns blue in alkaline conditions and remains red in acidic conditions.

Blue litmus paper turns red in acidic conditions and remains blue in alkaline conditions.

Litmus paper cannot indicate the degree of acidity or alkalinity.

The pH scale ranges from 0 to 14, with 0 being extremely acidic, 7 neutral, and 14 extremely alkaline.

Universal indicator is a mixture that shows the pH value of a solution through various color changes.

Universal indicator can be used as a liquid or on paper.

Stomach acid has a pH of about 2, indicating it is a strong acid.

Acid rain has a pH of about 5.5.

Milk is neutral with a pH of 7.

Seawater is slightly alkaline.

Soapy water and bleach are examples of strong alkaline substances.

A pH meter provides more accurate pH readings to 0.01.

Indicators can tell us if a substance is acidic or alkaline and the degree of acidity or alkalinity.

Acids range from 0 to 6 on the pH scale, neutral is 7, and alkalis are from 8 to 14.