Grade 8----Chapter 7 Acids, Bases And pH

The pH scale is a measure of the acidity or alkalinity of a solution. It ranges from 0 to 14, where 0 is highly acidic, 7 is neutral, and 14 is highly alkaline. A neutral substance has a pH of 7, which means it is neither acidic nor alkaline. Therefore, the correct answer is 7.

Some acids should be treated very carefully because they are corrosive. This means that they have the ability to cause damage or destruction to materials they come into contact with. Corrosive acids can cause chemical burns, damage to skin and eyes, and can even be harmful if inhaled or ingested. Therefore, it is important to handle them with caution, wear protective gear, and follow proper safety protocols to avoid any accidents or injuries.

Neutralization is a reaction between an acid and a base. In this reaction, the acid donates a proton (H+) to the base, forming water and a salt. The acid loses its acidic properties by losing a proton, while the base loses its basic properties by accepting the proton. This reaction results in the formation of a neutral solution, where the pH is close to 7.

A base is commonly used in the production of soaps and detergents. Bases, also known as alkaline substances, are used in these products to help remove dirt and grease. They react with fats and oils to form soap molecules, which can then be used for cleaning purposes. The other options listed, such as being a vitamin in food or making foods taste sour, do not typically involve the use of bases. Etching metals for printing may involve the use of acids, rather than bases.

Sulfuric acid is a highly corrosive substance that can react with metals, causing them to corrode. It is a strong acid that can easily break down the protective oxide layer on the surface of metals, exposing them to further oxidation and corrosion. In comparison, salt solution, lemon juice, and vinegar are relatively less corrosive and would not cause as much damage to metals.

Lemon juice is an acid because it contains citric acid, which gives it a sour taste. Acids are substances that release hydrogen ions when dissolved in water, and lemon juice is acidic due to the presence of citric acid.

A litmus indicator can be used to determine the pH of a substance because it is a pH indicator. Litmus paper changes color depending on the acidity or alkalinity of a solution. When the litmus paper turns red, it indicates that the substance is acidic, while a blue color indicates alkalinity. By observing the color change of the litmus paper after it comes into contact with a substance, one can determine its pH level.

Acids are described as "corrosive" because they have the ability to chemically react with and degrade other materials. This process is commonly referred to as "eating away" at other materials. Acids can cause damage and destruction to substances they come into contact with, making them highly corrosive.

When handling acids and alkalis, it is crucial to wear safety goggles. This is because acids and alkalis can be extremely corrosive and can cause severe damage to the eyes if they come into contact. Safety goggles provide a protective barrier that shields the eyes from any splashes or spills that may occur during the handling process. Wearing safety goggles ensures the safety and well-being of the individual by minimizing the risk of eye injuries.

Red cabbage can be used to make an indicator because it contains a pigment called anthocyanin, which can change color depending on the pH of the solution it is in. When the cabbage juice is added to an acidic solution, it turns pink or red, while in a basic solution it turns green or blue. This property makes red cabbage a suitable substance for creating an indicator to test the acidity or alkalinity of other substances.

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Acids and alkalis can cause dyes to change color, and the dyes that are specifically designed to undergo this color change are called indicators. Indicators are substances that change color depending on the pH of the solution they are in. They are commonly used in chemistry to determine whether a solution is acidic or alkaline. Therefore, indicators are the correct answer in this context.

Acids are known to turn blue litmus paper red. This is because acids release hydrogen ions (H+) when dissolved in water, which react with the blue litmus paper and cause it to change color from blue to red. This is a characteristic property of acids and can be used to identify their presence.

Baking soda is a basic substance, also known as sodium bicarbonate. When applied to a bee sting, it can help neutralize the acidic venom and provide relief from the pain. This is because baking soda has alkaline properties that can counteract the acidity of the sting.

In water, bases form hydroxide ions. When a base is dissolved in water, it dissociates to release hydroxide ions (OH-) into the solution. These hydroxide ions can accept a hydrogen ion (H+) from an acid, forming water (H2O) and neutralizing the acidic solution. This process is known as neutralization. Therefore, the correct answer is hydroxide ions.

Sodium hydroxide/bleach is the strongest alkali among the given substances. Alkalis are substances that can neutralize acids, and sodium hydroxide is a strong alkali that is commonly used in cleaning products like bleach. It has a high pH level and can cause severe burns and damage to the skin and eyes if not handled properly. Hydrochloric acid is an acid, not an alkali, and is not as strong as sodium hydroxide. Soap and toothpaste may have some alkaline properties, but they are not as strong as sodium hydroxide.

Universal indicator is a pH indicator that changes color depending on the acidity or alkalinity of a solution. In the presence of a strong acid, the cabbage solution, which is used as a universal indicator, turns red. This indicates a low pH level, as strong acids have a high concentration of hydrogen ions. Therefore, the correct answer is red.

The given options include Coke, Lemon, Baking Soda, and Vinegar. Coke, Lemon, and Vinegar are all acidic substances commonly used in cooking or cleaning. Baking soda, on the other hand, is a basic substance often used as a leavening agent in baking. Therefore, Baking Soda does not belong in this group of acidic substances.

The given options consist of different substances and their corresponding pH levels. Apple Juice with a pH of 5 is the correct answer because it is the only acidic substance among the options. Ammonia has a pH of 8, Tums/Rolaids has a pH of 9, and Shampoo/conditioner has a pH of 7.5, all of which are either neutral or alkaline.

The pH scale measures the concentration of hydrogen ions in a solution. It indicates the level of acidity or alkalinity of a substance. A lower pH value indicates a higher concentration of hydrogen ions, making the substance more acidic. Conversely, a higher pH value indicates a lower concentration of hydrogen ions, making the substance more alkaline. Therefore, the correct answer is the concentration of hydrogen ions.