Acids Bases And Salts

Dry HCl gas is not acidic because it does not ionize in the absence of water. An acid is defined as a substance that produces ions in aqueous solution. When HCl is dissolved in water (aqueous HCl), it ionizes completely to produce ions: Therefore, aqueous HCl is acidic. NaOH and NH₄OH are bases.

NaOH and NH₄OH are bases.The correct option is (B): Aqueous HCl

Methyl orange is a pH indicator that changes color depending on the acidity or basicity of the solution.

• In acidic solutions (like HCl), methyl orange turns red-pink.
• In basic solutions, it appears yellow.

Since HCl is a strong acid, methyl orange shows a pink/red color in its presence.

The correct answer is option (A): pink

A neutralization reaction occurs when an acid reacts with a base to form salt and water. This type of reaction removes the acidic and basic properties, forming a neutral product. The general form is: For example:

The correct option is (C):

Correct answer: acidic

Explanation:
The oxides of non-metals are generally acidic in nature. When dissolved in water, they form acids.

Examples:
- (carbonic acid)
- (sulphurous acid)

These acidic oxides react with bases to form salt and water.

Hence, the correct answer is: acidic.

Correct answer: a base

Explanation:
An antacid is a substance that is used to neutralize excess acid in the stomach. Since it neutralizes acid, it must be a base.

Common antacids include:
- Magnesium hydroxide
- Aluminium hydroxide
- Sodium bicarbonate

Hence, the correct answer is: a base.

Correct answer:

Explanation:
When sodium carbonate ( ) reacts with an acid (such as HCl), it produces a salt, water, and carbon dioxide gas.

The reaction is:
The gas evolved in this reaction is carbon dioxide ( ).

Hence, the correct answer is: .

Potassium hydroxide (KOH) is a strong base. It turns red litmus paper blue and blue litmus paper red. This is because red litmus paper turns blue in a basic solution, while blue litmus paper turns red in an acidic solution. Since potassium hydroxide is basic, it causes this color change.
Thus, the correct answer is Red litmus turns to blue and blue litmus turns to red.

Step 1: Understand the mechanism of electrical conduction in solutions.
Electrical conductivity in a solution requires the presence of mobile charged particles, which are typically ions. These ions can carry an electric current when a voltage is applied across the solution.
Step 2: Analyze what happens when an acid dissolves in water.
Acids are substances that, when dissolved in water, produce hydrogen ions ( ). For example, hydrochloric acid ( ) dissociates in water as follows: In reality, the ion exists as a hydronium ion ( ) due to its strong interaction with water molecules: So, an acidic solution contains hydronium ions ( ) and the anions of the acid (e.g., for hydrochloric acid, for sulfuric acid).
Step 3: Evaluate the given options.

1. Due to the presence of water molecules:
   While water is the solvent in acidic solutions, water molecules themselves are neutral and do not carry an electric charge. Pure water is a poor conductor of electricity.
2. Due to the presence of free electrons:
   Free electrons are the charge carriers in metals, which are solid conductors. In solutions, the charge carriers are ions, not free electrons.
3. Due to the presence of ions in the solution:
   As explained in
   Step 2, acids produce ions when dissolved in water. These mobile ions ( and anions) can carry an electric current, making acidic solutions conductive.
   
4. Because acids are solid conductors:
   Most pure acids are not solid conductors. For example, hydrochloric acid is a gas, sulfuric acid is a liquid, and solid acids like citric acid do not conduct electricity well in their solid state. It is when acids are dissolved in water that they form ions and conduct electricity.

Step 4: Conclude why acidic solutions conduct electricity.
Acidic solutions conduct electricity due to the presence of mobile ions (hydronium ions and anions) formed when the acid dissociates in water. These ions act as charge carriers.

Step 1: Understand the difference between natural and synthetic indicators.
Indicators are substances that change colour with a change in pH. They can be obtained from natural sources or synthesized in the laboratory.
Step 2: Analyze the origin of each of the given indicators.

• Turmeric:
  Turmeric is a common spice obtained from the turmeric plant. It acts as a natural pH indicator, turning yellow in acidic and neutral solutions and reddish-brown in basic solutions.
• Methyl orange:
  Methyl orange is an azo dye synthesized in the laboratory. It is a synthetic pH indicator that shows a colour change from red in acidic solutions to yellow in basic solutions, with a transition range of pH 3.1 to 4.4.
• Litmus solution:
  Litmus is a natural indicator obtained from lichens. It is commonly used in the form of litmus paper (red and blue) or as a solution. Blue litmus turns red in acidic solutions, and red litmus turns blue in basic solutions.
• Red cabbage extract:
  Red cabbage contains pigments called anthocyanins that change colour depending on the pH of the solution. It is a natural indicator, showing a range of colours from red in acidic solutions to green and yellow in alkaline solutions.

Step 3: Identify the synthetic indicator among the options.
Methyl orange is synthesized chemically in the laboratory, making it a synthetic indicator. Turmeric, litmus solution, and red cabbage extract are obtained from natural sources.

Step 1: Understand the function of an indicator.
An indicator is a substance that shows a visible change, usually a colour change, when the conditions in its environment change, particularly the pH. It is often used to determine the endpoint of a titration reaction.
Step 2: Recall the colour changes of phenolphthalein in different pH ranges.
Phenolphthalein is a pH indicator that is:

• Colourless in acidic solutions (pH 8.2)
• Pink to magenta in basic solutions (pH 10.0)
• Colour changes occur in the pH range of 8.2 to 10.0

Step 3: Analyze the given reaction types.
Acid and base: The reaction between an acid and a base is a neutralization reaction, which results in a change in pH. Phenolphthalein's colour change in the pH range of 8.2 to 10.0 makes it suitable for indicating the endpoint of titrations involving strong acids and strong bases, or strong acids and weak bases where the equivalence point is in the basic range.
Acid and metal: The reaction between an acid and a metal typically produces a salt and hydrogen gas. This reaction does not necessarily involve a significant change in pH that would be effectively indicated by phenolphthalein.
Base and metal oxide: The reaction between a base and a metal oxide usually does not occur, except for amphoteric metal oxides. Even if a reaction occurs, it may not involve a clear pH change suitable for phenolphthalein.
Acid and non-metallic oxide: The reaction between an acid and a non-metallic oxide generally does not occur. Non-metallic oxides are typically acidic or neutral and react with bases.
Step 4: Identify the reaction type where phenolphthalein is commonly used as an indicator.
Phenolphthalein is most commonly used as an indicator in acid-base titrations where the pH at the equivalence point is in the basic range, allowing for a clear colour change from colourless to pink.