Olympiad Test: Acids, Bases And Salts - 1 - Class 7 MCQ

Acid present in amla and lemon is citric acid.
Explanation:
- Amla (Indian gooseberry) and lemon are both citrus fruits that are known for their sour taste.
- The acid responsible for their sour taste is citric acid.
- Citric acid is a weak organic acid that is found naturally in many fruits, especially citrus fruits.
- It is often used as a flavoring agent in various food and beverages.
- Citric acid is also used for its preservative and cleaning properties.
- It is a common ingredient in skincare products and household cleaners.
- The sour taste of amla and lemon can be attributed to the citric acid present in them.
- Other fruits like oranges, grapefruits, and pineapples also contain citric acid.
- However, it is important to note that amla and lemon have higher citric acid content compared to other citrus fruits.
Therefore, the correct answer is option C: citric acid.

Answer:
Introduction:
In this question, we are asked to identify a substance that is present in each cell of our body, as well as in our proteins and fat. We are given four options to choose from: acid, base, salt, or none of these. The correct answer is acid.
Explanation:
1. Acid: Acid is the correct answer as it is present in each cell of our body, as well as in our proteins and fat. Acids are a type of chemical compound that release hydrogen ions (H+) when dissolved in water.
2. Proteins: Proteins are made up of amino acids, which contain acidic and basic groups. These acidic and basic amino acids help in maintaining the overall charge balance and structure of proteins.
3. Fat: Fats, also known as lipids, consist of fatty acids. Fatty acids are carboxylic acids, which are a type of acid.
4. Cell: Each cell in our body contains various acids, such as nucleic acids (DNA and RNA), which play a vital role in genetic information transfer and protein synthesis.
5. Base: Bases are compounds that release hydroxide ions (OH-) when dissolved in water. They are not present in each cell of our body or in proteins and fat.
6. Salt: Salts are compounds formed by the reaction between an acid and a base. While salts are present in our body, they are not present in each cell and are not specifically mentioned in the question.
Therefore, the correct answer is acid (option A). Acids are present in each cell of our body, as well as in our proteins and fat.

Common Name of Copper Sulphate: Blue Vitriol
Explanation:
- Copper sulphate is a chemical compound with the formula CuSO4.
- It is commonly known by the name "Blue Vitriol" due to its blue color and crystal-like appearance.
- The name "vitriol" refers to a class of compounds that are known for their corrosive and acidic properties.
- Copper sulphate is often used in various industries and applications, including agriculture, medicine, and laboratory experiments.
- It is used as a fungicide, herbicide, and pesticide in agriculture to control various plant diseases and pests.
- In medicine, copper sulphate is used in the treatment of certain skin conditions and as an emetic to induce vomiting.
- It is also used in laboratory experiments and educational demonstrations, such as growing copper crystals or testing for the presence of copper ions.
- Copper sulphate has a wide range of industrial uses, including electroplating, dyeing, and as a catalyst in chemical reactions.
- The blue color of copper sulphate is attributed to the presence of hydrated copper ions in its crystal structure.
- Overall, the common name "Blue Vitriol" accurately describes the appearance and properties of copper sulphate.

To determine the products of the given chemical reaction, we need to identify the ions present in the reactants and then combine them to form the products. Let's break down the reaction step by step:
1. NaOH: Sodium hydroxide is a strong base that dissociates in water to form sodium ions (Na+) and hydroxide ions (OH-).
2. MgSO₄: Magnesium sulfate is an ionic compound composed of magnesium ions (Mg2+) and sulfate ions (SO₄2-).
Now, let's combine the ions to form the products:
3. The sodium ions (Na+) from NaOH will combine with the sulfate ions (SO₄2-) from MgSO₄ to form sodium sulfate (Na₂SO₄).
4. The remaining ions, magnesium ions (Mg2+) and hydroxide ions (OH-), will combine to form magnesium hydroxide (Mg(OH)₂).
Therefore, the balanced chemical equation for the reaction is:
2NaOH + MgSO₄ → Mg(OH)₂ + Na₂SO₄
Answer: B:

Mg(OH)₂ Na₂SO₄

Common Name of Sodium Carbonate: Washing Soda
Explanation:
- Sodium carbonate is commonly known as washing soda.
- It is a chemical compound with the formula Na2CO3.
- Washing soda is a white, crystalline powder that is highly alkaline in nature.
- It is called washing soda because it is often used as a laundry detergent and cleaning agent due to its ability to remove stains and soften water.
- Washing soda is also used in various other applications such as making glass, soap, and paper.
- It is not to be confused with baking soda (sodium bicarbonate), which is a different compound with different properties and uses.
- The common name of sodium carbonate is washing soda, not baking soda, blue vitriol, or POP.

Common Name of H₂SO₄

• Answer: C

Explanation:
H₂SO₄ is commonly known as Oil of Vitriol.

• A: Blue vitriol refers to Copper(II) sulfate (CuSO₄).


• B: Green vitriol refers to Iron(II) sulfate (FeSO₄).


• D: Muriatic acid refers to Hydrochloric acid (HCl).

Therefore, the correct answer is C: Oil of Vitriol.

To determine the chemical formula of baking soda, we need to analyze its composition. Baking soda is a common household chemical compound used in baking and cleaning. Its chemical name is sodium bicarbonate.
Chemical formula of baking soda:
- Baking soda is chemically represented as NaHCO₃.
Explanation:
- Sodium bicarbonate is composed of the elements sodium (Na), hydrogen (H), carbon (C), and oxygen (O).
- The chemical formula NaHCO₃ indicates that there is one sodium atom (Na), one hydrogen atom (H), one carbon atom (C), and three oxygen atoms (O) in each molecule of baking soda.
- The presence of sodium (Na) in the formula indicates that the compound is a sodium salt.
- The carbonate ion (CO₃) in the formula indicates the presence of a bicarbonate group.
Summary:
- Baking soda is chemically represented by the formula NaHCO₃.
- The formula indicates the presence of sodium (Na), hydrogen (H), carbon (C), and oxygen (O) in the compound.

Introduction:
An indicator is a substance that is used to detect the presence of a chemical substance. It is widely used in various scientific experiments and analytical techniques. Indicators work by undergoing a physical or chemical change when they come into contact with the target substance. One of the most common ways an indicator shows the presence of a chemical substance is by changing color.
Explanation:
Indicators are used in various fields, including chemistry, biology, and environmental science, to determine the presence or absence of specific substances. Here, we will discuss in detail how indicators work and why changing color is the most common way they indicate the presence of a chemical substance.
Working of an Indicator:
When an indicator is exposed to a specific chemical substance, it undergoes a change in its physical or chemical properties. This change can be observed and used to determine the presence or absence of the target substance. The change can occur due to various factors such as pH, temperature, or the formation of a complex between the indicator and the target substance.
Why changing color is a common indicator:
The most common way an indicator shows the presence of a chemical substance is by changing its color. This is because:
1. Selectivity: Indicators are designed to be selective towards specific substances. They react only with the target substance and undergo a change in color, making it easier to identify the presence of that particular substance.
2. Visual Observation: Color change is easily visible to the naked eye. It provides a clear and immediate indication of the presence of the target substance without the need for complex instruments or equipment.
3. Sensitivity: Indicators can exhibit different shades or intensities of color change depending on the concentration of the target substance. This allows for the detection of even small amounts of the substance.
4. Versatility: Indicators can be used in various forms such as solutions, paper strips, or solid powders. This makes them adaptable to different experimental setups and analytical techniques.
Conclusion:
Indicators are crucial tools in chemical analysis and scientific research. Their ability to change color in the presence of specific substances makes them highly effective in detecting and identifying the presence of chemicals. By understanding the principles behind indicator reactions, scientists can leverage their properties to conduct accurate and reliable experiments.

Definition:
An indicator is a substance that undergoes a distinct observable change when conditions in its surroundings change. It is used to detect the presence, absence, or concentration of specific substances in a solution.
Given options:
A: Turmeric
B: Litmus
C: HCl
D: Methyl orange
Explanation:
To determine which option is not an indicator, we need to understand the properties of each substance.
- Turmeric: Turmeric is a spice commonly used in cooking. It does not have any specific indicator properties.
- Litmus: Litmus is a natural dye extracted from lichens. It is widely used as an indicator to determine whether a substance is acidic or basic.
- HCl: Hydrochloric acid (HCl) is a strong acid. It is not an indicator but rather a substance commonly used in chemical reactions and laboratory experiments.
- Methyl orange: Methyl orange is a pH indicator that changes color in acidic and basic solutions. It is frequently used in titration experiments.
Conclusion:
Based on the given options, the substance that is not an indicator is HCl (hydrochloric acid). It is a strong acid used in various chemical processes but does not possess indicator properties.

The incorrect statement among the given options is D: water change the colour of a litmus.
Explanation:
- Litmus is a natural dye extracted from lichens and is used as an indicator to test the acidity or alkalinity of a substance.
- Acidic substances turn blue litmus paper red, indicating the presence of an acid (Option A).
- Basic substances turn red litmus paper blue, indicating the presence of a base (Option B).
- When water is tested with litmus paper, it remains neutral and does not change the color of the litmus paper. Water is considered a neutral substance (pH 7) and does not have acidic or basic properties (Option D).
- Therefore, Option D is incorrect, and the correct answer is D: water change the colour of a litmus.

Explanation:
Salt is formed when a base reacts with an acid. This is known as a neutralization reaction. During a neutralization reaction, the hydrogen ions from the acid react with the hydroxide ions from the base to form water. At the same time, the cations from the base combine with the anions from the acid to form a salt.
Here is a detailed explanation of each option and why it is incorrect or correct:
A: Metals react with water - This is incorrect because when metals react with water, they typically form metal oxides or metal hydroxides, not salt.
B: Metals react with oxygen - This is incorrect because when metals react with oxygen, they typically form metal oxides, not salt.
C: Base reacts with acid - This is correct. When a base reacts with an acid, a neutralization reaction occurs and salt is formed.
D: None of these - This is incorrect because the correct answer is C, as explained above.
To summarize, the correct answer is C: base reacts with acid.

Neutralization Reaction:
A neutralization reaction is a chemical reaction in which an acid and a base react to form a salt and water. The reaction typically involves the transfer of a proton (H+) from the acid to the base.
Given Reactions:
A: 4Na O2 -> 2Na2O
B: NaOH HCl -> NaCl H2O
C: 2Ca O2 -> 2CaO
D: Na2O H2O -> 2NaOH
Identifying the Neutralization Reaction:
To determine the neutralization reaction, we need to identify the acid and base in each reaction and check if they react to form a salt and water.
Analysis:
A: This reaction does not involve an acid or base. It is the combination of sodium and oxygen, forming sodium oxide. Not a neutralization reaction.
B: This reaction involves the acid HCl and the base NaOH. They react to form the salt NaCl and water (H2O). This is a neutralization reaction.
C: This reaction does not involve an acid or base. It is the combination of calcium and oxygen, forming calcium oxide. Not a neutralization reaction.
D: This reaction involves the base Na2O and water (H2O). They react to form the salt NaOH. This is a neutralization reaction.
Conclusion:
The neutralization reaction is option B: NaOH + HCl -> NaCl + H2O. This reaction involves an acid (HCl) and a base (NaOH), which react to form a salt (NaCl) and water (H2O).

Acid reacts with metal to form
When acid reacts with metal, it forms salt and hydrogen gas. This is known as a metal-acid reaction. The specific reaction depends on the type of acid and metal involved. In this case, the reaction can be represented as:
Acid + Metal → Salt + Hydrogen gas
The correct answer is D: Salt + H₂
Explanation:
- When an acid comes into contact with a metal, a chemical reaction occurs. The acid donates hydrogen ions (H+) to the metal, resulting in the formation of salt and the release of hydrogen gas.
- The salt formed is a compound composed of the metal cation and the anion from the acid.
- The hydrogen gas is released as a byproduct of the reaction.
- The specific salt formed depends on the metal and acid involved. For example, if hydrochloric acid (HCl) reacts with sodium metal (Na), the salt formed would be sodium chloride (NaCl).
To summarize:
- Acid reacts with metal to form salt and hydrogen gas.
- The specific salt formed depends on the metal and acid involved.
- In this case, the correct answer is D: Salt + H₂.
Remember to always consider the specific acid and metal involved in the reaction to determine the correct products formed.

Because of the tremendous heat liberated always acids are added to water and not vice versa. 

To determine the correct answer, let's analyze the options given:
A: NaOH in water - This is not correct as lime water is not a solution of sodium hydroxide (NaOH) in water.
B: NaCl in water - This is also not correct as lime water is not a solution of sodium chloride (NaCl) in water.
C: Ca(OH)₂ in water - This is the correct answer. Lime water is a solution of calcium hydroxide (Ca(OH)₂) in water. Calcium hydroxide is commonly known as lime and is sparingly soluble in water.
D: CaCl₂ in water - This is not correct as lime water is not a solution of calcium chloride (CaCl₂) in water.
Therefore, the correct option is C: Ca(OH)₂ in water. Lime water is a solution of calcium hydroxide in water.