Chemical Reactions — Set 4
Chemistry · रासायनिक अभिक्रियाएं · Questions 31–40 of 40
When Iron nails are placed in Copper Sulfate solution, the blue color fades to?
Correct Answer: B. Light green
Iron displaces copper to form ferrous sulfate, which has a light green color. The blue color of copper sulfate disappears as the copper ions are reduced. This is a standard demonstration of the displacement reaction.
Which of the following is a balanced chemical equation for the formation of water?
Correct Answer: D. $2H_2 + O_2 \rightarrow 2H_2O$
The correct answer is '$2H_2 + O_2 \rightarrow 2H_2O$'. This equation has four hydrogen atoms and two oxygen atoms on both sides. Balancing ensures that the law of conservation of mass is satisfied. Hydrogen and oxygen exist naturally as diatomic molecules.
What type of chemical reaction is the fermentation of grapes?
Correct Answer: D. Chemical change
Fermentation is a chemical change because sugar is converted into alcohol and carbon dioxide. This process is driven by yeast or bacteria acting as biological catalysts. The new substances formed have entirely different properties.
Which gas is produced when Sodium Bicarbonate reacts with Acetic Acid?
Correct Answer: C. Carbon dioxide
The reaction between baking soda and vinegar produces brisk effervescence of carbon dioxide. This is a common acid-base reaction involving a carbonate. It is frequently used in kitchen science experiments and baking.
Copper vessels develop a green coating when exposed to moist air due to?
Correct Answer: A. Copper carbonate and hydroxide
The green layer is a mixture of basic copper carbonate and copper hydroxide. It forms due to the reaction of copper with oxygen, water, and carbon dioxide in the air. This green layer is commonly known as patina.
Which of the following is considered the most definitive indicator that a chemical reaction has occurred, as it confirms the formation of a new substance?
Correct Answer: C. Formation of a precipitate
The formation of a precipitate (an insoluble solid formed from two solutions) is considered one of the most definitive indicators of a chemical reaction because it directly demonstrates the formation of a new substance with different solubility properties. While changes in colour, gas evolution, and temperature change can all indicate a chemical reaction, they can sometimes also occur in physical changes. Precipitation is unambiguous — it shows that a new compound with different properties has been formed, making it the clearest single indicator among the options.
What happens to the oxidation number of an element during oxidation?
Correct Answer: D. It increases
Oxidation involves the loss of electrons, which leads to an increase in the oxidation state. For example, when $Fe$ becomes $Fe^{2+}$, its oxidation number increases from 0 to +2. This is a key concept in identifying redox processes.
Which of the following is a common reducing agent used in metallurgy?
Correct Answer: D. Carbon (Coke)
Carbon is used to extract metals from their oxides by removing oxygen. It acts as a reducing agent because it gains oxygen itself during the process. This is a fundamental step in the production of iron and steel.
The formula $Na_2SO_4 + BaCl_2 \rightarrow BaSO_4 + 2NaCl$ represents which reaction?
Correct Answer: C. Double displacement
Sodium and barium ions swap their partners to form new salt compounds. Since two compounds exchange components, it is a double displacement reaction. Barium sulfate forms as a white solid precipitate in this reaction.
What is the primary reason for balancing a chemical equation?
Correct Answer: A. To satisfy Law of Conservation of Mass
The correct answer is 'To satisfy Law of Conservation of Mass'. Balancing ensures that the number of atoms for each element is the same on both sides. This confirms that no matter is lost or gained during the chemical process. It is a mandatory step for performing any stoichiometric calculations.