Test: Reactivity - Year 9 MCQ

The law of conservation of mass states that the mass of reactants before a chemical reaction equals the mass of products after the reaction. This principle is fundamental in chemistry, as it confirms that atoms are neither created nor destroyed during a chemical reaction. For example, in a sealed container, the total mass remains constant even if gases are produced, emphasizing the importance of balancing chemical equations.

When a copper nail is placed in iron sulfate solution, no reaction occurs because copper is less reactive than iron and cannot displace it. This lack of reaction illustrates the principles of the reactivity series and is essential for understanding how metals interact in displacement reactions.

Sodium chloride, commonly known as table salt, serves the primary purpose of preserving and flavoring food. It inhibits the growth of bacteria, thereby extending the shelf life of food products. Additionally, salt enhances the taste of food by balancing flavors. Its role in culinary practices underscores the importance of salts in everyday life.

In a displacement reaction, a more reactive metal displaces a less reactive metal from its compound. For example, when an iron nail is placed in copper sulfate solution, iron displaces copper, resulting in iron sulfate and copper. This principle is essential in understanding metal reactivity and is widely applied in industrial processes.

Aluminium is the metal used to displace iron from iron oxide in the thermite reaction. This highly exothermic reaction produces molten iron and is utilized in welding railway tracks due to the intense heat generated. The thermite reaction showcases the principle of displacement in metallurgy and demonstrates how chemical reactions can be harnessed for practical applications.

The reaction between sodium hydrogencarbonate and citric acid is an endothermic reaction because it absorbs energy from the surroundings, resulting in a cooling effect. This absorption of energy is why the reaction is often used in making sherbet sweets, creating a refreshing sensation when consumed. In contrast, burning magnesium and mixing strong acids with bases typically releases energy.

In a chemical reaction, atoms rearrange to form new substances without any atoms being lost or created. This process involves breaking and forming bonds, where the same atoms present in the reactants are found in the products, albeit in different arrangements. Understanding this concept is crucial for grasping the fundamentals of chemical processes and balancing equations, as it highlights the nature of matter in reactions.

The general equation for a neutralization reaction is Acid + Base → Salt + Water. This reaction occurs when an acid reacts with a base (alkali), resulting in the formation of a salt and water. For instance, when hydrochloric acid reacts with sodium hydroxide, sodium chloride (table salt) and water are produced. Neutralization reactions are fundamental in chemistry, particularly in titrations and various industrial processes.

Potassium (K) is the most reactive metal in the reactivity series. It reacts vigorously with water and oxygen, often producing heat and light. This high reactivity is due to its single electron in the outer shell, which it readily loses to form positive ions. In contrast, metals like silver and copper have higher oxidation states and are less willing to lose electrons, placing them lower in the reactivity series.

Carbon reduction involves the reaction of carbon with metal oxides to produce metals and carbon dioxide. This process is fundamental in metallurgy, especially for extracting metals from their ores in a blast furnace. For instance, in the extraction of iron, carbon (in the form of coke) reacts with iron oxide to yield molten iron and carbon dioxide, illustrating the reduction of metal oxides.

A displacement reaction occurs when a more reactive metal replaces a less reactive metal in a compound. For example, when iron is placed in copper sulfate, iron displaces copper, forming iron sulfate and releasing copper. This principle is important for identifying unknown metals and is widely used in various industrial applications.

In an exothermic reaction, energy is released into the surroundings, often in the form of heat or light. This is seen when potassium reacts with water, resulting in a vigorous release of energy. Understanding exothermic reactions is crucial in fields such as thermodynamics and industrial chemistry, as they can influence reaction conditions and product stability.

Neutralization occurs when an alkali reacts with an acid to produce a salt and water. For example, when sodium hydroxide reacts with hydrochloric acid, sodium chloride (table salt) and water are formed. This reaction is fundamental in chemistry and is widely applied in various applications, including titration in analytical chemistry.

The reaction between a carbonate and an acid typically produces a salt, water, and carbon dioxide. For instance, when calcium carbonate reacts with sulfuric acid, it generates calcium sulfate, water, and carbon dioxide. This reaction illustrates how carbonates can be used in various applications, including effervescent tablets and geological processes such as limestone erosion.

When a metal reacts with a dilute acid, it produces a salt and hydrogen gas. For example, zinc reacts with hydrochloric acid to form zinc chloride and hydrogen:

Word equation: zinc + hydrochloric acid → zinc chloride + hydrogen
Symbol equation: Zn + 2HCl → ZnCl₂ + H₂