Chemistry Unit 2 Revision

The given reactivity series lists elements in order of their reactivity, with the most reactive element at the top. The series starts with Potassium, followed by Calcium, Magnesium, and so on. The correct answer, Sodium, falls between Potassium and Calcium in the reactivity series.

Chlorine and fluorine are both highly reactive elements that can displace bromine from its compounds through a chemical reaction known as displacement or substitution. This occurs because chlorine and fluorine have a higher reactivity than bromine, meaning they are more likely to form bonds with other elements. When chlorine or fluorine react with a compound containing bromine, they can replace the bromine atom, forming a new compound. Therefore, both chlorine and fluorine can replace bromine from its compounds.

Rusting can be prevented by various methods such as galvanizing with zinc, greasing, oiling, painting, and using plastic coatings. Galvanizing with zinc involves coating the metal surface with a layer of zinc, which acts as a protective barrier against rust formation. Greasing and oiling create a barrier between the metal and moisture, preventing rust from occurring. Painting provides a protective layer that seals the metal surface and prevents contact with air and moisture. Using plastic coatings also acts as a barrier, preventing the metal from coming into direct contact with water and oxygen, thus inhibiting rust formation.

A row in a Periodic Table is called a period. Periods are horizontal rows that represent the number of electron shells in an element's atomic structure. Each period corresponds to a different energy level or shell, with the first period containing only two elements and subsequent periods adding more elements as the number of electron shells increases. Therefore, the correct answer is "Period."

Helium has only one electron shell. This is because helium has an atomic number of 2, which means it has two electrons. The first electron shell can hold a maximum of 2 electrons, so all of helium's electrons are in the first shell. Therefore, the correct answer is 1.

All alkalis have OH- ions because alkalis are a type of base that can dissolve in water to release hydroxide ions (OH-) into the solution. These hydroxide ions are responsible for the alkaline properties of alkalis, such as their ability to neutralize acids and react with certain metals. Therefore, OH- ions are a characteristic feature of alkalis.

Carbon dioxide is denser than air. This is because carbon dioxide molecules are heavier than the molecules that make up air, which primarily consist of nitrogen and oxygen. When carbon dioxide is released into the atmosphere, it tends to sink and accumulate near the ground. This is why carbon dioxide is often used as a fire suppressant, as it can displace oxygen and smother the fire.

A positive Chloride test does not give a yellow precipitate. This statement is incorrect because a positive Chloride test actually gives a white precipitate, not a yellow one.

The flame test is used to identify the presence of certain metal ions, including calcium cations. When a calcium compound is heated in a flame, it emits a characteristic orange-red color. This color is unique to calcium and can be distinguished from other metal ions. Therefore, the flame test is a reliable method for testing the presence of calcium cations in a solution.

To test for pure water, one can check the melting and boiling points. Pure water has a melting point of 0 degrees Celsius and a boiling point of 100 degrees Celsius at sea level. By heating the water and observing at what temperature it starts to boil and at what temperature it turns into ice, one can determine if it is pure or not. Impurities in water can alter its melting and boiling points, so if the observed temperatures deviate from the expected values, it indicates the presence of impurities.

Hydrogen Peroxide (H202) is the correct answer. It is a chemical compound consisting of two hydrogen atoms bonded to two oxygen atoms. It is a pale blue liquid that is commonly used as a disinfectant, bleach, and oxidizer. It has various industrial and medical applications, including as a hair bleach and wound disinfectant. Hydrogen Peroxide is not to be confused with Dihydrogen Dioxide, Hydrogen monooxide, or Dihelium Dioxide as they are not valid chemical compounds.

Carbon dioxide is the correct answer because it is the gas that has a percentage of 0.04 in normal air. Normal air consists mainly of nitrogen (approximately 78%) and oxygen (approximately 21%), with trace amounts of other gases including carbon dioxide (approximately 0.04%). Helium, ammonia, and iron are not typically present in significant amounts in normal air.

When Chlorine gas is present, it reacts with Blue Litmus paper. Initially, the Blue Litmus paper turns red due to the acidic nature of Chlorine gas. However, as the reaction progresses, the Chlorine gas bleaches the Blue Litmus paper, causing it to lose its color. This change in color from blue to red and then to bleached confirms the presence of Chlorine gas, making it a positive test.

The metals in period 1 are Hydrogen and Helium. Hydrogen is a nonmetal but is often included in the alkali metal group. Helium is a noble gas and is not considered a metal.

When HCl (hydrochloric acid) reacts with CaCO3 (calcium carbonate), it forms CO2 (carbon dioxide) as one of the products. This reaction is a common example of an acid-base reaction, where the HCl acts as an acid and the CaCO3 acts as a base. The reaction can be represented by the equation: HCl + CaCO3 → CO2 + H2O + CaCl.

Oxidation refers to the process in which a substance loses electrons or gains oxygen. In this case, the correct answer is "Gain of Oxygen, Loss of Electrons." This means that during oxidation, a substance gains oxygen atoms and loses electrons.