1.
Which of the following correctly represents 360g of water?a) 2 moles of waterb) 20 moles of waterc) 6.022 x 1023 molecules of waterd) 1.2044 x 1025 molecules of water
Correct Answer
D. B) and d)
Explanation
The correct answer is b) and d) because 360g of water can be represented as both 20 moles of water and 1.2044 x 10^25 molecules of water. The molar mass of water is approximately 18g/mol, so 360g of water is equal to 20 moles. Additionally, using Avogadro's number (6.022 x 10^23 molecules/mol), we can calculate that 20 moles of water is equivalent to 1.2044 x 10^25 molecules of water. Therefore, both options b) and d) correctly represent 360g of water.
2.
Which one of the following statements is not true about an atom
Correct Answer
A. Atoms are not able to exist independently
Explanation
The statement "Atoms are not able to exist independently" is incorrect because atoms can exist independently, particularly noble gas atoms and monatomic gases like helium. Other atoms typically form molecules or ions, but this doesn't mean they inherently can't exist independently.
3.
Which of the following types of chemical bonds involves the sharing of electron pairs between atoms?
Correct Answer
C. Covalent bond
Explanation
A covalent bond is a type of chemical bond that involves the sharing of electron pairs between atoms. These pairs of electrons are known as shared pairs or bonding pairs, and they create a stable balance of attractive and repulsive forces between atoms. Ionic bonds, on the other hand, involve the transfer of electrons between atoms, resulting in charged ions. Hydrogen bonds are weak attractions between a hydrogen atom in one molecule and an electronegative atom in another. Metallic bonds involve the sharing of free electrons among a lattice of metal atoms.
4.
Which molecular shape best describes a molecule with four bonded pairs and no lone pairs on the central atom?
Correct Answer
D. Tetrahedral
Explanation
A molecule with four bonded pairs and no lone pairs on the central atom forms a tetrahedral shape. This is because the four pairs of electrons around the central atom repel each other equally, resulting in a tetrahedral geometry with bond angles of 109.5°. Linear molecules have two bonded pairs with no lone pairs. Trigonal planar shapes occur with three bonded pairs and no lone pairs. Bent shapes involve lone pairs, causing the bonded atoms to deviate from a straight line.
5.
All samples of carbon dioxide contain carbon and oxygen in the mass ratio of 3:8. This is in agreement with the Law of ___________.
Correct Answer
B. Constant Proportion
Explanation
The given statement suggests that all samples of carbon dioxide have a consistent mass ratio of carbon to oxygen, which is 3:8. This is in agreement with the Law of Constant Proportion, which states that a given compound always contains the same elements in the same proportions by mass. This law is a fundamental principle in chemistry and helps to explain the consistent composition of compounds.
6.
In the periodic table, which group contains elements that are highly reactive and tend to form salts with metals?
Correct Answer
C. Group VIIA (Halogens)
Explanation
Group VIIA, known as the halogens, includes fluorine, chlorine, bromine, iodine, and astatine. These elements are highly reactive and often combine with metals to form salts. For example, sodium chloride (table salt) is a combination of sodium (a metal) and chlorine (a halogen). Alkali metals (Group I) and alkaline earth metals (Group II) are also reactive but do not form salts with other metals. Noble gases (Group VIII) are largely unreactive due to their stable electron configurations.
7.
Avogadro's number represents the number of atoms in ________.
Correct Answer
A. 12 grams of 12C
Explanation
Avogadro's number represents the number of atoms in 12 grams of 12C. This is because the atomic mass of carbon is 12 atomic mass units (AMU), and Avogadro's number is defined as the number of atoms in 12 grams of carbon-12. Therefore, the answer is 12 grams of 12C.
8.
A sample contains 22 g of carbon dioxide. This is equal to
Correct Answer
C. Half mole of carbon dioxide
Explanation
The molar mass of carbon dioxide (CO2) is approximately 44 g/mol. Therefore, 22 g of carbon dioxide is equal to half a mole (0.5 mol) of carbon dioxide.
9.
Select the ionic compound from the following
Correct Answer
D. Copper nitrate,
Explanation
Copper nitrate is the correct answer because it is an ionic compound. Ionic compounds are formed when a metal and non-metal combine through an electrostatic attraction between positively and negatively charged ions. In the case of copper nitrate, copper is a metal and nitrate is a polyatomic ion consisting of nitrogen and oxygen. Therefore, copper nitrate is an ionic compound.
10.
Chose the option which does not change when a chemical reaction takes place
Correct Answer
B. Mass
Explanation
Mass is a measure of the amount of matter in an object and is a fundamental property that remains constant during a chemical reaction. In a chemical reaction, the atoms of the reactants rearrange to form new products, but the total mass of the reactants is always equal to the total mass of the products. This is known as the law of conservation of mass. Therefore, mass does not change when a chemical reaction takes place.
11.
Select the option which does not represent molar mass of a substance?
Correct Answer
C. 16 gm of
Explanation
Option B, "6.022 × 10²³ molecules of helium," does not directly represent the molar mass of a substance. While this number (Avogadro's number) signifies the number of particles in one mole, it does not specify the molar mass itself. In contrast, options A, C, and D all directly represent the molar mass of their respective substances: HCl (36.5 g/mol), CH₄ (16 g/mol), and CO₂ (44 g/mol). Therefore, Option B does not represent the molar mass of a substance.
12.
Which term describes a molecule consisting of two or more atoms held together by chemical bonds?
Correct Answer
D. Molecule
Explanation
A molecule is a group of two or more atoms held together by chemical bonds. These atoms can be the same (as in O₂ or H₂) or different (as in H₂O or CO₂). An element refers to a pure substance composed of only one type of atom. Isotopes are variants of a particular chemical element that differ in neutron number. An ion is an atom or molecule that has gained or lost one or more electrons, thus acquiring an electrical charge.
13.
Which of the following substances has the highest molar mass?
Correct Answer
C. CO₂
Explanation
Among the given substances, NH₃ (ammonia) has a molar mass of about 17 g/mol, H₂O (water) is approximately 18 g/mol, CO₂ (carbon dioxide) is around 44 g/mol, and CH₄ (methane) is roughly 16 g/mol. CO₂ has the highest molar mass among these substances at 44 g/mol.
14.
The chemical symbol for nitrogen gas is
Correct Answer
B.
Explanation
The correct answer is N. Nitrogen gas is represented by the chemical symbol N. The symbol Ni represents the element nickel, while N+ is not a valid chemical symbol.
15.
Which one of the following would weigh the highest?
Correct Answer
C. 2 moles of
Explanation
Multiplying the molar mass by the number of moles of each compound will calculate the mass of each sample. 2 moles of calcium carbonate weigh the most. Calcium carbonate’s molar mass is 100 g/mol, so 2 moles of calcium carbonate weigh 200 g.