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 statement is not true about an atom
Correct Answer
D. Atoms aggregate in large numbers to form the matters that we can see, feel or touch
Explanation
Atoms do aggregate in large numbers to form the matters that we can see, feel or touch. This statement is true, as atoms combine and interact with each other to form molecules and compounds, which make up the various substances and materials that we encounter in our everyday lives.
3.
What is the ratio of hydrogen and oxygen in water
Correct Answer
A. 1: 8
Explanation
The ratio of hydrogen to oxygen in water is 1:8. This means that for every 1 hydrogen atom, there are 8 oxygen atoms. Water is composed of two hydrogen atoms bonded to one oxygen atom, which gives it the chemical formula H2O. Since there are two hydrogen atoms and one oxygen atom in each water molecule, the ratio of hydrogen to oxygen is 2:1. Therefore, the correct answer is 1:8.
4.
An example of polyatomic molecule
Correct Answer
C. Sulphur
Explanation
Sulphur is an example of a polyatomic molecule because it exists as S8, which means it consists of eight sulphur atoms bonded together. This arrangement of atoms forms a stable molecule with its own unique properties.
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.
The smallest particle of a substance that is capable of independent existence is _________.
Correct Answer
B. Molecule
Explanation
A molecule is the smallest particle of a substance that can exist independently. It is made up of two or more atoms that are chemically bonded together. Atoms, on the other hand, are the basic building blocks of matter, but they cannot exist independently and always combine to form molecules. Electrons and protons are subatomic particles that make up atoms, but they cannot exist independently as a substance on their own. Therefore, the correct answer is molecule.
7.
Avogadro 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
The molar mass of a substance is defined as the mass of one mole of that substance. In the given options, all the options except "16 gm of" represent molar mass. "16 gm of" does not provide any information about the number of moles or the substance itself, so it cannot be considered as a representation of molar mass.
12.
Select the case where formula mass is not used
Correct Answer
A. NaCl
Explanation
In this case, the correct answer is NaCl because the formula mass is not used to determine the compound. NaCl is a simple ionic compound made up of sodium (Na) and chlorine (Cl) ions, where the ratio of ions is 1:1. The formula mass, also known as the molar mass, is not necessary to determine the compound as it can be deduced from the charges and the periodic table.
13.
The average atomic mass of a sample of an element X is 16.2 u. What is the % of isotopes 8X16 and 8X18 in the sample?
Correct Answer
B. 10%
Explanation
The average atomic mass of an element is calculated by taking into account the masses of all its isotopes and their relative abundance. In this case, the average atomic mass of element X is 16.2 u. The question asks for the percentage of isotopes 8X16 and 8X18 in the sample. Since the average atomic mass is closer to 8X16, it suggests that this isotope is more abundant in the sample. Therefore, the percentage of 8X16 is higher than the percentage of 8X18. The correct answer of 10% indicates that 8X16 makes up 10% of the sample, while 8X18 makes up the remaining percentage.
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