Some Basic Concepts of Chemistry: Important Questions

Very Short Answer Questions [1 Mark Questions]

Ques. State the SI unit of length.

Ans. The SI unit of length is a meter.

Ques. State the SI unit of density.

Ans. The SI unit of density is kg m^-3

Ques. Which law deals with volume ratios of gas-related products.

Ans. Gay Lussac's law of combining volume deals with volume ratios of gas-related products.

Ques. State the empirical formula of benzene.

Ans. The empirical formula of benzene is CH.

Ques. What will be the SI unit if the density of vanadium is 5.96g/cm³?

Ans. The SI unit if the density of vanadium is 5.96g/cm³ is 5960 kg/m³.

Ques. What are the 3 common compounds of dinitrogen and dioxygen?

Ans.

Nitrous Oxide

Nitric Oxide

Nitrogen Pentoxide.

Ques. State the relationship between vapor density and molecular weight.

Ans. The molecular weight of gas is two times the vapor density of the gas.

Molecular density = 2 × Vapor Density.

Short Answer Questions [2 Marks Questions]

Ques. Why do atomic masses always have average values?

Ans. The isotopes of different elements are different. Due to the presence of such elements invariant isotopes, the average values are considered. If chlorine has two isotopes with the mass number of 35 and 37 then the issue will come to three. This is how the balance should be maintained by taking the average values of the two masses.

Ques. Define stoichiometry.

Ans. Stoichiometry has come from the Greek words which define different elements and their measurements. It is used for calculating the masters and their related reactions and the products. When the chemical reactions take place it gives rise to different reactions that might affect the elements. For defining such elements and measuring such elements these reactors are formed. Limiting reagents are also used for creating reactions.

Ques. Define precision and accuracy.

Ans. Precision defines the different measures for the same amount of item. On the other hand, accuracy is the real-time value of the absolute outcome of any element. It gives accurate results of the measurements or is almost close to the answer. Significant figures are determined from the accuracy levels and not from the precision levels.

Ques. Find out the molarity when 4l of water is added to 2l of HCI Solution. 

Ans. Consider the initial volume to be V₁ = 2L

Final volume to be V₂ = 4L + 2L = 6L

Initial Molarity is stated as 6M

Long Answer Questions [3 Marks Questions]

Ques. What do you understand about chemical equations? State the essential features of chemical equations.

Ans. The change in the different formulas and the system is considered the chemical equation. The isotopes are present in different elements. The combination of different isotopes in different formulas is known as the chemical equation.

The essential features of a chemical equation are as follows:

1. When the two elements are combined, it gives rise to a new chemical and thus represents a true change in the chemical.
2. The chemical equation should be balanced. If the atom of one element is plus then the other should be minus to create a proper balance.
3. The chemical equation should be molecular. If the molecules are not present then it cannot be defined as a chemical equation.

Ques. State 3 effective significance of chemical equation.

Ans. The significance of chemical equations is as follows:

1. Different products are formed as a result of a chemical change. When the two molecules or the two atoms of an element combine and react with each other it gives rise to a different chemical equation or product.
2. One can get a clear idea about the atom numbers and the molecule reactor numbers. The products have different atoms and relative numbers altogether. With the chemical equation, you can get through the relative atom numbers and the molecular reactants.
3. The most important significance of the chemical equation is the related weights of the product and the reactions. As the weights should be balanced of different atoms and molecules, one can get a clear idea about the weights of the reactants from the chemical equation.

Ques. Define formality.

Ans. Formality is defined as the weights that are represented in forming different formulas expectedly in one liter of a solution. It is not molecular. Generally, ionic compounds such as NaCl are used to test the formality. When one needs to define or express the concentration of any solution then formality is used. Molarity is not suitable for defining the concentration of the compounds.

Ques. How can you use chemistry for the benefit of the whole nation?

Ans. With the help of chemistry, one can easily identify the weather patterns from a computer operation, chemical industries, action for fertilizers, reactions created by alkalis, salts, acids, medicines, soaps, detergents, and different alloys. Whether it be medicines, polymers, or different brain activities everything leads to a chemical reaction With the help of chemistry one can identify the composition, characteristics, and different interactions of the molecules and atoms that exist in the universe. Therefore chemistry has a lot to contribute to the development of a nation.

Ques. Calculate the moles when Fe = 7.85g.

Ans. 56g Fe has 6.022 × 10²³ atoms = 1 mole

56g Fe = 1 mole

So, 7.85g Fe = 1/56 × 7.85

= 0.14 moles.

Ques. Produce 2.24 oxygen at NTP using Potassium chloride.

Ans. 2 KCIO = 2KCI + 3O₂

2 moles of potassium chlorate and 3 moles of oxygen are used to create the compound.

67.2L of oxygen will be produced from 245g of KCIO₃.

Therefore to produce 2.24L of oxygen 

245/67.2 × 2.24

= 8.17g KCIO₃ is required.

Ques. If the initial volume is 2 litres, the initial molarity is 6M and the final volume is 6 litres. Find the Final Molarity. Consider final molarity to be M₂.

Ans. The relation between molarity and volume is

M₁V₁ = M₂V₂

6M × 2L = M₂ × 6L

M₂ = 6M × 2L/6L

= 2M

Very Long Answer Questions [5 Marks Questions]

Ques. Explain the law of multiple proportions along with a few proper examples. 

Ans. The Law of multiple proportions is defined as follows 

“When two elements combine to form two or more two chemical compounds than the weights of one element combine with a fixed weight of the other, to create a simple ratio to one another.”

It means when the two compounds are combined into a single compound. The weights of the different compounds are different. Therefore the weights of the different parts combine and give rise to a different combined ratio.

When carbon and oxygen are combined it gives rise to CO₂.

Here C has 32 parts while O has 12 parts and when they are mixed they give rise to a ratio of 1:2. 

Another good example of such compounds is the combination of sulfate and oxygen. S has two oxides while oxide has three parts. When they are combined they come across 48 parts. SO2 has 32 parts. The combination of such gives rise to a ratio of 1:2.

Ques. Explain the law of constant composition along with two examples. 

Ans. The Law of constant composition is defined as follows. A chemical compound is always found, to be made up of the same elements combined in the same fixed proportion by weight.

The examples of such laws of constant composition are as follows:

Ques. Establish the relationship between the empirical formula and the molecular formula along with two proper examples. 

Ans. The empirical formula is defined as the simple whole-number ratio that defines the atom of different elements that one can find in the compound molecules. A proper example of the empirical formula is benzene which is represented as CH. It means that in this element one can find one atom of carbon and one atom of hydrogen. The combination of these two elements will give rise to a single element of benzene. Therefore the empirical formula is the atomic ratio of different elements present in the molecule.

On the other hand, the molecular formula stands out to be the absolute formula of the atom or the molecule. One will get the absolute number of atoms in the element that can be found in the different molecules of a compound. The proper example of such a formula is benzene which is represented by C₆ and H₆. It means here 6 atoms of carbon and six atoms of hydrogen will be found in such element when the same will be combined it will give rise to such atomic reaction of benzene.

The relationship between the empirical formula and the molecule is formula stands out to be the following:

Molecular formula = n × molecular formula

Here, n stands out to be any integer.

In short, when the atomic mass of different elements is added together it gives rise to the empirical formula of any mass.

The empirical formula of glucose is

CH₂O= 1×12 + 2×1 + 1×16 = 30u

Ques. State the differences between molarity and molality.

Ans. 

1. Molarity is the total number of moles in a one-liter solution absolute. Molality is the total number of moles in one kilogram of a solvent.
2. The Molarity is measured from the volume of the solution. The molality is measured from the mass of the solvent.
3. The unit expressing the molarity is M. The unit expressing the molality is m. 
4. Molarity is taken from one liter of solution. Molality is taken from 1 kilogram of solution.
5. Molarity is expressed as
   M = number of moles of solute / Volume of solution given in terms of liters.
   Molality is expressed as
   m = number of moles of solute/Mass solvent in kgs.

Ques. Define Dalton's atomic theory.

Ans. Dalton's atomic theory states the following:

1. If one can see matter then one must also understand the concept of atoms. But it is not possible to see atoms. Atoms are invisible.
2. The atomic mass of the atoms of most of the elements is similar. But if the elements are different then only the mask will differ otherwise the atomic reactions will not change.
3. One can create the compound using the different atomic structures of the elements only when they have different elements of different ratios. The atoms of similar items will not give rise to any compound of equal weight.
4. For creating a reorganization of atoms chemical reactions are very important. One must always remember that atoms are never created nor destroyed. It is the combination of the atoms that either give rise to new compounds.

Ques. The weight of crystalline salt is 45.6%, the percentage of aluminum is 10.5%. Potassium stands out to be 15.1%, Sulpher is 24.96%, and Oxygen is 49.92%. Sort out the formula of anhydrous and crystalline salt. 

Ans. First, calculate the empirical formula of the salt.

The formula stands out to be KAIS₂O₈.

Then get the mass formula of anhydrosis salt.

It stands out to be 39 + 27 + 2×32 + 8×16

= 258u

Then calculate the empirical formula of hydrated salt.

Given the dehydration of water = 45.6%.

Therefore, the formula is

100 – 45.6

= 54.4u.

Therefore the formula of 100 hydrated mass is 100/54.4 × 258

= 473.3u.

Then calculate the loss due to dehydration using the given data

= 473.3 – 258

= 215.3

Therefore the number of water molecules stands out to be 

215.3/18

= 11.96 (approx)

Chemistry Related Links: