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Q1. The law of definite proportions states that compounds have
The law of definite proportions states that compounds have constant composition. This means that a chemical compound always contains the same elements in the same proportion by mass, regardless of its source or method of preparation. For example, water always has 1 part hydrogen and 8 parts oxygen by mass. This law is also called the Law of Constant Proportions.
Q2. Atomic mass unit is now represented by
The atomic mass unit is now represented by the symbol ‘u’ (unified atomic mass unit). Previously, it was represented by ‘amu’ (atomic mass unit). The unified atomic mass unit is defined as one-twelfth of the mass of a carbon-12 atom. It is used to express the masses of atoms and molecules. 1 u is approximately equal to 1.66 × 10⁻²⁷ kg.
Q3. The first letter of a chemical symbol is always
The first letter of a chemical symbol is always a capital letter. This is a convention established by Berzelius. For example, H for hydrogen, O for oxygen, C for carbon. If the symbol has two letters, the second letter is written in lowercase, such as He for helium, Ca for calcium, and Fe for iron.
Q4. John Dalton was born in
John Dalton was born in 1766 in Eaglesfield, England. He was a British chemist and physicist who is best known for developing the atomic theory. He made significant contributions to the understanding of matter and is considered the father of modern atomic theory.
Q5. Dalton was the first scientist to use symbols for
Dalton was the first scientist to use symbols for elements. He introduced a system of symbols to represent different elements, using circles with different patterns and letters. While his symbols were not the ones used today, he pioneered the use of symbols to represent elements in chemical reactions.
Q6. Dalton presented his atomic theory in
Dalton presented his atomic theory in 1808. He published his work in a book called “A New System of Chemical Philosophy.” This work laid the foundation for modern chemistry by providing a scientific explanation for the laws of chemical combination.
Q7. After how many years did Dalton become a school principal?
Dalton became a school principal after seven years. This shows his dedication to education and his career progression. He began teaching at a young age and worked his way up to become a principal, reflecting his commitment to the field of education.
Q8. The building blocks of all matter are
Atoms are the building blocks of all matter. According to Dalton’s atomic theory, all matter is made up of tiny indivisible particles called atoms. These atoms combine in different ways to form molecules, compounds, and all the substances we see around us.
Q9. Which of the following is larger than an atom?
A water molecule is larger than an atom because it is made up of multiple atoms (two hydrogen atoms and one oxygen atom). An electron, proton, and hydrogen atom are all smaller than or equal to an atom in size. Atoms are the smallest unit of matter, but molecules are made of atoms.
Q10. The second letter of a chemical symbol is written as
The second letter of a chemical symbol is written as a small letter (lowercase). This is the established convention for writing chemical symbols. For example, in “He” for helium, ‘H’ is capital and ‘e’ is small. If the symbol has only one letter, it is always capital. This helps distinguish between elements with similar names.
Q11. Relative atomic masses were determined using
Relative atomic masses were determined using the laws of chemical combination. Scientists used the Law of Constant Proportions and the Law of Conservation of Mass to determine the ratios in which elements combine. By measuring these ratios, they could calculate the relative masses of atoms. This was possible even before modern instruments were available.
Q12. John Dalton began his career as a teacher at the age of
John Dalton began his career as a teacher at the age of 12. He started teaching at a village school at a very young age. Despite coming from a poor family, he was determined and hardworking, which allowed him to become a successful scientist later in life.
Q13. An ant has a size of approximately
An ant has a size of approximately 10⁻³ m (about 1 millimetre). This is a typical size for an ant. 10⁻¹ m is about 10 cm, 10⁻⁸ m is the size of a virus, and 10⁻¹⁰ m is the size of an atom. This comparison helps us understand the relative sizes of different objects.
Q14. The symbol K for potassium comes from
The symbol K for potassium comes from the Latin word “Kalium.” The name potassium is derived from “potash,” but the symbol K comes from the Latin name. Many element symbols are derived from their Latin names, such as Na for sodium (Natrium) and Fe for iron (Ferrum).
Q15. According to Dalton, matter is made up of
According to Dalton, matter is made up of atoms. He proposed that all matter consists of tiny, indivisible particles called atoms. These atoms are the fundamental building blocks of all substances. Atoms combine in fixed ratios to form compounds, but the basic unit of matter is the atom.
Q16. In CO, carbon combines with oxygen in the mass ratio
In CO (carbon monoxide), carbon combines with oxygen in the mass ratio of 3 : 4. The atomic masses are C=12 and O=16. Since there is one atom of each in CO, the mass ratio is 12:16, which simplifies to 3:4. This demonstrates the Law of Constant Proportions, where compounds always have a fixed mass ratio.
Q17. John Dalton was born in a family of
John Dalton was born in a family of poor weavers. He grew up in a modest household and had to work hard from a young age. Despite his humble background, he became one of the most important scientists in history. His story is an inspiration for anyone pursuing a career in science.
Q18. Carbon monoxide is represented by the formula
Carbon monoxide is represented by the formula CO. It consists of one atom of carbon and one atom of oxygen. This is different from carbon dioxide (CO₂), which has one carbon and two oxygen atoms. The formula CO indicates the composition of the compound.
Q19. Atoms combine to form compounds in the ratio of
Atoms combine to form compounds in the ratio of small whole numbers. This is a key part of Dalton’s atomic theory. For example, water is H₂O (2:1 ratio), ammonia is NH₃ (1:3 ratio), and carbon dioxide is CO₂ (1:2 ratio). These small whole-number ratios are characteristic of chemical compounds.
Q20. Atoms of the same element are identical in
Atoms of the same element are identical in mass and chemical properties. This is one of Dalton’s postulates. All atoms of a given element have the same mass and behave the same way chemically. Atoms of different elements differ in their mass and chemical properties.
Q21. In Manchester, Dalton taught
In Manchester, Dalton taught mathematics, physics, and chemistry. He was a versatile teacher and taught multiple subjects. His teaching career gave him the opportunity to develop his ideas about matter and chemistry, which eventually led to his atomic theory.
Q22. Hydrogen and oxygen combine by mass in the ratio
Hydrogen and oxygen combine by mass in the ratio of 1 : 8 to form water (H₂O). This means that 1 gram of hydrogen combines with 8 grams of oxygen to form 9 grams of water. This is a classic example of the Law of Constant Proportions and was one of the laws that Dalton’s atomic theory explained.
Q23. The compound formed by hydrogen and oxygen is
The compound formed by hydrogen and oxygen is water (H₂O). When hydrogen reacts with oxygen, it forms water. This is a chemical reaction where two hydrogen atoms combine with one oxygen atom. Water is the most common compound formed from hydrogen and oxygen.
Q24. The symbol Co stands for
The symbol Co stands for cobalt. It is important to note that Co is the symbol for cobalt, while CO is the formula for carbon monoxide (one carbon and one oxygen). The difference is that Co has two letters (C and o) while CO has two letters as well but both are capital, representing two different elements.
Q25. The symbol of iron is derived from the Latin word
The symbol of iron (Fe) is derived from the Latin word “Ferrum.” This is why the chemical symbol for iron is Fe, not Ir. Many element symbols come from their Latin names, including Na (Natrium for sodium) and K (Kalium for potassium). This convention helps avoid confusion.
Q26. Which cannot be created or destroyed in a chemical reaction?
Atoms cannot be created or destroyed in a chemical reaction. This is one of Dalton’s postulates. In a chemical reaction, atoms are rearranged to form new substances, but the atoms themselves remain unchanged. The number of atoms of each element is the same before and after a reaction. This explains the Law of Conservation of Mass.
Q27. Determining the mass of an individual atom is
Determining the mass of an individual atom is relatively difficult because atoms are extremely small and their masses are very tiny. However, scientists can determine atomic masses relative to a standard (like carbon-12). Modern techniques like mass spectrometry can measure atomic masses accurately, but it is not a simple task.
Q28. Atoms of different elements differ in
Atoms of different elements differ in mass and chemical properties. This is another postulate of Dalton’s atomic theory. Each element has its own unique atomic mass and specific chemical properties. These differences allow elements to combine in different ways to form various compounds.
Q29. Dalton’s atomic theory was a turning point in the study of
Dalton’s atomic theory was a turning point in the study of matter. It provided a scientific explanation for the laws of chemical combination and gave chemists a way to understand the composition and behaviour of matter. The theory laid the foundation for modern chemistry and our understanding of the microscopic world.
Q30. One nanometre (nm) equals
One nanometre (nm) equals 10⁻⁹ m (one billionth of a metre). This unit is used to measure very small things like atoms and molecules. Atomic radii are typically measured in nanometres. 10⁻⁶ m is a micrometre, 10⁻⁸ m is about the size of a virus, and 10⁻¹⁰ m is smaller than an atom.
Q31. A grain of sand has a size of approximately
A grain of sand has a size of approximately 10⁻⁴ m (about 0.1 mm). This is about 0.1 millimetres. 10⁻⁸ m is the size of a virus, 10⁻¹⁰ m is the size of an atom, and 10⁻¹ m is about 10 cm. Sand grains are small but still visible to the naked eye.
Q32. Atoms are considered indivisible in
Atoms are considered indivisible in chemical reactions. According to Dalton’s theory, atoms cannot be broken down in chemical reactions—they are the smallest particles that participate in chemical changes. However, in nuclear reactions and atomic explosions, atoms can be split into subatomic particles (protons, neutrons, electrons).
Q33. Atoms participate in
Atoms participate in chemical reactions. In chemical reactions, atoms rearrange to form new substances. Atoms are the basic units that combine, separate, or rearrange during chemical reactions. This is a core concept in chemistry and was a key part of Dalton’s atomic theory.
Q34. In a given compound, the relative number of atoms is
In a given compound, the relative number of atoms is constant. This follows from the Law of Constant Proportions. A compound always has the same atoms in the same ratio. For example, water always has two hydrogen atoms and one oxygen atom (H₂O). This constant ratio is what makes compounds distinct from mixtures.
Q35. Atomic radius is measured in
Atomic radius is measured in nanometres (nm). Atoms are extremely small, and their radii are in the order of 10⁻¹⁰ m, which is 0.1 nm. Nanometres are a convenient unit for measuring atomic and molecular sizes. Micrometres are used for larger particles, and metres and centimetres are too large for atomic measurements.
Q36. In the given reaction, sodium carbonate reacts with
In the reaction, sodium carbonate reacts with acetic acid to produce sodium acetate, carbon dioxide, and water. This is a typical acid-base reaction where carbon dioxide gas is evolved. The chemical equation shows the reactants and products involved in the reaction.
Q37. Modern techniques allow us to see
Modern techniques, such as Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM), allow us to see magnified images of atoms. This is a remarkable achievement in science because atoms are incredibly small (about 10⁻¹⁰ m). These techniques allow us to visualize individual atoms on surfaces.
Q38. Dalton moved to Manchester in
Dalton moved to Manchester in 1793. He went there to teach at the New College. Manchester was a centre of scientific activity at the time, and Dalton’s move there allowed him to develop his ideas and conduct his research.
Q39. Which is the correct symbol for aluminium?
The correct symbol for aluminium is Al. The first letter is capital (A) and the second letter is small (l). This follows the convention for chemical symbols. “Al” is correct, while “AL” (both capitals) would be incorrect. The symbol represents the element aluminium.
Q40. Dalton’s symbols represented
Dalton’s symbols represented one atom of the element. He used circles with different patterns to represent individual atoms of different elements. This was a visual way to show the composition of compounds. Modern symbols are different, but Dalton was the first to use symbols to represent atoms of elements.
Q41. The smallest building block mentioned in the passage is
The smallest building block mentioned in the passage is the atom. Atoms are the fundamental particles of matter. While molecules are made of atoms, atoms are the smallest unit described in the text. The passage discusses how everything is made of atoms, making them the ultimate building blocks of matter.
Q42. The law of conservation of mass states that mass is
The Law of Conservation of Mass states that mass is neither created nor destroyed during a chemical reaction. This means the total mass of the reactants equals the total mass of the products. This law was established by Lavoisier and is a fundamental principle of chemistry.
Q43. Berzelius suggested symbols using
Berzelius suggested symbols using one or two letters. This is the system we use today. He proposed using the first letter of the element’s name (capital) and, if needed, a second letter (lowercase). This simplified Dalton’s earlier symbol system and made it easier to write chemical formulas. This system is still used today.
Q44. The size of an atom is approximately
The size of an atom is approximately 10⁻¹⁰ m (one ten-billionth of a metre). This is about 0.1 nanometres. Atoms are extremely small and cannot be seen with the naked eye or even with ordinary microscopes. 10⁻¹ m is 10 cm, 10⁻³ m is a millimetre, and 10⁻⁴ m is about the size of a grain of sand.
Q45. One of the products formed in the reaction is
One of the products formed in the reaction of sodium carbonate with acetic acid is carbon dioxide (CO₂). The reaction produces sodium acetate, carbon dioxide, and water. The carbon dioxide gas is released as bubbles, which is often observed in this type of acid-base reaction.
Q46. Atoms affect our lives because
Atoms affect our lives because everything is made of atoms. All matter around us—from the air we breathe to the food we eat—is composed of atoms. Understanding atoms helps us understand the nature of matter and the chemical reactions that sustain life. Atoms are the foundation of all substances.
Q47. The symbol Na comes from the word
The symbol Na for sodium comes from the Latin word “Natrium.” This is why the chemical symbol is Na, not So. The name sodium comes from soda, but the symbol is derived from the Latin name. Similarly, K comes from “Kalium” (potassium) and Fe from “Ferrum” (iron).
Q48. An apple has a size of approximately
An apple has a size of approximately 10⁻¹ m (about 10 cm). This is a typical size for an apple. 10⁻⁴ m is a grain of sand, 10⁻³ m is an ant, and 10⁻⁸ m is a virus. This comparison helps us appreciate the relative sizes of objects in our world.
Q49. Atomic mass is characteristic of
Atomic mass is characteristic of elements. Each element has a specific atomic mass that distinguishes it from other elements. While compounds have molecular masses, atomic mass specifically refers to the mass of an atom of a given element. This property is unique to each element.
Q50. The organisation that approves element names and symbols is
The organisation that approves element names and symbols is IUPAC (International Union of Pure and Applied Chemistry). IUPAC is the international authority on chemical nomenclature, terminology, and symbols. It standardizes the names and symbols of elements, ensuring consistency worldwide. WHO is for health, ICSE is an education board, and UNESCO is for education and culture.