1. In a reaction, 5.3g of sodium carbonate reacted with 6 g of acetic acid. The products were 2.2 g of carbon dioxide, 0.9 g of water and 8.2 g of sodium acetate. Show that these observations are in agreement with the law of conservation of mass.
Ans:
Reaction:
Sodium carbonate + Acetic acid → Sodium acetate + Carbon dioxide + Water
Mass of reactants (LHS):
5.3 g (Sodium carbonate) + 6 g (Acetic acid) = 11.3 g
Mass of products (RHS):
8.2 g (Sodium acetate) + 2.2 g (Carbon dioxide) + 0.9 g (Water) = 11.3 g
Conclusion:
Since the total mass of reactants equals the total mass of products (11.3 g = 11.3 g), this reaction follows the Law of Conservation of Mass.
2. Hydrogen and oxygen combine in a ratio of 1:8 by mass to form water. What mass of oxygen gas would be required to react completely with 3 g of hydrogen gas?
Ans:
The ratio of hydrogen to oxygen in water (H₂O) is 1:8 by mass.
For every 1 gram of hydrogen, 8 grams of oxygen are required to form water.
Therefore, if you have 3 grams of hydrogen gas, you would need 3 × 8 = 24 grams of oxygen to completely react with it.
3.Which postulate of Dalton’s atomic theory is the result of the law of conservation of mass?
The postulate of Dalton’s atomic theory that is a result of the law of conservation of mass is:
“Atoms are neither created nor destroyed in a chemical reaction.”
This principle directly aligns with the law of conservation of mass, which states that the total mass of reactants is equal to the total mass of products in a chemical reaction. According to Dalton, atoms are indivisible and retain their identity during chemical reactions, ensuring that mass is conserved.
4. Which postulate of Dalton’s atomic theory can explain the law of definite proportions?
The postulate of Dalton’s atomic theory that explains the law of definite proportions is:
“Atoms combine in simple whole-number ratios to form compounds.”
This postulate aligns with the law of definite proportions, which states that in any given chemical compound, the elements are always combined in a fixed ratio by mass. Dalton’s theory suggests that the atoms of different elements combine in specific, constant ratios to form compounds, thereby ensuring that the composition of a compound remains the same regardless of the sample size.
5. Define the atomic mass unit.
An atomic mass unit (amu) is a standard unit of mass used to measure the mass of atoms and molecules. It is defined as 1/12th of the mass of a carbon-12 atom. This reference allows scientists to compare the masses of different atoms relative to carbon-12. For example, the atomic mass of hydrogen is approximately 1 amu, and that of oxygen is about 16 amu. The atomic mass unit is crucial in calculating atomic and molecular masses and in understanding the composition of substances.
6. Why is it not possible to see an atom with the naked eyes?
It is not possible to see an atom with the naked eye because:
Size of Atoms: Atoms are extremely small, typically measuring in the range of nanometers (nm). For example, a hydrogen atom has a diameter of about 0.1 nm, and even larger atoms, like uranium, are around 0.5 nm. This small size makes them invisible to the naked eye and beyond the resolving power of most optical microscopes.
Existence of Atoms: Atoms usually do not exist independently in nature; they bond with other atoms to form molecules. For example, hydrogen and oxygen atoms combine to form water molecules (H₂O). Since atoms are not visible individually and are always part of larger structures, observing them with the naked eye is not possible.