1. The Law of Constant Proportions is also called the Law of Definite Proportions.
2. In water, the mass ratio of hydrogen to oxygen is always 1: 8.
3. Dalton's Atomic Theory explained both the Law of Conservation of Mass and the Law of Definite Proportions.
4. In ammonia, nitrogen and hydrogen are always present in the ratio 8: 1 by mass.
Analysis of Chemical Laws and Atomic Theory Statements
This question requires evaluating the correctness of four statements related to fundamental chemical laws and atomic theory. Let's analyze each statement individually.
Statement 1: Law of Constant Proportions vs. Law of Definite Proportions
Statement: The Law of Constant Proportions is also called the Law of Definite Proportions.
Analysis: This statement is correct. The Law of Constant Proportions, which states that a pure chemical compound always contains the same elements in the same definite proportions by mass, is commonly referred to as the Law of Definite Proportions. Both terms describe the same principle, emphasizing the fixed composition of compounds.
Statement 2: Mass Ratio in Water
Statement: In water, the mass ratio of hydrogen to oxygen is always 1:8.
Analysis: This statement is correct. The chemical formula for water is H2O. We can determine the mass ratio using the atomic masses of hydrogen (H ≈ 1 unit) and oxygen (O ≈ 16 units).
- Mass of Hydrogen (H) in H2O = 2 atoms × 1 unit/atom = 2 units.
- Mass of Oxygen (O) in H2O = 1 atom × 16 units/atom = 16 units.
- The mass ratio of Hydrogen to Oxygen is $2 : 16$, which simplifies to $1 : 8$.
Thus, the mass ratio of hydrogen to oxygen in water is consistently $1:8$, regardless of the source.
Statement 3: Dalton's Atomic Theory Explanation
Statement: Dalton's Atomic Theory explained both the Law of Conservation of Mass and the Law of Definite Proportions.
Analysis: This statement is correct. Dalton's Atomic Theory was foundational in explaining the laws of chemical combination observed at the time:
- Law of Conservation of Mass: Dalton proposed that atoms are indivisible and cannot be created or destroyed during a chemical reaction, merely rearranged. This directly explains why the total mass remains constant before and after a reaction.
- Law of Definite Proportions: Dalton suggested that atoms of different elements combine in simple, fixed, whole-number ratios to form compounds. Since atoms have specific masses, these fixed ratios of atoms lead to fixed mass ratios within a compound.
Dalton's theory provided a theoretical basis for these empirical laws.
Statement 4: Mass Ratio in Ammonia
Statement: In ammonia, nitrogen and hydrogen are always present in the ratio 8:1 by mass.
Analysis: This statement is incorrect. The chemical formula for ammonia is NH3. Let's calculate the mass ratio using the atomic masses of nitrogen (N ≈ 14 units) and hydrogen (H ≈ 1 unit).
- Mass of Nitrogen (N) in NH3 = 1 atom × 14 units/atom = 14 units.
- Mass of Hydrogen (H) in NH3 = 3 atoms × 1 unit/atom = 3 units.
- The mass ratio of Nitrogen to Hydrogen is $14 : 3$.
The ratio $14:3$ is approximately $4.67:1$, not $8:1$. Therefore, this statement is false.
Conclusion
Based on the analysis, statements 1, 2, and 3 are correct, while statement 4 is incorrect. The correct combination is therefore 1, 2, and 3 only.
Important Questions from Critical thinking (Notes)
- An empty plastic mug floats in a bucket of water. When a solid iron ball is kept in the mug it doesn't sink. When the ball is put in the water it sinks. Compared to when the ball is in water, the water level in the bucket when the ball is in the mug is
Given below are two statements : one is labelled as Assertion (A) and the other is labelled as Reason (R).
Assertion (A): Creative thinking always requires divergent thinking.
Reason (R): Divergent thinking helps in generating multiple solutions to a single problem.
In the light of the above statements, choose the most appropriate answer from the options given below:
- One day I lost my ear ring. To keep from losing earrings, further I used to thermocool to keep the earring in place. Using the thermocool as a temporary earring back showed that I overcome from the following:
- Match List - I with List - II.Choose the correct answer from the options given below :
List - I List - II A. Availability heuristic I. Presentation of information concening potential outcomes B. Representativeness heuristic II. Reference points that may lead us for problem solving C. Anchoring-and-Adjustment heuristic III. What comes to mind first D. Framing IV. Assuming that what is typical is also likely the solution - Select the correct statement related to learner centred approach
(a) Pupil is actively involved in the teaching-learning process.
(b) The main function of the teacher is not to instruct but to evoke learning.
Select the correct answer.
