Chemistry Class 10 Chapter 1: History of Chemistry
Free chapter
This is the free study page for Chemistry Class 10, Chapter 1: History of Chemistry. It follows the Federal Board (FBISE) SSC-II syllabus. This chapter has 4 learning outcomes, and Parhayi.com has 40 MCQs, 8 short questions and 4 long questions for it. Read the topics and the key questions with their answers below, then tap Practice this chapter to try the questions yourself.
Chemistry is the study of matter and how it changes. Learn the definitions first, then practise equations, balancing and numericals until they feel easy.
What you will learn
- Justify, with examples, that to do science is to be involved in a community of inquiry.
- Explain, with examples, that a 'scientific paradigm' is a theoretical model of how nature…
- Explain, with examples, how scientists speak of 'levels of confidence' (or uncertainty)…
- Explain the difference between repeatability and reproducibility in chemistry.
Key questions and answers
These are the short questions of this chapter with their answers (8 questions).
Q1. What is a community of inquiry? Give two principles followed by it. (3 marks)
A community of inquiry is a group of scientists who share common principles and methods to build reliable knowledge. Principles: use of empirical evidence, controlled experiments, peer review, objectivity and skepticism.
Q2. State the law of conservation of mass and give one daily-life example. (3 marks)
In a chemical reaction in a closed system, the total mass of reactants equals the total mass of products (Lavoisier). Example: when coal burns, the ash is lighter but the missing mass is in the CO2 and water vapour released.
Q3. What is a scientific paradigm? Give an example of one being replaced. (3 marks)
A scientific paradigm is a set of ideas and rules that guide scientists; a theoretical model of how nature works. Example: the phlogiston theory was replaced by Lavoisier’s oxygen theory of combustion.
Q4. Name three models of the atom in order and the scientist for each. (3 marks)
(1) Plum-pudding model – J. J. Thomson. (2) Nuclear model – Rutherford. (3) Energy-level (planetary) model – Bohr.
Q5. What is the meaning of a 95% confidence interval of 0.48–0.52 mol/dm3 for a measured 0.50 mol/dm3? (3 marks)
It means we are 95% confident that the true concentration lies between 0.48 and 0.52 mol/dm3. A narrower interval means the measurement is more precise.
Q6. Distinguish between p-value and uncertainty. (3 marks)
The p-value tells the probability that a result is due to chance (small p = a meaningful result). Uncertainty (±) tells how reliable a single measurement is, e.g. 0.250 ± 0.005 mol/dm3.
Q7. Differentiate between repeatability and reproducibility with one example each. (3 marks)
Repeatability: same result when repeated under the same conditions (same lab, equipment, person), e.g. one chemist gets 120 °C five times. Reproducibility: same result in different labs with different equipment or scientists, e.g. chemists in three cities all find about 120 °C.
Q8. Why are repeatability and reproducibility important in chemistry? (3 marks)
They help scientists make sure that a discovery is accurate and not due to chance or a mistake in one lab. Reproducible results are accepted by the wider scientific community.
Long questions with answers
Q1. Explain any four principles used by chemists: conservation of mass, controlled experiments, peer review, objectivity or skepticism. Give an example of each. (6 marks)
1. Conservation of mass: total mass of reactants equals products (burning coal).
2. Controlled experiments: change only one variable (testing washing powders with the same water and cloth).
3. Peer review: experts check work before publication (a new catalyst re-tested).
4. Skepticism: scientists doubt and verify new claims (a new element tested many times).
Q2. Explain how scientific paradigms change with the help of (a) the phlogiston theory and (b) the models of the atom. (6 marks)
(a) Scientists once believed burning releases phlogiston. Lavoisier showed that burning is combination with oxygen, so the paradigm was replaced by oxidation.
(b) Thomson’s plum-pudding model (1904) was replaced by Rutherford’s nuclear model (1911) after the gold foil experiment; Bohr then added fixed energy levels and the quantum model followed. Each model changed because of better evidence.
Q3. A student measures the concentration of a solution five times: 0.52, 0.50, 0.51, 0.49, 0.50 mol/dm3. (a) Calculate the mean. (b) Give the range. (c) Explain what a 95% confidence interval would tell us. (6 marks)
| Step | Reason |
|---|---|
| Given: 0.52, 0.50, 0.51, 0.49, 0.50 mol/dm3 | Data from the question |
| Mean = sum of the valuesnumber of values | Average of the readings |
| (a) Mean = 0.52 + 0.50 + 0.51 + 0.49 + 0.505 = 2.525 = 0.504 mol/dm3 | Add and divide by 5 |
| (b) Range = highest − lowest = 0.52 − 0.49 = 0.03 mol/dm3 | Spread of the readings |
| (a) Mean = 0.504 mol/dm3; (b) range = 0.49 to 0.52 (spread 0.03 mol/dm3) |
Q4. (a) Define repeatability and reproducibility. (b) Give two differences. (c) A new reaction works in only one laboratory. What should scientists conclude and do? (6 marks)
(a) Repeatability: same result under the same conditions. Reproducibility: same result in different labs with different equipment or scientists.
(b) Repeatability is in one place and one setting; reproducibility is in different settings. Repeatability is checked first; reproducibility gives stronger proof.
(c) The result is not yet reliable. The scientists should check for errors, repeat the experiment and ask other labs to reproduce it before accepting it.
Practice MCQs
Choose the answer in your mind first. The answer is shown below each question.
1. A group of scientists who share methods and check each other’s work is called a:
- team of players
- community of inquiry
- school class only
- crowd
Answer: b
They share common principles and methods.
2. A burning coal appears to lose mass in the open air. Which statement agrees with conservation of mass?
- The mass is now in the air as gases
- The balance used must have been faulty
- Mass has been destroyed in the burning
- Mass has turned into energy only
Answer: a
Products include gases.
3. Mendeleev arranged elements mainly by their:
- colour
- date of discovery
- atomic number only
- atomic mass and properties
Answer: d
1869 periodic table.
4. A small p-value (such as 0.01) means that the result is:
- definitely wrong
- unlikely to be due to chance
- random
- not measured
Answer: b
Only a 1% chance the result is random.
5. Getting the same result when an experiment is repeated under the same conditions is called:
- objectivity
- uncertainty
- reproducibility
- repeatability
Answer: d
Same lab, tools, person.
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