ECAT Chemistry — Gases
Gases is part of the Chemistry section of the UET ECAT (30 of the 100 MCQs). It breaks into 3 subtopics, and we hold 31 ECAT-pattern practice MCQs on it, each with a written explanation. Tap a subtopic below to practise just that.
Subtopics (3)
How Gases is tested
Across the 7 ECAT past papers on ParhaiKrlo, Gases accounts for 8 questions. It appears in 6 of them, about 1.3 questions a paper. The heaviest was ECAT Past Paper 01, with 3 questions, and the most recent is ECAT Past Paper 07, with 1.
| Paper | Questions |
|---|---|
| ECAT Past Paper 07 | 1 |
| ECAT Past Paper 06 | 1 |
| ECAT Past Paper 05 | 1 |
| ECAT Past Paper 03 | 1 |
| ECAT Past Paper 02 | 1 |
| ECAT Past Paper 01 | 3 |
Gases MCQs from the ECAT past papers
Try each one before opening the answer. Each comes with a short explanation.
- Q1 · ECAT Past Paper 07 · Gases
The effect of pressure on the density of a gas (at constant temperature) is:
- A.An increase in pressure causes a decrease in density
- B.A decrease in pressure results in an increase in density
- C.An increase in pressure causes an increase in density
- D.No effect
Show answer
Answer: C. An increase in pressure causes an increase in density — d = PM/RT: density is directly proportional to pressure.
- Q2 · ECAT Past Paper 06 · Gases
The volume of a gas at 0 °C is 100 cm³. What will its volume be at 546 °C if the pressure remains constant?
- A.5460 cm³
- B.200 cm³
- C.300 cm³
- D.546 cm³
Show answer
Answer: C. 300 cm³ — Charles's law: V₂ = V₁ × T₂/T₁ = 100 × 819/273 = 300 cm³.
- Q3 · ECAT Past Paper 05 · Gases
0.10 g of a gas occupies 83.1 cm³ at 27 °C and 1.0 × 10⁵ Pa. Its relative molecular mass is: (R = 8.31 J K⁻¹ mol⁻¹)
- A.3.0
- B.300
- C.24
- D.30
Show answer
Answer: D. 30 — M = mRT/(PV) = 0.10 × 8.31 × 300/(1.0 × 10⁵ × 83.1 × 10⁻⁶) = 249.3/8.31 = 30.