The diagram shows the spacing of the particles in a substance Z at two different temperatures. Which of the following could be substance Z?
| melting point / °C | boiling point / °C | |
|---|---|---|
| A | −21 | −9 |
| B | 160 | 210 |
| C | 183 | 253 |
| D | 194 | 229 |
Source: 2023 GESS Sec 3 End-of-Year P1 Q7
The apparatus shown is set up. Molecules of ammonia and hydrogen chloride react to form ammonium chloride. After 20 minutes, a white ring of ammonium chloride is seen at position Y. Which statement best explains this observation?
Source: 2023 XMS Sec 3 WA1 P1 Q4
Bromine gas and air are mixed together to form a homogeneous mixture in a closed vessel. Bromine has a higher density than air. What will be observed after several hours?
Source: 2024 CHS Sec 3 End-of-Year Section A Q6
A student investigated the diffusion of two gases, NH3 and HCl. Two sets of apparatus were set up as shown at room temperature and pressure. The damp red litmus paper in apparatus 1 changed colour after 30 seconds. How long did it take for the damp blue litmus paper to change colour in apparatus 2?
Source: 2024 CHS Sec 3 End-of-Year Section A Q7
When the glass plate is removed from the set-up on the left, the colour of the gas becomes the same in both jars after several days, as shown on the right. Which statement best explains the appearance after a few days?
Source: 2020 XMS Sec 3 WA1 P1 Q1
Gas X is in the gas jar and gas Y is in the porous pot. Which pair of gases will cause the water level in the left side of the tube to fall?
| X | Y | |
|---|---|---|
| A | N2 | CO |
| B | Ne | F2 |
| C | SO2 | NO2 |
| D | Cl2 | CO2 |
Source: 2020 XMS Sec 3 WA1 P1 Q4
The figure shows the heating curve for a substance X.
Source: 2023 GESS Sec 3 End-of-Year P2 A8
Z is a covalent substance. In an experiment, a sample of pure solid Z was continuously heated for 9 minutes. The figure shows how the temperature of the sample changed over time.
Source: 2024 CHS Sec 3 End-of-Year Section B Q2
A student conducted an experiment with the apparatus set-up below. Three unknown gases, X, Y, Z and chlorine gas are compared to oxygen gas. All the porous containers are filled with oxygen gas.
Source: 2023 GESS Sec 3 End-of-Year P2 A4
Pure stearic acid melts at 69.3 °C and boils at 361 °C. A solid sample of stearic acid was heated to 80 °C and allowed to cool to 30 °C. The graph of temperature against time for the cooling process is shown below.
Source: SJI 2020 Year 3 End-of-Year P2 A2(a) and (c)
Dmelting point 194 °C and boiling point 229 °C[1]
Z is a gas at 232 °C, so its boiling point is below 232 °C. Z is a solid at 179 °C, so its melting point is above 179 °C.
DMolecules in ammonia diffuse more quickly because they have a smaller mass than molecules of hydrogen chloride.[1]
The ring forms nearer the hydrogen chloride end, so the ammonia molecules travelled further. Lighter molecules diffuse faster.
AThe two gases remain mixed.[1]
Gas particles are in constant random motion, so a mixed gas stays mixed. It does not separate into layers.
C64 seconds[1]
Hydrogen chloride (Mr 36.5) is heavier than ammonia (Mr 17), so it diffuses more slowly and takes longer than 30 seconds.
DBoth the air and bromine particles move randomly.[1]
The particles of both gases are in constant random motion, so they diffuse until they are evenly mixed.
BX is neon and Y is fluorine[1]
Neon (Mr 20) is lighter than fluorine (Mr 38), so neon diffuses into the pot faster than fluorine diffuses out. The pressure in the pot rises and pushes the water level on the left side down.
The particles are vibrating and rotating about their fixed positions. [1]
They are very closely packed in an orderly manner. [1]
10 min [1]
Units are needed.
The forces of attraction between the particles at B are stronger than at C. [1]
The kinetic energy of the particles at B is lower than at C. [1]
80 °C [1]
The energy is absorbed to overcome the attractive forces between the molecules. [1]
The particles vibrate faster [1] about their fixed positions. [1]
Gases X and Y have a lower relative molecular mass than oxygen. [1]
The gases diffuse faster into the container filled with oxygen than the oxygen diffuses out of the container. [1]
The gases are then pushed down the tube, into the water, and escape as bubbles. [1]
Carbon dioxide or sulfur dioxide or nitrogen dioxide. Accept any gas with a higher relative molecular mass than oxygen. [1]
Chlorine has a higher relative molecular mass than the surrounding air, so it has a higher density than air. [1]
The comparison must be with air, not oxygen.
Bubbles would be produced faster in the beakers of gases X and Y, or water would rise faster up the tubes of gas Z and chlorine. [1]
As the temperature increases, the rate of diffusion increases. [1]
More thermal energy is converted into kinetic energy in the gas particles, so they move and diffuse faster. [1]
"More bubbles" is not accepted, because the idea of speed must be there.
The particles roll and slide over each other at first, and vibrate about fixed positions afterwards. [1]
The particles are closely packed and disorderly at first, and become closely packed and orderly. [1]
The liquid turns into a gas. [1]
Heat energy is absorbed and overcomes the forces of attraction between the particles, so the particles move further apart from each other. [1]