Page 28 - ACE YR IGCSE A TOP APPROACH TO CHEM

(b) (i) Particles are irregularly arranged [1] and collide more frequently with the walls of
and far apart. [1] the balloon. [1]
They move in all directions. [1] The pressure inside the balloon increases. [1]
(ii) As the temperature increases, the pressure (e) Helium has a smaller M [1]
increases. [1] and diffuses faster. r [1]
Particles gain energy and move faster. [1] M He = 4; M N = 28
Particles collide with the walls more often. r r 2
[1] (f) Particles are far apart. [1]
Particles can move closer. [1]
3 (a) Melting [1]
6 (a) White [1]
(b) Particles are regularly arranged [1]
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and close together. [1] (b) NH + HCl ➞ NH Cl [1]
4
3
They vibrate on the spot. [1] (c) Diffusion [1]
(c) The particles gain kinetic energy and move (d) Ammonia and hydrochloric acid gas particles
faster [1] diffused from each end [1]
to overcome the forces in between particles. [1] to meet at a point to react. [1]
They move slightly further apart / can move Ammonia is a weak base, and hydrochloric acid
past each other. [1] is a strong acid. They react. It is a neutralisation
The change of state is from solid to liquid. reaction.
(d) (e) Ammonia has a lower relative molecular mass.
[1]
It moves faster. [1]
or vice versa
Particles are close together [1] Relative molecular mass of NH = 14 + 1(3)
irregularly arranged [1] 3 = 17
4 (a) Brownian motion [1] Relative formula mass of HCl = 1 + 35.5
Brownian motion is the random movement of = 36.5
particles. Particles move in a zigzag motion. Note: Must use word of comparison.
(b) Particles that move in a zigzag manner [1] (f) The white spot will form faster. [1]
bombarded / hit [1] Note: Word of comparison must be used.
by unseen tiny particles. [1]
(g) Gas particles still diffuse [1]
(c) Dust particles under the sunlight, [1] Gas particles are constantly moving. Therefore,
or any acceptable answer. diffusion will still happen.
(d) (i) Movement of particles [1] but no white spots form. [1]
from a region of higher concentration [1] But there is no chemical reaction that happens.
to a region of lower concentration. [1] 7 (a)
(ii) Gas particles move in a fast manner. [1] Solid Gas
They collide and bound back quickly in all
directions. [1] Arrangement / Regular / Irregular / [1]
pattern lattice random
5 (a) Lower density than air / lighter than air [1]
Helium has a lower density than the air and this Distance Close Far apart / [1]
property allows balloons filled with helium to float. spread out
(b) Movement Vibrate / Moving [1]
fixed
position
Max 2 marks for a correct drawing.
Arrangement – Irregular / no fixed Note: Comparison must be made. 1 mark is given
arrangement [1], far apart [1] for each comparison.
Movement – Move in all directions [1]
(b) Particles / molecules have more energy / move
(c) Kinetic energy causes gas particles to move. [1] faster, [1]
Particles collide with the walls of the balloon. [1] collide harder / collide more frequently / more
(d) Particles has more kinetic energy and move collisions / collide with more force (with the
faster [1] walls) [1]

Cambridge IGCSE TM
140 Ace Your Chemistry

Answers.indd 140 3/4/22 3:54 PM