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CIE iGCSE Co-Ordinated Science C1.1 Solids, liquids and gases Exam Style Questions Paper 4

CIE iGCSE Co-Ordinated Science Paper 4 - All Chapters

Question

A student investigates black ink using paper chromatography.
Fig. 5.1 shows:
  • the chromatogram the student obtains
  • the measurements the student may make.
(a) State if black ink is a pure or impure substance. Use Fig. 5.1 to explain your answer.
(b) State which two measurements on Fig. 5.1 are needed to calculate the \(R_f\) value of spot X.
(c) The student calculates the \(R_f\) value of spot Y to be 0.80.
The distance travelled by spot Y is 2.8 cm.
Calculate the distance travelled by the solvent.
(d) Paper chromatography has a stationary phase and a mobile phase.
The stationary phase is a solid.
The mobile phase is a liquid.
Describe what happens to the separation and motion of the particles when a solid changes to a liquid.
(e) Different substances have different structures.
Draw one line from each statement to the structure.

Most-appropriate topic codes (Cambridge IGCSE Co-ordinated Sciences 0654):

• Topic C12.3 — Chromatography (Parts (a), (b) & (c))
• Topic C1.1 — Solids, liquids and gases (Part (d))
• Topic C2.5 — Simple molecules and covalent bonds / C2.6 — Giant covalent structures (Part (e))

▶️ Answer/Explanation

(a) Statement: Black ink is an impure substance.
Explanation: The chromatogram shows more than one spot, indicating that the ink contains multiple different substances (components).

(b) Measurements A and B.
\(R_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}\).
A is the distance travelled by spot X from the origin, and B is the distance travelled by the solvent front from the origin.

(c) Calculation:
\(R_f = \frac{\text{distance travelled by substance}}{\text{distance travelled by solvent}}\)
\(0.80 = \frac{2.8}{\text{distance travelled by solvent}}\)
Distance travelled by solvent = \(\frac{2.8}{0.80} = 3.5\text{ cm}\)

(d) Separation: Particles in a liquid are slightly further apart than in a solid (but still touching).
Motion: Particles in a liquid move faster than in a solid. They move randomly in a liquid, whereas they vibrate about a fixed position in a solid.

(e) Correct matching:

Question

Water exists in the solid, liquid or gas state. The particles are arranged differently in each physical state.
(a) Name the state where the water particles are furthest apart.
(b) Describe what happens to the movement of water particles during melting.
(c) A student takes some ice out of the freezer and leaves it in a beaker in a warm room. Fig. 5.1 shows how the temperature in the beaker changes.
(i) Label the part of the graph where the ice is melting with the letter X.
(ii) Describe how Fig. 5.1 shows that the ice is pure rather than a mixture.
(d) Domestic water is treated so that it is pure enough to drink. Draw one line from each treatment to show why it is used.
(e) Water, \(\text{H}_2\text{O}\), is a simple covalent molecule.
(i) Complete the dot-and-cross diagram in Fig. 5.2 to show the bonding in water. Only show the outer-shell electrons.
(ii) Explain why pure water is a poor conductor of electricity.

Topic codes:

• Topic C1.1 — Solids, liquids and gases (Part (a) & (b))
• Topic C10.1 — Water (Part (c) & (d))
• Topic C2.5 — Simple molecules and covalent bonds (Part (e))

▶️ Answer/Explanation

(a) Gas — water particles are furthest apart in the gaseous state.

(b) During melting, the movement of water particles changes from vibrating about fixed positions (in the solid state) to moving around each other (in the liquid state). The particles gain kinetic energy and move faster as the solid melts.

(c)(i) The ice is melting during the horizontal part of the graph where the temperature remains constant at 0°C (the plateau). The letter X should be placed on this horizontal section.

(c)(ii) Fig. 5.1 shows that the ice is pure because there is a horizontal part to the graph at the melting point. A pure substance melts at a single, specific temperature, whereas a mixture melts over a range of temperatures.

(d) The correct matching is:

(e)(i) The completed dot-and-cross diagram for water should show:

  • Oxygen atom with 6 outer-shell electrons (2 pairs and 2 unpaired)
  • Two hydrogen atoms each with 1 electron
  • Two shared pairs of electrons (covalent bonds) between oxygen and each hydrogen
  • The remaining 4 electrons on oxygen shown as two lone pairs

(e)(ii) Pure water is a poor conductor of electricity because it does not contain any free (moving) electrons or ions. For electrical conduction, charged particles (ions or electrons) must be free to move. In pure water, the molecules are neutral and there are no mobile charge carriers.

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