MYP 4 & 5 · Chemistry
C1 - Particles, states and separation
20 questions across 5 sub-topics
Use the Sub-Topic filter above to focus on one.
C1.1 - Particle model and changes of state
C1.2 - Diffusion and particle motion
C1.3 - Pure substances, mixtures and purity
C1.4 - Filtration, crystallization and distillation
C1.5 - Chromatography and interpreting chromatograms
C1.1 - Particle model and changes of state 4 questions
QUESTION 1
6 marks
Criterion A
Medium
Interpreting a heating curve
A pure solid is heated at a constant rate. The graph shows two horizontal sections, X and Y.
a.
State what happens to the temperature during section X.
[1] b.
Explain, using the particle model, why energy is transferred to the substance although its temperature does not rise during X.
[3] c.
Identify the changes of state at X and Y.
[2] Show complete worked solution
(a)
The temperature remains constant.
(b)
The transferred energy weakens and overcomes attractive forces between particles. The potential energy of the particles increases while their average kinetic energy remains constant, so the temperature does not rise.
(c)
X is melting (solid to liquid). Y is boiling (liquid to gas).
QUESTION 2
11 marks
Criterion B
Hard
Cooling a drinks pouch
A manufacturer claims that adding dissolved salt makes a water-based drinks pouch remain liquid below \(0\,^{\circ}\mathrm{C}\). Design a laboratory investigation of this claim.
a.
State a testable hypothesis and identify the independent and dependent variables.
[3] b.
Describe a method that would produce sufficient reliable data.
[5] c.
State two controlled variables and one safety precaution.
[3] Show complete worked solution
(a)
Hypothesis: increasing salt concentration lowers the freezing temperature. The independent variable is salt concentration; the dependent variable is the temperature at which freezing begins.
(b)
Prepare equal volumes of at least five salt solutions of known concentration, including pure water. Cool each solution in the same controlled bath while stirring gently. Record temperature at fixed time intervals and identify the plateau or first persistent crystals. Repeat each concentration at least three times and calculate the mean freezing temperature.
(c)
Control the solution volume and cooling-bath conditions; use the same container and thermometer depth. Wear eye protection and handle the cold bath with insulated gloves.
QUESTION 3
6 marks
Criterion C
Medium
Energy during vaporization
Four equal samples of water are supplied with different amounts of energy at their boiling temperature. The mass vaporized is recorded: 5.0 kJ gives 2.2 g, 10.0 kJ gives 4.4 g, 15.0 kJ gives 6.5 g and 20.0 kJ gives 8.8 g.
a.
Describe the relationship between supplied energy and mass vaporized.
[2] b.
Calculate the energy required per gram using the 20.0 kJ result.
[2] c.
Suggest why the 15.0 kJ value is slightly below the proportional prediction.
[2] Show complete worked solution
(a)
The mass vaporized is approximately directly proportional to the supplied energy. Doubling the energy from 5.0 kJ to 10.0 kJ doubles the mass from 2.2 g to 4.4 g.
(b)
\[\frac{20.0\ \mathrm{kJ}}{8.8\ \mathrm{g}}=2.27\ \mathrm{kJ\,g^{-1}}\]
(c)
Some energy may have warmed the container or been transferred to the surroundings, or the mass measurement may have had uncertainty.
QUESTION 4
6 marks
Criterion D
Hard
Selecting a thermal store
A clinic must transport a medicine at \(5\,^{\circ}\mathrm{C}\). Pack A contains melting ice and is reusable; pack B contains a single-use chemical mixture that cools rapidly but must be discarded.
a.
Explain one scientific advantage of using a phase-change pack.
[2] b.
Evaluate the two packs and recommend one for routine deliveries.
[4] Show complete worked solution
(a)
While the material changes state, it absorbs thermal energy at nearly constant temperature. This helps keep the medicine close to the required temperature.
(b)
Pack A gives stable cooling and can be reused, reducing waste and repeated cost, but it must be frozen before use. Pack B works without a freezer and is useful in emergencies, but its temperature may change rapidly and it creates chemical waste. For routine deliveries with freezer access, pack A is the better supported choice.
C1.2 - Diffusion and particle motion 4 questions
QUESTION 1
7 marks
Criterion A
Medium
Explaining diffusion
The diagrams show two gases immediately after a partition is removed and 20 minutes later.
a.
Describe the change in particle distribution.
[2] b.
Explain why this change occurs without stirring.
[3] c.
Predict how increasing temperature affects the time required and justify your answer.
[2] Show complete worked solution
(a)
Initially the two particle types are concentrated in different regions. Later both particle types are distributed throughout the container.
(b)
Gas particles move continuously and randomly. There is a net movement from regions of higher concentration to regions of lower concentration until the particles are evenly mixed.
(c)
The time decreases because particles have greater average kinetic energy and move faster.
QUESTION 2
9 marks
Criterion B
Hard
Agar diffusion investigation
Phenolphthalein agar cubes are pink in alkali. Dilute acid diffuses into the cubes and makes the agar colorless. Plan an investigation of how cube size affects diffusion.
a.
Write a focused research question.
[2] b.
Describe the measurements and processing required.
[5] c.
Explain why percentage volume is more useful than the absolute colorless volume.
[2] Show complete worked solution
(a)
How does the side length of a phenolphthalein agar cube affect the percentage of its volume that becomes colorless after a fixed time in acid of constant concentration?
(b)
Cut cubes with several measured side lengths. Immerse each in equal volumes of acid of the same concentration for the same time and at the same temperature. Remove, blot and cut each cube through the center. Measure the remaining pink core. Calculate total volume and pink-core volume, then calculate the percentage that became colorless. Repeat each size and calculate means.
(c)
The starting volumes differ. A percentage normalizes the result, allowing diffusion in different-sized cubes to be compared fairly.
QUESTION 3
6 marks
Criterion C
Medium
Temperature and diffusion rate
A dye takes 420 s to spread a fixed distance in water at \(15\,^{\circ}\mathrm{C}\), 270 s at \(25\,^{\circ}\mathrm{C}\), 165 s at \(35\,^{\circ}\mathrm{C}\) and 115 s at \(45\,^{\circ}\mathrm{C}\).
a.
Calculate the diffusion rate at \(35\,^{\circ}\mathrm{C}\), using rate \(=1/t\).
[2] b.
Describe the trend in the results.
[2] c.
Identify one limitation of using the time for a color boundary to disappear.
[2] Show complete worked solution
(a)
\[\text{rate}=\frac{1}{165\ \mathrm{s}}=6.06\times10^{-3}\ \mathrm{s^{-1}}\]
(b)
As temperature increases, the time decreases and therefore the diffusion rate increases. The change is not linear over the full range.
(c)
The end point is judged visually and may differ between observers. A colorimeter or image analysis would give a more objective measure.
QUESTION 4
6 marks
Criterion D
Medium
Positioning an ammonia sensor
A refrigeration room uses ammonia gas. One proposal places a single sensor beside the ceiling because ammonia is less dense than air. Another places several sensors at breathing height and near likely leak points.
a.
Explain why gas density alone does not determine where a leak will first be detected.
[2] b.
Recommend a monitoring arrangement and justify it.
[4] Show complete worked solution
(a)
Air currents, ventilation, temperature gradients and the position and rate of the leak affect how the gas spreads. Diffusion is also gradual.
(b)
Use several sensors, including near likely leak points and in occupied zones, with at least one higher sensor. This accounts for buoyancy while also protecting workers from local concentrations before complete mixing. The system should be tested under realistic ventilation conditions.
C1.3 - Pure substances, mixtures and purity 4 questions
QUESTION 1
5 marks
Criterion A
Medium
Pure substance or mixture
Sample R melts sharply at \(80.0\,^{\circ}\mathrm{C}\). Sample S begins melting at \(74\,^{\circ}\mathrm{C}\) and is completely liquid at \(79\,^{\circ}\mathrm{C}\).
a.
Identify which sample is more likely to be pure.
[1] b.
Use the data to explain your choice.
[2] c.
State why a sharp melting point does not by itself identify the substance.
[2] Show complete worked solution
(a)
Sample R.
(b)
A pure substance has a sharp melting point. Sample S melts over a range and has a depressed onset, which indicates impurities.
(c)
Different substances can have similar melting points. Identification needs comparison with reliable reference data and preferably another independent test.
QUESTION 2
9 marks
Criterion B
Hard
Testing salt purity
A student has three batches of crystalline sodium chloride and wants to compare their purity using evaporation and mass measurements.
a.
Describe a quantitative method.
[5] b.
Explain one important limitation of this method.
[2] c.
Suggest one additional test that improves confidence.
[2] Show complete worked solution
(a)
Measure equal masses of each batch and dissolve each in the same measured volume of distilled water. Filter to remove insoluble impurities, washing the residue. Evaporate the filtrate to dryness in a pre-weighed dish, cool and reweigh. Repeat to constant mass. Calculate recovered sodium chloride as a percentage of the starting mass and repeat each batch.
(b)
Soluble impurities would remain with the sodium chloride and be counted in the recovered mass, so the method measures insoluble contamination rather than complete chemical purity.
(c)
Measure the melting point, perform suitable ion tests, or compare conductivity at a fixed concentration with a pure standard.
QUESTION 3
7 marks
Criterion C
Medium
Assessing purity data
A 12.50 g fertilizer sample is dissolved and filtered. The dried insoluble residue has a mass of 0.38 g.
a.
Calculate the percentage by mass of insoluble material.
[3] b.
The balance uncertainty is \(\pm0.01\ \mathrm{g}\) for each mass. Explain why the percentage uncertainty is dominated by the residue measurement.
[2] c.
State a conclusion that the data support and one they do not support.
[2] Show complete worked solution
(a)
\[\%\,\text{insoluble}=\frac{0.38}{12.50}\times100=3.04\%\]
(b)
The same absolute uncertainty is a much larger fraction of 0.38 g than of 12.50 g. Therefore it contributes most to the relative uncertainty in the percentage.
(c)
The sample contains about 3.0% insoluble material. The data do not show that the remaining 97% is one pure substance because soluble impurities may be present.
QUESTION 4
6 marks
Criterion D
Hard
Quality control for recycled solvent
A factory accepts recycled ethanol if its boiling range is within \(77.5\) to \(79.0\,^{\circ}\mathrm{C}\). Batch A boils from \(78.1\) to \(78.6\,^{\circ}\mathrm{C}\); batch B boils from \(76.8\) to \(80.4\,^{\circ}\mathrm{C}\).
a.
Decide which batch meets the stated criterion.
[2] b.
Evaluate whether boiling range is sufficient for safe reuse.
[4] Show complete worked solution
(a)
Batch A meets the criterion because its entire boiling range lies between 77.5 and 79.0 degrees Celsius. Batch B does not.
(b)
A narrow correct range supports high purity, but it cannot identify every contaminant and some substances may have similar boiling points. The factory should also use a composition-specific method such as chromatography and check contaminants relevant to the intended process before reuse.
C1.4 - Filtration, crystallization and distillation 4 questions
QUESTION 1
6 marks
Criterion A
Medium
Choosing separation methods
A mixture contains iron filings, insoluble sand, sodium chloride and water.
a.
Give a sequence of methods that separates all four components.
[4] b.
Explain why evaporation to dryness is unsuitable if the water must also be recovered.
[2] Show complete worked solution
(a)
Use a magnet to remove the iron. Filter the remaining mixture to separate the sand. Use simple distillation on the filtrate to collect water as distillate, leaving sodium chloride in the flask. Crystallize and dry the salt if solid crystals are required.
(b)
Evaporation releases the water vapor to the surroundings. Distillation condenses the vapor so the water can be collected.
QUESTION 2
8 marks
Criterion B
Medium
Improving a crystallization method
A student heats a copper sulfate solution strongly until every drop of water has evaporated, then scrapes the hot solid from the dish.
a.
Identify two weaknesses in the method.
[2] b.
Write an improved method for obtaining dry crystals.
[4] c.
Explain why the rinse water should be cold and used sparingly.
[2] Show complete worked solution
(a)
Heating to complete dryness can decompose or dehydrate the salt, and handling or scraping a hot dish is unsafe and can lose product.
(b)
Heat gently to evaporate some water until the solution is near saturation. Allow it to cool so crystals form. Filter the crystals, rinse them with a small amount of cold distilled water and dry them between filter papers or in a warm place.
(c)
Copper sulfate is soluble in water. Cold water and a small volume remove surface solution while minimizing dissolution and product loss.
QUESTION 3
6 marks
Criterion C
Hard
Distillation temperatures
A mixture contains propanone, boiling point \(56\,^{\circ}\mathrm{C}\), and water, boiling point \(100\,^{\circ}\mathrm{C}\). During heating, the thermometer remains near \(57\,^{\circ}\mathrm{C}\) and later rises toward \(99\,^{\circ}\mathrm{C}\).
a.
Identify the main liquid collected during the first temperature plateau.
[1] b.
Explain the change in thermometer reading.
[3] c.
State where the thermometer bulb should be positioned in the apparatus shown and why.
[2] Show complete worked solution
(a)
Propanone.
(b)
The more volatile propanone vaporizes first, so vapor at the thermometer is near its boiling point. Once most propanone has distilled, the vapor contains a greater proportion of water and the temperature rises toward water's boiling point.
(c)
Place the bulb level with the entrance to the condenser so it measures the temperature of vapor entering the condenser.
QUESTION 4
6 marks
Criterion D
Medium
Water recovery choices
A coastal field station can obtain fresh water either by distilling seawater using electricity or by collecting rainwater and filtering it.
a.
Compare the chemical effectiveness of the two methods.
[2] b.
Recommend a strategy for the station, considering reliability and environmental impact.
[4] Show complete worked solution
(a)
Distillation removes dissolved salts and most non-volatile impurities. Filtration removes suspended particles but does not remove dissolved ions.
(b)
Use captured rainwater when available, followed by filtration and disinfection, because its energy demand is lower. Keep distillation as a reliable backup during dry periods, preferably powered by renewable energy. Water quality should be tested because neither source is automatically safe to drink.
C1.5 - Chromatography and interpreting chromatograms 4 questions
QUESTION 1
5 marks
Criterion A
Medium
Reading a chromatogram
The chromatogram shows three ink samples, P, Q and R.
a.
State which sample contains the greatest number of soluble dyes.
[1] b.
Identify one dye that P and Q have in common and justify your answer.
[2] c.
State whether R could be a component of Q.
[2] Show complete worked solution
(a)
Q, because it produces three spots.
(b)
P and Q share the lower spot because the two spots finish at the same height, giving the same \(R_f\) value under identical conditions.
(c)
R is not a single component because it contains two spots. However, both of R's dyes appear at heights also present in Q, so Q could contain the same two dyes.
QUESTION 2
9 marks
Criterion B
Hard
Planning paper chromatography
A food laboratory must compare dyes in four drink samples with five permitted reference dyes.
a.
Describe a method that allows valid comparison.
[5] b.
State how each \(R_f\) value is calculated.
[2] c.
Explain why references and samples should be run on the same paper.
[2] Show complete worked solution
(a)
Draw a pencil baseline on chromatography paper. Apply small concentrated spots of all samples and references at labelled positions on the same baseline. Stand the paper in a suitable solvent with the spots above the solvent level, cover the chamber and allow the solvent to rise. Remove the paper before the solvent reaches the top, mark the solvent front immediately and dry the paper.
(b)
\[R_f=\frac{\text{distance travelled by dye from baseline}}{\text{distance travelled by solvent front from baseline}}\]
(c)
The solvent composition, temperature, paper and run time are then the same, so differences in spot position are less likely to be caused by changing conditions.
QUESTION 3
6 marks
Criterion C
Medium
Calculating retention factors
The solvent front moves 8.0 cm. Dye spots move 2.4 cm, 5.6 cm and 7.2 cm from the baseline.
a.
Calculate the three \(R_f\) values.
[3] b.
A reference dye has \(R_f=0.70\) in the same solvent. State what the matching result suggests.
[2] c.
Explain why an \(R_f\) value should not exceed 1.
[1] Show complete worked solution
(a)
\[R_f=\frac{2.4}{8.0}=0.30\]\[R_f=\frac{5.6}{8.0}=0.70\]\[R_f=\frac{7.2}{8.0}=0.90\]
(b)
It suggests that the middle spot may be the reference dye, but matching \(R_f\) values alone do not prove identity.
(c)
A dissolved substance cannot travel farther than the solvent front that carries it.
QUESTION 4
6 marks
Criterion D
Hard
Evidence for an unknown pigment
An unknown pigment and a banned reference pigment both give \(R_f=0.62\) in ethanol. A manager concludes that the product definitely contains the banned pigment.
a.
Evaluate the manager's conclusion.
[3] b.
Propose two steps that would strengthen the identification.
[3] Show complete worked solution
(a)
The result is evidence of a possible match, but it is not conclusive because different substances can share an \(R_f\) value and measurement uncertainty may make close values appear equal.
(b)
Repeat the chromatography and run both substances in a second solvent with different polarity. Also use an independent method such as spectroscopy or instrument-based chromatography. Agreement across independent methods would provide stronger evidence.