IB myp 4-5 Chemistry – Practice Questions- All Topics
Topic :Pure and impure substances–separation techniques including: filtration, distillation [including crude oil]
Topic :Pure and impure substances- Weightage : 21 %
All Questions for Topic : types of mixtures [solutions, oils, alloys, emulsions],separation techniques including: filtration, distillation [including crude oil],chromatography
Question (27 marks)
After a natural disaster people need help to re-establish basic living conditions. In most survival guides, the three basic requirements to survive are water, food and shelter. Doctors estimate that you can survive for between three and five days without water and much longer without food. Obtaining clean water is a priority for survival. This clean water would have several uses including drinking and cooking.
a (1 mark) One method of collecting water in a hot, dry climate is to use the following equipment. Identify the physical process shown in Diagram 1.
▶️Answer/Explanation
Answer:
Evaporation
Explanation:
The diagram shows a solar still where water evaporates from the ground/leaves, condenses on the plastic sheet, and drips into the container. The initial process that moves water vapor into the air is evaporation.
b (2 marks) Explain what happens during this process.
Process 1:
Process 2:
▶️Answer/Explanation
Answer:
1. Water loses heat/energy
2. Condensation (or changes from gas/vapor to liquid)
Explanation:
In the solar still: (1) Water evaporates (losing heat energy to change from liquid to vapor), then (2) the vapor condenses on the cooler plastic surface (releasing heat as it changes back to liquid). Both processes are needed for this water collection method.
c (3 marks) After a disaster, the water available is often contaminated. Select and label the equipment needed to remove objects from dirty water and arrange them for use.
 |
 |
Select equipment (choose 2):
Arrange the equipment:
▶️Answer/Explanation
Answer:
Essential items: Filter paper, funnel, and container (any 2)
Arrangement: Fold filter paper into cone, place in funnel, place funnel in container, pour water through
Explanation:
For basic filtration: (1) Fold filter paper into a cone shape, (2) Place it in a funnel, (3) Support the funnel over a clean container. The filter paper removes solid particles while allowing water to pass through. Full marks require correct selection AND arrangement description.
d (3 marks) Complete the paragraph about conductivity testing:
At the start of the experiment the conductivity is.
As NaCl is added, the conductivityas insoluble AgCl is formed.
This is because there are fewer silverpresent in the solution.
▶️Answer/Explanation
Answer:
high, decreases, ions
Explanation:
1. Initial high conductivity due to silver ions (Ag+)
2. Conductivity decreases as Ag+ reacts with Cl– to form insoluble AgCl
3. Conductivity measures ion concentration – fewer Ag+ ions means lower conductivity
e (2 marks) State how the conductivity changes when 20-25 cm³ of NaCl is added. Suggest a reason for this change.
Conductivity change:
Reason:
▶️Answer/Explanation
Answer:
Change: Sharp drop in conductivity
Reason: Silver ions are reacting/being removed (precipitating as AgCl)
Explanation:
The graph shows a steep decrease in conductivity between 20-25 cm³ as the equivalence point is reached where nearly all Ag+ ions have precipitated out as AgCl, dramatically reducing the number of charge carriers in solution.
f (2 marks) Identify the variables in an experiment to determine which filter is most effective.
Independent variable: Filter type (pre-filled)
Dependent variable:
Control variable 1: Volume of water (pre-filled)
Control variable 2:
▶️Answer/Explanation
Answer:
Dependent: Conductivity/water purity/microbe count
Control 2: Temperature/concentration/time/initial contamination level
Explanation:
The experiment measures how different filters affect water quality. Key controls ensure fair comparison: (1) Same water volume, (2) Constant temperature, (3) Same initial contamination level. The dependent variable measures filter effectiveness.
g (14 marks) Design a method to test which water filter is most effective.
Research question:
Variables:
Equipment list:
Method description:
Data collection:
▶️Answer/Explanation
Example high-scoring answer:
Research Question: “Which purification method (carbon/silver/ceramic filter) produces water with the lowest conductivity?”
Variables: Measure conductivity after each filtration type, control water source/temperature/volume
Equipment: Conductivity meter, beakers, filters, thermometer, measuring cylinder
Method: 1. Collect 100ml samples from same source 2. Filter each through different systems 3. Measure conductivity immediately 4. Record results
Data: Minimum 3 trials per filter type, calculate averages, repeat if results vary >5%
Marking notes:
Full marks require: Clear research question, measurable variables, complete equipment list, replicable method, and specific data collection plan. Higher bands include justification, environmental factors, and error reduction methods.