Unit Test (Solutions): Is Matter Around Us Pure?

Time: 1 hour 

M.M. 30 

Attempt all questions. 

• Question numbers 1 to 5 carry 1 mark each. 
• Question numbers 6 to 8 carry 2 marks each. 
• Question numbers 9 to 11 carry 3 marks each. 
• Question numbers 12 & 13 carry 5 marks each

Q1: Which of the following is a homogeneous mixture?
a) Oil and water
b) Air
c) Sand and iron filings
d) Soil
Ans: b) Air
Air is a homogeneous mixture of gases where the composition is uniform throughout.

Q2: The scattering of light by colloidal particles is known as the __________ effect.
Ans: Tyndall
The Tyndall effect is the scattering of light by particles in a colloid.
Q3: Which of the following is a suspension?
a) Salt in water
b) Milk
c) Muddy water
d) Sugar solution
Ans: c) Muddy water
Muddy water is a suspension where the particles of mud do not dissolve but remain suspended in water.

Q4: A solution in which no more solute can dissolve at a given temperature is called a __________ solution.
Ans: Saturated 
A solution in which no more solute can dissolve at a given temperature is called a saturated solution, meaning it has reached its maximum capacity for solute dissolution under those specific conditions.

Q5: The process used to separate a mixture of iodine and sand is __________.
a) Filtration
b) Sublimation
c) Evaporation
d) Distillation
Ans: b) Sublimation
Iodine sublimates directly from solid to gas, leaving sand behind.

Q6: Define a colloid and give an example.
Ans: A colloid is a heterogeneous mixture where the particle size is between that of a solution and a suspension, and the particles do not settle out on standing. The particles in a colloid are small enough to remain dispersed throughout the medium and are capable of scattering light. An example of a colloid is milk, which is a mixture of fat globules dispersed in water.

Q7: Explain the Tyndall effect with an example.
Ans: The Tyndall effect is the scattering of light by particles in a colloid, making the path of the light beam visible. An example of the Tyndall effect can be seen when sunlight passes through the canopy of a dense forest; the light beams become visible as they are scattered by tiny water droplets or dust particles suspended in the air.

Q8: How can we separate a mixture of salt and camphor?
Ans: A mixture of salt and camphor can be separated by the process of sublimation. Camphor is a substance that sublimates, meaning it changes directly from a solid to a gas when heated, without passing through a liquid phase. As the camphor turns into vapor upon heating, it leaves behind the non-volatile salt, which does not sublimate. 

Q9: Differentiate between a solution and a suspension.
Ans: 

Q10: What is the difference between a compound and a mixture?
Ans: 

Q11: Explain how you would separate a mixture of iron filings and sulphur.
Ans:  To separate a mixture of iron filings and sulphur: 
i) Use a magnet to attract the iron filings away from the sulphur, as iron is magnetic while sulphur is not. This method allows the iron filings to be easily removed from the mixture. 
ii) Alternatively, if the mixture is heated, a chemical reaction occurs, forming iron sulphide, a compound that cannot be separated by simple physical means. However, if no chemical reaction is intended, physical separation using a magnet is the most effective approach. 
iii) After separating the iron, the sulphur can be collected and used as it remains unchanged in the process.

Q12: Describe Crystallisation and give its applications.
Ans: Crystallization is a widely used technique for purifying solid substances. The process begins by dissolving an impure solid in a suitable solvent at a high temperature, creating a saturated solution. 
Applications:
i) Purification of Salt: Common salt, often mixed with impurities, is purified through crystallization to obtain pure sodium chloride crystals, which are essential for consumption and various industrial uses.
ii) Pharmaceuticals: In the pharmaceutical industry, crystallization is crucial for obtaining pure drugs. This ensures that medications meet stringent purity standards, which is vital for their efficacy and safety.
iii) Sugar Refining: Crystallization is used extensively in sugar refining to produce pure sugar crystals from raw sugar syrup. This process removes impurities, resulting in the white sugar commonly used in households.
iv) Production of Gemstones: Crystallization plays a key role in the formation of synthetic gemstones, which are created under controlled conditions to mimic natural processes, leading to high-quality gems used in jewelry.

Q13: Explain the differences between elements, compounds, and mixtures with examples.
Ans: