Which one of the following is a heterogeneous mixture?
- A.Hydrochloric acid
- B.Vinegar
- C.Milk
- D.Soda water
Correct answer
Explanation
The correct answer is C, Milk. Milk is a colloid in which tiny droplets of fat are dispersed in water, so it is not uniform at the microscopic level and counts as a heterogeneous mixture.
A homogeneous mixture, or solution, has the same composition throughout and its particles cannot be seen even under a microscope. A heterogeneous mixture has parts that differ from one another. Milk is an emulsion: fat globules and protein particles are spread through water, and they scatter light, which is why milk looks white and opaque. If milk is left to stand, cream collects on top, another sign that it is not a true solution. Colloids such as milk, butter, fog and smoke are classed as heterogeneous.
A is wrong: hydrochloric acid is a uniform solution of hydrogen chloride gas in water.
B is wrong: vinegar is a uniform solution of acetic acid in water.
D is wrong: soda water is a uniform solution of carbon dioxide in water.
Exam tip: true solutions are homogeneous; colloids and suspensions are heterogeneous, and milk is a colloid.
Practice Questions
View allThe speed of the wind is measured by
- A.wind vane
- B.wind rose
- C.barometer
- D.anemometer
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An anemometer measures how fast the wind is blowing; its name comes from the Greek word anemos, meaning wind.
Read the full explanation →Brilliance of diamond is due to
- A.interference of light
- B.diffraction of light
- C.polarization of light
- D.total internal reflection of light
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Light that enters a cut diamond is reflected again and again inside it before it escapes, which makes the stone sparkle.
Read the full explanation →Which one of the following is NOT an electromagnetic wave ?
- A.Light wave
- B.Radio wave
- C.Sound wave
- D.Micro wave
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Sound is a mechanical wave that needs a medium to travel, while the other three are electromagnetic waves. Sound travels as a longitudinal wave of compressions and rarefactions in air, water or solids, which is why it cannot pass through a vacuum.
Read the full explanation →Which one of the following is NOT true for an electromagnetic wave ?
- A.Electromagnetic wave transports energy and momentum
- B.Electromagnetic wave can be polarized and reflected
- C.Electromagnetic wave is longitudinal
- D.Electromagnetic wave propagation is described by the varying electric and magnetic fields
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Electromagnetic waves are transverse, not longitudinal, so this statement is false. In an electromagnetic wave the electric field and the magnetic field oscillate at right angles to each other and both at right angles to the direction in which the wave travels.
Read the full explanation →Which one of the following frequency ranges is sensitive to human ears ?
- A.0-200 Hz
- B.20-20,000 Hz
- C.200-20,000 Hz only
- D.2,000-20,000 Hz only
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The normal human ear hears sound from about 20 hertz to 20,000 hertz, the audible range. Frequency, measured in hertz, is the number of vibrations per second, and it decides the pitch of a sound: the higher the frequency, the shriller the note.
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