Answered

16.
17.
(a) (i) Why is it difficult to wash an oily plate with water only?
(b)
(ii) Why are oil and grease used as lubricants?
(iii) Distinguish between cohesion and adhesion.
A sample of a radioactive element, with a half-life of 6 days, has an initial mass of
250 g.
(i) Obtain the values for the mass of the element remaining after 6, 12, 18 and
24 days.
(ii) Plot a decay curve of the element using the values obtained in b(i) above.
(a)(i) Mention two countries contributing to the international Disaster Monitoring
(b)
Constellation (DMC) project.
(ii) Mention two uses of NigeriaSat-1 in demography.
In the electroplating of an iron spoon with silver, state which material is used as
the:
(i) Anode
(ii) Cathode
(iii) Electrolyte
(c)
State one similarity between simple and compound microscopes.
(d)
A projector with a lens of focal length 6 cm is used to project the image of a slide
40 mm²
on a screen. If the image formed on the screen is 520 mm², calculate the:
(i) Magnification of the image
(ii) Image distance from the lens



Answer :

GinnyAnswer

Final answer:

Water and oil do not mix due to polarity differences, oil and grease are used as lubricants to reduce friction, and cohesion involves same-substance molecule attraction while adhesion involves different-substance attraction.


Explanation:

Why is it difficult to wash an oily plate with water only? Water and oil do not mix due to their different polarities. Water has a polar nature, while oil is nonpolar, causing the oil to form droplets that do not easily dissolve in water. This is due to the intermolecular forces between water molecules being stronger than the forces between water and oil molecules.

Why are oil and grease used as lubricants? Oil and grease are used as lubricants because they reduce friction between surfaces in contact by forming a layer that separates the moving parts. This layer prevents direct contact, allowing smoother movement and reducing wear and heat generation.

Distinguish between cohesion and adhesion: Cohesion refers to the attraction between molecules of the same substance, leading to the formation of surface tension, whereas adhesion is the attraction between molecules of different substances, causing them to stick together. An example is water molecules sticking to each other (cohesion) and water sticking to a glass surface (adhesion).


Learn more about Intermolecular Forces here:

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