Category: FAQs

Describe how a barometer work.

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A barometer consist of a long glass tube and a liquid reservoir, usually mecury.

The tube is first submerged in the reservoir, and completely filled with the liquid in the reservoir.

Then, the tube is held inverted to a vertical position, with the mouth of the tube still in the liquid reservoir, and a pocket of vacuum above the liquid column inside the tube.

The atmospheric pressure exerts a force on the surface of the liquid reservoir, pushing the liquid up the tube. The pressure of the liquid column in the tube will be equal to the atmospheric pressure.

Describe how a hydraulic press work.

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A hydraulic press consists of two pistons of different sizes.

The space between the two pistons is filled completely with a liquid, usually hydraulic oil.

When a force is applied on the smaller piston, the pressure exerted on the liquid at the smaller piston is transmitted equally throughout the liquid.

Hence, the same pressure is also exerted at the bigger piston.

Since P = F/A, the F/A ratio will be the same at both pistons.

Since A1 < A2, hence F1 < F2.

So a smaller effort on the smaller piston (F1) will be able to lift a bigger load at the bigger piston (F2).

Describe a simple test for the presence of a reducing agent using aqueous potassium manganate (VII) solution.

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Add a few drops of acidified potassium manganate(VII) solution to a solution containing an unknown agent.

If a reducing agent is present in the solution, the KMnO4 solution will turn from purple to colorless.

In the presence of a reducing agent, a redox reaction occurs, turning the Mn7+ ion in KMnO4 (which is purple) to Mn2+ ion (which is colorless or slightly pinkish).

Describe a simple test for the presence of an oxidizing agent using aqueous potassium iodide.

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Add a few drops of aqueous potassium iodide to a solution containing an unknown agent.

If an oxidizing agent is present in the solution, aqueous potassium iodide will turn from colorless to brown.

In the presence of an oxidizing agent, a redox reaction occurs, turning the iodide ion in KI (which is colorless) to iodine, I2 (which is brown).