Chemical Reactions and Equations — Science STD 10 — Question

If you walk from a dark room into sunlight and back again into dark room, how would your pupils alter in size? What makes this happen?

Explain the formation of scum when hard water is treated with soap.

Does geographical isolation of individuals of a species lead to the formation of a new species? Provide a suitable explanation for your answer.

State three ways in which the strength of an electromagnet can be increased.

Give a test that can be used to differentiate chemically between butter and cooking oil.

What is the force on a current-carrying wire that is parallel to a magnetic field? Give reason for your answer.

A communications satellite in orbit sends a parallel beam of signals down to earth. If these signals obey the same laws of reflection as light and are to be focussed onto a small receiving aerial, what should be the best shape of the metal 'dish' used to collect them?

Which of the following are endothermic reactions and which are exothermic reactions?

1. Burning of natural gas.
2. Photosynthesis.
3. Electrolysis of water.
4. Respiration.
5. Decomposition of calcium carbonate.

Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?

In three test tubes A, B, and C, three different liquids namely, distilled water, underground water and distilled water in which a pinch of calcium sulphate is dissolved, respectively are taken. Equal amount of soap solution is added to each test tube and the contents are shaken. In which test tube will the length of the foam (lather) be longest? Justify your answer.