Q1 of 216 Page 478

How many molecules of water of crystallisation are there in

i. Plaster of Paris


ii. washing soda crystals?

(i) The chemical formula of Plaster of Paris is CaSO4. 1/2 H2O, so it has 1/2 molecules of water of crystallisation.


(ii) The chemical formula of Washing soda crystals is Na2CO3.10H2O, so it has 10 molecules of water of crystallisation.


More from this chapter

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26

In an experiment on tracing the path of a ray of light through a rectangular glass slab, four students A, B, C and D used the following values of angle of incidence and the distance between the feet of the two pins (fixed on the incident ray):

A. (30°, 45°, 60°) and 1 cm


B. (30°, 45°, 60°) and 6 cm


C. (20°, 50°, 80°) and 10 cm


D. (20°, 50°, 80°) and 15 cm


Whose choice is the best choice and why?

 27

The rest positions of the needles in a milliammeter and voltmeter not in use are as shown in Fig. A. When a student uses these in his experiment, the readings of the needle are in the positions shown in Fig. B.


Find the corrected values of current and voltage in the experiment.


OR


While experimentally verifying Ohm’s law a student observed that the pointer of the voltmeter coincides with 15thdivision when the voltmeter has a least count of 0.05 V. Find the observed reading of voltmeter.

 2

Write the molecular formula of first two members of homologous series having functional group – Cl.

 3

Why is a normal eye not able to see clearly the objects placed closer than 25 cm?