Washing soda (Na₂CO₃·10H₂O) is obtained from sodium carbonate by:
A. Adding acid
B. Heating
C. Electrolysis
D. Crystallisation from its aqueous solution
Answer: Option D
Solution (By JKSSB Mock Tests)
Sodium carbonate decahydrate (washing soda) is prepared by dissolving soda ash (anhydrous Na₂CO₃) in water and allowing it to crystallise. Heating would remove water of crystallization (efflorescence). Adding acid would decompose it. Electrolysis would produce NaOH and Cl₂ from brine, not washing soda directly.
Explanation:
The root mean square velocity (urms) of gas molecules can be expressed in multiple equivalent ways. It is √(3RT/M) where R is the gas constant, T is temperature, and M is molar mass. Since P = dRT/M (where d is density), it can also be written as √(3P/d). Both formulas are correct.
Explanation:
Teflon (PTFE) has a very low coefficient of friction and surface energy because the fluorine atoms form a protective shield around the carbon backbone, making it difficult for other substances to adhere. This is not due to polarity (C-F bonds are polar but the molecule overall is non-polar due to symmetry). It is extremely inert, resisting most chemicals.
Explanation:
The diagonal relationship occurs when elements in the second period resemble elements in the third period of the next group due to similar ionic sizes and charge-to-radius ratios (polarizing power). Li-Mg, Be-Al, and B-Si are all classic examples of this phenomenon.
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