Q1. Questions a-d are based on the Table A and Table B. Study these tables
related to boiling points of different substances and humidity and answer the
following questions.
Table A: Boiling points of different substances
Substance Boiling
point (?C)
Methanol 64.7
Ethanol 78.4
Nitric Acid 83
Water 100
Iodine 184.3
Table B: Humidity
Humidity
percentage
in three
situations
Humidity
(%)
Situation A >75
Situation B 50 ? 75
Situation C a. Refer Table B and find out in which situation a bowl of water will
evaporate away the fastest and in which situation the slowest.
b. A bowl of water and a bowl of ethanol are kept inside a room. Which
bowl will get empty first?
c. ?Evaporation is a surface phenomenon.? Explain.
d. Refer Table A and Table B and find in which situation out of the
following, the substance will evaporate the fastest.
(i) Methanol in situation C (ii) Iodine in situation A
(iii) Nitric acid in situation A (iv) Iodine in situation C

Dear student,
Relative humidity greatly affects evaporation rates. When it is high, relative humidity slows evaporation. 
a. So in situation B water will evaporate fastest. 
b. As the humidity is same for both water and ethanol. Ethanol will evaporate faster because its boiling point is lesser than water. 
c. Surface phenomenon is the phenomenon where only surface of any substance or object is involved in the process. On the other hand, bulk phenomenon refers to the phenomenon where whole of the substance or object is involved in the process and is affected in bulk completely. In evaporation, only the molecules of the liquid present on the surface of the liquid leave the liquid state and change into vapour state. It does not affect the molecules present in the bulk of the liquid. Thus, evaporation is a surface phenomena. If the surface area is increased, the rate of evaporation increases. For example, while putting clothes for drying up we spread them out.
d. Methanol in situation C will evaporate fastest because boiling point of methanol is least here and also humidity of situation C is less than that of situation A. 
Regards

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