A student prepared hydrogen chloride gas by treating sodium chloride with concentrated sulphuric acid in a test-tube. He held a strip of dry blue litmus paper in HCl gas coming out of the test-tube. The student observed that on coming in contact with HCl gas, the colour of blue litmus paper :
(1)turned yellow (2)turned violet
(3)remained blue (4)turned red
"

Correct answer: (4) turned red

Explanation: Litmus is an acid-base indicator. Acids turn blue litmus to red and bases turn red litmus to blue. As HCl is an acid, it will turn blue litmus to red.

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Updated on: 10-Oct-2022

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(i) Draw a labelled diagram to show the preparation of hydrogen chloride gas in the laboratory.(ii) Test the gas evolved first with dry and then with wet litmus paper. In which of the two cases, does the litmus paper show change in colour?(iii) State the reason of exhibiting acidic character by dry HCl gas / HCl solution.
Why does dry HCl gas not change the colour of the dry litmus paper?
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During the preparation of hydrogen chloride gas on a humid day, the gas is usually passed through the guard tube containing calcium chloride. The role of calcium chloride taken in the guard tube is to(a) absorb the evolved gas(b) moisten the gas(c) absorb moisture from the gas(d) absorb Cl– ions from the evolved gas
A student placed a few drops of a liquid over a portion of the red litmus paper as shown here. He observed that the red litmus paper turned blue. The liquid could be :(1) dilute hydrochloric acid (2) dilute sodium hydroxide(3)water(4)dilute acetic acid"

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(1)turned yellow	(2)turned violet
(3)remained blue	(4)turned red