NCERT Solution for Class Tenth Science Chapter 2
Acids, Bases and Salts
Intext Questions
Page No-2
Questions No-1
You have been provided with three test tubes. One of them contains distilled water and the other two contain an acidic solution and a basic solution, respectively. If you are given only red litmus paper, how will you identify the contents of each test tube?
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If the colour of red litmus paper gets changed to blue, then it is a base and if there is no colour change, then it is either acidic or neutral. Thus, basic solution can be easily identified.
Let us mark the three test tubes as A, B, and C. A drop of the solution in A is put on the red litmus paper. Same is repeated with solution B and C.
If either of them changes colour to blue, then it is basic. Therefore, out of three, one is eliminated.
Out of the remaining two, any one can be acidic or neutral. Now a drop of basic solution is mixed with a drop of each of the remaining two solutions separately and then the nature of the drops of the mixtures is checked.
If the colour of red litmus turns blue, then the second solution is neutral and if there is no change in colour, then the second solution is acidic.
This is because acidic and basic solutions neutralize each other. Hence, we can distinguish between the three types of solutions.
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Add few drops of solution from all three test tubes on the red litmus paper separately. The solution which turns red litmus to blue contains basic solution. Use this blue litmus paper to test the solutions in other two test tubes. The solution from the test tube which turns blue litmus paper to red will be the acidic solution and solution of the test tube which do not change either red or blue litmus paper contain water.
Litmus papers are indicators that differentiate between acidic, basic and neutral solutions. Red litmus changes to blue with basic solution If the colour of red litmus paper gets changed to blue, then it indicates that the given solution is a base and if there is no colour change, then it is either acidic or neutral. Whereas blue litmus turns to red with acidic solution. If the colour of blue litmus paper gets changed to red, then it indicates that the given solution is a acid and if there is no colour change, then it is either basic or neutral. This can be best explained by a simple experiment. Let’s take 3 test tubes and labelled as A, B, and C which contain water, acidic and basic solutions respectively by using litmus paper test. We confirm that test tube A does not show any change in that indicates it is not acid and base. Test tube B also does not show any change in litmus paper. Only test tube C changes red litmus to blue indicating the solution is base.
Litmus paper is a simple and quick method to determine whether a solution is acidic or basic.
we use red litmus paper to identify the contents of each test tube:
1. Testing for Acidity:
» Dip the red litmus paper into the solution in one of the test tubes.
» If the litmus paper turns blue, it indicates that the solution is basic.
» If there is no color change, it suggests that the solution is either neutral or acidic.
2. Testing for Basicity:
» Dip the red litmus paper into the solution in another test tube.
» If the litmus paper remains red, it suggests that the solution is either neutral or acidic.
» If the litmus paper turns blue, it indicates that the solution is basic.
3. Identifying Distilled Water:
» Dip the red litmus paper into the solution in the third test tube.
» If the litmus paper remains red, it suggests that the solution is either neutral or acidic.
» Distilled water is generally neutral, so if the litmus paper remains red, the solution is likely neutral.
By comparing the results from all three test tubes, you can identify the contents:
» The test tube where litmus paper turned blue contains a basic solution.
» The test tube where litmus paper remained red likely contains distilled water or a neutral solution.
» The remaining test tube, where there was no color change in the litmus paper, contains an acidic solution.
This method relies on the fact that litmus paper changes color in response to the pH of the solution. Red litmus paper turns blue in a basic solution and remains red in an acidic or neutral solution.