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Question
Blue litmus paper is dipped in a solution. It remains blue. What is the nature of the solution? Explain.
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Solution
- We know that basic and neutral solutions do not change the colour of blue litmus paper. Since blue litmus remains blue after dipping in the solution, the solution is either basic or neutral in nature.
- Put a drop of this solution on a red litmus paper. If it turns blue, the above solution is basic in nature. If no colour change occurs, it is neutral.
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RELATED QUESTIONS
What colour will universal indicator show if you add it to the following substances?
(a) potassium hydroxide, pH = 12
(b) soda water, pH = 5
(c) sulphuric acid, pH = 2
Under what soil conditions do you think a farmer would treat the soil of his fields with quicklime (calcium oxide), or slaked lime (calcium hydroxide) or chalk (calcium carbonate)?
Which of the following elements would from oxides which would indicate pH values less than seven, using moist pH paper?
Magnesium, Carbon, Sulphur, Hydrogen, Copper
The pH values of five solutions A, B, C, D and E are given below:
| A | 1 |
| B | 5 |
| C | 7 |
| D | 11 |
| E | 13 |
Here are some results of solutions tested with universal indicator paper:
| Sulphuric acid | : Red |
| Metal polish | : Dark blue |
| Washing-up liquid | : Yellow |
| Milk of magnesia | : Light blue |
| Oven cleaner | : Purple |
| Car batter acid | : Pink |
Arrange the solutions in order of their increasing pH value (starting with the one with the lowest pH).
Neutral substances do not bring about any change in colour of indicators.
Assertion: Methyl orange and phenolphthalein are natural indicators.
Reason: Methyl orange is yellow in colour while phenolphthalein is pink.
Write a note on:
Litmus
Take some lemon juice in a tumbler and add baking soda slowly. What do you see? What do you infer from this?
Prepare red cabbage juice by boiling a piece of red cabbage in water. Use it as an indicator and test the acidic and basic solutions with it. Present your observations in the form of a table.
