When litmus is added to a solution of borax, it turns _______.
- A.Pink
- B.Orange
- C.Red
- D.Blue
Correct answer
Explanation
The correct answer is D, blue. Borax, sodium tetraborate, is the salt of a strong base, sodium hydroxide, and a weak acid, boric acid, so its solution in water is basic. A basic solution turns litmus blue, which is the standard test. Option A is wrong because pink is the colour phenolphthalein takes in a base, not the colour of litmus; mixing up the two indicators is the usual mistake in this question. Option B is wrong because orange belongs to methyl orange, which is red in acid and yellow in base, and never gives a plain orange reading as an answer here. Option C is wrong because litmus turns red in an acidic solution, the opposite of what borax gives. Remember the pairing: salts of a strong base with a weak acid, such as borax, sodium carbonate and sodium acetate, all give a basic solution.
Read the full article: Acids, Bases and Salts: pH Scale and Common Salts
Practice Questions
View allWhich of the following contains citric acid?
- A.Tomato
- B.Orange
- C.Tamarind
- D.Sour milk
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Citrus fruits such as orange, lemon, lime and grapefruit owe their sharp sour taste to citric acid, which is the acid textbooks name for this family and the one examiners expect here.
Read the full explanation →The pH of a solution is 3. When its pH changes to 6, then the hydrogen ion concentration
- A.Increases 2 times
- B.Increases three times
- C.Decreases 100 times
- D.Decreases 1000 times
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The pH is the negative logarithm of the hydrogen ion concentration, so each rise of one unit means the concentration has fallen to one tenth.
Read the full explanation →What is the chemical formula of baking soda?
- A.Na2CO3
- B.NaHCO3
- C.NaOH
- D.CaOCl2
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Baking soda is sodium hydrogen carbonate, a mild, non corrosive base used as an antacid, as an ingredient of baking powder along with a mild edible acid such as tartaric acid, and in soda acid fire extinguishers, where it releases carbon dioxide.
Read the full explanation →The acid present in the sting of an ant is
- A.Formic acid
- B.Citric acid
- C.Lactic acid
- D.Tartaric acid
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The sting of an ant and the hairs of the nettle plant inject formic acid, also called methanoic acid, which is why the skin burns; rubbing on a mild base such as baking soda or the leaf of the dock plant relieves it by neutralising the acid.
Read the full explanation →Plaster of Paris is obtained by heating which of the following?
- A.Limestone
- B.Gypsum
- C.Quick lime
- D.Washing soda
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Plaster of Paris is calcium sulphate hemihydrate, made by heating gypsum, which is calcium sulphate dihydrate, to about 373 kelvin so that it loses three fourths of its water of crystallisation.
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