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The MCQs below are drawn from the Chemistry subject category.
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4351
Evaluate the following statements regarding acids, bases, and indicators: 1. Acids taste sour and turn blue litmus red. 2. Bases taste bitter and turn red litmus blue. 3. Litmus is a natural indicator. Which are correct?
All three statements are chemically accurate. Acids are characterized by a sour taste and the ability to turn blue litmus red. Bases are characterized by a bitter taste and the ability to turn red litmus blue. Litmus is indeed a natural indicator derived from lichens.
4352
Which indicator is commonly employed for the titration of a strong acid against a strong base?
Phenolphthalein is the standard indicator for strong acid-strong base titrations because its color change interval (pH 8.2 to 10.0) falls within the steep vertical portion of the titration curve, ensuring a sharp and accurate endpoint detection.
4353
What color change occurs when phenolphthalein is added to vinegar?
Vinegar is a dilute solution of acetic acid, which is acidic. Phenolphthalein is an acid-base indicator that is colorless in acidic solutions and turns pink in basic (alkaline) solutions. Therefore, when added to vinegar, the solution remains colorless.
4354
Which of the following substances is classified as an olfactory indicator?
An olfactory indicator is a substance whose odor changes in the presence of an acid or a base. Clove oil is a well-known olfactory indicator because its characteristic smell is lost or altered when it reacts with a basic solution. Other common examples include onion and vanilla extract, which also exhibit distinct odor changes in different pH environments.
4355
What color change is observed when litmus paper is introduced into an aqueous solution of borax?
Borax (sodium tetraborate decahydrate) undergoes hydrolysis in water to form a solution that is slightly alkaline due to the presence of borate ions. Since litmus turns blue in the presence of a base, the litmus paper will turn blue when placed in a borax solution.
4356
If a solution does not change the color of red litmus paper, what conclusion can be drawn regarding its chemical nature?
Red litmus paper turns blue in the presence of a base. If the red litmus paper remains red, it indicates that the solution is not basic. However, it could still be acidic or neutral, as both acidic and neutral solutions do not cause red litmus to change color. Therefore, the only definitive conclusion is that the solution is not a base.
4357
What color does litmus solution turn when mixed with sulphuric acid?
Litmus is a natural pH indicator. In an acidic environment, such as that created by sulphuric acid, the litmus solution changes color from purple to red. This is a standard test for identifying acidic solutions in a laboratory setting.
4358
When is methyl orange indicator used in volumetric analysis?
Methyl orange is used in volumetric analysis when titrating a strong acid. It changes color at a pH range suitable for strong acid titrations, typically turning red in acidic conditions.