Chemistry MCQs

Acids are substances that donate protons and turn blue litmus paper red. Conversely, alkalis (bases) are substances that accept protons or provide hydroxide ions, which turn red litmus paper blue. Therefore, the correct sequence to fill the blanks is acid, alkali, and red.

Litmus is a water-soluble mixture of different dyes extracted from lichens, specifically species like Roccella tinctoria. It is widely used in laboratories as an acid-base indicator because it changes color from red to blue in basic solutions and blue to red in acidic solutions.

Litmus is a natural pH indicator obtained from various species of lichens, particularly Roccella tinctoria. The dye is extracted from these organisms and processed into a solution or impregnated onto paper strips to serve as a diagnostic tool for identifying acidic or basic substances in a laboratory setting.

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.

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.

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.

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.

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.

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.

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.