The acid test is a metaphor for a definitive test of something, like how well a product works or how honest a person is. In chemistry, it is used to check the quality of rocks, chemicals, minerals, materials, or anything else that is given as a sample.
Definition: An acid test is a chemical or metallurgical process that uses acids to find out the quality of the material in samples of rocks and minerals.
Acid Test Chemistry Questions with Solutions
Q-1: How can natural indicators be used to determine whether a substance is acidic?
Answer: A natural indicator is one that is derived from natural resources such as plants. The colour may or may not change when such indicators are mixed with the substances. The colour change predicts whether the substance is acidic or not.
For example A China rose indicator is a light pink-coloured solution. Its colour changes from light pink to magenta (deep pink), indicating that the solution is acidic.
Q-2: When an acid test is performed on the mineral magnesite, which gas is released?
- Hydrogen
- Carbon Dioxide
- Oxygen
- Carbon monoxide
Answer: b) carbon dioxide
Explanation: Magnesite is a mineral with the chemical formula MgCO3. When the acid test is performed the following reaction takes place:
MgCO3 + 2HCl → CO2 + H2O + MgCl2
Q-3: A cold acid test of dolomite is
- Weak
- Strong
- Very weak
- No reaction
Answer: a) weak
Explanation: Dolomite (CaMg(CO3)2) is a carbonate mineral. When one drop of cold hydrochloric acid is placed on a piece of dolomite, the reaction is weak or non-existent. Instead of a visible fizz, you will notice a drop of acid on the surface of the mineral, possibly with a few bubbles of carbon dioxide gas slowly growing on the surface of dolomite.
Q-4: Which of the following carbonate minerals gives a strong warm acid test?
- Magnesite
- Azurite
- Siderite
- Witherite
Answer: b) Azurite
Explanation: The mineral azurite has the chemical formula Cu3(CO3)2(OH)2.
When warm acid is applied to azurite, the entire drop erupts with bubbles and a vigorous fizz lasts for a few seconds. This happens because at higher temperatures, the acid and rock react more vigorously.
Q-5: What can be done if a specific mineral gives a weak acid test?
Answer: Hydrochloric acid has different effects on different carbonate minerals. With a mineral with a weak acid test, you must be observant and patient. In order to obtain a visible reaction, always powder a small amount of mineral on a streak plate and place a drop of acid on it. This results in an increase in surface area, which allows the acid to access more minerals and the reaction occurs.
Q-6: What colour changes occur when red cabbage juice is subjected to an acid test?
- Bluish green
- Red
- Blue
- Purple
Answer: b) Red
Explanation: The juice of red cabbage is a dark reddish-purple solution. It can be used as a natural indicator. An acid test on red cabbage juice causes the colour to change to red.
Q-7: The stone used for acid scratch test for precious metals is
a) Egg stone
b) Ruby stone
c) Kasauti stone
d) Sunstone
Answer: c) Kasauti stone
Explanation: A Kasauti is a small piece of black stone used by goldsmiths during acid scratch tests to check the quality of gold/silver(precious metals).
Q-8: Do non metals give a positive acid test?
Answer: No,nonmetals do not react with acids because when a substance reacts with acids, it provides electrons to the H+ ions produced by the acids. Non-metals are electron acceptors and thus cannot donate electrons.
Q-9: What precautions should be taken when performing an acid test?
Answer: Concentrated acids are highly corrosive to all body tissues, particularly the eyes and skin. Acids are extremely toxic due to their high corrosiveness. Acids, on the other hand, need not be feared if handled safely and with the proper equipment.
Hence, it is recommended to wear protective gloves, glasses, paper towels, and have immediate access to an eyewash station when dealing with acids. It is also necessary to always use acid-compatible containers such as PVC,LDPE etc. for their storage.
Q-10: Which of the following specimens has a strong reaction to acid?
- Coquina
- Oolite
- Rhodochrosite
- None of the above
Answer: a) and b)
Explanation: A few rocks can cause drastic reactions with hydrochloric acid. These are usually calcite or aragonite rocks with a lot of pore space or a lot of surface area. Some examples include chalk, oolite,coquina, and tufa. When a drop of dilute hydrochloric acid is applied to these specimens, an eruption of acid foam can arise and spread to an unexpected diameter.
Q-11: The compound formed by dissolving elemental gold in aqua regia during acid test is
a) AuCl
b) AuNO3
c) H[AuCl4]
d) H[Au(O3)4]
Answer: c) H[AuCl4]
Explanation: Aqua regia is made by mixing three parts concentrated HCl and one part concentrated HNO3.It is used to dissolve noble metals like gold and platinum.
The reaction of gold with aqua regia is shown below:
Au + 4H+ + NO3– + 4Cl– → AuCl4– + NO + 2H2O
Q-12: Can we add water to acid?
Answer: No, it is not recommended to add water to acid.
Explanation: When diluting an acid, it is preferable to add the acid to water rather than the water to the acid. Because adding water to a concentrated acid generates a lot of heat, it can result in an explosion and acid burns on your skin, clothing, and other body parts.
As a result, mixing acid with water is safe, but mixing acid with water is not.
Q-13: How litmus paper is used to measure the acidity of a solution?
Answer: A paper that changes colour in response to the acidity of the solution in which it is dipped is litmus paper. Hence can be used to measure acidity.
When blue litmus paper is dipped in an acid solution, it turns red, but red litmus paper remains unaffected.In this way, one can check the acidity of the solution.
Q-14: The chemical formula of fluoroantimonic acid is
- SbHF6
- SbHF5
- SbF6
- Sb2HF6
Answer: a) SbHF6
Q-15: How is the chromic acid test performed?
Answer: It is performed by taking three drops of the test compound and mixing it with five drops of acetone and five drops of chromic acid solution (an orange solution).
A positive test is indicated by the disappearance of the red-orange colour of chromic acid and the formation of a blue-green colour of the Cr (III) ion.
