Test: Acids, Bases & Salts - Class 9 MCQ

Bases generate hydroxide ions or OH^- ions in water. Thus option C is correct

 

 

Litmus', a natural dye extracted from Lichen which is a composite organism emerges from algae.

The acid present in the body of a red ant is formic acid. Formic acid is also known as methanoic acid, and its chemical formula is HCOOH.

It is an example of a neutralization reaction in which an acid (carbon dioxide) reacts with base (calcium hydroxide) to form salt and water.

 

 

Borax is often used for several closely related minerals or compounds that differ in the crystal water content anhydrous borax, borax pentahydrate, borax decahydrate(general name of borax).

 

 

Sodium carbonate is known as soda ash or washing soda Na₂CO₃ • 10H₂O. It is the sodium salt of carbonic acid. It is white hygroscopic in nature and has an alkaline taste. It is used as a water softener.

Metal oxides react with acid to form salt and water because most of the metal oxides are basic or amphoteric in nature.

 

 

Explanation:
Introduction:
The question asks why some alkali metal salts are colored, specifically Na₂CrO₄, KMnO₄, and K₂MnO₄. It provides four options to choose from, and the correct answer is option B, which states that anions are colored ions.
Explanation:
To understand why these salts are colored, we need to look at the chromophores present in each compound. Chromophores are responsible for the absorption of specific wavelengths of light, resulting in the observed color.
Na₂CrO₄ (yellow):
- The chromophore in Na₂CrO₄ is the CrO₄^2- anion.
- The yellow color is due to the absorption of light in the blue region of the visible spectrum by the CrO₄^2- anion.
KMnO₄ (pink):
- The chromophore in KMnO₄ is the MnO₄^- anion.
- The pink color is due to the absorption of light in the green region of the visible spectrum by the MnO₄^- anion.
K₂MnO₄ (green):
- The chromophore in K₂MnO₄ is also the MnO₄^- anion.
- The green color is due to the absorption of light in the red region of the visible spectrum by the MnO₄^- anion.
Conclusion:
From the above explanations, it is clear that the colored ions responsible for the observed colors in these alkali metal salts are the anions, specifically CrO₄^2- and MnO₄^-. Therefore, option B, which states that anions are colored ions, is the correct answer.

NaCl is a neutral salt formed by the reaction between strong acid HCl and strong base NaOH. The reaction occurs as follows.

Natural indicators are obtained from natural sources. All of the above examples are natural indicators. A solution of china rose turns green in a basic solution and bright pink or magenta in an acidic solution. Morning glories contain an anthocyanin called "heavenly blue anthocyanin" which changes from purplish red at pH 6.6 to blue at pH 7.7. Blueberries change from blue (around pH 2.8 — 3.2) to red in a strongly acidic solution.

Non-metals do not react with acids. Thus, option D is correct.

Sodium aluminate and hydrogen gas are formed when sodium hydroxide reacts with aluminium metal.

2NaOH + 2Al + 2H₂O ⇨ 2NaAlO₂ + 2H₂

Sodium chloride is known as rock salt, common salt, table salt.

Current is the rate of flow of charge. NaCl an ionic solid. An ionic solid consists of a lattice of Na+ and Cl ions in which these ions are fixed in their places. Solid NaCI does not contain any mobile charge carriers that can facilitate the flow of charge. But molten NaCI contains free mobile ions Na+ and Cl- ions which allow the passage of current.

Groups IIA, IIIA, and IVA metals are less reactive than the neighbouring alkali metals. Thus Al and Zn are less reactive metals than Na, K and Mg.

pH above 7 confirms the compound to be alkaline in nature so it can be either sodium carbonate or sodium hydroxide as HCl and CH₃COOH are acidic in nature. Sodium hydroxide is a strong base, so it has the highest pH of about 14, while sodium carbonate is a weak base to have pH 9.

Decay of teeth is because of the sweetening agents we eat as it increases the acidity inside the mouth, which can be prevented if the toothpaste used is alkaline or basic in nature. Baking soda or sodium hydrogen carbonate is also used to clean the teeth as it is alkaline in nature.

Sodium chloride imparts a yellow colour to the Bunsen flame. This can be interpreted due to the emission of excess energy absorbed as radiation in the visible region.

When an alkali or alkaline earth metal (or its salt) is introduced in the flame, the metal's valence electrons absorb energy and are excited to the higher energy level. When excited electrons return to their ground state, they release the absorbed energy as visible light.

Aqueous solution of NaCl is neutral and therefore, does not change the colour of either red or blue litmus.

 

 

The milkman adds baking soda to milk so that milk becomes slightly alkaline (pH > 7). The milk will not be converted to acidic curd readily.