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CLASS 10TH CHEMISTRY MCQ ON ACIDS , BASES AND SALTS
CLASS 10TH MCQ ON ACIDS , BASES AND SALTS An acid is defined as a substance whose water solution tastes sour, turns blue litmus red and neutralizes bases. A substance is called base if its aqueous solution tastes bitter, turns red litmus blue or neutralizes acids. Salt is a neutral substance whose aqueous solution does not affect litmus.
What is acid base and salt with example?
Common examples include hydrochloric acid, sulfuric acid, citric acid and ethanoic acid (vinegar/acetic acid). Bases are a group of substances that neutralise acids. Soluble bases are called alkalis. … Salts are odourless and have a salty taste, and many are soluble in water.
Acids and bases will fall under one or more of the following three categories:
- Arrhenius acids/bases
- Bronsted-Lowry acids/bases
- Lewis acids/bases
The key here is to recognize that while each classification has a specific definition, any given molecule can fall into more than one category, some into all 3. Again, something we’ll look at later in this article.
CLASS 10TH MCQ ON ACIDS , BASES AND SALTS
Arrhenius Acid
An Arrhenius acid is a molecule that when dissolved in water will donate an H+ in solution. Simply put, a proton donor.
The trick to recognizing an Arrhenius acid is to look for a molecule that starts with an H, and typically contains an oxygen or halogen.
Common examples of Arrhenius acids include:
- Hydrochloric Acid – HCl
- Nitric Acid – HNO3
- Sulfuric Acid – H2SO4
- Acetic Acid – HCH3CO2
- and so many more…
An acid dissociating in water does not form a free-floating proton. Instead one of the water molecules in solution will grab the H+ yielding a hydronium or H3O+ ion. Here’s what happens when nitric acid dissociates in water.
CLASS 10TH MCQ ON ACIDS , BASES AND SALTS Arrhenius Base
An Arrhenius base is a molecule that when dissolved in water will break down to yield an OH- or hydroxide in solution. To recognize the Arrhenius base look for a molecule ending in OH, but not following CHx which refers to an alcohol.
Arrhenius base examples include:
- Sodium hydroxide – NaOH
- Potassium hydroxide – KOH
- Magnesium hydroxide – Mg(OH)2
- and so many more…
The Arrhenius definition for acids and bases only refers to compounds dissolved in water. Does this mean that acids and bases cannot exist out of water? Not quite, that’s where the Bronsted-Lowry definition comes in.
CLASS 10TH MCQ ON ACIDS , BASES & SALTS
Bronsted-Lowry Acid
A Bronsted-Lowry acid, like an Arrhenius acid, is a compound that breaks down to give an H+ in solution. The only difference is that the solution does not have to be water. We can still refer to the exact same acids as listed for the Arrhenius acid examples, but this time we’ll change the solvent to ammonia, alcohol, or anything else.
We saw what happens when nitric acid (HNO3) dissolves in water. Now let’s see what happens when it dissolves in ammonia (NH3) or even methanol (CH3OH)
Nitric acid still dissolved to yield an H+ and NO3-, but this time it was NH3 and not water that picked up the free-floating proton.
Bronsted-Lowry Base
This is where we start to see the difference between the Bronsted-Lowry and Arrhenius definitions. While the Arrhenius base referred specifically to the hydroxide (OH-) ion, the Bronsted-Lowry base refers to any atom or ion capable of accepting or bonding to a free proton in solution.
Referring back to the HNO3 + NH3 reaction above, when ammonia picks up the free H+ it acts as a proton-acceptor. NH3 is the Bronsted-Lowry base in this example.
Additional examples include:
- Methanol – CH3OH
- Formaldehyde – H2CO
- And even water – H2O
Lewis Acids and bases
The Lewis definition for acids and bases is the most extreme because it’s not dealing with protons specifically. Instead the Lewis definition deals with the movement of electrons.
Lewis Acid/Base Mnemonic
Think of Lewis as ‘lectrons’
Lewis Acid
A Lewis acid refers to an atom or molecule that accepts an electron pair. Think back to your ‘pushing arrows’ for orgo mechanisms. Every time you draw an arrow representing the movement of electrons, the atom getting attacked or accepting those electrons is the Lewis acid in that reaction.
Common Lewis Acid Examples in Organic Chemistry
- Borane – BH3 (hydroboration reaction)
- Aluminum Chloride – AlCl3 (electrophilic aromatic substitution reaction)
- Iron (III) Bromide – FeBr3 (electrophilic aromatic substitution reaction)
- and our good friend H+ (keep reading)
Lewis Base
Since the Lewis definition has to do with the transfer of electrons, you can guess by now that a Lewis Base is an electron pair donor. Once again think back to your reaction mechanisms. The molecule using its electrons to attack another atom is an electron pair donor and a Lewis Base.
Arrhenius Acid Definition: Hydronium breaks up to yield an H+ in solution.
Arrhenius Base Definition: Hydroxide is an OH- dissolved in water.
Bronsted-Lowry Acid Definition: Hydronium is an H+ donor regardless of solution
Bronsted-Lowry Base Definition: Hydroxide attacks and accepts the H+ from hydronium.
Lewis Acid Definition: The H+ on Hydronium accepts the attacking electron pair to form a bond.
Lewis Base Definition: Hydroxide donates its electron pair to form a bond between itself and H+
Types of Salt
1. Acidic salt – The salt formed by partial neutralization of a diprotic or a polyprotic acid is known as an acidic salt. These salts have ionizable H+ ion along with another cation. Mostly the ionizable H+ is a part of the anion. Some acid salts are used in baking.
For eg:- NaHSO4, KH2PO4 etc.
2. Basic or Alkali Salt – The salt formed by the partial neutralization of a strong base by a weak acid is known as a basic salt. They hydrolyze to form a basic solution. It is because when hydrolysis of basic salt takes place, the conjugate base of the weak acid is formed in the solution.
For eg:- White lead (2PbCO3·Pb(OH)2).
3. Double salt – The salts that contain more than one cation or anion are known as double salt. They are obtained by the combination of two different salts crystallized in the same ionic lattice.
For eg:- Potassium sodium tartrate (KNaC4H4O6.4H2O) also known as Rochelle salt.
4. Mixed Salts – The salt that consists of a fixed proportion of two salts, often sharing either a common cation or common anion is known as mixed salt.
For e.g. :- CaOCl2
Properties of Salt
The compound’s sodium chloride has very different properties from the elements sodium and chlorine.
- Saltwater contains ions and is a fairly good conductor of electricity.
- This electrostatic force of attraction holds the ions together and a chemical bond is said to form between them.
Hydrolysis of a Salt
Hydrolysis of salt refers to the reaction of salt with water. It is the reverse of a neutralization reaction. In this reaction, when salt undergoes reaction with water, the constituent acid and base are formed as products. In hydrolysis, the salt dissociates to form ions, completely or partially depending upon the solubility product of that salt.
For a detailed discussion on acids, bases and salts and the reactions salts undergo like Hydrolysis of salts, check out our app BYJU’S – The Learning App.
ANSWER KEY
B
Q.2 A
Q.3 C
Q.4 A
Q.5 C
Q.6 C
Q.7 A
Q.8 A
Q.9 C
Q.10 A
Q.11 C
Q.12 B
Q.13 A
Q.14 C
Q.15 B
Q.16 A
Q.17 D
Q.18 A
Q.19 B
Q.20 C
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