Acids, Bases and Salts
10th Class Chemistry Chapter 10 Solved Exercise Short Questions
Q 1 : Name three common household substances having
a. pH value greater than 7
- Caustic soda ( NaOH )
- Milk of magnesia ( Mg(OH)2 )
- Ca (OH)2
- Soap
- Detergents
- Shampoo
b. pH value less than 7
- Sour milk ( lactic acid )
- Apple ( Malic acid )
- Lemon ( citric acid )
c. pH value equal to 7
- Table salt solution ( NaCl )
- Water ( H2O)
- Calcium Chloride ( CaCl2 )
Q 2 : Define a base and explain that all alkalies are bases, but all bases are not alkalies .
Base :
” A specie that releases OH– ions in an aqueous solution , accepts a proton and donates an electron pair is called a base . “
Alkali :
” Water soluble base is called an alkali . ”
Explanation : Alkali gives ( OH– ) hydroxide ions in solution rapidly but all bases do not give OH– ions . So , all alkalies are bases but all bases are not alkalies .
Q 3 : Define Bronsted-Lowry base and explain with an example that water is a Bronsted-Lowry base .
Bronsted-Lowry base :
” A base is a substance that can accept a proton ( H+ ) from another substance .”
Explanation : Water is a Bronsted-Lowry base because water accepts a proton to form hydronium ion .
Q 4 : How can you justify that Bronsted-Lowry concept of acid and base is applicable to non-aqueous solutions ?
Justification : According to Bronsted-Lowry concept :
- An Acid is a substance which donates a proton ( H+ ).
- A Base is a substance which accepts a proton ( H+ ).
→ So , there is no need of water for a specie to b called Bronsted-Lowry acid or base .
Hence , this concept is applicable to non-aqueous solutions .
Q 5 : Which kind of bond is formed between Lewis acid and a base ?
Q 6 : Why H+ ion act as a Lewis acid ?
H+ ( Lewis acid ) : H+ ion acts as a Lewis acid because H+ can accept a pair of electrons due to empty first shell .
→ It completes its valence shell by gaining a pair of electrons , So ,it acts as Lewis acid .
Q 7 : Name two acids used in the manufacture of fertilizers .
- Nitric acid ( HNO3 )
- Sulphuric acid ( H2SO4 )
Q 8 : Define pH . What is the pH of pure water ?
pH :
” The negative logarithm of molar concentration of hydrogen ion is called pH . “
Q 9 : How many times a solution of pH 1 will be stronger than that of a solution having pH 2 ?
→ The solution of pH 1 is 10 times stronger than the solution of pH 2 .
→ Because solution of pH 1 has 10 times higher concentration of [ H+ ] ions than pH 2 .
Q 10 : Define the followings :
i . Normal salt :
ii. Basic salt :
Q 11 : Na2SO4 is a neutral salt while NaHSO4 is an acid salt. Justify .
- NaHSO4 is formed by Na+ ions by partial replacement of hydrogen ions . It turns blue litmus paper to red . So , it is an acidic salt .
- While Na2SO4 is formed by complete replacement of hydrogen ions by Na+ ions . It does not turn blue litmus paper red . So, it is normal or neutral salt .
Q 12 : Give a few characteristic properties of salts .
Characteristic Properties of Salts :
- Salts are found in crystalline form .
- Salts have high melting and boiling points .
- Mostly salts have water of crystallization which is responsible for shape of crystals .
- Salts are neutral compounds .
- Salts are usually soluble in water
Examples :
- CuSO4.5H2O
- CaSO4.2H2O
Q 13 : How are the soluble salts recovered from water ?
→ First saturated solution is prepared by dissolving the given salt in water .
→ Then solution is filtered using a funnel .
→ Then the filtrate is crystallized by slow evaporation .
- So, In this way , Soluble salts are separated / recovered by Filtration and Crystallization process .
Q 14 : How are the insoluble salts prepared ?
Preparation of Insoluble Salts :
In this method , usually solution of soluble salts are mixed . During the reaction , exchange of ionic radicals takes place to produce two new salts . One is insoluble and the other is soluble . Insoluble salt precipitates and is filtered out .
Q 15 : Why is a salt neutral ? Explain with an example .
Q 16 : Name an acid used in the preservation of food .
Acetic acid ( CH3COOH ) and Benzoic acid ( C6H6COOH ) are natural food preservatives .
Q 17 : Name the acids present in :
i. Vinegar :
→ Acetic acid
ii. Ant sting :
→ Formic acid
iii. Citrus fruit :
→ Citric acid
iv. Sour milk :
→ Lactic acid
Q 18 : How can you justify that Pb(OH)NO3 is a basic salt ?
Justification :
Pb(OH)NO3 is formed by the incomplete neutralization of poly-hydroxy base with acids , so it is a basic salt .
- It means that normal salt will be formed if reacts with acid .
Q 19 : You are in a need of an acidic salt. How can you prepare it ?
Q 20 : Which salt is used to prepare plaster of Paris ?
Calcium Sulphate (Gypsum) CaSO4.2H2O , is used to prepare Plaster of Paris .
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