In the previous section, we saw how to predict the name of the salt that will be formed from a neutralisation reaction. We have also seen how to write it's chemical formula. In this section we will see a few more solved examples.
Solved example 6.3
Some cations and anions are given below:
Cations: • Ca2+ (Calcium ion) • NH4+ (Ammonium ion)
Anions: • Cl- (Chloride ion) • SO42- (Sulphate ion) • PO43- (Phosphate ion)
Write the chemical formulae of all the salts possible by combining them
Solution:
In this problem, we do not have to split the acid and alkali into cations and anions. They are already given separately
Case 1: Combination between Ca2+ and Cl-.
1. Assemble the cation and anion with cation first: Ca2+ Cl- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in Cl- ion = 1
• Number of Cl- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: CaCl2.
Case 2: Combination between Ca2+ and SO42-.
1. Assemble the cation and anion with cation first: Ca2+ SO42- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in SO42- ion = 2
• Number of SO42- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: Ca2(SO4)2.
4. Here, the subscripts (2 and 2) have a common factor. The common factor is '2'. In such cases we must divide the subscripts by the common factor. We get 2 ÷ 2 = 1
5. We can write: Ca1(SO4)1. When the subscript is '1', it is not usually written.
6. So final chemical formula is CaSO4.
Case 3: Combination between Ca2+ and PO43-.
1. Assemble the cation and anion with cation first: Ca2+ PO43- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in PO43- ion = 3
• Number of PO43- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: Ca3(PO4)2.
Case 4: Combination between NH4+ and Cl-.
1. Assemble the cation and anion with cation first: NH4+ Cl- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in Cl- ion = 1
• Number of Cl- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)1(Cl)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is NH4Cl.
Case 5: Combination between NH4+ and SO42-.
1. Assemble the cation and anion with cation first: NH4+ SO42- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in SO42- ion = 2
• Number of SO42- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)2(SO4)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is (NH4)2SO4.
Case 6: Combination between NH4+ and PO43-.
1. Assemble the cation and anion with cation first: NH4+ PO43- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in PO43- ion = 3
• Number of PO43- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)3(PO4)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is (NH4)3PO4
In the next chapter, we will see compounds of non-metals.
Solved example 6.3
Some cations and anions are given below:
Cations: • Ca2+ (Calcium ion) • NH4+ (Ammonium ion)
Anions: • Cl- (Chloride ion) • SO42- (Sulphate ion) • PO43- (Phosphate ion)
Write the chemical formulae of all the salts possible by combining them
Solution:
In this problem, we do not have to split the acid and alkali into cations and anions. They are already given separately
Case 1: Combination between Ca2+ and Cl-.
1. Assemble the cation and anion with cation first: Ca2+ Cl- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in Cl- ion = 1
• Number of Cl- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: CaCl2.
Case 2: Combination between Ca2+ and SO42-.
1. Assemble the cation and anion with cation first: Ca2+ SO42- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in SO42- ion = 2
• Number of SO42- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: Ca2(SO4)2.
4. Here, the subscripts (2 and 2) have a common factor. The common factor is '2'. In such cases we must divide the subscripts by the common factor. We get 2 ÷ 2 = 1
5. We can write: Ca1(SO4)1. When the subscript is '1', it is not usually written.
6. So final chemical formula is CaSO4.
Case 3: Combination between Ca2+ and PO43-.
1. Assemble the cation and anion with cation first: Ca2+ PO43- .
2. Do the interchanging:
• Number of Ca2+ ions = Number of charges in PO43- ion = 3
• Number of PO43- ions = Number of charges in Ca2+ ion = 2
3. So chemical formula of the final salt is: Ca3(PO4)2.
Case 4: Combination between NH4+ and Cl-.
1. Assemble the cation and anion with cation first: NH4+ Cl- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in Cl- ion = 1
• Number of Cl- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)1(Cl)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is NH4Cl.
Case 5: Combination between NH4+ and SO42-.
1. Assemble the cation and anion with cation first: NH4+ SO42- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in SO42- ion = 2
• Number of SO42- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)2(SO4)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is (NH4)2SO4.
Case 6: Combination between NH4+ and PO43-.
1. Assemble the cation and anion with cation first: NH4+ PO43- .
2. Do the interchanging:
• Number of NH4+ ions = Number of charges in PO43- ion = 3
• Number of PO43- ions = Number of charges in NH4+ ion = 1
3. So chemical formula of the final salt is: (NH4)3(PO4)1.
4. When the subscript is '1', it is not usually written.
5. So final chemical formula is (NH4)3PO4
Uses of salts
We come across salts on many occassions in our day to day life. Some of them which occur naturally are listed below:
■ Sodium chloride (NaCl). It's common name is table salt.
• It is mainly used for cooking purposes.
• Another important use is in the making of freezing mixtures
• It is mainly used for cooking purposes.
• Another important use is in the making of freezing mixtures
■ Potassium chloride (KCl). It's common name is Sylvite/Muriate of potash. It occurs naturally at some places.
• Industrial production of KCl is done using naturally occuring sylvite.
• It is used as a fertilizer. It is also used in the laboratory for various experiments.
■ Potassium nitrate (KNO3). It is one of the several nitrogen containing compounds. These nitrogen containing compounds are collectively called as saltpetre.
• It's main use is in the making of fertilizers.
■ Sodium nitrate (NaNO3). It's common name is Chile salt peter or Peru saltpetre. These names are derived because of the vast deposits of NaNO3 compounds in the atacama desert in Chile and Peru.
• It is mainly used in the making of fertilizers
■ Calcium sulphate (CaSO4). It is a hygroscopic substance. That means, it has the ability to attract and hold water molecules from the surroundings.
• So it is used as a desiccant. A desiccant is a substance that is used in certain containers to keep it's contents dry
• When it reacts attracts and reacts with water, it forms a hydrate (CaSO4.2H2O). This is known as gypsum. It occurs naturally at some places.
• Another hydrate is commonly known as plaster of paris. It is used for moulding various objects
■ Calcium carbonate (CaCO3). It occurs naturally as limestones and in the shells or marine organisms. It's main use in the manufacture of cement.
Now we will see some salts which are made artificially:
■ Sodium carbonate (Na2CO3.10H2O). It's common name is washing soda. It's main uses are in the manufacture of soaps, detergents, glass etc.,
■ Sodium bicarbonate (NaHCO3). It's common name is baking soda. It's main uses are in the making of antacids, fire extinguishers etc., It is also used for baking purposes.
■ Copper sulphate (CuSO4.5H2O). It's common name is blue vitriol. It's main use is in the preparation of fungicides. It is also used in the laboratory for various experiments.
• Industrial production of KCl is done using naturally occuring sylvite.
• It is used as a fertilizer. It is also used in the laboratory for various experiments.
■ Potassium nitrate (KNO3). It is one of the several nitrogen containing compounds. These nitrogen containing compounds are collectively called as saltpetre.
• It's main use is in the making of fertilizers.
■ Sodium nitrate (NaNO3). It's common name is Chile salt peter or Peru saltpetre. These names are derived because of the vast deposits of NaNO3 compounds in the atacama desert in Chile and Peru.
• It is mainly used in the making of fertilizers
■ Calcium sulphate (CaSO4). It is a hygroscopic substance. That means, it has the ability to attract and hold water molecules from the surroundings.
• So it is used as a desiccant. A desiccant is a substance that is used in certain containers to keep it's contents dry
• When it reacts attracts and reacts with water, it forms a hydrate (CaSO4.2H2O). This is known as gypsum. It occurs naturally at some places.
• Another hydrate is commonly known as plaster of paris. It is used for moulding various objects
■ Calcium carbonate (CaCO3). It occurs naturally as limestones and in the shells or marine organisms. It's main use in the manufacture of cement.
Now we will see some salts which are made artificially:
■ Sodium carbonate (Na2CO3.10H2O). It's common name is washing soda. It's main uses are in the manufacture of soaps, detergents, glass etc.,
■ Sodium bicarbonate (NaHCO3). It's common name is baking soda. It's main uses are in the making of antacids, fire extinguishers etc., It is also used for baking purposes.
■ Copper sulphate (CuSO4.5H2O). It's common name is blue vitriol. It's main use is in the preparation of fungicides. It is also used in the laboratory for various experiments.
We have completed the discussion on acids, alkalies and salts. Now we will see some solved examples in general from this chapter
Solved example 6.4
Complete the chemical equations for the following ionisation reactions:
KCl → K+ + Cl-.
HNO3 → H+ + NO3-
Mg(OH)2 → Mg2+ + 2(OH)-
H2SO4 → 2H+ + SO42-
NH4Cl → NH4+ + Cl-
CaSO4 → Ca2+ + SO42-.
Solved example 6.5
Identify the symbols of ions given below, and write their names
SO32-, NO3-, HCO3-, OH-, CO32-, HSO4-
Carbonate - CO32-
Bisulphate - HSO4-
Sulphite - SO32-
Nitrate - NO3-
Hydroxide - OH-
Bicarbonate - HCO3-
Solved example 6.6
A little distilled water is taken in a beaker
(a) What is the pH value of distilled water?
(b) What happens to the pH value when the following substances are added to the water in the beaker? Justify your answer.
(i) Caustic soda
(ii) Vinegar
Solution:
(a) Distilled water is neutral. It is neither acidic nor alkaline. So it's pH value is 7
(b.i) Caustic soda is sodium hydroxide. It is an alkali. When it is added to water concentration of (OH)- ions will increase. That means, the solution will become alkaline. So the pH value will increase.
(b.ii) Vinegar is acetic acid. When it is added to water concentration of H+ ions will increase. That means, the solution will become acidic. So the pH value will decrease.
Solved example 6.7
Some salts are given in column A. Their chemical formulae and uses are given in column B and column C irregularly. Match the columns by identifying the correct chemical formulae and uses of the salts.
Solution:
The corrected table is given below:
Solved example 6.8
The pH values of some substances are given in the table. Analyse the table and answer the questions that follow.
(a) Is blood acidic or alkaline in nature
(b) The pH value of pure milk is 6.4. Does the pH value increase or decrease when milk changes to curd?. Justify your answer
(c) Among the substances given in the table,
(i) Which one is strongly alkaline?
(ii) Which one has weak acidic nature?
Solution:
(a) The pH value of blood is given as 7.36. This is greater than 7. So blood is alkaline in nature
(b) The pH value of pure milk is given as 6.4. This is less than 7. So pure milk is acidic. When it changes to curd, the pH value will be come less than 6.4. This is because curd is acidic
(c) i. Substances which have pH greater than 7 are all alkaline. So lime water, tooth paste, and blood are alkaline. Among them, lime water has the greatest difference from 7. So it is the most alkaline in the given table
ii. Substances which have pH less than 7 are all acidic. So vinegar and milk are acidic. Among them, milk has the smallest difference from 7. So it is the weakest acidic nature in the given table
More precisely it can be written as follows:
• Vinegar has pH value 4.2. So [H+] = 10-4.2. That means there are 10-4.2 mols of H+ ions in 1 litre of vinegar
• Milk has pH value 6.4. So [H+] = 10-6.4. That means there are 10-6.4 mols of H+ ions in 1 litre of milk
• 10-6.4 < 10-4.2. So the number of H+ ions is less in Milk. So it is a weaker acid than vinegar.
Solved example 6.5
Identify the symbols of ions given below, and write their names
SO32-, NO3-, HCO3-, OH-, CO32-, HSO4-
Carbonate - CO32-
Bisulphate - HSO4-
Sulphite - SO32-
Nitrate - NO3-
Hydroxide - OH-
Bicarbonate - HCO3-
Solved example 6.6
A little distilled water is taken in a beaker
(a) What is the pH value of distilled water?
(b) What happens to the pH value when the following substances are added to the water in the beaker? Justify your answer.
(i) Caustic soda
(ii) Vinegar
Solution:
(a) Distilled water is neutral. It is neither acidic nor alkaline. So it's pH value is 7
(b.i) Caustic soda is sodium hydroxide. It is an alkali. When it is added to water concentration of (OH)- ions will increase. That means, the solution will become alkaline. So the pH value will increase.
(b.ii) Vinegar is acetic acid. When it is added to water concentration of H+ ions will increase. That means, the solution will become acidic. So the pH value will decrease.
Solved example 6.7
Some salts are given in column A. Their chemical formulae and uses are given in column B and column C irregularly. Match the columns by identifying the correct chemical formulae and uses of the salts.
| A | B | C |
|---|---|---|
| Salt | Chemical formula | Use |
| Washing soda | CuSO4.5H2O | Fire extinguisher |
| Gypsum | NaHCO3 | Fungicide |
| Blue vitriol | Na2CO3.10H2O | Cement manufacture |
| Baking soda | CaSO4.2H2O | Glass manufacture |
The corrected table is given below:
| A | B | C |
|---|---|---|
| Salt | Chemical formula | Use |
| Washing soda | Na2CO3.10H2O | Glass manufacture |
| Gypsum | CaSO4.2H2O | Cement manufacture |
| Blue vitriol | CuSO4.5H2O | Fungicide |
| Baking soda | NaHCO3 | Fire extinguisher |
Solved example 6.8
The pH values of some substances are given in the table. Analyse the table and answer the questions that follow.
| Substance | pH value |
|---|---|
| Vinegar | 4.2 |
| Lime water | 10.5 |
| Milk | 6.4 |
| Water | 7 |
| Tooth paste | 8.7 |
| Blood | 7.36 |
(b) The pH value of pure milk is 6.4. Does the pH value increase or decrease when milk changes to curd?. Justify your answer
(c) Among the substances given in the table,
(i) Which one is strongly alkaline?
(ii) Which one has weak acidic nature?
Solution:
(a) The pH value of blood is given as 7.36. This is greater than 7. So blood is alkaline in nature
(b) The pH value of pure milk is given as 6.4. This is less than 7. So pure milk is acidic. When it changes to curd, the pH value will be come less than 6.4. This is because curd is acidic
(c) i. Substances which have pH greater than 7 are all alkaline. So lime water, tooth paste, and blood are alkaline. Among them, lime water has the greatest difference from 7. So it is the most alkaline in the given table
ii. Substances which have pH less than 7 are all acidic. So vinegar and milk are acidic. Among them, milk has the smallest difference from 7. So it is the weakest acidic nature in the given table
More precisely it can be written as follows:
• Vinegar has pH value 4.2. So [H+] = 10-4.2. That means there are 10-4.2 mols of H+ ions in 1 litre of vinegar
• Milk has pH value 6.4. So [H+] = 10-6.4. That means there are 10-6.4 mols of H+ ions in 1 litre of milk
• 10-6.4 < 10-4.2. So the number of H+ ions is less in Milk. So it is a weaker acid than vinegar.
In the next chapter, we will see compounds of non-metals.
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