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A balanced chemical equation is in accordance with
- Avogadro's law
- Law of multiple proportion
- Law of conservation of mass
- Law of gaseous volumes
Answer
- Law of conservation of mass
Explanation - In a balanced chemical equation, the number of atoms of each element is balanced on the left and right side of the equation and thus the mass is considered to be balanced in the process.
Hence it is in accordance with the Law of conservation of mass
Which of the following is not a balanced equation?
- Ca(OH) 2 + CO 2 → CaCO 3 + H 2 O
- Fe + CuSO 4 → FeSO 4 + Cu
- KClO 4 → KCl + 2O 2
- Cu+ 2HNO 3 → Cu(NO 3 ) 2 + 2NO 2 + H 2 O
Answer
-
Cu+ 2HNO
3
→ Cu(NO
3
)
2
+ 2NO
2
+ H
2
O
Explanation - The number of atoms of each element on the reactants and products side of the equation are equal.
Write the balanced chemical equations for the following reactions and identify the type of reaction in each case.
(a) Thermite reaction, iron (III) oxide reacts with aluminium and gives molten iron and aluminium oxide.
(b) Magnesium ribbon is burnt in an atmosphere of nitrogen gas to form solid magnesium nitride.
(c) Chlorine gas is passed in an aqueous potassium iodide solution to form potassium chloride solution and solid iodine.
(d) Ethanol is burnt in air to form carbon dioxide, water and releases heat
(e) Nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773 K to form ammonia gas.
(f) Sodium hydroxide solution is treated with acetic acid to form sodium acetate and water.
Answer
-
Fe
2
O
3
(s)
+ 2Al(s) → Al
2
O
3
(s)
+ 2Fe(l) + Heat
Iron (III) Oxide Aluminium Aluminium Oxide Molten Iron
This is a displacement reaction ; Al is more reactive than Fe and displaces Fe from Fe2O3
THERMITE REACTION - IRON OXIDE REACTS WITH ALUMINIUM
-
3Mg(s) + N
2
(g) → Mg
3
N
2
(s)
Magnesium Nitrogen BURNING Magnesium Nitride
This is a combination reaction ; Mg burns and reacts with N 2 to form a single product Mg 3 N 2
MAGNESIUM NITROGEN MAGNESIUM NITRIDE
-
Cl
2
(g)
+ 2KI(aq) → 2KCl(aq) + I
2
(s)
Chlorine Potassium Iodide Potassium Chloride Iodine
This is a displacement reaction ; Chlorine is more reactive than Iodine and displaces Iodine from KI and this form KCl and solid I2
-
C
2
H
5
OH(l) + 3O
2
(g)
→ 2CO
2
(g) + 3H
2
O(l) + Heat
Ethanol Oxygen Carbon Dioxide Water
It is a Combustion reaction , which is a type of Oxidation reaction
-
N
2
(g) + 3H
2
(g)
→ 2NH
3
(g)
Nitrogen Hydrogen 773K Ammonia
This is a combination reaction . N 2 and H 2 react to form one product NH 3
-
NaOH + CH
3
COOH → CH
3
COONa + H
2
O
Sodium Hydroxide Acetic acid Sodium acetate Water
This is a double displacement reaction as the ions of both the reactants get exchanged to form the products.
Grapes hanging on the plant do not ferment but after being plucked from the plant can be fermented. Under what conditions do these grapes ferment? Is it a chemical or a physical change?
Answer
- Fermentation takes place when microbes utilise the sugars and convert it into alcohol in the absence of air
- When hanging on the plant , there is an abundance of air around . The immune system of the plant also prevents the action of microbes on the grapes.
- After plucking , grapes can be stored in anaerobic (free of air) conditions to undergo fermentation
- This is a chemical change , that follows the process:
During the reaction of some metals with dilute hydrochloric acid, following observations were made.
- Silver metal does not show any change.
- The temperature of the reaction mixture rises when aluminium (Al) is added.
- The reaction of sodium metal is found to be highly explosive.
- Some bubbles of a gas are seen when lead (Pb) is reacted with the acid. Explain these observations giving suitable reasons.
Answer
-
According to the reactivity series,
Silver is less reactive than Hydrogen
and cannot displace Hydrogen from the dilute Hydrochloric acid
Ag + dil HCl → No reaction
SILVER DOES NOT UNDERGO REACTION WITH dil HCl
- Reaction of Aluminium and Hydrochloric acid is an exothermic reaction and thus there is an increase in the temperature.
-
In the presence of moisture (H
2
O), Sodium forms Hydrogen gas;
Na + H 2 O → NaOH + H 2
It thus catches fire as Hydrogen is highly inflammable and the reaction is exothermic.
NOTE : SHOW THE FIRE IN METAL, AND BUBBLES IN WATER
-
The bubbles are due to the evolution of gas. Here Hydrogen gas is evolved following the reaction;
Pb(s) + 2 dil HCl → PbCl 2 (s) + H 2 (g)
After a while, the surface of Lead (Pb) gets coated with Lead Chloride ( PbCl 2 ) and the reaction becomes slow.
LEAD IN HCl
A silver article generally turns black when kept in the open for a few days. The article when rubbed with toothpaste again starts shining.
(a) Why do silver articles turn black when kept in the open for a few days? Name the phenomenon involved.
(b) Name the black substance formed and give its chemical formula.
Answer
-
Reaction of Silver with Hydrogen Sulphide
in the atmosphere results in Silver articles turning black.
The phenomenon is called Corrosion .
-
The black coating on silver articles is
Silver Sulphide
.
CORROSION OF SILVER METAL
