(a) Calcium carbide is used for the artificial ripening of fruits. Actually the fruit ripens because of the heat evolved while calcium carbide reacts with moisture. During this reaction calcium hydroxide and acetylene gas is formed. If 200 cm³ of acetylene is formed from a certain mass of calcium carbide, find the volume of oxygen required and carbon dioxide formed during the complete combustion. The combustion reaction can be represented as below:
2C₂H₂_(g)+ 5O₂_(g) → 4CO₂_(g) + 2H₂O_(g)

(b) A gaseous compound of nitrogen and hydrogen contains 12.5% hydrogen by mass. Find the molecular formula of the compound if its relative molecular mass is 37.
[N = 14, H = 1].

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Solution

(a) According to the balanced chemical reaction, for two unit volume of acetylene, five unit volume of oxygen is required.
Volume of oxygen required by 200 cm³ of acetylene = $\frac{5}{2} \times 200 \times 10^{- 3} {dm}^{3} = 500 \times 10^{- 3} {dm}^{3} = 500 {cm}^{3}$
Also, two units of acetylene produce four units of carbon dioxide.
Volume of carbon dioxide produced by 200 cm³ of acetylene = $\frac{4}{2} \times 200 \times 10^{- 3} {dm}^{3} = 400 \times 10^{- 3} {dm}^{3} = 400 {cm}^{3}$

(b)

Element Atomic mass Percentage Relative ratio of atoms Simplest ratio of atoms

H 1 12.5 12.5 $\frac{12.5}{6.25} = 2$

N 14 =(100−12.5) = 87.5 $\frac{87.5}{14} = 6.25$ $\frac{6.25}{6.25} = 1$

Empirical formula of compound is NH₂.
Empirical formula mass = (14 + 2) g = 16 g
Relative molecular mass of the compound is 37.
Molecular formula of the compound = (Empirical formula of the compound)_n
$n = \frac{Molecular formula mass}{Empirical formula mass} = \frac{37}{16} = 2.3 \approx 2$
Molecular formula = (NH₂)₂ = N₂H₄

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Calcium carbide is used for the artificial ripening of fruits. Actually, the fruit ripens because of the heat evolved while calcium carbide reacts with moisture. During the reaction, calcium hydroxide and acetylene gas is formed.

If 200 $c m^{3}$ of acetylene is formed from a certain mass of calcium carbide. Find the volume of oxygen required and carbon dioxide formed during the complete combustion. The combustion reaction can be represented as below:

$2 C_{2} H_{2} (g) + 5 O_{2} (g) \to 4 C O_{2} (g) + 2 H_{2} O (g)$

200 c c

of acetylene is formed form a certain mass of calcium carbide. Find the volume of oxygen required and carbon dioxide formed during its complete combustion. The combustion reaction can be represented as:

2 C_{2} H_{2} (g) + 5 O_{2} (g) \to 4 C O_{2} (g) + 2 H_{2} O (g)

(a) A gas cylinder of capacity of $20 d m^{3}$ is filled with gas X the mass of which is 10 g. When the same cylinder is filled with hydrogen gas at the same temperature and pressure the mass fo the hydrogen is 2 g, hence the relative molecular mass of the gas is :
(i) 5 (ii) 10 (iii) 15 (iv) 20
(b) (i) Calcium carbide is used for the artificial ripening of fruits. Actually the fruit ripens beause fo the heat evolved while calcium carbide reacts with and acetylene gas is formed. If $200 c m^{3}$ of acetylene is formed from a certain mass of calcium carbidem, find the volume of oxygen required and carbon dioxide formed during the complete combustion. The combustion reaction can be represented as below.
$2 C_{2} H_{2} (g) + 5 O_{2} (g) \to 4 C O_{2} (g) + 2 H_{2} O (g)$
(ii) A gaseous compound of nitrogen and hydrogen contains 12.5% hydrogenj by mass. Find the molecular formula of the ocmpound if its relative molecular mass is 37. $[N = 14, H = 1] .$
(c) (i) A gas cylinder contains $24 \times 10^{24}$ moleules of nitrogen gas. If avogadro's number is $6 \times 10^{23}$ and the relative atomic mass of nitrogen is 14, calculate:
(1) Mass of nitrogen gas in th ecylinder
(2) Volume of nitrogen at STP in $d m^{3}$
(ii) Commercial sodium hydroxide wieghing 30 g has some sodium chloride in it. The mixture on dissolving in water and subsequent treatment with excesss silver nitrate solution formed a precipitate weighing 14.3 g. What is the percentage fo sodium chloride in the commercial sample of sodium hydroxide? The equation for the reaction is
$N a C l + A g N O_{3} \to A g C l + N a N O_{3}$
[Relative molecular mass of $N a C l = 58; A g C l = 143$ ]
(iii) A certain Gas 'X' occupies a volume of $100 c m^{3}$
at S.T.P. and weighs 0.5 g. Find its relative moleular mass.

Q. Write balanced equations for the following reactions.
(a) Combustion of

C_{2} H_{10}

in a limited supply of oxygen to form carbon monoxide and water.
(b)The reaction of calcium carbide with water to form acetylene.
(c)The precipitation of calcium cyanamide from calcium carbide and nitrogen.
(d)Formation of hydrogen cyanide from methane and ammonia.

Q. Calcium carbide is also used for ripening fruit artificially in some countries. Calcium carbide reacts with water to produce acetylene, which acts as an artificial ripening agent. Industrial-grade calcium carbide may contain traces of arsenic and phosphorus which makes it a human health concern Consider the following statements about acetylene
(a) It is used in welding industry
(b) It is a raw material for preparing plastics
(c) It is easily obtained by mixing silicon carbide and water
of these statements

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Element	Atomic mass	Percentage	Relative ratio of atoms	Simplest ratio of atoms
H	1	12.5	12.5	$\frac{12.5}{6.25} = 2$
N	14	=(100−12.5) = 87.5	$\frac{87.5}{14} = 6.25$	$\frac{6.25}{6.25} = 1$