Question

Topic - Language of Chemistry
Class - 8
$\tt\large{\pink{\underline{Question:}}}$
1. Explain Criss-cross method. Give at least 5
examples.
2. Explain Hit and Trial method.
Balence these chemical equations.
$\sf{1. \: KCIO_3\rightarrow \: KCI+O_2\uparrow}$
$\sf{2. \: MnO_2+HCL\rightarrow \: MnCl_2+Cl_2\uparrow \: +H_2O}$
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Answer 1

Solution :

The two equations to be balanced -

KClO3 >> KCl + O2↑

MnO2 + HCL >> MnCl2 + Cl2 + H2O

For the first one, pottasium chlorate on heating decomposes to give pottasium chloride and oxygen is evolved as effervescence .

It is already balanced and the coefficients for all are 1 .

For the second one, manganese(4) oxide reacts with hydrogen chloride to produce a manganese salt(manganese chloride) , chlorine and water as a by product.

There are two oxygen atoms on rhe LHS so it will be 2(H2O) in the RHS

There are four hydrogen atoms on the RHS ( in 2H2O) so it should be 4HCL on the LHS

Now it's balanced .

MnO2 + 4 HCL >> MnCl2 + Cl2 + 2 H2O

Criss Cross Method of balancing is mostly used in balancing reactions involving ionic radicals and is used to determine the charge on any element

Let us take an example of sodium reacting with air .

Na¹ + O^2-

Now , the charge on Na is +1 and that on Oxygen is 2- .

The net charge coefficient of Na goes to O and that of Oxygen goes to Na ( i.e this occurs in a criss cross fashion. This is from where the name of the method arises .)

The final compound formed becomes Na2O

Similarly, the reaction between C^4+ + O^2- given C2O4 ( Which is basically 2 × a CO2 molecule )

Another example can be Ca^2+ + P^3- gives Ca3P2

Na^1+ + Cl^1- >> NaCl

K^1+ + So4^2- >> K2So4

In the hit and trial method of balancing , basically you have to take one element and try to balance it first. Following it , change the rest. This element is usually the one with least occurence frequency.

For examples to this, see how I balanced the manganese oxide reaction.

If you still have any queries, feel free to reach me in the comments or messáge me.

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Answer 2

Answer:

Explanation

given :

• Explain Criss-cross method. Give at least 5
• examples.
• 2. Explain Hit and Trial method.
• Balence these chemical equations.
• $\sf{1. \: KCIO_3\rightarrow \: KCI+O_2\uparrow}$
• $\sf{2. \: MnO_2+HCL\rightarrow \: MnCl_2+Cl_2\uparrow \: +H_2O}$

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to find :

• Explain Hit and Trial method.

Balence these chemical equations

solution :

• 1. KCIO3 → KC1+302 There are 6 0 on the right and 3 on the left

• so multiply the KC103 by 2

• 2KC103 KC1+302

• now there are 6 O on both sides Balance the K and Cl by multiplying KCl on

• the right by 2

• 2K CIO3 → 2KC1+302

• 2 ans Here HCl is oxidized to Cl2 and Mno2 is reduced to MnCl2.

• The reaction in which oxygen is either gained or hydrogen is lost by a substance is called oxidation reaction.

• The reaction in which hydrogen is gained or oxygen is lost by a substance is called reduction reaction.