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Stoichiometric Calculations

Cu+HNO3⟶ Cu2+...

Question

$C u + H N O_{3} ⟶ C u^{2 +} + N O_{2} (g) + H_{2} O$

$Z n + H^{+} + N O_{3}^{-} ⟶ N H_{4}^{+} + Z n^{2 +} + H_{2} O$

The above reaction takes place when $1.5$ g of brass containing $C u$ and $Z n$ reacts with $3 M H N O_{3}$ solution. The liberated $N O_{2}$ (g) was found to be $1.04$ litres at $25^{\circ} C$ and one atm pressure. Calculate the $%$ composition of brass.

A

90 %

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B

10 %

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C

80 %

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D

20 %

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Solution

The correct option is A $90 %$
The redox changes are as follows:

For $N^{5 +} + e^{-} ⟶ N^{4 +}$

$C u^{0} ⟶ C u^{2 +} + 2 e^{-}$

Equivalents of $C u =$ Equivalents. of $N O_{2} =$ Moles of $N O_{2} = \frac{P V}{R T}$
$\frac{W}{\frac{63.6}{2}} = \frac{1 \times 1.04}{0.0821 \times 298}$
$∴ W_{C u} = 1.35$ g
$∴ W_{Z n} = 1.5 - 1.35 = 0.15$ g ........ Mass of brass = 1.5 g
$% Z n = \frac{0.15}{1.5} \times 100 = 10 %$
$% C u = \frac{1.35}{1.5} \times 100 = 90 %$

Hence, correct answer is $(A)$ .

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Similar questions

C u + H N O_{3} ⟶ C u^{2 +} + N O_{2} (g) + H_{2} O

Z n + H^{+} + N O_{3}^{-} ⟶ N H_{4}^{+} + Z n^{2 +} + H_{2} O

The above reaction takes place when

1.5

g of brass containing

C u

Z n

3 M H N O_{3}

solution. The liberated

N O_{2}

(g) was found to be

1.04

25^{\circ} C

and one atm pressure. How many mL of

3 M

H N O_{3}

will be required for completely reacting

1

1.5

g of brass containing

C u

Z n

3.0 M

H N O_{3}

solution. The following reactions take place:

C u + H N O_{3} \to C u^{2 +} + N O_{2} (g) + H_{2} O

Z n + H^{⨁} + N O_{3}^{⊝} \to N H_{4}^{⨁} + Z n^{2 +} + H_{2} O

N O_{2} (g)

was found to be

1.04

25^{o} C

1

atm.
a. Calculate the percentage composition of brass.
b. How many mL of

3.0 M

H N O_{3}

will be required for complete reaction with

1.0

2

g of brass containing Cu and Zn only reacts with

3

H N O_{3}

solution. Following are the reactions taking place:

C u (s) + H N O_{3} (a q) \to C u^{2 +} (a q) + N O_{2} (g) + H_{2} O (l)

Z n (s) + H^{+} (a q) + N O_{3}^{-} (a q) \to N H_{4}^{+} (a q) + Z n^{2 +} (a q) + H_{2} O (l)

N O_{2} (g)

was found to be

1.04

25^{o}

1

[C u = 63.5, Z n = 65.4]

The percentage by mass of Cu in brass was?

Q. The composition of brass is

C u = 60 % - 80 %, Z n = 20 % - 40 %

.

For cell reaction, $Z n + C u^{2 +} \to Z n^{2 +} + C u,$ cell representation is

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