# 6. TO FIND THE EQUIVALENT WEIGHT OF THE GIVEN METAL VOLUMETRICALLY.

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## THEORY:

Suppose, the given metal is magnesium. A definite weight of the metal is taken in the chemical balance. It is allowed to react with a known excess volume of fairly strong H₂SO4 which has been already standardised. The metal consumes part of the acid. The excess unused acid remaining after reaction is calculated by back titration against the standard alkali supplied. Then, by knowing the volume of the acid used by the metal, the equivalent wt. of the metal can be calculated.

We have,

Equivalent wt of the acid = Eq. wt. of the metal

or 1000 ml of (N) acid = Eq wt of the metal

1) Burette

2) Pipette

4) Burette stand

5) Clamps

## CHEMICAL:

1) Methyl orange or phenolphthalein

## PROCEDURE :

i) The given piece of magnesium metal is cleaned by using a sandpaper, and is accurately weighed in the chemical balance.

ii) Introduce the metal in a 250 ml measuring flask, and add a known volume of fairly strong H₂SO4 (say 25 ml). which has already been standardised.

iii) After the completion of reaction, dilute the acid with distilled water, and make up to the volume. Shake well.

iv) Rinse a clean burette with this diluted acid, and fill it up.

v) Titrate this diluted acid against the standard alkali supplied.

## RESULTS:

Wt. of magnesium metal taken = 0.18 gm

Vol. of strong H₂SO4 taken = 25 ml of 2N H₂SO4

Solution taken in the burette = diluted acid

Alkali taken for each titration = 10 ml

Indicator used = methyl orange

End point = from yellow to light pink

Normality of standard alkali = N / 10 (f = 1.148)

## CALCULATIONS :

Volume of strong acid taken = 25 ml of (2 N) H2SO4

= 50 ml of (N) H₂SO4.

From titration.

8.2 ml of diluted acid = 10 ml of N / 10 (f = 1.148) alkali

=(10 x 1 x 1.148) / 10  ml (N) alkali

= 1.148 ml (N) alkali.

250 ml of diluted acid= 1.148 × 250 / 8.2  ml (N) alkali

= 35.0 ml (N) alkali

= 35.0 ml (N) H₂SO4

= Vol. of acid left.

Vol. of acid used by 0.18 gm metal

= (50 – 35) ml of (N) H₂SO4

= 15 ml of (N) H₂SO4

Hence, 15 ml of (N) H₂SO4 = 0.18 gm Mg

1000 ml of (N) H₂SO4 =0.18 × 1000 / 15   gm Mg = 12 gm

Equivalent wt. of Mg = 12.