Experiment: Gravimetric Estimation of Ba2+ in BaCl2 Solution

Theory:

Ba²⁺ ions present in the given solution are precipitated as Barium Chromate (BaCrO₄) by adding a slight excess of K₂CrO₄. The resulting BaCrO₄ precipitates can be filtered, washed, dried, and then weighed.

Equipment:

• Analytical balance
• Oven
• Funnel
• Wash bottle
• Whatman filter paper No. 42
• Glass rod
• Beakers
• Desiccators
• Pipette
• Burner
• Matches
• Safety goggles

Chemicals:

• Distilled water
• Potassium chromate solution
• Barium chloride solution
• Conc. HCl

Equation:

BaCl₂(aq) + K₂CrO₄ → BaCrO₄(s) + 2KCl(aq)

Procedure:

1. Take 20 ml of the given solution of barium ions in a beaker and add 1 ml of conc. HCl and heat to boiling.
2. Then add potassium chromate solution dropwise with constant stirring till the precipitation is complete. Boil the mixture for about three minutes and allow the precipitate to settle down.
3. Test the supernatant liquid with a few drops of K₂CrO₄ in order to make sure of the complete precipitation. If no precipitate appears it means precipitation is complete.
4. Now filter precipitate through a pre-weighed Whatman filter paper No. 42.
5. Wash the precipitate with hot water until the precipitate is free from Cl^– ions.
6. Now heat the filter paper containing precipitate in the drying oven for about 30 minutes. Cool it in a desiccator and weigh it. Repeat the process of heating and cooling till to a constant weight.

Observation and Supposed Calculations:

The volume of solution taken = 20.0 ml Weight of filter paper = 1.0g Weight of filter paper + ppt. Weight of ppt. = 1.8 – 1.0 = 0.8 g The molecular weight of BaCrO₄ = 253.4 g Weight of Ba²⁺ ion = 137.4 g Now, 253.4 g of BaCrO₄ is obtained from Ba²⁺ ion = 137.4 g 1 g of BaCrO₄ is obtained from Ba²⁺ ion = 137.4/253.4 g 100 g of BaCrO₄ is obtained from Ba²⁺ ion = 137.4/253.4 x 100 = 0.433 g 20 mL of solution contains Ba²⁺ ion = 0.433 g 1000 mL of solution contains Ba²⁺ ion = 54.2/20 x 1000 = 21.56 g/L

Result:

The given solution contains 21.56 g of Ba²⁺ ion/L.

PRECAUTIONS:

1. Wash the precipitates with hot water.
2. Place a reasonable amount of drying agent in the desiccator.
3. The process of heating and cooling should be repeated until the weight of the ppt becomes constant.

Experiment Glossary

Ba: A chemical symbol for the element Barium.

Ba²⁺: A chemical notation that represents the Barium ion with a positive charge of 2.

BaCrO4: A chemical formula for Barium Chromate, which is the precipitate formed during the experiment.

Gravimetric analysis: A quantitative method used in analytical chemistry to determine the amount of an analyte (substance being analyzed) based on its mass.

K2CrO4: A chemical formula for Potassium Chromate, which is used as a reagent to precipitate Barium ions.

Concentrated HCl: A solution of Hydrochloric acid that has a higher concentration than usual.

Beaker: A cylindrical container used in the laboratory for holding and mixing liquids.

Analytical balance: A sensitive and precise weighing instrument used for measuring mass.

Whatman filter paper No. 42: A type of filter paper that is commonly used in laboratory experiments to separate solids from liquids.

Oven: An appliance used to heat materials at high temperatures, usually for drying.

Desiccator: A container used for drying or storing substances in a low-humidity environment.

Pipette: A laboratory tool used to measure and transfer small volumes of liquids.

Burner: A device used for heating, such as a Bunsen burner.

Safety goggles: Protective eyewear worn to protect the eyes from chemical splashes, fumes, and other hazards.

Precipitation: A process in which a solid substance separates from a liquid solution.

Molecular weight: The sum of the atomic weights of all atoms in a molecule.

Volume: The amount of space occupied by a substance.

Weight: A measure of the force of gravity on an object, often used interchangeably with mass in everyday language.

Constant weight: The state at which a sample no longer loses weight upon repeated heating and cooling cycles, indicating that all moisture has been removed.

Precautions: Measures taken to prevent accidents, injury, or damage during an experiment.