Experiment 7 - Determination of Purity of an Impure Soda Ash

sodium carbonate, Na2CO3

Soda ash is a common name for the inorganic compound, __________________ with the chemical formula ______________

106 g/mol

Its anhydrous form has the molar mass of ______________

white solid; hygroscopic in nature

At standard temperature and pressure, soda ash is known to exist as a ______________ that is ________________

cleaning agent

Soda ash is widely used as a _______________ for several domestic purposes such as the washing of clothes

dry soap powders

It is also known to be an important component of several _______________

baking powder; carbon dioxide gas

It is also a component of ______________ as it releases _______________ when heated which makes the baked products rise

silica flux

Soda ash functions as a _____________, working to reduce the melting point of the mixture without any need for special materials

slightly water-soluble; calcium carbonate

The resulting “soda glass” is _______________, so the melt mixture is added with some _______________ to make the glass insoluble

sodium carbonate, calcium carbonate, and silica sand

The melting of such blends of _____________, _____________, and _____________ (also known as silicon dioxide) creates bottle and window glass (soda-lime glass)

water-soluble, slightly alkaline solution

Soda ash is ______________ and is known to form _____________ when dissolved in water. This property is what is made used for this method.

total alkalinity of the soda ash; methyl orange

Titrating with standard acid, usually HCl, makes it possible to determine the _____________. The indicator to be used for this analysis is _____________ indicator

yellow; light orange

At the start of the titration, this indicator appears ____________. The endpoint is signaled when the indicator turned ____________. Do not allow for the titration to go to very deep orange.

carbonate and bicarbonate

Neutralization of soda ash has 2 end point because there 2 weak bases involved:

Na2CO3 + HCl ↔ NaHCO3 + NaCl
NaHCO3 + HCl ↔ NaCl + H2O + CO2

The reactions involved are:

second end point

The _____________ is always used for analysis because the change in pH is greater than that at first.

eliminate carbonic acid and carbon dioxide

An even sharper end point can be achieved by boiling the solution briefly to ________________, the reaction products. The sample is titrated to the first appearance of the acid color of the indicator.

dissolved carbon dioxide; carbonic acid; unreacted hydrogen carbonate

The solution contains a large amount of ____________, and small amounts of ______________, and ______________

eliminating the carbonic acid; residual hydrogen carbonate ion

Boiling effectively destroys this buffer by ______________. The solution then becomes alkaline again due to the ________________

decrease in pH

The titration is completed after the solution has cooled, resulting in a substantially larger ______________during the final additions of acid.

Na2CO3 + 2HCl ↔ 2 NaCl + H2O + CO2

mass % Na2CO3 in soda ash is:

1 mol Na2CO3/ 2 mol HCl

stoichiometric ratio between Na2CO3 and HCl