Estimation of Chlorine in Household Bleach

Estimation of Chlorine in Household Bleach

In this investigation, I am looking to determine the amount of

chlorine present in household bleach. However, in order to do this I

would have to calculate the mass represented by chlorine in the mass

of the household bleach. After doing that, I would then have to

represent this as a percentage.

In order to calculate the mass represented by the chlorine in the mass

of the household bleach, I would have to titrate this solution, along

with an excess of potassium iodide and ethanoic acid against sodium

thiosulphate from the burette using starch solution as an indicator.

The reason for this choice of indicator is that iodine is turned blue

black by the starch solution, and this therefore helps to indicate any

colour change that occurs.

I began my investigation by measuring out 10mls of household bleach

using a measuring cylinder. I poured this into a volumetric flask, and

used distilled water to ensure that all 10mls of the bleach were in

the volumetric flask and not in the measuring cylinder. This was then

topped up to 250ml using distilled water in the volumetric flask. I

had to make sure that the bleach solution is mixed completely and

shook the flask from top to bottom. This results in air bubbles

forming along with some froth, meaning I had to leave the flask to

settle.

While I was leaving the bleach to settle, I must transfer 30 cm3 of

sodium thiosulphate from its beaker to the burette. Before doing that,

I had washed the burette with a little bit of sodium thiosulphate,

which would allow the solution to run smoothly into the tip of the

burette. Having done that, I would need to see where the bottom of the

meniscus lies, i.e. V1, unless it lies on zero, and then record this

value. Also a funnel should be used to ensure that all 30 cm3 of

sodium thiosulphate is in the burette.

Back to the bleach, where I would have to transfer 25mls of the bleach