Acid-Base: Water of Crystallisation in Sodium Carbonate

Identify a primary standard that could have been used to standardise the hydrochloric acid solution for this analysis

Anhydrous sodium carbonate / Na₂CO₃

Describe how the 250cm³ solution of washing soda was prepared starting with 3.46g of washing soda measured out accurately on a weighing boat

washing soda transferred to a beaker and dissolved in deionised water / washing soda rinsed into beaker with deionised water //

use funnel //

transfer solution to volumetric flask //

rinse beaker and glass rod into volumetric flask //

add deionised water to 250cm³ with bottom of meniscus on calibration mark //

stopper and invert several times

Name a suitable indicator for this titration

Methyl Orange

Justify your choice of indicator

Strong acid weak base titration / end point below pH 7 / colour change coincides with end point

Using this indicator what colour change was observed in the conical flask at the end point?

Orange → red

Explain the term standardised

Concentration is known by another titration

State one precaution that should have been taken as the end point of the titration was approached. Explain how this precaution would have contributed to the accuracy of the titration result

Add drop by drop / wash down inner sides of conical flask / swirl flask contents

Add dropwise so that end point will be precisely detected / one drop of solution would change colour near end point /

Wash sides so that all reagent is in the reaction mixture /

Swirl to ensure thorough mixing of reactants