BEETROOT AS AN INDICATOR

GROUP MEMBERS :Asela

ChamaliDhammika

DunhindaNuwan

OshadiPulasthi

SamindaSudeera

R13

CONTENTWhat is a pH indicator and its PH range….Preparation of the Beetroot indicator and identification of its pH range.Applications of acid-base titrations.Discussion.Conclusion.References.

What is a pH indicator?

Its pH range

A pH indicator (An acid-base indicator ) is either a weak acid or weak base that exhibits a color change as the concentration of hydrogen (H+) or hydroxide (OH-) ions changes in an aqueous solution.

Examples:

Thymol Blue, Phenolphthalein, Methyl Orange, Bromocresol Green, Bromophenol Blue and etc;

An Indicator’s colour change occurs over a range of hydrogen ion concentrations. This range is termed the colour change interval. It is expressed as the Indicator’s pH range.

Reference: Anne Marie Helmenstine, Ph.D., (2011). Acid-Base Indicators. Available: http://chemistry.about.com.

ABILITY OF USING BEETROOT AS AN

INDICATOR Beetroot Red, is a red glycosidic food dye obtained from its

aglycone, obtained by hydrolyzing the glucose molecule, Betanin. The colour of Betanin depends on pH. It is bright bluish-red,

becoming blue-violet as the pH increases. Once the pH reaches alkaline levels Betanin degrades by hydrolysis, resulting in a yellow-brown colour.

Moira Sheehan, Carol Chapman. (2003). Make your own indicator. Available: http://www.pearsonschoolsandfecolleges.co.uk.

ProcedurePreparation of the Indicator:1. 300.0 g of chopped Beetroot was added to 50.00 cm3 of boiling water in a beaker and was boiled continuously for 45 minutes.

2. After allowing the beaker to cool for 15 minutes, boiled Beetroot were squashed and the liquid was filtered.

3. The residues were squeezed once again and the liquid was evaporated to get a highly concentrated portion of the indicator.

Detection of the pH range: A series of solutions in the range pH 1.0 -13.0 was prepared by using 1.0 M NaOH and 1.0 M HCl acid.

When the indicator was added the to the prepared series of solutions the colour was changed from red to yellow in between pH 10.0 -12.0.

In order to get the exact pH range, another series of solutions was prepared by diluting the pH 10-12 solution range into 10.10, 10.20,……..,12.00 and 0.05 ml of the indicator was added to each solution.

A colour change was observed in the pH range 10.80-11.20, which is the working pH range of Beetroot.

Applications of titrations

ii) Strong Acid – Weak Base Titration

Colour Change: Red Yellow

A colour change was not observed.

i) Strong Acid – Strong Base Titration

iii) Weak acid – Strong Base Titrations

With 0.1M NaOH

With 0.001M NaOH

.

A colour change was not observed.

Colour Change: Red Yellow

Discussion A colour change was observed only in strong acid – strong base titration and weak acid-strong base titration (with 0.10 M NaOH), as

the working pH range of the indicator falls to the vertical portion of those reactions.

But when the base is diluted, a colour change was not observed, as the pH range of the Beetroot indicator doesn’t fall within the rapid pH change of the reaction.

Although a colour change was observed in above two titrations, the most applicable titration is weak acid-strong base titration, because the vertical portion of the reaction shifts upwards.

ConclusionWorking pH range of BEETROOT is pH 10.80 - 11.20

(Above result was obtained on 28th of March 2012 at 11.50 a.m. at B2 102 laboratory under the room temperature 270 C.)BEETROOT is a good indicator.But it is not a very suitable indicator for laboratory

experiments as it should be prepared at the time the experiment is done. The prepared indicator also cannot be kept for a long time as it is a biological sample.

Acidic Basic

RED YELLOW

REFERENCES Anne Marie Helmenstine, Ph.D., (2011). Acid-Base Indicators.

Available: http://chemistry.about.com. Last accessed 5th April 2012. Australian Broadcasting Corporation(ABC). (2007). Teaching Science -

Cool Chemistry(PH Indicator). Available: http://www.abc.net.au. Last accessed 4th April 2012.

Lange's Handbook of Chemistry, 8th Edition, Handbook Publishers Inc; 1952.

Moira Sheehan, Carol Chapman. (2003). Make your own indicator. Available: http://www.pearsonschoolsandfecolleges.co.uk. Last accessed 2nd April 2012.

Volumetric Analysis, Kolthoff & Stenge, Interscience Publishers, Inc; New York, 1942 and 1947.

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