Acid neutralizing capacity of antacid tablet Flashcards
what was the objective of this experiment
find the neutralizing capacity of antacid tablet
what methods were used in this experiment
back titration and standardization
what is back titration
a titration method where the concentration of an unknown compound is determined by reacting with a known amount of excess reagent
what is standardization
the process of determining the exact concentration (molarity) of a solution
what method was used for part a
back titration
why was the method used for part a
- antacid tablets dissolve faster in acid than in water as they react as they dissolve
- carbon dioxide in the air will dissolve in water and act as an acid reacting right away to neutralize any basic solution
what were two indicators used in this experiment
- phenolphthalein
- bromocresol green
what are the colour changes for phenolphthalein
1, colourless in acidic or near-neutral conditions
2, pinky-fuchsia colour in basic/alkaline conditions
what are the colour changes for bromocresol green
1, yellow in acidic solution
- blue in basic solution
the stomach contains an acid similar to what acid solution
0.1 M HCl
what acid solution was used to dissolve the antacid tablet
1 M HCl
what does ANC stand for
acid neutralizing capacity
what is the equation for decomposition of carbonic acid
H2CO3 (aq) —> H20 (l) + Co2 (g)
what changes when preforming a dilution
the volume
what does NOT change when preforming a dilution
amount of solute is constant = moles are unchanging
what does one add first to a volumetric flask during a dilution
add the solute first than dilute to the mark with the RO wate r
steps to charge a burette
- sheet the burette with water at least twice
- sheet at least twice with the solution
- make sure to run both RO water and solution through stopcock
- fill the burette with designated solution and begin the titration
why is standardization of solutions important
to know the exact concentration of the titrant you are using for your results to be accurate and repeatable by other analysts
why was the stock HCl diluted before titrating with NaOH
to ensure the reactants are within suitable ranges for more precise measurements
equivalence point
the moles of titrant are stoichiometrically equivalent to the moles of analyte
end point
point the indicator changes colour
titration
the slow addition of one solution of a known concentration to solution of unknown concentration until the reaction reaches neutralization
analyte
substance being analyzed (what is in the flask)
titrant
the substance being used to analyze the analyte (what is in the burette)
why could the titrated solution in the Erlenmeyer flasks be poured down the sink
because it was neutralized
is an antacid a weak acid or base
base
what do most antacids contain
some kind of carbonate
why do antacids contain carbonates
they react with strong acids to make carbonic acid which is decomposed to water and carbon dioxide
can we assume a bigger antacid tablet is more effective? or or why not?
NOT
- because tablets often contain binders and flavoring agents along with the weak base
what test will give an antacid tablets neutralizing capacity
determining the exact number of moles of base in a tablet by reacting it with acid
how was back titration used for determining ANC
we added an antacid tablet to a known, excess quantity of acid and was then the remaining acid was titrated with a strong base
what formula is used for dilution calculations
c1v1 = c2v2
what is the general formula for an acid base reaction
acid + base —> salt + water
why was a neutralizing reaction needed for this experiment
to determine how much acid remains in the beaker after reacting with an antacid tablet
what is part A of this experiment
ANC of antacid tablet
what is part B of this experiment
standardization of stock HCl solution
what is used to determine when an a solution has been neutralized
an indicator
why do acid-base indicators work well for standardizations
because techy exist in two different forms each being a different colour (acid vs base solutions)
when is an indicator in acidic form
at low PH values
when is indicator in basic form
at high PH values
does the indicator lose or gain a proton at high PH
loses a proton to become basic
what indicator was used in part A
bromocresol green
what indicator was used in part B
phenolphthalein
describe the behavior of phenolphthalein
loses a molecule of water at the same time as it loses a proton
what PH range does phenolphthalein have
8 - 10
do you want the end point far from the equivalence point
NO - want it CLOSE
safety notes of HCl
- causes severe burns
safety notes of NaOH
- cause severe burns
is NaOH a strong or weak base
strong base
how much stock HCl and at what concentration was initially transferred to a beaker at the start of the experiment
about 70 ml of 1 M HCl
how much and what concentration of NaOH was transferred to a beaker at the start of the experiment
about 75 ml of 0.1 M NaOH
how much of the 1 M HCl was pipetted to a new beaker (PART A)
25 ml
what was placed in the 25 ml HCl solution (PART A)
a crushed antacid tablet
what was done to the HCl and antacid tablet solution after the reaction was complete (PART A)
10 ml of it was pipetted into a clean 100 ml volumetric flask
what was done with the 10 ml solution in the volumetric flaks (PART A)
diluted to the mark with RO water and inverted 20 times to ensure fully mixed
what was added to an Erlenmeyer flask before titration began (PART A)
- 25 ml of the diluted antacid-HCl solution
- 25 ml of RO water
- 4 to 6 drops bromocresol green
when was the titration for part A deemed neutralized
when the bromocresol green turned from yellow to blue
what was a clue of an intermediate colour of the titration for part A
a teal colour
how times was the titration done for PART A
three times
what was the first steps in Part B of the experiment
1, transferring 35 ml of 1 M stock HCl into a clean beaker
2, transferring 100 ml of 0.1 M NaOH into a beaker
what was added to a volumetric flask in (PART B
10 ml of the 1 M HCl and diluting to the mark with RO water before inverting 20 times
what was added to an erenmeyer flaks before titrating in (PART B
- 25 ml of the diluted HCl
- 3 to 5 drops phenolphthalein
what was the analyte of PART B
the 25 ml of diluted HCL with the phenolphthalein
what was the titrant of PART B
0.1 M NaOH
what was the titrant of PART A
0.1 M NaOH
what was the analyte of PART A
25 ml of the diluted antacid - HCl
how many times was the titration done in PART B
three times
how were the solutions in the Erlenmeyer flasks disposed of
down the sink with lots of water
how were excess HCl and antacid-HCl disposed of
down the sink after diluting to 0.1 M and discarded down the sink
how to calculate the molar concentration of the dilute antacid HCl
- calculate the moles of HCl from the volume of NaOH
( V NaOH x mol NaOH/ V NaOH x 1 mol HCl / 1 mol NaOH) - calculate the molar concentration of dilute HCl: mol HCl / volume HCl
how to calculate the molar concentration of the ORIGINAL antacid HCl
- calculate the moles of HCl from the volume of NaOH
( V NaOH x mol NaOH/ V NaOH x 1 mol HCl / 1 mol NaOH) - calculate the molar concentration of dilute HCl:
V1C1 = V2C2
(volume antacid HCl) (Moles Original HCl) = (0.1L Volume HCl diluted) (moles HCl dilute)
how to find moles of H+ BEFORE neutralized by antacid tablet
N = CV
N = moles of H+
C = ave concentration of HCL stock solution
V = volume of HCl (25 ml)
how to find the moles of H+ AFTER neutralized by antacid tablet
N = CV
N = moles of H+
C = ave concentration of HCl antacid tablet
V = volume of HCl (25 ml)
how to find the ANC of one tablet
moles H+ BEFORE - moles H+ AFTER
