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Chemistry 2000 lab exam > Acid neutralizing capacity of antacid tablet > Flashcards

Acid neutralizing capacity of antacid tablet Flashcards

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1
Q

what was the objective of this experiment

A

find the neutralizing capacity of antacid tablet

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2
Q

what methods were used in this experiment

A

back titration and standardization

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3
Q

what is back titration

A

a titration method where the concentration of an unknown compound is determined by reacting with a known amount of excess reagent

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4
Q

what is standardization

A

the process of determining the exact concentration (molarity) of a solution

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5
Q

what method was used for part a

A

back titration

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6
Q

why was the method used for part a

A
  1. antacid tablets dissolve faster in acid than in water as they react as they dissolve
  2. carbon dioxide in the air will dissolve in water and act as an acid reacting right away to neutralize any basic solution
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7
Q

what were two indicators used in this experiment

A
  1. phenolphthalein
  2. bromocresol green
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8
Q

what are the colour changes for phenolphthalein

A

1, colourless in acidic or near-neutral conditions

2, pinky-fuchsia colour in basic/alkaline conditions

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9
Q

what are the colour changes for bromocresol green

A

1, yellow in acidic solution

  1. blue in basic solution
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10
Q

the stomach contains an acid similar to what acid solution

A

0.1 M HCl

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11
Q

what acid solution was used to dissolve the antacid tablet

A

1 M HCl

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12
Q

what does ANC stand for

A

acid neutralizing capacity

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13
Q

what is the equation for decomposition of carbonic acid

A

H2CO3 (aq) —> H20 (l) + Co2 (g)

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14
Q

what changes when preforming a dilution

A

the volume

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15
Q

what does NOT change when preforming a dilution

A

amount of solute is constant = moles are unchanging

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16
Q

what does one add first to a volumetric flask during a dilution

A

add the solute first than dilute to the mark with the RO wate r

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17
Q

steps to charge a burette

A
  1. sheet the burette with water at least twice
  2. sheet at least twice with the solution
  3. make sure to run both RO water and solution through stopcock
  4. fill the burette with designated solution and begin the titration
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18
Q

why is standardization of solutions important

A

to know the exact concentration of the titrant you are using for your results to be accurate and repeatable by other analysts

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19
Q

why was the stock HCl diluted before titrating with NaOH

A

to ensure the reactants are within suitable ranges for more precise measurements

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20
Q

equivalence point

A

the moles of titrant are stoichiometrically equivalent to the moles of analyte

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21
Q

end point

A

point the indicator changes colour

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22
Q

titration

A

the slow addition of one solution of a known concentration to solution of unknown concentration until the reaction reaches neutralization

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23
Q

analyte

A

substance being analyzed (what is in the flask)

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24
Q

titrant

A

the substance being used to analyze the analyte (what is in the burette)

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25
Q

why could the titrated solution in the Erlenmeyer flasks be poured down the sink

A

because it was neutralized

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26
Q

is an antacid a weak acid or base

A

base

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27
Q

what do most antacids contain

A

some kind of carbonate

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28
Q

why do antacids contain carbonates

A

they react with strong acids to make carbonic acid which is decomposed to water and carbon dioxide

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29
Q

can we assume a bigger antacid tablet is more effective? or or why not?

A

NOT
- because tablets often contain binders and flavoring agents along with the weak base

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30
Q

what test will give an antacid tablets neutralizing capacity

A

determining the exact number of moles of base in a tablet by reacting it with acid

31
Q

how was back titration used for determining ANC

A

we added an antacid tablet to a known, excess quantity of acid and was then the remaining acid was titrated with a strong base

32
Q

what formula is used for dilution calculations

A

c1v1 = c2v2

33
Q

what is the general formula for an acid base reaction

A

acid + base —> salt + water

34
Q

why was a neutralizing reaction needed for this experiment

A

to determine how much acid remains in the beaker after reacting with an antacid tablet

35
Q

what is part A of this experiment

A

ANC of antacid tablet

36
Q

what is part B of this experiment

A

standardization of stock HCl solution

37
Q

what is used to determine when an a solution has been neutralized

A

an indicator

38
Q

why do acid-base indicators work well for standardizations

A

because techy exist in two different forms each being a different colour (acid vs base solutions)

39
Q

when is an indicator in acidic form

A

at low PH values

40
Q

when is indicator in basic form

A

at high PH values

41
Q

does the indicator lose or gain a proton at high PH

A

loses a proton to become basic

42
Q

what indicator was used in part A

A

bromocresol green

43
Q

what indicator was used in part B

A

phenolphthalein

44
Q

describe the behavior of phenolphthalein

A

loses a molecule of water at the same time as it loses a proton

45
Q

what PH range does phenolphthalein have

A

8 - 10

46
Q

do you want the end point far from the equivalence point

A

NO - want it CLOSE

47
Q

safety notes of HCl

A
  1. causes severe burns
48
Q

safety notes of NaOH

A
  1. cause severe burns
49
Q

is NaOH a strong or weak base

A

strong base

50
Q

how much stock HCl and at what concentration was initially transferred to a beaker at the start of the experiment

A

about 70 ml of 1 M HCl

51
Q

how much and what concentration of NaOH was transferred to a beaker at the start of the experiment

A

about 75 ml of 0.1 M NaOH

52
Q

how much of the 1 M HCl was pipetted to a new beaker (PART A)

A

25 ml

53
Q

what was placed in the 25 ml HCl solution (PART A)

A

a crushed antacid tablet

54
Q

what was done to the HCl and antacid tablet solution after the reaction was complete (PART A)

A

10 ml of it was pipetted into a clean 100 ml volumetric flask

55
Q

what was done with the 10 ml solution in the volumetric flaks (PART A)

A

diluted to the mark with RO water and inverted 20 times to ensure fully mixed

56
Q

what was added to an Erlenmeyer flask before titration began (PART A)

A
  1. 25 ml of the diluted antacid-HCl solution
  2. 25 ml of RO water
  3. 4 to 6 drops bromocresol green
57
Q

when was the titration for part A deemed neutralized

A

when the bromocresol green turned from yellow to blue

58
Q

what was a clue of an intermediate colour of the titration for part A

A

a teal colour

59
Q

how times was the titration done for PART A

A

three times

60
Q

what was the first steps in Part B of the experiment

A

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

61
Q

what was added to a volumetric flask in (PART B

A

10 ml of the 1 M HCl and diluting to the mark with RO water before inverting 20 times

62
Q

what was added to an erenmeyer flaks before titrating in (PART B

A
  1. 25 ml of the diluted HCl
  2. 3 to 5 drops phenolphthalein
63
Q

what was the analyte of PART B

A

the 25 ml of diluted HCL with the phenolphthalein

64
Q

what was the titrant of PART B

A

0.1 M NaOH

65
Q

what was the titrant of PART A

A

0.1 M NaOH

66
Q

what was the analyte of PART A

A

25 ml of the diluted antacid - HCl

67
Q

how many times was the titration done in PART B

A

three times

68
Q

how were the solutions in the Erlenmeyer flasks disposed of

A

down the sink with lots of water

69
Q

how were excess HCl and antacid-HCl disposed of

A

down the sink after diluting to 0.1 M and discarded down the sink

70
Q

how to calculate the molar concentration of the dilute antacid HCl

A
  1. calculate the moles of HCl from the volume of NaOH
    ( V NaOH x mol NaOH/ V NaOH x 1 mol HCl / 1 mol NaOH)
  2. calculate the molar concentration of dilute HCl: mol HCl / volume HCl
71
Q

how to calculate the molar concentration of the ORIGINAL antacid HCl

A
  1. calculate the moles of HCl from the volume of NaOH
    ( V NaOH x mol NaOH/ V NaOH x 1 mol HCl / 1 mol NaOH)
  2. calculate the molar concentration of dilute HCl:

V1C1 = V2C2
(volume antacid HCl) (Moles Original HCl) = (0.1L Volume HCl diluted) (moles HCl dilute)

72
Q

how to find moles of H+ BEFORE neutralized by antacid tablet

A

N = CV

N = moles of H+
C = ave concentration of HCL stock solution
V = volume of HCl (25 ml)

73
Q

how to find the moles of H+ AFTER neutralized by antacid tablet

A

N = CV

N = moles of H+

C = ave concentration of HCl antacid tablet

V = volume of HCl (25 ml)

74
Q

how to find the ANC of one tablet

A

moles H+ BEFORE - moles H+ AFTER

Chemistry 2000 lab exam (5 decks)

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