SEE DATA SHEET AND QUESTIONS BELOW IT DATA SHEET ii. Estimating the pH of an Aqu

Question

SEE DATA SHEET AND QUESTIONS BELOW IT

DATA SHEET

ii. Estimating the pH of an Aqueous Solution of HNO3

            Indicator paper or solution                                                             observations

blue litmus Red

red litmus Red

thymol blue orange

methyl orange Red

phenolphthalein colorless

Is an aqueous solution of HNO3 acidic or basic? Acidic

What evidence supports your conclusion? Color changes of some solutions help us conclude this

By using the information in Table 2 and the color of the indicators, estimate the pH of a        solution. 1.2-2.8

iii. Estimating the pH of Solutions of Various Substances

                                                                                 Observations

1 x 10-1

Blue Litmus (9)

Red Litmus (10)

Thymol Blue (11)

Methyl orange (12)

Phenolphthalein

Sulfuric Acid

red

red

red

pink

colorless

Acetic Acid

red

red

yellow

red

colorless

Sodium Hydroxide

blue

blue

blue

orange

pink

Ammonia and water

blue

blue

blue

yellow

pink

Sodium Carbonate

blue

blue

blue

yellow

Pink

QUESTIONS

Briefly comment on effect, if any, the following procedural changes would have on the observations you made while doing this experiment.

You poured too much 0.1MNH3/H2O solution into test tubes #1 and #2, leaving only 1 mL of the solution in the test tube #3. You added phenolphthalein indicator solution as directed.

You poured too much 0.1MNH3/H2O solution into test tubes #1 and #2, so you added 2MLH2O to the solution in the test tube #3 to bring the total solution volume to 3mL. You added phenolphthalein indicator solution as directed.

You added only 1 drop of phenolphthalein indicator solution to 3 mL of NH3/H20 solution in test tube #3.

The identification labels fell off three test tubes, each containing a colorless solution. A student knew that one of the test tubes contained 0.1MHCI solution, another contained 0.1% phenolphthalein indicator solution. To determine the identity of each solution, the student temporarily labeled the test tubes, “A”, “B”, and “C”. The student mixed the solutions in various combinations. Recording all observations in the table below

Table 3 Observations made after mixing three solutions

                  mixture                                                     observations

1 drop “A”                                              red solution

+ 1 drop “B”

Solution form (1)                                  solution became

+1 drop “C”                                           colorless

                                      

Solution from (2)                                  solution turned red

+1 drop “b”                                         

Determine which original label should be attached to each of the test tubes.

Each people who are not familiar with the study of chemistry use the expression, “the litmus test,” when referring to a test that produces an unquestionable result. On the basis of your experimental results, can you conclude that using litmus paper provides a “litmus test” for determining whether a solution is acidic or basic? Briefly explain.

1 x 10-1

Blue Litmus (9)

Red Litmus (10)

Thymol Blue (11)

Methyl orange (12)

Phenolphthalein

Sulfuric Acid

red

red

red

pink

colorless

Acetic Acid

red

red

yellow

red

colorless

Sodium Hydroxide

blue

blue

blue

orange

pink

Ammonia and water

blue

blue

blue

yellow

pink

Sodium Carbonate

blue

blue

blue

yellow

Pink

Explanation / Answer

1) You poured too much 0.1MNH3/H2O solution into test tubes #1 and #2, leaving only 1 mL of the solution in the test tube #3. You added phenolphthalein indicator solution as directed.

Ans: Phenolphthalein indicator (ie, the entire solution) would turn red.

Note: The color of the indicator solution does not depend on the amount of acid or base added but rather depends on their concentration

2) You poured too much 0.1MNH3/H2O solution into test tubes #1 and #2, so you added 2MLH2O to the solution in the test tube #3 to bring the total solution volume to 3mL. You added phenolphthalein indicator solution as directed.

Ans: Phenolphthalein indicator (ie, the entire solution) would turn red, but the intensity of red color would be more in test tubes# 1 and 2 compared to #3.

Note: The concentration of ammonia is less in test tube #3 compared to 1 and 2.

3) You added only 1 drop of phenolphthalein indicator solution to 3 mL of NH3/H20 solution in test tube #3.

Ans: The solution would be pale red

Note: Effect of dilution

4) The identification labels fell off three test tubes, each containing a colorless solution. A student knew that one of the test tubes contained 0.1MHCI solution, another contained 0.1% phenolphthalein indicator solution. To determine the identity of each solution, the student temporarily labeled the test tubes, “A”, “B”, and “C”. The student mixed the solutions in various combinations.

Ans: A+B=red color i.e., one of them is base (name not mentioned in question) and the other is phenolphthalein

red color (A+B) + C =colorless i.e., C is 0.1 M HCl

Colorless (A+B+C) + B = red color ie, B is base, Thus A is 0.1% phenolphthalein

The table provided in iii. Estimating the pH of Solutions of Various Substances, clearly shows that the litmus paper turns red for all acidic solutions and turns blue for all basic solutions thus giving the 'litmus test' for acids and bases.

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