HW From textbook “CHEMISTRY a Contemporary Approach”

• Read “Indicators” p401&402

• Do "Questions for Review" 5 p415

The acidity or alkalinity of a solution can be measured by its pH value.

On the pH scale, each decrease of one unit of pH represents a tenfold increase in hydronium ion concentration.

Example

If the pH of a solution changes from 4 to 8 what is the change in hydronium ion concentration?

The change is 4 pH units up the pH scale. Therefore, the change in hydronium concentration is 10x10x10x10 or 10,000 times less since from 4 to 8 there is a decrease in hydronium ions in the solution.

Problems

1. What is the change in hydrogen ions concentration  if the pH of a solution changes from 6 to 2?

2. What is the change in hydronium ions  concentration  if the pH of a solution changes from 9 to 14?

3. What is the change in hydroxide ions  concentration  if the pH of a solution changes from 5 to 8?

The relative level of acidity or alkalinity of a solution can be shown by using indicators.

Example

See table M

Problem 

Use table M to describe the color of the indicators in the solutions given below.

TEST YOUR UNDERSTANDING

1/07

47 In which 0.01 M solution is phenolphthalein pink?    (1) CH₃OH(aq)      (2) Ca(OH)₂(aq)    (3) CH₃COOH(aq)                (4) HNO₃(aq)

48 As the pH of a solution is changed from 3 to 6, the concentration of hydronium ions

(1) increases by a factor of 3 (2) increases by a factor of 1000  (3) decreases by a factor of 3 (4) decreases by a factor of 1000

64 Identify two indicators from Reference Table M that are yellow in solutions with a pH of 5.5

6/07

Base your answers to questions 67 and 68 on the information below.

Sulfur dioxide, SO₂, is one gas produced when fossil fuels are burned. When this gas reacts with water in the atmosphere, an acid is produced forming acid rain. The pH of the water in a lake changes when acid rain collects in the lake.

Two samples of the same rainwater are tested using two indicators. Methyl orange is yellow in one sample of this rainwater. Litmus is red in the other sample of this rainwater.

67 Identify a possible pH value for the rainwater that was tested.

68 Write the formula for one substance that can neutralize the lake water affected by acid rain.

8/07

47 The table below shows the color of the indicators methyl orange and litmus in two samples of the same solution.

Which pH value is consistent with the indicator results? (1) 1        (2) 5        (3) 3        (4) 10

48 What is the pH of a solution that has a hydronium ion concentration 100 times greater than a solution with a pH of 4? (1) 5 (2) 2 (3) 3 (4) 6

1/06

6/06

8/06

1/05

26 According to Reference Table M, what is the color of the indicator methyl orange in a solution that has a pH of 2?     (1) blue (2) yellow(3) orange (4) red

6/05

50 In which solution will thymol blue indicator appear blue?  (1) 0.1 M CH₃COOH (2) 0.1 M KOH (3) 0.1 M HCl (4) 0.1 M H₂SO₄

Base your answers to questions 74 through 76 on the passage below.

        Acid rain is a problem in industrialized countries around the world. Oxides of sulfur and nitrogen are formed when various fuels are burned. These oxides dissolve in atmospheric water droplets that fall to earth as acid rain or acid snow. While normal rain has a pH between 5.0 and 6.0 due to the presence of dissolved carbon dioxide, acid rain often has a pH of 4.0 or lower. This level of acidity can damage trees and plants, leach minerals from the soil, and cause the death of aquatic animals and plants. If the pH of the soil is too low, then quicklime, CaO, can be added to the soil to increase the pH. Quicklime produces calcium hydroxide when it dissolves in water.

74 Balance the neutralization equation in your answer booklet, using the smallest whole number coefficients.

75 A sample of wet soil has a pH of 4.0. After the addition of quicklime, the H+ ion concentration of the soil is 1,000 less of the original H⁺ ion concentration of the soil. What is the new pH of the soil sample?

76 Samples of acid rain are brought to a laboratory for analysis. Several titrations are performed and it is determined that a 20.0-milliliter sample of acid rain is neutralized with 6.50 milliliters of 0.010 M NaOH. What is the molarity of the H⁺ ions in the acid rain?

1/04

25 Which of these pH numbers indicates the highest level of acidity? (1) 5 (2) 8 (3) 10 (4) 12

35 Which solution when mixed with a drop of bromthymol blue will cause the indicator to change from blue to yellow?   (1) 0.1 M HCl (2) 0.1 M NH₃ (3) 0.1 M CH₃OH (4) 0.1 M NaOH

Base your answers to questions 80 and 81 on the information below.
Calcium hydroxide is commonly known as agricultural lime and is used to adjust the soil pH. Before the lime was added to a field, the soil pH was 5. After the lime was added, the soil underwent a 100-fold decrease in hydronium ion concentration.
80 What is the new pH of the soil in the field?

81 According to Reference Table F, calcium hydroxide is soluble in water. Identify another hydroxide compound that contains a Group 2 element and is also soluble in water.

6/04

45 Which pH indicates a basic solution? (1) 1 (3) 7 (2) 5 (4) 12

Base your answers to questions 56 through 58 on the information below.
A student titrates 60.0 mL of HNO₃ (aq) with 0.30 M NaOH(aq). Phenolphthalein is used as the indicator. After adding 42.2 mL of NaOH( aq), a color change remains for 25 seconds, and the student stops the titration.

56 What color change does phenolphthalein undergo during this titration?

57 Show a correct numerical setup for calculating the molarity of the HNO₃ (aq).

58 According to the data, how many significant figures should be present in the calculated molarity of the HNO₃ (aq)?

8/04

30 Which pH change represents a hundredfold increase in the concentration of H₃O⁺?   (1) pH 5 to pH 7 (2) pH 13 to pH 14 (3) pH 3 to pH 1 (4) pH 4 to pH 3

48 Which statement correctly describes a solution with a pH of 9?

                1) It has a higher concentration of H₃O⁺ than OH^- and causes litmus to turn blue.

                2) It has a higher concentration of OH^- than H₃O⁺ and causes litmus to turn blue.

                3) It has a higher concentration of H₃O⁺ than OH^- and causes methyl orange to turn yellow.

                4) It has a higher concentration of OH^- than H₃O⁺ and causes methyl orange to turn red.

1/03

1. Which of these 1 M solutions will have the highest pH? (1) NaOH    (2) CH₃OH       (3) HCl     (4) NaCl

2.  Given the following solutions:  Solution A: pH of 10  Solution B: pH of 7  Solution C: pH of 5

    Which list has the solutions placed in order of increasing H⁺ concentration? (1) A, B, C     (2) B, A, C     (3) C, A, B   (4) C, B, A

3.  A compound whose water solution conducts electricity and turns phenolphthalein pink is (1) HCl    (2) HC₂H₃O₂     (3) NaOH  (4) CH₃OH

6/03

48. A student was given four unknown solutions. Each solution was checked for conductivity and tested with phenolphthalein. The results are shown in the data table below.

Based on the data table, which unknown solution could be 0.1 M NaOH?  (1) A (2) B (3) C (4) D

Base your answers to questions 77 through 79 on the information below.

A truck carrying concentrated nitric acid overturns and spills its contents. The acid drains into a nearby pond. The pH of the pond water was 8.0 before the spill. After the spill, the pond water is  1,000 times more acidic.

77. Name an ion in the pond water that has increased in concentration due to this spill.

78. What is the new pH of the pond water after the spill?

79. What color would bromthymol blue be at this new pH?

6/02

A student is given two beakers, each containing an equal amount of clear, odorless liquid. One solution is acidic and the other is basic.

a) State two safe methods of distinguishing the acid solution from the base solution.

b) For each method, state the results of both the testing of the acid solution and the testing of the base solution.

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