37. A student used blue litmus paper and phenolphthalein paper as indicators to test the pH of distilled water and five
aqueous household solutions. Then the student used a pH meter to measure the pH of the distilled water and each
solution. The results of the student’s work are recorded in the table below.
a)
Identify the liquid tested that has the lowest hydronium ion concentration.
b)
Explain, in terms of the pH range for color change on Reference Table M, why litmus is not appropriate to
differentiate the acidity levels of tomato juice and vinegar.
c)
Based on the measured pH values, identify the liquid tested that is 10 times more acidic than vinegar.
38. In performing a titration, a student adds three drops of phenolphthalein to a flask containing 25.00 milliliters of
HCl(aq). Using a buret, the student slowly adds 0.150 M NaOH(aq) to the flask until one drop causes the indicator
to turn light pink. The student determines that a total volume of 20.20 milliliters of NaOH(aq) was used in this
titration.
a)
The concentration of the NaOH(aq) used in the titration is expressed to what number of significant figures?
b)
Calculate the molarity of the HCl(aq) used in this titration. Your response must include both a correct
numerical setup and the calculated result.
39. The graph shows the relationship between pH value and hydronium ion concentration for common aqueous solutions
and mixtures.
a)
What is the hydronium ion concentration of tomato juice?
c)
What color is thymol blue when added to milk of magnesia?
c)
According to this graph, which mixture is approximately 100 times more acidic than milk of magnesia?
40. In a titration, 15.65 milliliters of a KOH(aq) solution exactly neutralized 10.00 milliliters of a 1.22 M HCl(aq)
solution.
a)
Write the equation for the titration reaction.
b)
Show a correct numerical setup for calculating the molarity of the KOH(aq) solution.
41. Soil pH can affect the development of plants. For example, a hydrangea plant produces blue flowers when grown in
acidic soil but pink flowers when grown in basic soil. Evergreen plants can show a yellowing of foliage, called
chlorosis, when grown in soil that is too basic. Acidic soil can be neutralized by treating it with calcium hydroxide,
Ca(OH)2, commonly called slaked lime. Slaked lime is slightly soluble in water.
a) Compare the hydrogen ion concentration to the hydroxide ion concentration in soil when a hydrangea plant
produces pink flowers.
b) An evergreen plant has yellowing foliage. The soil surrounding the plant is tested with methyl orange and
bromthymol blue. Both indicators turn yellow in the soil tests. State, in terms of pH value, why the yellowing
of the plant is not due to chlorosis.
c) Write an equation, using symbols or words, for the neutralization of the ions in acidic soil by the ions released
by slaked lime in water.
42.
The health of fish depends on the amount of oxygen dissolved in the water. A dissolved oxygen (DO)
concentration between 6 parts per million and 8 parts per million is best for fish health. A DO concentration greater
than 1 part per million is necessary for fish survival. Fish health is also affected by water temperature and
concentrations of dissolved ammonia, hydrogen sulfide, chloride compounds, and nitrate compounds. Most
freshwater fish thrive in water with a pH between 6.5 and 8.5.
A student’s fish tank contains fish, green plants, and 3800 grams of fish-tank water with 2.7 ×10–2gram of
dissolved oxygen. Phenolphthalein tests colorless and bromthymol blue tests blue in samples of the fish-tank water.
a)
Based on the test results for the indicators phenolphthalein and bromthymol blue, what is the pH range of the
fish-tank water? [1]
b)
When the fish-tank water has a pH of 8.0, the hydronium ion concentration is 1.0 ×10–8 mole per liter. What
is the hydronium ion concentration when the water has a pH of 7.0?
43. A beaker contains 100.0 milliliters of a dilute aqueous solution of ethanoic acid at equilibrium.
a)
Describe what happens to the concentration of H+(aq) when 10 drops of concentrated ethanoic acid are added
to this system.
44. A laboratory worker filled a bottle with a hydrochloric acid solution. Another bottle was filled with methanol, while
a third bottle was filled with a sodium hydroxide solution. However, the worker neglected to label each bottle.
After a few days, the worker could not remember which liquid was in each bottle.
The worker needed to identify the liquid in each bottle. The bottles were labeled A, B, and C. Using materials
found in the lab (indicators, conductivity apparatus, and pieces of Mg metal), the worker tested samples of liquid
from each bottle. The test results are shown in the table below.
a)
Using the test results, state how the worker differentiated the bottle that contained methanol from the other
two bottles. [1]
b)
The worker concluded that bottle C contained hydrochloric acid. Identify one test and state the
corresponding test result that supports this conclusion. [1]
c)
Explain, in terms of pH, why the methyl orange indicator test results were the same for each of the three
liquids. [1]
44. What color is bromcresol green after it is added to a sample of NaOH(aq)?
45. In a laboratory activity, 0.500 mole of NaOH(s) is completely dissolved in distilled water to form 400. milliliters of
NaOH(aq). This solution is then used to titrate a solution of HNO3(aq).
a)
Identify the negative ion produced when the NaOH(s) is dissolved in distilled water.
b)
Calculate the molarity of the NaOH(aq).
c)
Complete the equation representing this titration reaction by writing the formulas of the products.
NaOH + HNO3 →