Science 30. Unit B: Chemistry and the environment Chapter 1: Acid Deposition. 1.1- Products of Combustion Reactions. Combustion reactions (eg. Cellular respiration, burning fossil fuels) are useful but produce emissions. Collisions between the methane and oxygen molecules form new molecules.
Unit B: Chemistry and the environment
Chapter 1: Acid Deposition
Greenhouse Effect - animated diagram
Catalytic Converters again
Energy efficient homes
Reduce recycle reuse
See page 174 Example problem 1.2/1.3
1.89 x 10-4 mol/L
= 10-7 = 1 x 10-7 mol/L
= 10-11 = 1 x 10-11 mol/L
= 10-2 = 1 x 10-2 mol/L
= 10-4 = 1 x 10-4 mol/L
= 10-14 = 1 x 10-14 mol/L
pH = - log [ 10-3 ] = 3.00
pH = - log [ 10-5 ] = 5.00
pH = - log [ 10-7 ] = 7.00
pH = - log [ 10-10 ] = 10.00
Note: Answers have the correct amount of significant digits
First nations used natural acids to adjust the color of the dyes made from leaves, berries and bark.
An indicator is anything that changes color in response to a change in pH.
Common indicators are shown in the table on page 12 of your booklet.
Used to measure the pH of a substance.
pH meter is more accurate and gives exact measure of pH.
According to the acid-base indicator table, what is the color of each of the following indicators in the solutions of given pH?
(a) Phenolphthalein in a solution with a pH = 12.7.
(b) Bromothymol blue in a solution of pH = 2.8
(c) Methyl orange in a solution of pH = 3.
(d) Thymol blue in a pH = 5.0 solution
(e) Litmus in a solution with a pH of 8.2
Separate samples of an unknown solution turned both methyl orange and bromothymol blue to yellow, and turned bromocresol green to blue. The pH of the unknown solution is likely __________
methyl orange = yellow = 4.4+
bromothymol blue = yellow = 6.0-
bromocresol green = blue = 5.4+
The pH of the unknown solution is likely between 5.4 and 6.0.
Higher levels of sulphates and nitrates in rainwater = higher concentration of hydronium ions and lower pH in water.
Wind patterns affect the deposition; provides way to trace pollution.
Alberta soil is slightly basic (alkaline) from the carbonate caused by erosion of limestone; neutralizes the acid deposition.
A buffer is used to resist pH change in soil or lake water.
The buffering capacity is the ability of a substance to resistance pH change when an acid/base is added.
Specific plants need to be used in acidic soils; most are not able to grow due to lack of nutrients.
Nutrients are deposited in soil from biogeochemical cycles and through neutralization reactions.
Plants absorb nutrients into the roots from the soil, up to the leaves.
Acid deposition changes nutrients so they are insoluble; plants can not use them.
Nutrient deficiencies causes plants to die or become diseased.
Chlorosis = calcium deficiency causes decreased chlorophyll = yellow leaves.
A neutral pH is best for plant growth; too acidic or basic results in death.
acid in soil makes metal ions (aluminum and mercury) available to plants.
Plants take those nutrients into their roots and they dissolve in the soil or groundwater = leaching.
Affects ecosystem by:
Decreased root growth.
Prevents absorption of calcium.
Reduce decomposing soil bacteria.
Mercury causes damage to gills.
Methyl mercury traps in tissues = bioaccumulation
A pollutant increases in concentration up a food chain.
Causes disease and death.
Measured in ppm (106) or ppb (109) or ppt (1012)
The abiotic (non-living) factors in an ecosystem affect the biotic (living).
Acid deposition decreases the biodiversity of the system.
Acid deposition affects the ecosystem in:
Decreasing soil bacteria.
Destroying waxy coating on plants.
Damaging aquatic ecosystems.
Classification of acids is done in 2 ways:
Quantitatively = involves measurement (pH, titration)
Qualitative = involves properties, characteristics, attributes (color, observations)
Used to determine the amount of acid/base present.
Uses an acid, base and an indicator.
When the “end point” is reached, the indicator will change color and the amount of acid/base needed to neutralize the solution is known.
Calculating concentrations: Calculate the concentration, in moles per litre, of 250 mL of a solution containing 0.243 mol of potassium hydroxide, KOH (s), used to analyze the concentration of an acid solution.
n = .243 mol V= 250 mL (0.250 L)
Formula: C = n/V
= 0.243 mol/0.250 L
= 0.972 mol/L
Answer: The KOH has a concentration of 0.972 mol/L
The CONCENTRATIONof an acid can easily be changed by adding more solvent (water).
What would the concentration of KOH be if an additional 150 mL of water was added to the solution?
Solution #1: “standard solution”
Will know the concentration and the volume used.
Solution #2: “unknown”
Will know volume used but NOT the concentration
Acid / Base titrations will involve a NEUTRALIZATION Reaction
acid + base → salt + water
HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
solution with known concentration
goes in the buret
The titrant will be added to sample drop by drop until they have reacted fully (there is an equal amount of acid and base) and the ENDPOINT is reached.
How do you know you have reached the endpoint?
The Erlenmeyer flask will also contain an INDICATOR that will change color when the reaction has reached the endpoint.
The indicator changes colour at the endpoint because the [H3O+] and therefore pH will have changed sufficiently.
Read the volume of titrant in the buret before the titration begins AND once the endpoint has been reached
Subtract the volumes
REMEMBER - read the bottom of the meniscus!!
KOH(aq) + HCl(aq) KCl(aq) + HOH(aq)
Calculate ‘n’ for the given substance
Use a molar ratio to calculate ‘n’ for the required substance
Make the appropriate calculation to answer the question you are asked.
Find the concentration of a solution of potassium hydroxide, KOH(aq), if it requires 8.32 mL of a 0.100 mol/L standard solution of hydrochloric acid to neutralize 10.0 mL of the potassium hydroxide solution.
Note: the balanced chemical equation is a 1 to 1 mole ratio, therefore nHCl = nKOH
Strength ≠ Concentration
Strength refers to the % of the acid or base that dissociates in water
You can change the concentration but you can NOT change strength
Strong acids and strong bases dissociate completely in aqueous solutions
Weak acids - only a portion of the acid molecules release protons
Weak base – only a portion of the base molecules accept protons
NaOH is a strong base
NaOH dissociates completely in H2O
NaOH Na+ and OH-
Acetic Acid is a weak acid
Most acetic acid molecules DO NOT release protons but instead remain in undissociated form
CH3COOH + H2O CH3COO- + H3O+
For every weak acid there is a conjugate base
(See page 12 of Data Booklet)
What is the conjugate base of acetic acid?
A Buffer is a weak acid / weak base conjugate pair
Most effective when there are equal amount of acid and base
Example: H2CO3 in Blood
CO2 and H2O react to make H2CO3 (carbonic acid)
Carbonic acid resists changes in blood pH
H2CO3 + H2O →H3O+ + HCO3 -
Natural sources include hydrogen carbonate in your blood, levels of carbonate in the soil and limestone deposits.
Buffers do not work forever however; Eastern Canada has reached the capacity to buffer soil and has acidic deposition currently.