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8. Students should be able to investigate the reactions between acids and bases; use indicators and pH scale

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They contain Citric Acid (pH 3-6)

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Acids and Bases are measured with the pH scale

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Acids and Bases are measured with the pH scale

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Litmus Paper is an example of an indicator

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Litmus Paper is an example of an indicator

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Acid and Base | Acids, Bases & pH | Video for Kids

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Acid rain describes any form of precipitation that contains high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth. Normal rain is slightly acidic, with a pH of 5.6, while acid rain generally has a pH between 4.2 and 4.4.

Causes of acid rain

Rotting vegetation and erupting volcanoes release some chemicals that can cause acid rain, but most acid rain is a product of human activities. The biggest sources are coal-burning power plants, factories, and automobiles.

When humans burn fossil fuels, sulfur dioxide (SO ₂) and nitrogen oxides (NO x) are released into the atmosphere. Those air pollutants react with water, oxygen, and other substances to form airborne sulfuric and nitric acid. Winds may spread these acidic compounds through the atmosphere and over hundreds of miles. When acid rain reaches Earth, it flows across the surface in runoff water, enters water systems, and sinks into the soil.

Effects of acid rain

Sulfur dioxide and nitrogen oxides are not primary greenhouse gases that contribute to global warming, one of the main effects of climate change; in fact, sulfur dioxide has a cooling effect on the atmosphere. But nitrogen oxides contribute to the formation of ground-level ozone, a major pollutant that can be harmful to people. Both gases cause environmental and health concerns because they can spread easily via air pollution and acid rain.

Acid rain has many ecological effects, especially on lakes, streams, wetlands, and other aquatic environments. Acid rain makes such waters more acidic, which results in more aluminum absorption from soil, which is carried into lakes and streams. That combination makes waters toxic to crayfish, clams, fish, and other aquatic animals. ( Learn more about the effects of water pollution.)

Some species can tolerate acidic waters better than others. However, in an interconnected ecosystem, what affects some species eventually affects many more throughout the food chain, including non-aquatic species such as birds.

Acid rain and fog also damage forests, especially those at higher elevations. The acid deposits rob the soil of essential nutrients such as calcium and cause aluminum to be released in the soil, which makes it hard for trees to take up water. Trees' leaves and needles are also harmed by acids.

The effects of acid rain, combined with other environmental stressors, leave trees and plants less healthy, more vulnerable to cold temperatures, insects, and disease. The pollutants may also inhibit trees' ability to reproduce. Some soils are better able to neutralize acids than others. But in areas where the soil's "buffering capacity" is low, such as parts of the U.S. Northeast, the harmful effects of acid rain are much greater.

Acid deposits damage physical structures such as limestone buildings and cars. And when it takes the form of inhalable fog, acid precipitation can cause health problems including eye irritation and asthma.

What can be done?

The only way to fight acid rain is by curbing the release of the pollutants that cause it. This means burning fewer fossil fuels and setting air-quality standards.

In the U.S., the Clean Air Act of 1990 targeted acid rain, putting in place pollution limits that helped cut sulfur dioxide emissions 88 percent between 1990 and 2017. Air-quality standards have also driven U.S. emissions of nitrogen dioxide down 50 percent in the same time period. These trends have helped red spruce forests in New England and some fish populations, for example, recover from acid rain damage. But recovery takes time, and soils in the northeastern U.S. and eastern Canada have only recently shown signs of stabilizing nutrients.

Acid rain problems will persist as long as fossil fuel use does, and countries such as China that have relied heavily on coal for electricity and steel production are grappling with those effects. One study found that acid rain in China may have even contributed to a deadly 2009 landslide. China is implementing controls for sulfur dioxide emissions, which have fallen 75 percent since 2007 -but India's have increased by half.

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The fossil fuels that humans burn for energy can come back to haunt us as acid rain.

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- Soil acidification is a natural process in high rainfall environments where leaching slowly acidifies soil over time.

- Intensive agriculture can speed up soil acidification through many processes - increasing leaching, addition of fertilizers, removal of produce and build-up of soil organic matter.

- Of all the major fertilizer nutrients, nitrogen is the main nutrient affecting soil pH, and soils can become more acidic or more alkaline depending on the type of nitrogen fertilizer used.

- Nitrate-based products are the least acidifying of the nitrogen fertilizers, while ammonium-based products have the greatest potential to acidify soil.

- Soil acidification due to use of phosphorus fertilizers is small compared to that attributed to nitrogen, due to the lower amounts of this nutrient used and the lower acidification per kg phosphorus. Phosphoric acid is the most acidifying phosphorus fertilizer.

- Potassium fertilizers have little or no effect on soil pH.
Background
Soil acidification is a widespread natural phenomenon in regions with medium-to-high rainfall. Agricultural production systems can accelerate soil acidification processes through:

- Perturbation of the natural cycles of nitrogen (N), phosphorus (P) and sulfur (S) in soil

- Removal of agricultural produce from the land

- The addition of fertilizers and soil amendments that can either acidify soil or make it more alkaline
Source: Kennedy 1986
Changes in soil pH may be advantageous or detrimental depending on the starting pH of the soil and the direction and speed of pH change - for example decreases in soil pH in alkaline soils may be advantageous for crop production due to benefits in terms of the availability of P and micronutrients e.g. zinc (Zn) (Mitchell et al. 1952).

On the other hand, decreases in soil pH for a highly acidic soil may be detrimental in terms of increasing crop susceptibility to toxicity induced by increased solubility of aluminium (Al) or manganese (Mn) as soil pH falls (Wright 1989).

Key processes and reasons for changes in soil pH in agricultural systems are as follows.
Fertilizer use
Use of mineral or organic fertilizers in agriculture increases inputs of nutrients to soils, and the form in which the nutrients are applied and their fate in the soil-plant system determine the overall effects on soil pH.

Macronutrients (N, P, potassium (K) and S) have the major effects on as they are added in much larger quantities to soil than micronutrients.

The form of N and the fate of N in the soil-plant system is probably the major driver of changes in soil pH in agricultural systems.

Nitrogen can be added to soils in many forms, but the predominant forms of fertilizer N used are:

- Urea (CO(NH₂)₂)

- Monoammonium phosphate (NH₄H₂PO₄)

- Diammonium phosphate ((NH₄)₂HPO₄)

- Ammonium nitrate (NH₄NO₃)

- Calcium ammonium nitrate (CaCO₃+NH₄(NO₃))

- Ammonium sulfate ((NH₄)₂SO₄)

- Urea ammonium nitrate (a mixture of urea and ammonium nitrate)

- Ammonium polyphosphate ([NH₄PO₃]n)

The key molecules of N in terms of changes in soil pH are the uncharged urea molecule ([CO(NH₂)₂]0), the cation ammonium (NH₄+) and the anion nitrate (NO₃-). The conversion of N from one form to the other involves the generation or consumption of acidity, and the uptake of urea, ammonium or nitrate by plants will also affect acidity of soil (Figure 1).

Figure 1. Soil acidity and nitrogen fertilizers (modified from (Davidson 1987)). MAP = monoammonium phosphate, DAP = diammonium phosphate, SoA = sulfate of ammonia, CAN = calcium ammonium nitrate, sodium nitrate

It can be seen in Figure 1 that ammonium-based fertilizers will acidify soil as they generate two H⁺ ions for each ammonium molecule nitrified to nitrate. The extent of acidification depends on whether the nitrate produced from ammonium is leached or is taken up by plants.

If nitrate is taken up by plants the net acidification per molecule of ammonium is halved compared to the scenario when nitrate is leached. This is due to the consumption of one H⁺ ion (or excretion of OH⁻) for each molecule of nitrate taken up - this is often observed as pH increases in the rhizosphere (Smiley and Cook 1973).

Anhydrous ammonia and urea have a lower acidification potential compared to ammonium-based products as one H⁺ ion is consumed in the conversion to ammonium. Nitrate-based fertilizers have no acidification potential and actually can increase soil pH as one H⁺ ion is absorbed by the plant (or OH⁻ excreted) in the uptake of nitrate.

The form of phosphorus fertilizer added to soil can affect soil acidity, principally through the release or gain of H⁺ ions by the phosphate molecule depending on soil pH (Figure 2).

Figure 2. Soil acidity and P fertilizers. MAP = monoammonium phosphate, DAP = diammonium phosphate,

SSP = single superphosphate, TSP = triple superphosphate, APP = ammonium polyphosphate.

If phosphoric acid (PA) is added to soil, the molecule will always acidify soil as H⁺ ions will be released - one H⁺ ion if the soil pH is less than ~6.2 and two H⁺ ions is the soil pH is above 8.2.

Monoammonium phosphate (MAP), single superphosphate (SSP) and triple superphosphate (TSP) all add P to soil in the form of the H₂PO₄⁻ ion, which can acidify soil with a pH greater than 7.2 but has no effect on soil pH in acidic soils. The form of P in diammonium phosphate (DAP) is HPO₄²⁻ which can make acidic soils ( pH<7.2) more alkaline but has no effect on soil with a pH>7.2. The hydrolysis of ammonium polyphosphate (APP), where the P present as the P₂O₇⁴⁻molecule converts to HPO₄²⁻, is pH neutral and hence any acidification due to adding P can be regarded as similar to DAP. SSP or TSP are sometimes declared to cause soil acidification due to reaction products being very acidic;

Ca(H₂PO₄)₂+ ₂H₂O -> CaHPO₄ + H⁺ + H₂PO₄⁻

but in soils with pH values less than 7.7 the following reaction neutralizes the acidity produced so that there is no net acidification;

CaHPO₄ + H₂O -> Ca₂+ + H₂PO₄⁻ + OH⁻

In high pH soils ( pH >7.2), dissociation of H+ ion from the H₂PO₄⁻ molecule will generate some acidity.

Crop uptake of P has little effect on soil acidity due to the small amounts of fertilizer P taken up in any one year - hence fertilizer chemistry dominates pH changes and significant differences in rhizosphere pH have not been observed for uptake of different orthophosphate ions.
Sulfur
The form of sulfur fertilizer added to soil can affect soil acidity, principally through the release of H⁺ ions by the addition of elemental S (S⁰) or thiosulfate (S₂O3²⁻, in ammonium thiosulfate - ATS) (Figure 3). However, the amounts of S added to soil and taken up by plants are generally small in comparison to N.

Figure 3. Soil acidity and S fertilizers. S⁰ = elemental S, ATS = ammonium thiosulfate, SoA = sulfate of ammonia.

For each molecule of S⁰ added to soil, two H⁺ ions will be generated, and these can be balanced through plant uptake by either uptake of H⁺ (same as excretion of OH⁻ ions) or the generation of OH⁻ (effectively organic anions) within the plant to form alkaline plant material ("ash alkalinity"). Where produce is removed (which is often the case in agricultural systems) net acidification of soil will occur if S⁰ or ATS are used.

The form in which potassium is added to soil - either muriate of potash (KCl) or sulfate of potash (K₂SO₄) - has no effect on soil acidification.

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Fertilizers and Soil Acidity | Mosaic Crop Nutrition

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In high rainfall environments, leaching slowly acidifies soil over time. Intensive agriculture can speed up soil acidification through many processes.

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The video outlines the causes and effects of acid rain in a simple manner that is of a suitable level for students. it is short and to the point, and so students will be able to maintain concentration

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What is Acid Rain? | National Geographic

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Nature of Science:

NoS2, NoS3, NoS4, NoS5, NoS6, NoS7,NoS10

Other Strands

EaS7, BW4, BW10

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offers opportunity to develop skills in reading a graph

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a suitable resource that offers a chance to develop literacy, as well as recapping words students may already know, as well as introducing new ones. (Scientific Terminology building)

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Here is a song to help you remember your theory!

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ACIDS AND BASES SONG | Science Music Video

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Paper on Acid Rain - affects on ecosystems and future implications

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Paper on Acid Rain - affects on ecosystems and future implications

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This paper discusses the history of acid rain, its effects on ecosystems, and its future implications. Understanding this social application of acids and bases is key, as it allows students to understand the real-life effects of pollution on the climate and why sustainability is crucial. understanding the implications of theory is key to future academic development

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This paper looks at inquiry-based learning as a method of keeping students engaged by creating relevant, worthwhile content in lessons. It argues that students leading their own learning in STEM subjects to inquiry is crucial for their achievement. This is worthwhile for this learning outcome, as in the lesson, I have included an inquiry-based investigation where students can design their own experiment to look at the pH of a variety of substances using indicators. They are able to actively participate in their own learning.

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5E model and how inquiry enhances science education

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5E model and how inquiry enhances science education

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This article looks at using inquiry-based learning, specifically the 5E model, as a way to enhance learning in education. It argues that implementing strategies like this promotes creativity and understanding. This is crucial to this learning outcome, as the experiments students perform with acids and bases are very much student-led and based around inquiry. this proves that this method of learning is effective and can be easily incorporated into the classroom