Homework answers / question archive / Lab #10: Chemical Weathering Purpose   In this experiment, you will learn the importance, abundance and some of the reactions of calcium and other carbonates normally found in Earth’s crust

Lab #10: Chemical Weathering Purpose   In this experiment, you will learn the importance, abundance and some of the reactions of calcium and other carbonates normally found in Earth’s crust

Chemistry

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Lab #10: Chemical Weathering

Purpose

 

In this experiment, you will learn the importance, abundance and some of the reactions of calcium and other carbonates normally found in Earth’s crust. You will explore how different types of rocks react to some of the weathering agents such as water and acid.

Materials

· Vinegar

· Lemon juice

· Water

· Clear plastic cups

· Dropper or plastic pipette

· Pieces of white chalk

· Optional- different rock types (quartz or granite)

 

Introduction

 

The Earth is not homogeneous and is composed of different layers. Each layer has a different composition. The lithosphere is the rigid outer layer that contains the crust and upper mantle. The lithosphere is composed of three equally important components, namely, inorganic (rocks and mineral), organic (soil and fossil fuel), and biological (flora and fauna). Our focus for this chapter and activity is on inorganic components.

Chemical Weathering

Rocks and mineral are all around us. Watch this video to understand the difference between rocks and minerals. Weathering describes the breaking down or dissolving of rocks and minerals on the surface of the Earth. Water, ice, acids, salts, plants, animals, and changes in temperature are all agents of weathering. Weathering wears away exposed surfaces over time. Chemical weathering occurs at a second stage of rock disintegration in which small pieces of rock produced by physical weathering are then further broken apart by chemical processes such acid reactions, hydrolysis and oxidation.

 

Acid rain is formed when certain pollutants dissolve in rain creating stronger acids. Learn more about acid rain here. Acid rain is one factor that can increase the rate of erosion, with effects that can be seen in just a few decades. Limestone and marble are composed calcium carbonate, the same material as chalk, and are commonly used for constructing buildings and statues. Rain that is too acidic will “eat away” at these structures very quickly.

 

Acids in rain such as sulfuric acid (H2SO4) dissolves the calcium carbonate to make a moderately soluble form of calcium, CaSO4 (called gypsum), along with carbon dioxide and water. This is an acid-base neutralization.

This could also have positive impact: the regions where the bedrock or soil contain large amounts of limestone are less likely to have polluted water due to acid rain than areas with igneous bedrock. This is because the limestone (which is a base) is able to neutralize acid rain before it gets into the lakes and rivers. This means that damage due to acid rain depends on both the pH (amount of acid in a substance) of the rain and the type of soil/bedrock.

 

In this activity, you will explore the effect of acetic acid (found in vinegar) and lemon juice on chalk. You can also repeat this activity with other rocks (if available) and record your observations.

 

Procedure

 

Prepare three clear plastic cups and label them as water (W), vinegar (V), and lemon juice (L). Add about 20 ml of each liquid into these cups respectively.

Crush Break chalk into approximately three 1/2 cm pieces.

Crush each 1/2 cm piece of chalk into smaller pieces, keeping each crushed 1/2 cm portion separate from each other.

Crush the first piece into smaller pieces and add to the cup containing water. Observe the changes that take place. Record your observations the data table.

Repeat with second piece of chalk and add to the cup containing vinegar. Record your observations. Take a picture.

Repeat with third piece of chalk and add to the cup containing lemon juice. Record your observations. Take a picture.

Look and listen carefully each time you add the chalk pieces to these liquids.

This is optional: You can also repeat the activity with other rock such as quartz or granite. You may not be able to break those into smaller pieces though, but you can still try by taking small pieces.

 

Credit: https://letstalkscience.ca/educational-resources/hands-on-activities/what-are-effects-acid-rain-on-rocks

 

 

 

 

 

Name __________________

Pre-laboratory Assignment

 

1. What do you understand by the term weathering in the context of this chapter?

 

 

 

 

 

2. Briefly describe the difference between minerals and rocks.

 

 

 

 

 

 

 

3. What is an acid rain? List one positive and one negative impact of the acid rain.

 

 

 

 

 

 

 

 

4. Which rock types are sensitive to acids?

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Results

 

Record your observations in the following data table:

	Water	Vinegar	Lemon Juice
Chalk
Granite (optional)
Limestone or quartz (optional)

 

Questions

1. Did the water and vinegar act the same way on chalk?

 

 

 

2. What type of reaction is occurring between the chalk and vinegar?

 

 

 

 

3. Write the chemical equation for the reaction between acetic acid (C2H4O2) and limestone (CaCO3).

 

 

 

 

4. Predict what could have happened if you added more chalk to the vinegar? Explain your prediction in terms of above neutralization reaction.