Gallery for Educators: Cave Chemistry, LAB: Creating a Precipitate

Cave Chemistry Lab

Prior to lab, watch speleothem slideshow (found under CAVE: links, slideshows...) and read the reading passage “Cave Chemistry”.

Introduction

Caves are formed through weathering and erosion. Most caves are solution caves, formed by the dissolving of bedrock by underground water (groundwater).

Chemical weathering plays a large part in a cave’s creation. Mild acids etch the limestone bedrock and produce solutions to help create cave formations. These formations are the result of a chemical reaction producing precipitates. Gradual deposition of calcite precipitates “grow” the cave formations known as speleothems.

how to pronounce SPELEOTHEM
(to hear: click on word, when page opens...place cursor on word)

Terminology for Lab (Students should be familiar with all terms except for precipitate)

Physical Property - a property that describes a substance by itself, such as color, shape, density, or hardness

Physical Change – a change that does not make a substance into a new substance

(i.e., tearing or cutting paper does not change the substance that is paper)

Chemical Property - a property that involves the ability of a substance to react with other materials and form new substances (i.e., ability to burn, smoke, fizz)

Chemical Change - change that forms new substances with new properties

(i.e., smoking, burning, producing a gas)

Chemical Reaction - a process that produces one or more new substances

Reactivity - the ability of a substance to go through a chemical change

Mixture – a combination of two or more substances that keep their original properties

Solute – the substance that dissolves (in a solution)

Solvent – the substance that dissolves the solute (in a solution)

Dissolve - in a cave, the process of a solid mixing with a liquid to become a liquid

Solution - a mixture in which all the substances are evenly distributed, created when acid water dissolves limestone

Precipitate - a precipitate is the insoluble solid created as a result of a liquid solution. (insoluble means it will not dissolve). Explanation: When two soluble substances react in a solution, the reaction produces an insoluble product. The insoluble product that separates from the liquid is called the "precipitate".
how to pronounce PRECIPITATE

Meniscus - The curved upper surface of a liquid in a container
how to pronounce MENISCUS

Graduated Cylinder – tool to measure liquids

Stirring Rod – tool for measuring and pouring liquids

Beaker – tool to measure liquids

Meniscus

graduated cylinders

Beaker and Stirring Rod

Objectives and Process Skills:

· Measure solids and liquids using scientific tools

· Record observations

· Identify a solute and a solvent

· Identify and describe physical properties of substances and solutions

· Identify and describe when a physical change takes place

· Identify and describe when a chemical change takes place

· Infer when a chemical change takes place

· Identify and describe when a precipitate is formed

· Summarize findings and results of lab

Materials:

2 beakers container of water 2 plastic spoons

graduated cylinder stirring rod (optional)

Epsom Salts(magnesium sulfate)

Arm and Hammer Laundry Powder (sodium carbonate) make sure to use fragrance free

Procedure:

Record Observations

Table A Write 2 Physical Properties for each substance

Substance	Physical Property	Physical Property
Laundry Soap Powder	1.	2.
Epsom Salts	1.	2.

Prepare Solutions

1. Measure 100 ml of water in each beaker

(Remember to check the meniscus of the water)

2. In Beaker A, add 10 cc of soap powder (10 ml = 10 cc)

3. In Beaker B, add 10 cc of Epsom Salt

4. Gently stir liquid in each beaker to dissolve solids

5. When all powder and salt is dissolved, set the beakers aside.

(This gives any bubbles time to settle in Beaker A)

6. Record observations on worksheet

7. Follow directions for “Creating a Precipitate” and record observations

Record Observations

Table B Making A Solution

Beaker	Describe Solution	Name Solute	Name Solvent
Beaker A : Water with Laundry Soap
Beaker B : Water with Epsom Salt

Creating a Precipitate

Place the stirring rod in the graduated cylinder, slowly pour 55ml liquid from

Beaker A (soap) into the graduated cylinder. Use the rod to help pour the liquid.

Give the liquid a few seconds to settle. Using the stirring rod, slowly pour 55 ml liquid

from Beaker B (salt) into the graduated cylinder on top of the soap liquid.

Special Notes:
1. Tilt the graduated cylinder when pouring in soap if you do not have a stirring rod so you do not create bubbles.
2. Pour only 55 ml of the prepared solutions instead of the full 100 ml. This prevents any undissolved solids from getting in the graduated cylinder.

Photos of Lab: Creating a Precipitate

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Student Worksheet Name

Science Observing a Chemical Change - Creating A Precipitate

I can:

________ Measure solids and liquids using scientific tools

________ Record observations

________ Identify a solute and a solvent

________ Identify and describe physical properties of substances and solutions

________ Identify when a physical change takes place

________ Identify and describe when a chemical change takes place

________ Infer when a chemical change takes place

________ Identify and describe when a precipitate is formed

________ Summarize findings and results of lab

Check off each goal above as you complete it.

Materials:

2 beakers container of water 2 plastic spoons graduated cylinder stirring rod

Epsom Salts (magnesium sulfate) Arm & Hammer Laundry Powder (sodium Carbonate)

1. Write 2 Physical Properties for each substance Table A

Substance	Physical Property	Physical Property
Laundry Soap Powder	1.	2.
Epsom Salts	1.	2.

2. Prepare Solutions

* Measure 100 ml of water in each beaker (Check the meniscus of the water)

* In Beaker A, add 10 cc of soap powder

* In Beaker B, add 10 cc of Epsom Salt

* Gently stir liquid in each beaker to dissolve solids

* When all powder and salt is dissolved, set the beakers aside.

(This gives any bubbles time to settle in Beaker A)

3. Making A Solution Table B

Beaker	Describe Solution	Name Solute	Name Solvent
Beaker A : Water with Laundry Soap
Beaker B : Water with Epsom Salt

4. Name 2 physical properties for the laundry soap solution in Beaker A.

5. Name 2 physical properties for the salt solution in Beaker B.

6. The Epsom Salt and water had a physical change when the salt ________________

in the water.

Creating a Precipitate

Place the stirring rod in the graduated cylinder, slowly pour 55 ml liquid from Beaker A (soap) into the graduated cylinder. Use the rod to help pour the liquid. Give the liquid a few seconds to settle. Using the stirring rod, slowly pour 55 ml liquid from Beaker B (salt) into the graduated cylinder on top of the soap liquid.

7. Describe what happened when the 2 solutions were combined in the cylinder.

8. When the 2 solutions were combined, a (physical/chemical)_____________________________

change occurred because (explain why)

9. How do you know a chemical reaction occurred?

10. sodium carbonate + magnesium sulfate produces sulfate + magnesium carbonate

solution A added to solution B Produces liquid and precipitate in graduated cylinder

Magnesium carbonate dos not dissolve well in water.

When it forms, it sticks together in small solid particles called precipitate.

How long did it take the precipitate to form?

Describe the precipitate.