Mini-Labs on Chemical Changes

7/30/2019 Mini-Labs on Chemical Changes

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Lab Skills Focus:

Filtration


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magnesium + sodium magnesium + sodium

sulfate carbonate carbonate sulfate

Chemical Equation

MgSO4 + Na2CO3 MgCO3(s) + Na2SO4

Word Equation

Clear liquid


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When solutions of two soluble salts are mixed, a

solid may form. This solid is called a precipitate.and the reaction is called a precipitation reaction.

Precipitation reactions are used to make insoluble

salts.

In this example the soluble salts are magnesiumsulfate and sodium carbonate, and the insolublesalt formed is magnesium carbonate.


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Law of Conservation of Mass


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Instructions

1. Measure 5 g of baking soda and

put into a flask.

2. Measure 20 mL of vinegar and carefully

pour it into a balloon.

3. Carefully attach the balloon to the top of the flaskwithout spilling the vinegar into the flask.

4. Place the flask with balloon on a weighing scale andrecord the mass of the system.

5. Tip the vinegar from the balloon into the flask andrecord your observations.

6. Measure the mass of the system after the reaction.

7. Pop the balloon and measure the mass again.


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Summary

1. Explain whether your results support

the Law of Conservation of Mass.


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There are times when mass might

appear to change during a chemical

reaction.

If you experience this during anexperiment, be sure to remember the

Law of Conservation of Mass.

The change in mass must be

accounted for in a way other than

destroying or creating atoms.


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Endothermic andExothermic Reactions

(Heat Change)


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Exothermic and Endothermic Reactions

An energy change accompanies the forming or

breaking of a bond between atoms in a molecule.

O Energy is released (produces heat) when a

bond forms

Exothermic

o Energy is absorbed from the surroundingsto break the bonds in a molecule

Endothermic


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In your notebook:

Draw a diagram of the set-up

Make a data table

Make a graph Calculate temperature change as a

function of time


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Maximum C Minimum C = Rate of temperature change

Total Time (sec)

Calculating Rate of temperature change

Temperature/T degrees C Time/sec

Starting temperature- ex. 28

27

26

25

24

23


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Endothermic

ReactionExplore Lab:

Energy change

Summary:

Explain how this lab shows a chemicalreaction.

How does the graph show that the reaction isendothermic? Explain.


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Endothermic reaction results:

Starts at around 25 degrees C andends at around 21 degrees C

Happens within about 2 minutes

http://www.youtube.com/watch?v=MyAzjSdc3Fc

Endothermic Reaction
http://www.youtube.com/watch?v=MyAzjSdc3Fchttp://www.youtube.com/watch?v=MyAzjSdc3Fchttp://www.youtube.com/watch?v=MyAzjSdc3Fc


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Exothermic Reaction: Oxidation of steel wool

1. Put 8 grams of wool into a 400 mL beaker.

2. Add enough acetic acid to completely

cover the wool.

3. Swirl for 2 minutes to remove the protective coating.

4. Pour the acetic acid into a waste beaker.

5. Quickly cover the beaker with Parafilm.

6. Insert a thermometer through

the film and into the steel wool.

7. Record the time for each degree Celsius rise and

follow the temperature/time profile through a 5

degree change.

Explore Lab 2:Energy change


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Exothermic reactions

The reaction produces heat.

In this reaction vinegar is used

to remove the protective coatingfrom steel wool, allowing it torust.

When the iron combines withoxygen, heat is released.


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Summary:

Explain how this lab shows a

chemical reaction.

On the same graph (endothermic), show a

graph of temperature change as a function of

time.

How does the graph show that the

reaction is exothermic? Explain.


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4Fe

+ 3O2

2Fe2O3

4 Fe + 6 O = 4 Fe + 6 O

4 Fe

+ ___ O2

2 Fe2O3

Applying the Law of Conservation of Mass:

How many atoms of Oxygen are needed to reactwith 4 atoms of Iron to form 2 units of Iron oxide?

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Mini-Labs on Chemical Changes