Which Statement Is a Hypothesis You Would Test Using a Solution With Bromothymol Blue

DRAFT: This module has unpublished changes.

General Biology

The Scientific Method

Introduction:

            Scientists try to understand the natural world by making observations and by performing experiments that enable them to make generalizations and predictions about natural phenomena.  Science is simply a way of organizing what we know about the world around us.  Scientists study nature in an organized, logical manner using an approach called the scientific method.  You will use the scientific method to solve the problem you are presented with in this lab.

Question 1

List and explain, in order, the steps that are used in the scientific method.

1. Observations – The problem is observed and past data that may help form a hypothesis is studied.
2. Hypothesis – a testable statement is formulated
3. Experimentation – The hypothesis is tested and observed
4. Conclusion – The results of the experiments are analyzed to determine if the hypothesis is correct.

Materials from your lab kit

Chemplate

Brom thymol blue

HCl

NaOH

ZnNO3

Materials You will need to supply

Unknown 1—vinegar (acetic acid)

Unknown 2 –ammonia (NH3)

Citric Acid – lemon or lime juice

Procedure :

  You are going to perform an experiment to try to understand the color changes that occur when the bromothymol blue is mixed with different solutions.

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Figure 1: BTB indicator in acidic, neutral, and alkaline solutions (left to right).

The color change that does occur is evidence of a chemical reaction.  Record the data you obtain in the chart on the following page as you proceed.

1. Place 1 drop of bromothymol blue  in cavities 1, 5, and 9 of the chemplate.
2. In cavity 1, add 1 drop of Unknown 1.  To cavity 5, add 1 drop of Unknown 2.  Add nothing to cavity 9.  Record your observations in the data chart.

Question:  Why was nothing added to the bromothymol blue in cavity 9?

Cavity 9 is used as the control in this experiment.

Question: Using your observations in step 1 and 2, can you explain what caused the bromothymol blue to change color?  Why or Why not?

I don't know what bromothymol blue does, but it appears like it changes color based on how acidic something is.

1. Add a drop of bromothymol blue to cavity 2,  and 3 in the chemplate.
2. Add 1 drop of hydrochloric acid (HCl) to cavity 2.  Record the results in the data chart.
3. Repeat this procedure with sodium hydroxide (NaOH) in the other cavity of the chemplate.  Record your results in the data table.

Question:  Use the data you have recorded to create a hypothesis which explains why bromothymol blue changes color.

Bromothymol blue changes orange when mixed with an acid and doesn't change color when mixed with a base.

1. Record your prediction for the color changes that will occur when bromothymol blue is mixed with the zinc nitrate (ZnNO3) and citric acid solutions.
2. Test your hypothesis and predictions by mixing bromothymol blue with these 2 solutions.  Record your results in the data table.

Question: Did the results you obtained in step 7 support your hypothesis?  Explain.

For the most part. ZnNO3 turned brownish, which I assume means that it's not quite as acidic as the other solutions.

Question:  If the results do not support your hypothesis, what should you do next?

Reformulate the hypothesis based on my conclusions.

Question:  If your hypothesis was not supported by your results, write a new hypothesis here.

When mixed with acids, bromothymol blue progressively turns more orange.

Cavity No.	Bottle	Contents of Solution	Original Color of Bromothymol Blue	Predicted Color	Observations Color Change
1	1	Unknown	Blue	XXXXXX XXXXXX	Orange
5	2	Unknown	Blue	XXXXXX XXXXXX	Blue
2	Sol. 1	HCl	Blue	XXXXXX XXXXXX	Orange
3	Sol. 2	NaOH	Blue	XXXXXX XXXXXX	Blue
4	Sol. 3	ZnNO3	Blue	Blue	Brown
6	Sol. 4	Citric Acid	Blue	Orange	Orange

Conclusions:

What type of chemicals do you think were in the unknown solutions?

Vinegar (an acid) and ammonia (a base)

What solution would be hardest to predict a color change?  Why?

A solution that is not as acidic as the others or a neutral. ZnNO3.

What is the difference between a fact and a hypothesis?

A fact has been proven to be true, a hypothesis is an educated guess.

Write a definition of a controlled experiment and explain the function of the control in this experiment.

A controlled experiment is an experiment in which a control group has been used. In this experiment, the control was used to see the function of the bromothymol blue by comparison. It remains blue even when a base is mixed with it, which means it must only react with acids.

What is unique about the scientific method of problem solving?

It requires trial-and-error, experimentation, and observations. For each possibility, an experiment must be conducted.

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Source: https://bhcc.digication.com/patrick_moreira_bio208/Practice_1

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