5-1B Properties of Acids and Bases Lab

Purpose:  The purpose of this lab is to determine the acidity and basicity of solutions with the properties of acids and bases using chemical indicators.

Materials:

• 4 x 6 spot plate (I used two 3 x 4 spot plates)
•  Masking tape  
• Solutions A,B,C and D 
• 4 pieces of magnesium ribbon
• 4 pieces of red litmus paper 
• 4 pieces of blue litmus paper
• Bromothymol blue solution 
•  Indigo carmine solution
• Methyl orange solution 

Procedure:  Refer to text in BC Science 10 textbook, page 230

Results:

Photo of solutions in chemical indicators

  A table of observations:

Mg ribbon	Red Litmus	Blue Litmus	Bromothymol Blue	Indigo carmine	Methyl Orange	Unknown
- bubbling - edges of ribbon turned white	- remained same colour	- remained same colour	-blue to yellow	-remained same colour	- orange to red	A
-no bubbling	-red to very blue	-turned very blue	-blue to cobalt blue	-indigo to green	-lightened orange	B
-no bubbling	-remained same colour	-remained same colour	-remained same colour	- remained same colour	- remained same colour	C
-no bubbling	-turned light blue	-turned blue	-blue to cobalt blue	-remained same colour	-remained same colour	D

Discussion:

Analyze: 

 1. List the solutions in order form most acidic to least acidic(most basic).

Solutions A, C, D ,B

2. Which solution do you think was neutral? 

Solution C is neutral because in all the litmus papers, the solution did not change colour.  That is a property of a neutral solution. Solution A did not change the litmus paper colours either but in bromothymol blue, it drastically went from blue to yellow and in the magnesium ribbon, it began to release hydrogen bubbles, indicating that it is very acidic.  I was left with solution C through elimination of properties.

3. You used two bases. Explain how you know which solution was more alkaline (more basic).

The two basic solutions were solution B and D. Solution B was more basic because in the magnesium ribbon, it did not release hydrogen at all then both red and blue litmus papers turned very blue. The bromothymol blue turned into a richer cobalt blue colour and the indigo carmine shifted into a green colour. In indigo carmine, as the solutions turn yellow, it indicates it is becoming more basic.

Solution D was less basic because in litmus papers, it only turned into a light blue colour and in indigo carmine, it did not change into a yellower tone. 

4. How can magnesium metal be used to distinguish between an acid and a base?

Metals react only with acids to produce hydrogen gas; therefore, it would not react with basic solutions.  If bubbles(hydrogen gas) are produced by a solution, it is acidic. 

Conclude and Apply:

 1. a) What colour would each of the five indicators be in a solution that is pH 3?

Blue Litmus	Red Litmus	Bromothymol blue	Indigo carmine	Methyl Orange	Phenolphthalein
Red	Red	Yellow	Blue	Red	Colourless

    b) What colour would each of the five indicators be in a solution that is pH 10?

Blue Litmus	Red Litmus	Bromothymol blue	Indigo carmine	Methyl Orange	Phenolphthalein
Blue	Blue	Blue	Blue	Yellow	Pink

  

2. Suppose you are asked to put together a test kit to determine whether water taken from a factory waste drain is acidic, basic, or neutral. Your kit can contain only three tests. Which tests would your kit contain? Explain.

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My kit will contain the universal indicator, pH meters/computer probes and litmus papers.
The universal indicator is versatile since it does contain multiple indicators that will help me determine the pH level by turning different colours based upon the acidity and basicity of the water.
The pH meters or computer probes are very simple. I can obtain a sample of the water and test the electrical properties with a sensor. The litmus paper is useful and straightforward into showing if the water is neutral. If it does not change colour, the water will be neutral.  

3. Refer to the photo of the lichen Roccella tinctoria on this page, from which litmus is extracted. If this lichen were ground up and then soaked in vinegar,what colour would the solution likely be?

Copyright 2012 - McGraw-Hill Ryerson

Vinegar is acetic acid. If the lichen were to be soaked in this acidic solution, it will likely be red in colour. With both red and blue litmus, acids appear red.

4. What is the colour of seawater that has had bromothymol blue added to it?
Since pure water has a pH level of 7, the pH level of seawater will likely range from 7 to 8. The bromothymol blue with seawater will be a greenish-blue colour because seawater is close to neutral. The seawater will create a yellower tone in the blue indicator.

5.    Consider the colour-coded map of the world’s oceans shown to the right.

Copyright 2012 - McGraw-Hill Ryerson

a) Which regions of the world’s oceans appear to be most affected by the drop in pH level?
The area in Northern Atlantic Ocean between the east coast of North America and Europe as well as the waters between the tip of Argentina and Africa appear to be most affected. Those areas in the map is the most red. 

b) Which regions are the least affected?
The oceans surrounding the continents and in the Arctic seem to be the least affected. Those areas on the map show a dark blue colour.

Conclusion:

During this lab, I examined the properties of an acidic solutions, a neutral solution and a couple bases. Through this lab, I learned to be very observant of everything that happens with the solutions during the process and that results need to be analyzed carefully since the colour charts can be confusing at times. Each indicator played a big part in determining the acidity and basicity with not only colours but properties dealing with the release of hydrogen. It was an interesting experience.
Next time, I would have a more consistent ratio of each liquid indicator to the solutions because that can affect the consistency and reliability of the results. For the magnesium ribbon, I would sand it down with sandpaper more thoroughly since the coating of magnesium oxide can affect the production of hydrogen molecules in relation to determining acidity.