Purpose The purpose of the pH Pointers lab is to work with both synthetic and natural pigments to study their behavior as acid- base indicators and to determine their transition ranges as well as finding the pH of the unknown solution.
Experimental Details Regarding the experimental details, three procedures were performed. In the first set of procedures, a well plate that accommodates twelve samples was obtained. Nine test tubes were obtained as well and were placed within the holes in the well plate. One drop of the same indicator was placed in each of the test tubes. The indicators included Methyl Red, Congo Red, Phenol Red, and Alizarin Yellow. After dropping one drop of the same indicator into each test tube, ten drops of a different pH was added to each of the test tubes. A pH of 1 was added to the first test tube and so on all the way to pH of 12. The solutions were mixed with glass rods and became uniform within the test tubes. The color of each solution was recorded (see table 1). The test tubes were rinsed out with tap water and DI water once and the cell wells were dried. The following steps were repeated for each of the four synthetic indicators. The second procedure involved testing the natural indicators. The first step was to obtain nine test tubes to correspond to the nine pH solutions. 1mL of hibiscus juice was then placed in each of the nine test tubes and pH solutions were then added to the test tubes as well. The color of each solution was recorded in Table 2. The test solutions were disposed in a beaker, not down the drain. The test tubes were then rinsed out with tap water and then DI water once and the previous steps were performed using cabbage juice instead of hibiscus juice. The third procedure involved estimating the pH of the unknown solution. Three indicators were chosen: Methyl Red, Alizarin Yellow, and cabbage juice. The unknown pH was added to the test tubes filled with Methyl Red, Alizarin Yellows, and cabbage juice. Based on the color that occurred within the test tubes, they were compared to the colors when known pH solutions were used. The results were recorded in table 5.
Calculations
No calculations were performed in this lab.
Results
Table 1: Synthetic Indicators pH of Solution Tested
Color Seen with Methyl Red
Color Seen with Congo Red
Color Seen with Phenol Red
Color Seen with Alizarin Yellow GG
1
Dark Red
Dark Violet
Red Orange
Dark yellow/green
2
Pink-red
Semi-dark violet
Dark orange
Dark yellow
4
Red
Dark purple
Dark yellow
Orange/yellow
5
Bright red
Purple
Light yellow
Dark yellow/orange
6
Orange red
Dark red
Yellow
Dark red
7
Yellow red
Red(no change)
Dark yellow/gold
Very dark red
9
Yellow-orange
Red
Gold
Dark purple/violet
10
Orange-gold
Red
Gold
Purple
12
Dark yellow
Red
Gold
Dark Purple
Table 2: pH Information about Synthetic Indicators
Indicator
Transition pH Range
Transition Color
Color at lower pH
Color at higher pH
Methyl Red
6-7
Orange Red
Dark Red
Dark yellow
Congo Red
5-6
Dark Red
Dark Violet
Red
Phenol Red
4-5
Orange
Red orange
Gold
Alizarin Yellow GG
5-6
Orange
Dark yellow/green
Purple
Table 3: Natural Indicators pH of Solution
Color Seen with Cabbage juice
Color Seen with Habiscus Tea
1
Pink/Red
Light Pink
2
Pink
Light Pink Orange
4
Lighter Pink
Light Orange
5
Light Purple
Light Orange
6
Light Purple
Light Peach
7
Purple/Clear
Darker Peach
9
Clear with blue tint
Orange
10
Light Green
Gold
12
Darker Green
Light Gold
Table 4: pH Information of Natural Indicators
Indicator
Transition pH Range
Transition Color
Color at lower pH
Color at higher pH
Cabbage
5-9
Purple
Pink/Red
Darker green
Habiscus Tea
9-12
Orange
Light Pink
Light Gold Table 5: Observations from Testing Unknown Solution
Indicator Used
Color Observed
Inference
Alizarin Yellow GG
Orange-yellow
pH 5
Methyl
