Reference no: EM13130908
PH indicators for acids / dilution
Scenario:
You took 7 test tubes. In one you mixed 5ml of 0.1M NaOH and 5ml water together. You add 9ml of water to the other 6 test tubes. If you take the original test tube ( the one that you mixed 5ml of 0.1M NaOH and 5ml of water) and put 1ml into test tube #2. If you took test tube # 2 and put 1ml into test tube # 3 and so on...(repeat till all are done). Add 2 drops of Bromothymol Blue to all 7 test tubes.
Repeat the procedure above using Red Cabbage Extract as the indicator.
Repeat the procedure above using Alizarin yellow as the indicator.
Repeat the procedure above using Phenolphthalein as the indicator.
Questions:
1. Calculate concentrations of OH- and the pH of each basic solution. Since NaOH donates on OH- ion for each NaOH molecule, the OH- concentration is equivalent to the NaOH molarity. The pOH is calculated as -log[OH-] and the pH is calculated as 14-pOH.
2. Estimate the useful range for each indicator from a minimum to a maximum pH. Range usually spans 1.5 to 2 pH units. For example, metacresol purple is considered to be useful in the range from 7.4 to 9.0
3. Which indicator is the best to use to observe pH changes around pH=7, pH=8, pH = 10 and pH=12?
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