Carry out Steps 1-5 to investigate three indicators (bromothymol blue, methyl orange and phenolphthalein). Follow the instructions carefully.
WEAR EYE PROTECTION.
Step 1:
Step 2:
Step 3:
Step 4:
Step 5:
Put 4 drops of 0.1 M HCl(aq) into circle A1 to create one large drop. Repeat for each circle B1 – D1.
Now use the solutions named at the top of the other columns (i.e. instead of HCl) to repeat Step 1 for A2 – D2, A3 – D3, A4 – D4 & A5 – D5.
Put 1 drop of bromothymol blue into each circle A1 to A5; 1 drop of methyl orange in B1 – B5 and 1 drop of phenolphthalein in C1 – C5.
Make a mixture of indicators (do this in a glass vial or well plate) using the recipe in the green-shaded box below.
Put 1 drop of your mixed indicator into each solution in circles D1 – D5. Make a note of your observations (take a photo?).
0.1 M HCl(aq)
(strong acid, pH = 1)
pH 4 buffer
“pure” water
(neutral, pH = 7)
(weak acid)
pH 9 buffer
(weak alkali)
0.1 M NaOH(aq)
(strong alkali, pH = 13)
A1
A2
A3
A4
A5
B1
B2
B3
B4
B5
C1
C2
C3
C4
C5
D1
D2
D3
D4
D5
bromothymol blue
(BB)
INDICATOR
methyl orange
(MO)
Phenolphthalein
(PP)
Mixed indicator:
BB = 10 drops
MO = 5 drops
PP = 5 drops