Hi All,
I don't have much information to work with here, but I am wondering if anyone out there knows about a prac which involves a measuring cylinder, universal indicator and probably a range of solutions which shows the gradient of ph. A teacher here was asking about it. I am guessing it looks a bit like the density pracs where the solutions are coloured and they layer out in the measuring cylinder. Any ideas? Guesses?
Also, I was preparing a prac exam earlier today and thought potassium hydroxide would be a good solution for testing ph (they have to do 4 solutions and sodium hydroxide seems to be the one which is always done). When I tested it, it was 11 and by the time I got through the other 3 solutions to record their phs the potassium hydroxide had changed to 8. I then tried diluting a few samples in various proportions in the test tubes and they all did the same thing. I decided to ditch the potassium hydroxide idea and use sodium hydrogen carbonate instead... But then when I came back from morning tea, one of the test tubes had separated into green on top and yellow underneath!! (perhaps this is a hint for what to do for the prac mentioned above??). Does anyone know why this happened?
Rosalie
ph prac and potassium hydroxide.
Re: ph prac and potassium hydroxide.
I have a great one called Rainbow experiment.
You need:
1L measuring cylinder
sodium carbonate decahydrate(washing soda)
vinegar
long stirring rod
universal indicator
Method:
fill measuring cylinder with water
stir in about 10-15mL universal indicator
add 30gm washing soda
add 80 mL vinegar
stir with a rotating/swirling action
adjust quantities for different size measuring cylinder
You need:
1L measuring cylinder
sodium carbonate decahydrate(washing soda)
vinegar
long stirring rod
universal indicator
Method:
fill measuring cylinder with water
stir in about 10-15mL universal indicator
add 30gm washing soda
add 80 mL vinegar
stir with a rotating/swirling action
adjust quantities for different size measuring cylinder
-
fibreweb
- Posts: 620
- Joined: 20 Jul 2006, 10:00
- School: Oxley High School
- Suburb: Tamworth
- State/Location: NSW
Re: ph prac and potassium hydroxide.
We often do the rainbow prac, especially with the year 6 kids coming up for an afternoon of fun in the various departments.
I have broken it down into large testtube quantities.
fill a large test tube to about 2.5 cm from the top with distilled/tap water add a couple of drops of universal indicator and stir with a skewer. Water is some shade of green dependinig on the water.
Drop a crystal or 2 of sodium carbonate (we use washing soda as it disolves slowly and is cheaper) Water turns purple
Add about 3 mls vinegar, now the bottom is purple and the very top red.
Gently stir with the skewer in a rotating action and watch the bands of colour appear.
They will keep for several days.
The kids enjoy seeing what happens if the add more of one thing or the other, or do it in a different order. The above order seems to work best.
Wendy
I have broken it down into large testtube quantities.
fill a large test tube to about 2.5 cm from the top with distilled/tap water add a couple of drops of universal indicator and stir with a skewer. Water is some shade of green dependinig on the water.
Drop a crystal or 2 of sodium carbonate (we use washing soda as it disolves slowly and is cheaper) Water turns purple
Add about 3 mls vinegar, now the bottom is purple and the very top red.
Gently stir with the skewer in a rotating action and watch the bands of colour appear.
They will keep for several days.
The kids enjoy seeing what happens if the add more of one thing or the other, or do it in a different order. The above order seems to work best.
Wendy
