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If you want to measure how alkaline a solution is you need a scale.
The pH scale is a way of describing the concentration of acid ions [H⁺(aq)] in a liquid.
Strong alkaline solutions have a high pH (14, 13, ..), schwache Säuren einen niedrigeren (..,9, 8).
Alkaline solutions have pH btween 8 and 14).

What you need: Box of a music cassette as a stand for six 3-ml injection bottles (1 - 6), 1-ml syringe, 1M-NaOH, pure water (for car battery), universal indicator solution (UI) red grape juice.
* Transfer 1.0 ml of 1 M sodium hydroxide solution into bottle 1 by a syringe.
* Transfer 0.9 ml of water into bottles 2 - 5.     * Remove 0.1 ml from bottle 1.
* Mix it with the water in bottle 2. Remove 0.1 ml from bottle 2.
* Mix it with the water in bottle 3. Remove 0.1 ml from bottle 3......
* Dilute this solution another two times in the same manner.
* Add one drop of UI to each of the bottles labelled 1 - 5.
* Do the same experiment replacing UI by the indicator red grape juice.
Observation The different colours of this dilution series can be compared to a colour scale.
Left: Using UI you will only see a colour change in bottle 5 (pH 9).
Right: Taking 2 drops of red grape juice the colour changes show: Green colour in bottle 1 and 2 (pH 14, 13),
violet at pH 12,  red at pH 11 (bottle 4), pH 10 (bottle 5).