Recognition of substances is a task which meets quite often during control and independent works, when performing laboratory and practical trials (including during the Olympic Games in chemistry) and also during a Unified State Examination. Acid and alkali belong to the class of inorganic substances which can be distinguished by means of the characteristic chemical reactions differently called qualitative. The easiest ways is definition of acids and alkalis by means of indicators.
It is required to you
- - test tubes;
- - acid;
- - alkali;
- - methyl orange;
- - litmus;
- - phenolphthalein.
Instruction
1. Acid is the complex substance consisting of ions of hydrogen and the acid rest. That is characteristic property of all acids is existence of an ion of hydrogen which causes chemical properties. The acid rest at each acid different. These substances have sour taste that is familiar on lemon or acetic acids. The general way of definition of acid is use of the indicator – the painting sensitive substance which depending on Wednesday changes own coloring.
2. Take a test tube with the defined substance and flow the indicator (or place in it the same indicator, only paper). Watch change of its coloring. For example, orange color the indicator – methyl orange - in acidic environment gets red coloring. Other indicator, litmus, at addition in acid also gains red color. Here excellently the reception of mnemonic used for storing approaches: "The indicator red - acid will specify litmus clearly".
3. For definition of concrete acid it is possible to use high-quality reactions to ions of the acid remains. For example, if to acid to flow chloride of barium and the white deposit will drop out, then it is possible to assume that in this test tube there is sulfuric acid. At silver nitrate addition to bromovodorodny acid the deposit of white-yellow color will drop out.
4. Alkali is a complex substance which properties are caused by existence in its structure of hydroxyl ions. Their presence can also be determined by indicators. Flow in a test tube with alkali methyl orange (or lower indicator paper). Orange color will turn into yellow coloring. The research can be continued by other indicators. Litmus in the alkaline environment becomes blue: "Indicator litmus blue. Alkali here — be not a gawk!". To confirm the assumptions add to a test tube with estimated alkali phenolphthalein – it will get characteristic crimson coloring. Traditionally alkali is also determined by the last indicator.