You start with a solution of your compound and then add a few drops of sodium hydroxide solution or ammonia solution. Note what happens. The next video shows these two reactions. If you look very closely at the ammonia one, you will see a slight trace of a precipitate.

Again, the precipitates are the metal hydroxides. Remember that ammonia solution contains some hydroxide ions. You can test for ammonium ions either in a solid or in solution by adding sodium hydroxide solution and warming gently.They dissolve in excess sodium hydroxide solution to produce soluble complex ions in which hydroxide groups are bound to the metal ion. With this test, you can compare the reaction time of one person at different times or compare the results of different people. So both of these give a white precipitate of the metal hydroxide and they both dissolve in excess sodium hydroxide to give a colourless solution. The problem in the calcium case is that calcium hydroxide is slightly soluble - we use its dilute solution as lime water. Ammonia solution contains far fewer hydroxide ions than sodium hydroxide solution of the same concentration. So you don't form enough calcium hydroxide to form a reasonable precipitate.

Most sulfates, including those of \(\ce{Na In each case the formation of the precipitates involves exactly the same chemistry as with sodium hydroxide solution. All that matters is the presence of the hydroxide ions, not where they came from. grades 9–12 K12 advanced subsidiary chemistry course etc. and help you to identify unknown inorganic and organic The presence of the hydroxide ions means that you might expect ammonia solution to react with metal ions in the same way as sodium hydroxide solution. The video shows what happens when you add sodium hydroxide solution to these three ions (and also to Al 3+ ions - ignore that for now.)Calcium ions give a white precipitate insoluble in excess sodium hydroxide solution, but no precipitate or a very slight precipitate in ammonia solution. What is happening here is that the excess ammonia solution reacts with the copper(II) ions to give the deep blue soluble ion [Cu(NH 3) 4] 2+ where ammonia molecules have attached themselves to the copper ion. Magnesium ions give a white precipitate insoluble in excess in both sodium hydroxide or ammonia solution. This reaction speed test is not very scientific, but just for fun and practice. How to do time reaction test Note: The video shows some very poor practice by heating a solution in a test tube using a very hot Bunsen flame. That is asking for trouble because there is a real risk of hot solution spurting out of the tube. Liquids should never be heated in a test tube with anything other than a small blue flame with no blue cone in it.

You should, of course, be able to write full equations if you were asked, but they are more time-consuming, with more chance of making mistakes. If the compound contains ammonium ions, you will get ammonia gas produced which you can test with damp red litmus paper which it turns blue.Remember that your speed on this test is the sum of the reaction time of your brain and the movement of your finger to press the button. This also works perfectly well if you add the sodium hydroxide solution to some solid containing ammonium ions and warm that mixture. newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}}}\) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash{#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)\(\newcommand{\AA}{\unicode[.8,0]{x212B}}\)

In fact, it is easier to write the ionic equation, which is the same for all cases - just choosing the (aq) or (s) as appropriate. These tests for metal ions are always done in solution and adding either sodium hydroxide solution or ammonia solution. Note: Strictly speaking this should be the [Cu(NH 3) 4(H 2O) 2] 2+ ion. At this level, all you may be expected to know is its deep blue colour.

There are two useful short pieces of video showing what happens in these reactions. They look at the aluminium ion reactions first, followed by the zinc ion reactions. This time, only the zinc hydroxide precipitate redissolves - for the same reason that the copper(II) hydroxide that we have already looked at dissolves in excess ammonia solution.