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Testing for ions

Testing for ions

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Explainer Video

Tutor: Alexander

Summary

Testing for ions

​​In a nutshell

Hydrochloric acid can be used to test for carbonates. Testing for sulfates requires hydrochloric acid and barium chloride, a positive result will return a white precipitate. Litmus paper and sodium hydroxide can be used to test for ammonium ions.



Equations


Word equation

Symbol equation

​carbonate ion + hydrogen ion → carbon dioxide + watercarbonate\ ion\ +\ hydrogen\ ion\ \rightarrow\ carbon\ dioxide\ +\ watercarbonate ion + hydrogen ion → carbon dioxide + water​​
​CO32−(aq) + 2H+(aq) → CO2(g) + H2O(l)CO_3^{2-}(aq)\ +\ 2H^+(aq)\ \rightarrow\ CO_2(g)\ +\ H_2O(l)CO32−​(aq) + 2H+(aq) → CO2​(g) + H2​O(l)​​
​hydrogen carbonate ion + hydrogen ion → carbon dioxide + waterhydrogen\ carbonate\ ion\ +\ hydrogen\ ion\ \rightarrow\ carbon\ dioxide\ +\ waterhydrogen carbonate ion + hydrogen ion → carbon dioxide + water​​
​HCO3−(s) + H+(aq) → CO2(g) + H2O(l)HCO_3^-(s)\ +\ H^+(aq)\ \rightarrow\ CO_2(g)\ +\ H_2O(l)HCO3−​(s) + H+(aq) → CO2​(g) + H2​O(l)​​
​barium (II) + sulfate ion → barium sulfatebarium\ (II)\ +\ sulfate\ ion\ \rightarrow\ barium\ sulfatebarium (II) + sulfate ion → barium sulfate​​
​Ba2+(aq) + SO42−(aq) → BaSO4(s)Ba^{2+}(aq)\ +\ SO_4^{2-}(aq)\ \rightarrow\ BaSO_4(s)Ba2+(aq) + SO42−​(aq) → BaSO4​(s)​​
​ammonium ion + hydroxide ion → ammonia + waterammonium\ ion\ +\ hydroxide\ ion\ \rightarrow\ ammonia\ +\ waterammonium ion + hydroxide ion → ammonia + water​​
​NH4+(aq) + OH−(aq) → NH3(g) + H2O(l)NH_4^+(aq)\ +\ OH^-(aq)\ \rightarrow\ NH_3(g)\ +\ H_2O(l)NH4+​(aq) + OH−(aq) → NH3​(g) + H2​O(l)​​



Testing for: carbonates

Dilute acid reacted with carbonates CO32−(aq)CO_3^{2-}(aq)CO32−​(aq) will produce bubbles because CO2CO_2CO2​ is given off.


CO32−(aq) + 2H+(aq) → CO2(g) + H2O(l)CO_3^{2-}(aq)\ +\ 2H^+(aq)\ \rightarrow\ CO_2(g)\ +\ H_2O(l)CO32−​(aq) + 2H+(aq) → CO2​(g) + H2​O(l)​​


Dilute hydrochloric acid and hydrogen carbonates will also produce bubbles because carbon dioxide is given off. 


​HCO3−(s) + H+(aq) → CO2(g) + H2O(l)HCO_3^-(s)\ +\ H^+(aq)\ \rightarrow\ CO_2(g)\ +\ H_2O(l)HCO3−​(s) + H+(aq) → CO2​(g) + H2​O(l)

​​


1.
Carbonate/hydrogencarbonate
2.
Pipette
3.
Gas being produced
4.
Limewater


​CO2CO_2CO2​ is then bubbled through limewater, saturated NaOHNaOHNaOH solution, if CO2CO_2CO2​ is present the solution will go from clear to cloudy.​



Testing for: sulfates

To identify the sulfate ion (SO42−)(SO_4^{2-})(SO42−​), add dilute (HCl)(HCl)(HCl) followed by barium chloride (BaCl2)(BaCl_2)(BaCl2​). Dilute (HCl)(HCl)(HCl) is added first to remove any trace carbonate ions since they would also produce a white precipitate.​


​Ba2+(aq) + SO42−(aq) → BaSO4(s)Ba^{2+}(aq)\ +\ SO_4^{2-}(aq)\ \rightarrow\ BaSO_4(s)Ba2+(aq) + SO42−​(aq) → BaSO4​(s)​​


If a white precipitate forms this is barium sulfate which means that the original compound contained sulfates. 


Chemistry; Inorganic chemistry and the periodic table; KS5 Year 12; Testing for ions
A. Metal sulfate solution, 1. Add dilute hydrochloric acid, 2. Add barium chloride, B. The solution is blue, C. A white precipitate forms



Testing for: ammonium ions

Ammonia gas is alkaline, and can be checked for using a damp piece of red litmus paper. If ammonia is present it will turn the red litmus paper blue. Ammonium ions (NH4+)(NH_4^+)(NH4+​) can be tested for by adding sodium hydroxide and gently heating the mixture. If ammonia is given off this means that there are ammonium ions present. This experiment should be carried out in a fume cupboard as it produces an irritant gas.


NH4+(aq) + OH−(aq) → NH3(g) + H2O(l)NH4Cl(aq) + NaOH(aq) → NH3(g) + H2O(l) +NaCl(aq)NH_4^+(aq)\ +\ OH^-(aq)\ \rightarrow\ NH_3(g)\ +\ H_2O(l) \\NH_4Cl(aq)\ +\ NaOH(aq)\ \rightarrow\ NH_3(g)\ +\ H_2O(l)\ +NaCl(aq)NH4+​(aq) + OH−(aq) → NH3​(g) + H2​O(l)NH4​Cl(aq) + NaOH(aq) → NH3​(g) + H2​O(l) +NaCl(aq)


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Ions and their formation

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Ions and their formation

Testing for anions

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Testing for anions

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Testing for ions

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FAQs - Frequently Asked Questions

How you test for ammonium ions?

Ammonium ions can be tested for by adding NaOH and heating. If ammonia is given off then ammonium ions are present.

How would you test for sulfates?

Sulfates can be tested for by adding dilute HCl followed by adding barium chloride. The formation of a white precipitate indicates the presence of sulfates.

How would you test for carbonates?

Carbonates can be tested for by reacting with acid and seeing if any bubbles are produced. This will be CO2.

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