The four gas tests
Gas
Test
Result
Hydrogen hold a burning splint at the open end of the test tube
burns rapidly with a squeaky pop
Oxygen put a glowing splint into the test tube
the splint relights
Carbon dioxide bubble through or shake with limewater
the limewater turns milky (cloudy)
Chlorine put damp litmus paper into the gas
the litmus is bleached white
Limewater is aqueous calcium hydroxide . It turns milky because
insoluble calcium carbonate forms
Chlorine may turn the litmus red first (it is acidic) before bleaching it
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Testing for the four gases hydrogen hold a LIT splint at the mouth of the tube burns with a squeaky pop oxygen put a GLOWING splint inside the tube the splint relights carbon dioxide bubble the gas through limewater the limewater turns milky chlorine hold DAMP litmus paper in the gas the paper is bleached white Learn the test AND the positive result — an exam question usually asks for both. Four small test tubes side by side showing each test: burning splint at the mouth for hydrogen, glowing splint inside for oxygen, limewater going milky, and damp litmus bleached white
Each test is a test and a result , two marks. "Squeaky pop" on its
own does not describe the test; say a lit splint is held at the
mouth of the tube
Oxygen relights a glowing splint. Do not describe lighting a splint
and blowing it out without saying it is still glowing
The litmus must be damp , and the test for chlorine gas is not
the test for chloride ions in solution
If asked what limewater is, it is a solution of calcium hydroxide
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