How do you test for hydrogen?
Take a splint (with a burning flame) and hold it close to the hydrogen gas (suspected) in the test tube.
What observation confirms hydrogen is present?
You hear a squeaky pop.
Why does hydrogen make a squeaky pop?
Because the burning flame gives the hydrogen enough energy to start reacting with oxygen in surrounding air. The reaction of oxygen and hydrogen goes to form water, resulting in the sound of the squeaky pop.
Write the word equation for hydrogen burning in air.
Hydrogen+oxygen->water
How do you test for oxygen?
Take a glowing splint (no flame but glowing red at the end) and place in the test tube with the sample of gas you suspect will be oxygen.
What observation confirms oxygen is present?
Glowing splint will re-ignite (re-light).
Why does oxygen relight a glowing splint?
Because combustion (burning) requires oxygen, so if the splint it supplied with plenty of oxygen the reaction will spark again.
How do you test for carbon dioxide?
Gas sample in one tube, aqueous solution of calcium hydroxide (limewater) in another. Bubble the gas through the calcium hydroxide.
Why does limewater turn cloudy?
Because carbon dioxide is present. CO2 and calcium hydroxide react to form calcium carbonate and water. The calcium carbonate is a solid, and its those solid particles than make the limewater appear cloudy.
Write the equation for carbon dioxide reacting with limewater.
CO2+Ca(OH)2 -> CaCO3+H2O
What is a flame test used to identify?
Used to see what colour flames a metal ion produces when it burns. Since different ions produce different coloured flames we can use the colour to identify the type of metal.
Why must a nichrome (or platinum) wire loop be cleaned before a flame test and how is it cleaned?
Clean it by: dip in dilute HCl, rinse in distilled water and then heat it over a Bunsen burner flame.
What are the steps that come after cleaning the nichrome wire loop?
Dip wire loop in compound you want to test, hold it in the clear blue part of the Bunsen burner flame (the hottest part), observe what colour the flame turns as the compound burns.
What flame colour identifies lithium ions?
Crimson
What flame colour identifies sodium ions?
Yellow
What flame colour identifies potassium ions?
Lilac
What flame colour identifies calcium ions?
Orange-red
What flame colour identifies copper(II) ions?
Green.
How could contamination affect flame test results? What if there were multiple metals in a sample?
Multiple metals=colours of flames mixing and you wont be able to tell very well which metals you have.
What reagent (solution) is used to test for metal ions in solution and do we carry out that test?
Sodium hydroxide (NaOH).
React metal ions with NaOH solution and observe colour change. Because some metal ions form coloured precipitates when they react with hydroxide ions, the precipitates then determine the colour of the solution. (Example Cu2+ (+) 2OH- -> Cu(OH)2).
What observation identifies Iron (ll and lll) ions using sodium hydroxide?
Iron (ll)- Green precipitate (and solution)
Iron (lll)- brown precipitate (and solution)
What observation identifies aluminium ions using sodium hydroxide?
First a white precipitate is formed, but if there’s excess NaOH it redissolves to form a colourless solution.
What observation identifies calcium ions using sodium hydroxide?
White precipitate formed (white solution)
What observation identifies magnesium ions using sodium hydroxide?
White precipitate (white solution).
