Chemistry - Analysis of Gas and Ions

What is a reaction that uses water, and releases hydrogen?

Metal + water -> metal hydroxide + hydrogen

What is a reaction that uses acid and releases hydrogen?

Metal + acid -> salt + hydrogen

What is the test for hydrogen, and what is the result if it is present?

Take a lit splint near the gas. A squeaky pop sound will be heard of hydrogen is present.

Name three uses of hydrogen

Fuel cells in electric cars, rocket fuel, and industrial processes, such as refining petroleum, producing ammonia for fertilisers and manufacturing methanol.

What is the most abundant gas in Earth’s atmosphere today? What is the percentage?

Nitrogen - 78%.

What other main gas makes up 21% of the atmosphere?

Oxygen.

Which gases make up the remaining 1% of the atmosphere?

Trace gases, like argon, helium and hydrogen, and also greenhouse gases, like carbon dioxide, methane and water vapour.

What experiment can you use to prove 21% of air is oxygen?

100 cubed cm of air is in a gas syringe, it is pushed through a silica tube packed with copper. 21 cubed cm of the air reacts with the copper, making copper oxide. The remaining 79% is nitrogen and other gases.

How does the appearance of copper change when it reacts with oxygen?

It changes colour from brown or orange to black.

How can you produce oxygen?

React manganese oxide (MnO2) with hydrogen peroxide (H2O2) in a conical flask. A trough with water is filled, and a boiling tube is placed upside down into it. The delivery tube is placed on the conical flask when the reaction begins, and the other end into the boiling tube in the trough. Once the gas produced has displaced all water it can, pull it out and keep upside down, and put a bung on it.

What is the test and positive result for oxygen?

Take a glowing splint near the oxygen. If it relights, oxygen is present.

What is one way to produce carbon dioxide, using heat?

Thermal decomposition - heating copper carbonate (a green powder) into copper oxide (a black powder) and carbon dioxide.

What is a way to produce carbon dioxide from acid?

React a metal carbonate with acid. You will get a salt, water and carbon dioxide as products.

What is the test and positive result for carbon dioxide?

Bubble the gas through limewater. If the gas is carbon dioxide, the limewater will turn from clear to cloudy white.

What is a cation?

A positively charged ion (an atom that has lost electrons).

What elements are typically cations?

Typically metals in the first three groups, like potassium, magnesium and aluminium.

How do you perform a flame test?

Take a damp splint and dip it in a sample of the metal. Place it in a roaring flame for a few seconds, and note the colour produced.

What colour flames will be produced for the metals in this order: lithium, sodium, potassium, copper, and calcium?

Red, yellow, lilac, green, and orange/brick-red.

How to produce ammonia gas?

Use a precipitation reaction. Add a few drops of sodium hydroxide to ammonium and warm it gently, this produces ammonia gas, turning damp red litmus paper blue.

What is a precipitation reaction?

A reaction producing a precipitate - an insoluble solid that has ‘dropped out’ of the solution and has become visible. A sample can be reacted with sodium hydroxide to produce a coloured precipitate.

What is the colour of iron 2 solution and its precipitate?

A pale green solution and a green/grey precipitate.

What is the colour of iron 3 solution and its precipitate?

Yellow/orange solution and orange/brown precipitate.

What is the colour of copper solution and its precipitate?

Blue solution and blue precipitate.

What is the colour of magnesium solution and its precipitate?

Colourless solution and colourless precipitate.

What is the colour of aluminium solution and its precipitate?

Colourless solution and colourless precipitate.

What is the colour of calcium solution and its precipitate?

Colourless solution and colourless precipitate.

What happens to the aluminium precipitate when excess sodium hydroxide is added?

It redissolves in it.

What are anions?

Negatively charged ions (atoms that have gained electrons).

Which elements are normally anions?

Normally non-metals in group 7, like fluorine, chlorine and bromine, which are all halides.

What chemical is added to chloride to get what result?

Sliver nitrate (AgNO3) added, white precipitate produced.

What chemical is added to bromide to get what result?

Silver nitrate added, cream precipitate produced.

What chemical is added to iodide to get what result?

Silver nitrate added, yellow precipitate produced.

What chemical is added to sulfate to get what result?

Barium chloride (BaCl2) added, white precipitate produced.

What chemical is added to carbonate (CO3)2- to get what result?

Hydrochloric acid added, colourless effervescence occurs.

What is the test and positive result for chlorine?

Damp blue litmus paper bleaches white in presence of chlorine.