Chemistry chapter 22- chemical changes

What is the test for hydrogen?

A burning splint is held at the open end of a test tube of the gas.

What is the positive test result for hydrogen?

Hydrogen burns rapidly with a pop sound.

What is the test for oxygen?

A glowing splint is inserted into a test tube of the gas.

What is the positive test result for oxygen?

The glowing splint relights in oxygen.

What solution is used for this test?(oxygen) Give the chemical name

An aqueous solution of calcium hydroxide (limewater).

What is the test for carbon dioxide?

Carbon dioxide is shaken with or bubbled through limewater.

What is the positive test result for carbon dioxide?

The limewater turns milky (cloudy).

What is used for the carbon dioxide test?

Litmus paper.

What is the test for chlorine?

Damp litmus paper is put into chlorine gas.

What is the positive test result for chlorine?

The litmus paper is bleached and turns white.

What type of ion can flame tests be used to identify?

Some metal ions (cations).

What colour flame do lithium ions produce?

Crimson.

What colour flame do sodium ions produce?

Yellow.

What colour flame do potassium ions produce?

Lilac.

What colour flame do calcium ions produce?

Orange-red.

What colour flame do copper ions produce?

Green.

What happens if a flame test sample contains a mixture of positive ions?

Some flame colours can be masked making identification more difficult/not possible.

What solution can be used to identify some metal ions?

Sodium hydroxide solution.

Which 3 metal ions form white precipitates when sodium hydroxide solution is added?

Calcium (Ca²⁺), magnesium (Mg²⁺) and aluminium (Al³⁺) ions.

Which 3 metal ions form coloured precipitates when dilute NaOH(aq) is added?

Copper(II) (Cu²⁺), iron(II) (Fe²⁺) and iron(III) (Fe³⁺) ions.

Give the ionic equation for the reaction between calcium ions & hydroxide ions? Incl. state symbols

Ca²⁺(aq) + 2OH⁻(aq) → Ca(OH)₂(s) insoluble calcium hydroxide forms.

What is the ionic equation for the reaction between magnesium ions & hydroxide ions? Incl. state symbols

Mg²⁺(aq) + 2OH⁻(aq) → Mg(OH)₂(s) insoluble magnesium hydroxide forms.

Give the ionic equation for the reaction between aluminium ions & hydroxide ions? Incl. state symbols

Al³⁺(aq) + 3OH⁻(aq) → Al(OH)₃(s) aluminium hydroxide forms.

Which white precipitate will dissolve in excess sodium hydroxide solution?

Aluminium hydroxide, Al(OH)₃.

What colour precipitate forms when copper(II) ions react with hydroxide ions?

Blue precipitate.

Give the ionic equation for the reaction between copper(II) ions & hydroxide ions? Incl. state symbols

Cu²⁺(aq) + 2OH⁻(aq) → Cu(OH)₂(s) insoluble copper(II) hydroxide forms.

What colour precipitate forms when iron(II) ions react with hydroxide ions?

Green precipitate.

Give the ionic equation for the reaction of iron(II) ions & hydroxide ions? Incl. state symbols

Fe²⁺(aq) + 2OH⁻(aq) → Fe(OH)₂(s) insoluble iron(II) hydroxide forms.

What colour precipitate forms when iron(III) ions react with hydroxide ions?

Brown precipitate.

Give the ionic equation for the reaction between iron(III) ions & hydroxide ions? Incl. state symbols

Fe³⁺(aq) + 3OH⁻(aq) → Fe(OH)₃(s) insoluble iron(III) hydroxide forms.

What forms when carbonates react with dilute acids?

Carbon dioxide.

What is the test for carbonate (CO₃²⁻) ions?

Add a few drops of dilute acid to the carbonate. (Carbonate can be in solution or a solid form.)

What is the positive test result for carbonate ions?

Fizzing (effervescence) occurs. (The gas formed can be tested with limewater to confirm it is CO₂ if needed.)

What is the ionic equation showing carbonate ions reacting with acid? Incl. state symbols

CO₃²⁻(aq) + 2H⁺(aq) → CO₂(g) + H₂O(l).

What is the test for halide ions in solution? (i.e. Group 7 ions?)

Add dilute nitric acid followed by silver nitrate solution.

What is produced in this test for halide ions?

A precipitate of a silver halide.

What colour is silver chloride?

A white precipitate.

What is the ionic equation showing the reaction between silver ions and chloride ions?

Ag⁺(aq) + Cl⁻(aq) → AgCl(s).

What colour is silver bromide?

A cream precipitate.

What is the ionic equation showing the reaction between silver ions and bromide ions?

Ag⁺(aq) + Br⁻(aq) → AgBr(s).

What colour is silver iodide?

A yellow precipitate.

What is the ionic equation showing the reaction between silver ions and iodide ions?

Ag⁺(aq) + I⁻(aq) → AgI(s).

What is the test for sulfate ions in solution?

Add dilute hydrochloric acid followed by barium chloride solution.

What is produced in this test for sulfate ions?

A white precipitate of barium sulfate.

What is the ionic equation showing the reaction between barium ions and sulfate ions?

Ba²⁺(aq) + SO₄²⁻(aq) → BaSO₄(s).

What are detected and identified by instrumental methods?

Elements and compounds.

Give four advantages of instrumental methods compared to chemical tests?

Sensitive (only use a tiny amount of substance)
Informative (provide a lot of valuable information about a substance),

Rapid, Accurate.

What is flame emission spectroscopy used to analyse?

Metal ions in solution.

What steps are taken to carry out a flame emission spectrum?

The sample is put into a flame and the light given out is passed through a spectroscope.

What is the output of flame emission spectroscopy?

A line spectrum – different ions produce lines at different wavelengths.

How is the concentration of the ion(s) in solution determined in flame emission spectroscopy?

By measuring the intensity of wavelength of light given out on the line spectrum – Greater the intensity, higher the concentration of ion.

Give three advantages of flame emission spectroscopy over flame tests

Identifies metal ions with more certainty.
Can analyse mixtures of ions.

Measures concentration of metal ions.

What is chromatography used for?

Separate mixtures and identify substances.

What are the names of the two phases in chromatography?

Mobile phase and stationary phase.

What is the mobile phase in paper chromatography?

A solvent.

What is the stationary phase in paper chromatography?

Chromatography paper.

What does the separation of substances in chromatography depend upon?

The distribution of substances between the phases, i.e. the relative attraction between the substance and the mobile and stationary phases.

Which substances move further up the chromatography paper?

Substances that are relatively more attracted to the mobile phase.

Which substances remain further down on the chromatography paper?

Substances which are relatively more attracted to the stationary phase.

How is the Rf value calculated?

Rf = distance moved by substance ÷ distance moved by solvent.

What affects the Rf value of a substance?

The solvent used – different compounds have different Rf values in different solvents.

What does each spot on the chromatography paper represent?

A pure compound.

How many spots appear on a chromatogram of a pure substance?

1 spot.

How many spots appear on the chromatogram of an impure substance (a mixture)?

2 or more spots. n