Inorganic Chemistry Chapter 18: Chemical Tests

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Questions and Answers

How does anhydrous copper (II) sulfate change in the presence of water?

It turns from white to blue.

What are the freezing and boiling points of pure water at atmospheric pressure?

Freezing point is 0°C and boiling point is 100°C.

What flame color indicates the presence of sodium ions ($Na^+$) during a flame test?

Yellow

Why is sodium hydroxide used to test for the presence of metal ions?

Most metal hydroxides are insoluble in water and form precipitates when sodium hydroxide is added. Signup and view all the answers

What is the chemical equation for the reaction of anhydrous copper (II) sulfate with water?

$CuSO_4(s) + 5H_2O(l) \rightleftharpoons CuSO_4.5H_2O(s)$ Signup and view all the answers

What is the flame color for lithium ions ($Li^+$) in a flame test?

Red Signup and view all the answers

Describe the change you would see when testing an impure water sample for its freezing point

The impure water sample would freeze at a temperature lower than 0°C. Signup and view all the answers

What precipitate forms when sodium hydroxide solution is added to a solution containing copper ions ($Cu^2+$)?

A blue precipitate of copper hydroxide. Signup and view all the answers

What is the visible result when testing for carbon dioxide gas with limewater?

The limewater turns milky or cloudy. Signup and view all the answers

Describe the chemical reaction that occurs when hydrogen gas reacts with a flame.

Hydrogen gas reacts with oxygen to produce water, represented by the equation $2H_2 + O_2 ightarrow 2H_2O$. Signup and view all the answers

How would you test for the presence of chlorine gas?

Chlorine gas turns damp red litmus paper white. Signup and view all the answers

What observation indicates the presence of ammonia using universal indicator paper?

The universal indicator paper turns blue. Signup and view all the answers

What happens when you place a glowing splint into a tube containing oxygen gas?

The glowing splint relights. Signup and view all the answers

What reagent is added to the solution to test for the presence of iodide ions?

Silver nitrate Signup and view all the answers

Why is dilute nitric acid added to the solution before silver nitrate?

To make the solution acidic Signup and view all the answers

What indicates the presence of iodide ions in the solution?

A yellow precipitate Signup and view all the answers

Write the chemical equation for the reaction that occurs when silver nitrate is added to a solution containing iodide ions.

Ag+(aq) + I-(aq) → AgI(s) Signup and view all the answers

What are the physical states of the reactants and product in the given chemical equation?

Aqueous reactants and solid product Signup and view all the answers

What color precipitate indicates the presence of copper ions (Cu2+)?

Blue Signup and view all the answers

Write the chemical equation for the reaction between iron(III) ions (Fe3+) and sodium hydroxide (NaOH).

Fe3+(aq) + 3NaOH(aq) -> Fe(OH)3(s) + 3Na+(aq) Signup and view all the answers

Which ion results in the formation of a green precipitate when reacting with sodium hydroxide?

Iron(II) ions (Fe2+) Signup and view all the answers

What gas is produced when ammonium salts react with sodium hydroxide?

Ammonia Signup and view all the answers

How can you confirm the presence of carbonate ions (CO3^2-)?

By adding dilute hydrochloric acid and testing the gas with lime water for carbon dioxide. Signup and view all the answers

Describe the test for sulfates (SO4^2-).

Add dilute hydrochloric acid followed by barium chloride solution to the suspected sulfate solution. Signup and view all the answers

Which reagent is added to a chloride solution to test for chloride ions?

Silver nitrate solution Signup and view all the answers

What is the chemical equation for the reaction between barium ions (Ba2+) and sulfate ions (SO4^2-)?

Ba2+(aq) + SO4^2-(aq) -> BaSO4(s) Signup and view all the answers

What is the expected observation when bromide ions (Br-) are tested with silver nitrate solution?

A cream precipitate Signup and view all the answers

Write the equation for the reaction of ammonium chloride (NH4Cl) with sodium hydroxide (NaOH).

NH4Cl(aq) + NaOH(aq) -> NaCl(aq) + NH3(g) + H2O(l) Signup and view all the answers

Study Notes

Chemical Tests

Testing for gases:
- Hydrogen gas: reacts with a flame producing a squeaky pop, $2H_2 + O_2 \longrightarrow 2H_2O$
- Oxygen: relights a glowing splint
- Carbon dioxide: turns limewater milky/chalky/cloudy, $CO_2(g) + Ca(OH)_2(aq) \longrightarrow CaCO_3(s) + H_2O(l)$
- Chlorine: bleaches (turns white) damp red litmus paper
- Ammonia: turns universal indicator paper/litmus paper blue

Testing for Water

Test for presence of water using anhydrous copper (II) sulfate: water turns white anhydrous copper (II) sulfate blue, $CuSO_4(s) + 5H_2O(l) \rightleftharpoons CuSO_4.5H_2O(s)$
Test for purity of water: pure water freezes at exactly 0°C and boils at exactly 100°C atmospheric pressure

Testing for Ions

Flame test for metal ions (cations):
- Lithium (Li+): red flame
- Sodium (Na+): yellow flame
- Potassium (K+): lilac flame
- Calcium (Ca+2): orange-red flame
- Copper (Cu+2): blue-green flame

Testing for Specific Ions (Cations)

Using sodium hydroxide solution:
- Copper (Cu2+): formation of a blue precipitate, Cu2+(aq) + 2NaOH(aq) -> Cu(OH)2(s) + 2Na+(aq)
- Iron (Fe3+): formation of an orange-brown precipitate, Fe3+(aq) + 3NaOH(aq) -> Fe(OH)3(s) + 3Na+(aq)
- Iron (Fe2+): formation of a green precipitate, Fe2+(aq) + 2NaOH(aq) -> Fe(OH)2(s) + 2Na+(aq)
- Ammonium (NH4+): formation of a colorless gas, NH4Cl(aq) + NaOH(aq) -> NaCl(aq) + NH3(g) + H2O(l)

Testing for Anions

Carbonate (CO32-): formation of carbon dioxide gas, 2HCl(aq) + CaCO3(s) -> CaCl2(aq) + CO2(g) + H2O(l)
Sulfates (SO42-): formation of a white precipitate of barium sulfate, Ba2+(aq) + SO42-(aq) -> BaSO4(s)
Chloride (Cl-): formation of a white precipitate of silver chloride, Ag+(aq) + Cl-(aq) -> AgCl(s)
Bromide (Br-): formation of a cream precipitate of silver bromide, Ag+(aq) + Br-(aq) -> AgBr(s)
Iodide (I-): formation of a yellow precipitate of silver iodide, Ag+(aq) + I-(aq) → AgI(s)

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Identify the chemical tests for different gases, including hydrogen, oxygen, and carbon dioxide. Learn the reactions and equations involved in these tests.