Chemical tests for ions and gases

Học bằng cách chơi

Trả lời những câu hỏi này để kiếm năng lượng, rồi câu cá và khám phá. Không cần tài khoản.

Dành cho nhà giáo dục: slide bài học, ghi chú ôn tập sẵn dùng cho Chemical tests for ions and gases (MYP Chemistry, Year 4) — dùng trong bài giảng của bạn, hoặc chạy chủ đề như một hoạt động lớp học tương tác để người học chơi như một trò chơi trực tiếp.

Ghi chú bài học

Big idea: chemical tests for ions and gases

Key concept: Relationships. Identification depends on a specific reagent and observation. Carbon dioxide turns limewater milky; other gas tests use different observations.
Related concepts: Models and evidence. Use a scientific explanation to make predictions, then test it against observations.
Global context: Scientific and technical innovation. Analytical tests identify substances in water and manufacturing samples.

Identification of Anions

Carbonate (CO₃²⁻): Add dilute acid → CO₂ gas → bubble through limewater → turns cloudy/milky (white CaCO₃ precipitate).
Halide (Cl⁻, Br⁻, I⁻): Acidify with dilute HNO₃, add AgNO₃(aq) → coloured precipitate: Cl⁻ = white (AgCl), Br⁻ = cream (AgBr), I⁻ = yellow (AgI).
Nitrate (NO₃⁻): Add aq. NaOH + Al foil, warm gently → ammonia gas (turns damp red litmus blue).
Sulfate (SO₄²⁻): Acidify with dilute HNO₃, add BaCl₂(aq) or Ba(NO₃)₂ → white precipitate (BaSO₄).
Sulfite (SO₃²⁻): Add dilute acid, warm, bubble gas through acidified KMnO₄ → purple to colourless.

Testing for carbonate ions

Identification of Cations – NaOH Test

Add few drops aq. NaOH → observe precipitate colour; then excess NaOH → note solubility.
Al³⁺: white ppt, soluble in excess NaOH → colourless solution.
NH₄⁺: ammonia gas on warming (turns damp red litmus blue).
Ca²⁺: white ppt, insoluble in excess NaOH.
Cr³⁺: green ppt, soluble in excess NaOH.
Cu²⁺: light blue ppt, insoluble in excess NaOH.
Fe²⁺: green ppt, insoluble in excess, surface turns brown on standing.
Fe³⁺: red-brown ppt, insoluble in excess.
Zn²⁺: white ppt, soluble in excess NaOH → colourless solution.

Identification of Cations – Ammonia Test

Add few drops aq. NH₃ → observe precipitate; then excess NH₃ → note solubility.
Al³⁺: white ppt, insoluble in excess NH₃.
Ca²⁺: no ppt or very slight white ppt; no change with excess.
Cr³⁺: green ppt, insoluble in excess NH₃.
Cu²⁺: light blue ppt, soluble in excess NH₃ → dark blue solution.
Fe²⁺: green ppt, insoluble in excess, surface turns brown.
Fe³⁺: red-brown ppt, insoluble in excess.
Zn²⁺: white ppt, soluble in excess NH₃ → colourless solution.

Flame Tests for Metal Cations

Clean nichrome or platinum wire by dipping in conc. HCl and heating until no colour.
Dip wire into sample and hold in blue Bunsen flame.
Li⁺ = red; Na⁺ = yellow; K⁺ = lilac; Ca²⁺ = orange-red; Ba²⁺ = light green; Cu²⁺ = blue-green.

Identification of Gases

Ammonia (NH₃): damp red litmus turns blue; sharp choking smell.
Carbon dioxide (CO₂): bubble through limewater → turns cloudy/milky.
Chlorine (Cl₂): damp blue litmus turns red then bleached white; toxic – use fume cupboard.
Hydrogen (H₂): burning splint → squeaky pop (rapid combustion).
Oxygen (O₂): glowing splint → relights (or glows brightly).
Sulfur dioxide (SO₂): bubble through acidified KMnO₄ → purple to colourless; sharp choking smell.

Testing for ammonia gas

Key Tips & Common Mistakes

For carbonate test: describe the test (bubble gas through limewater), not just the result.
Halide test: use HNO₃ to acidify, not HCl (Cl⁻ would interfere).
Sulfate test: add HNO₃ first to remove carbonates that also give white ppt.
Add NaOH/NH₃ slowly – some ppts dissolve in excess, so initial ppt may be missed.
Distinguish colourless (no colour) vs clear (transparent, may be coloured).
Flame test: sample must be pure (single cation) to avoid mixed colours.

Think like a scientist

Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution.
Comparison: the solution tested. Outcome: the colour or precipitate observed with a specified reagent.
Control: use equal sample volumes and the same reagent amounts. Explain why this makes the comparison fairer.
Evidence: Use a consistent method, repeated observations where appropriate and a table with labelled quantities and units. Keep unexpected results and investigate their cause.
Safety: Practical activities need teacher supervision and an appropriate risk assessment. Use the provided data or simulation where the investigation specifies it.
Inquiry task: State a testable question, predict the outcome using the science, then explain how your observations would support or challenge the prediction.

Evaluate the science

Analytical tests identify substances in water and manufacturing samples.
A single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests.
Evaluation task: Link your conclusion to evidence, identify a limitation and suggest a specific improvement. Distinguish a measured result from an explanation of its cause.

Slide

Step through every slide for this topic — plus flashcards and revision notes — with a free account.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 48 câu hỏi. Đăng ký để xem tất cả.

1.What is the test for carbonate ions?
Easy
- AAdd dilute acid and bubble the gas through limewater; limewater turns cloudy.
- BAdd silver nitrate solution; a white precipitate forms.
- CAdd barium chloride solution; a white precipitate forms.
- DAdd sodium hydroxide and warm; damp red litmus turns blue.
2.Which gas is produced when ammonium ions are warmed with sodium hydroxide solution?
Easy
- AAmmonia
- BNitrogen
- CHydrogen
- DOxygen
3.What is the colour of the precipitate formed when chloride ions are tested with silver nitrate solution?
Easy
- AWhite
- BCream
- CYellow
- DNo precipitate
4.A solution gives a white precipitate with barium nitrate solution after adding dilute nitric acid. Which ion is present?
Medium
- ASulfate
- BCarbonate
- CChloride
- DNitrate
5.A green precipitate forms when sodium hydroxide is added to a solution. The precipitate dissolves in excess sodium hydroxide. Which cation is present?
Medium
- AChromium(III)
- BIron(II)
- CCopper(II)
- DAluminium
6.Which gas relights a glowing splint?
Easy
- AOxygen
- BHydrogen
- CCarbon dioxide
- DChlorine
7.A student adds dilute hydrochloric acid to a solid and bubbles the gas through limewater. The limewater turns cloudy. What can be concluded?
Medium
- AThe solid contains carbonate ions.
- BThe solid contains sulfite ions.
- CThe solid contains hydrogencarbonate ions.
- DThe solid contains carbonate or hydrogencarbonate ions.
8.What is the colour of the flame produced by potassium ions in a flame test?
Easy
- AYellow
- BLilac
- CRed
- DGreen

Thêm câu hỏi

9.Which test is used to identify hydrogen gas?
Easy
- AA glowing splint relights.
- BA burning splint gives a squeaky pop.
- CDamp blue litmus turns red then bleached.
- DLimewater turns cloudy.
10.A solution gives a white precipitate with a few drops of sodium hydroxide, which dissolves in excess. The same solution gives a white precipitate with ammonia that does NOT dissolve in excess. Which cation is present?
Hard
- AAluminium
- BZinc
- CCalcium
- DLead
11.A gas turns damp blue litmus red and then bleaches it white. Which gas is it?
Medium
- AChlorine
- BSulfur dioxide
- CAmmonia
- DCarbon dioxide
12.A student carries out a flame test on a solid and observes a lilac flame. Which cation is present?
Easy
- Apotassium
- Bsodium
- Clithium
- Dcalcium
13.Which gas turns damp red litmus paper blue?
Easy
- Aammonia
- Bchlorine
- Ccarbon dioxide
- Dsulfur dioxide
14.A student adds dilute hydrochloric acid to a solid. The gas produced turns limewater cloudy. What is the solid?
Easy
- Aa carbonate
- Ba sulfate
- Ca chloride
- Da nitrate
15.A student adds excess aqueous sodium hydroxide to a solution and obtains a green precipitate that does not dissolve. Which cation is present?
Medium
- Airon(II)
- Biron(III)
- Cchromium(III)
- Dcopper(II)
16.A student bubbles a gas through acidified potassium manganate(VII) solution. The solution changes from purple to colourless. Which gas is present?
Medium
- Asulfur dioxide
- Bcarbon dioxide
- Cchlorine
- Dammonia
17.A student adds dilute hydrochloric acid to a solid and bubbles the gas produced through limewater. The limewater turns cloudy. Which ion is present in the solid?
Easy
- ACarbonate
- BSulfate
- CChloride
- DNitrate
18.A student is testing a solution that contains a mixture of chloride and iodide ions. After adding dilute nitric acid and silver nitrate, what colour precipitate would be observed?
Medium
- Awhite
- Byellow
- Ccream
- Dpale yellow
19.A gas turns damp red litmus paper blue. Which gas is it?
Easy
- Aammonia
- Bchlorine
- Ccarbon dioxide
- Dsulfur dioxide
20.A student adds dilute hydrochloric acid to a solid. The gas produced is bubbled through limewater. The limewater turns cloudy. Which ion is present in the solid?
Easy
- Acarbonate
- Bsulfate
- Cchloride
- Dnitrate
21.A solution gives a white precipitate with a few drops of sodium hydroxide. The precipitate does not dissolve in excess sodium hydroxide. What could the cation be?
Medium
- Acalcium
- Baluminium
- Czinc
- Dcopper
22.A student is testing a solution that contains a mixture of sulfate and sulfite ions. After adding dilute nitric acid and barium nitrate, a white precipitate forms. The mixture is then warmed and the gas bubbled through acidified potassium manganate(VII) solution. What is the expected result?
Hard
- AThe precipitate remains and the potassium manganate(VII) turns from purple to colourless.
- BThe precipitate dissolves and the potassium manganate(VII) turns colourless.
- CThe precipitate remains and the potassium manganate(VII) stays purple.
- DThe precipitate dissolves and the potassium manganate(VII) stays purple.
23.Which test is used to identify oxygen gas?
Easy
- Aa glowing splint relights
- Ba burning splint gives a squeaky pop
- Cdamp blue litmus paper turns red then white
- Dlimewater turns cloudy
24.A solution contains a cation that forms a green precipitate with sodium hydroxide. The precipitate does not dissolve in excess sodium hydroxide. Which cation is present?
Medium
- Airon(II)
- Biron(III)
- Cchromium(III)
- Dcopper(II)
25.A student adds dilute nitric acid and then silver nitrate solution to an aqueous solution. A cream precipitate forms. Which halide ion is present?
Easy
- Abromide
- Bchloride
- Ciodide
- Dfluoride
26.What is the test for the presence of sulfate ions in aqueous solution?
Easy
- AAdd dilute nitric acid and then barium nitrate solution; a white precipitate indicates sulfate ions.
- BAdd dilute nitric acid and then silver nitrate solution; a white precipitate indicates sulfate ions.
- CAdd sodium hydroxide solution and warm; ammonia gas indicates sulfate ions.
- DAdd dilute hydrochloric acid and bubble the gas through limewater; cloudy limewater indicates sulfate ions.
27.A solution gives a white precipitate with a few drops of sodium hydroxide solution. The precipitate dissolves in excess sodium hydroxide to give a colourless solution. Which cation could be present?
Medium
- ACalcium
- BCopper(II)
- CAluminium
- DIron(II)
28.The test for carbonate ions involves adding dilute acid and bubbling the gas through limewater. A positive result is limewater turning cloudy.
Easy
True or false?
29.What is the colour of the precipitate formed when bromide ions are tested with silver nitrate solution?
Easy
- AWhite
- BCream
- CYellow
- DNo precipitate
30.What is the test for hydrogen gas?
Easy
- ARelights a glowing splint
- BBurns with a squeaky pop
- CTurns limewater cloudy
- DBleaches damp litmus paper
31.Oxygen gas relights a glowing splint.
Easy
True or false?
32.When testing for halide ions, the sample must be acidified with hydrochloric acid before adding silver nitrate.
Medium
True or false?
33.Which gas turns damp blue litmus paper red and then bleaches it white?
Easy
- AAmmonia
- BChlorine
- CSulfur dioxide
- DCarbon dioxide
34.The white precipitate formed when testing for sulfate ions is barium sulfate, which is insoluble in dilute nitric acid.
Easy
True or false?
35.A solution contains a cation that forms a white precipitate with sodium hydroxide that does not dissolve in excess. The same solution gives no precipitate with ammonia. Which cation is present?
Medium
- AAluminium
- BCalcium
- CZinc
- DCopper
36.The test for nitrate ions involves adding aqueous sodium hydroxide and aluminium foil, then warming. The gas produced turns damp red litmus paper blue.
Medium
True or false?
37.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. What is the independent variable?
Easy
- Athe colour or precipitate observed with a specified reagent
- Bthe number of repeated trials
- Cthe scientific explanation written afterwards
- Dthe solution tested
38.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Which observation or quantity is the dependent variable?
Easy
- Athe colour or precipitate observed with a specified reagent
- Bthe solution tested
- Cthe title given to the investigation
- Dthe number of references in the report
39.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Which decision best controls another factor in this comparison?
Medium
- Achange every condition for each trial
- Buse equal sample volumes and the same reagent amounts
- Cuse a different measurement method for every result
- Drecord only results that agree with the prediction
40.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Why should the class repeat measurements or check multiple comparable observations?
Medium
- ATo guarantee that every systematic error disappears
- BTo make an unsupported prediction become correct
- CTo assess variation and judge how consistent the evidence is
- DTo avoid reporting results that disagree with a model
41.A class is evaluating an application of chemical tests for ions and gases. Which statement identifies a relevant limitation?
Hard
- AAll scientific models reproduce every feature of the real world
- BOne favourable result proves that a technology has no disadvantages
- CA conclusion needs no evidence when a scientific term is used
- DA single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests.
42.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Which conclusion is most justified by a controlled comparison?
Hard
- AA conclusion restricted to the tested conditions, with uncertainty and limitations stated
- BA claim that the result must hold in all possible conditions
- CA claim that alternative explanations never need testing
- DA claim based only on the most convenient observation
43.Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Select the two practices that strengthen the validity of this comparison.
Medium
- Ause equal sample volumes and the same reagent amounts
- Bchange the measurement method whenever a result is unexpected
- Crecord the colour or precipitate observed with a specified reagent using the same agreed procedure
- Dreport only observations that confirm the prediction
44.When evaluating evidence about chemical tests for ions and gases, select the two scientifically defensible statements.
Hard
- AOne result proves the explanation in every situation
- BA single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests.
- CA conclusion should state the conditions and uncertainty of the evidence
- DModels never need revision when new evidence appears
45.Design a fair investigation for this question: Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Identify what to compare, what to record and one control.
Medium
46.Explain one use of the science in chemical tests for ions and gases and evaluate one limitation of the evidence or application.
Hard
47.A gas turns limewater milky in a teacher demonstration. Which identification and explanation fit?
Hard
- AOxygen; calcium metal forms
- BCarbon dioxide; insoluble calcium carbonate forms
- CHydrogen; calcium chloride forms
- DNitrogen; the water turns into an element
48.An unknown solution gives a white precipitate in one ion test. Why should the class use additional tests and known references?
Hard
- AEvery white precipitate identifies exactly one possible ion
- BReference samples stop all chemical reactions
- CDifferent ions can give similar observations and contamination can affect the result
- DRepeating a label is equivalent to collecting evidence

Ghi chú ôn tập

## Big idea: chemical tests for ions and gases - **Key concept: Relationships.** Identification depends on a specific reagent and observation. Carbon dioxide turns limewater milky; other gas tests use different observations. - **Related concepts: Models and evidence.** Use a scientific explanation to make predictions, then test it against observations. - **Global context: Scientific and technical innovation.** Analytical tests identify substances in water and manufacturing samples. ## Identification of Anions - **Carbonate (CO₃²⁻)**: Add dilute acid → CO₂ gas → bubble through **limewater** → turns **cloudy/milky** (white CaCO₃ precipitate). - **Halide (Cl⁻, Br⁻, I⁻)**: Acidify with **dilute HNO₃**, add **AgNO₃(aq)** → coloured precipitate: **Cl⁻ = white** (AgCl), **Br⁻ = cream** (AgBr), **I⁻ = yellow** (AgI). - **Nitrate (NO₃⁻)**: Add **aq. NaOH + Al foil**, warm gently → **ammonia gas** (turns damp red litmus blue). - **Sulfate (SO₄²⁻)**: Acidify with **dilute HNO₃**, add **BaCl₂(aq)** or Ba(NO₃)₂ → **white precipitate** (BaSO₄). - **Sulfite (SO₃²⁻)**: Add **dilute acid**, warm, bubble gas through **acidified KMnO₄** → purple to **colourless**. ## Identification of Cations – NaOH Test - Add **few drops aq. NaOH** → observe precipitate colour; then **excess NaOH** → note solubility. - **Al³⁺**: white ppt, **soluble in excess** NaOH → colourless solution. - **NH₄⁺**: **ammonia gas** on warming (turns damp red litmus blue). - **Ca²⁺**: white ppt, **insoluble** in excess NaOH. - **Cr³⁺**: **green** ppt, **soluble** in excess NaOH. - **Cu²⁺**: **light blue** ppt, **insoluble** in excess NaOH. - **Fe²⁺**: **green** ppt, insoluble in excess, surface turns **brown** on standing. - **Fe³⁺**: **red-brown** ppt, insoluble in excess. - **Zn²⁺**: white ppt, **soluble** in excess NaOH → colourless solution. ## Identification of Cations – Ammonia Test - Add **few drops aq. NH₃** → observe precipitate; then **excess NH₃** → note solubility. - **Al³⁺**: white ppt, **insoluble** in excess NH₃. - **Ca²⁺**: no ppt or very slight white ppt; no change with excess. - **Cr³⁺**: **green** ppt, insoluble in excess NH₃. - **Cu²⁺**: light blue ppt, **soluble** in excess NH₃ → **dark blue** solution. - **Fe²⁺**: green ppt, insoluble in excess, surface turns brown. - **Fe³⁺**: red-brown ppt, insoluble in excess. - **Zn²⁺**: white ppt, **soluble** in excess NH₃ → colourless solution. ## Flame Tests for Metal Cations - Clean **nichrome or platinum wire** by dipping in conc. HCl and heating until no colour. - Dip wire into sample and hold in **blue Bunsen flame**. - **Li⁺** = red; **Na⁺** = yellow; **K⁺** = lilac; **Ca²⁺** = orange-red; **Ba²⁺** = light green; **Cu²⁺** = blue-green. ## Identification of Gases - **Ammonia (NH₃)**: damp **red** litmus turns **blue**; sharp choking smell. - **Carbon dioxide (CO₂)**: bubble through **limewater** → turns **cloudy/milky**. - **Chlorine (Cl₂)**: damp **blue** litmus turns **red then bleached white**; toxic – use fume cupboard. - **Hydrogen (H₂)**: **burning splint** → **squeaky pop** (rapid combustion). - **Oxygen (O₂)**: **glowing splint** → **relights** (or glows brightly). - **Sulfur dioxide (SO₂)**: bubble through **acidified KMnO₄** → purple to **colourless**; sharp choking smell. ## Key Tips & Common Mistakes - For carbonate test: describe the test (bubble gas through limewater), not just the result. - Halide test: use **HNO₃** to acidify, not HCl (Cl⁻ would interfere). - Sulfate test: add HNO₃ first to remove carbonates that also give white ppt. - Add NaOH/NH₃ **slowly** – some ppts dissolve in excess, so initial ppt may be missed. - Distinguish **colourless** (no colour) vs **clear** (transparent, may be coloured). - Flame test: sample must be **pure** (single cation) to avoid mixed colours. ## Think like a scientist - Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. - **Comparison:** the solution tested. **Outcome:** the colour or precipitate observed with a specified reagent. - **Control:** use equal sample volumes and the same reagent amounts. Explain why this makes the comparison fairer. - **Evidence:** Use a consistent method, repeated observations where appropriate and a table with labelled quantities and units. Keep unexpected results and investigate their cause. - **Safety:** Practical activities need teacher supervision and an appropriate risk assessment. Use the provided data or simulation where the investigation specifies it. - **Inquiry task:** State a testable question, predict the outcome using the science, then explain how your observations would support or challenge the prediction. ## Evaluate the science - Analytical tests identify substances in water and manufacturing samples. - A single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests. - **Evaluation task:** Link your conclusion to evidence, identify a limitation and suggest a specific improvement. Distinguish a measured result from an explanation of its cause.

Test for Anions: Identify carbonate, halide, nitrate, sulfate, and sulfite ions using appropriate chemical tests and observations.
Test for Cations: Identify ammonium ions and metal cations using sodium hydroxide, ammonia solution, and flame tests.
Test for Gases: Identify ammonia, carbon dioxide, chlorine, hydrogen, oxygen, and sulfur dioxide using characteristic tests.
Designing scientific inquiries: Plan a fair comparison: Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution.
Evaluating evidence and impacts: Analytical tests identify substances in water and manufacturing samples. A single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests.
Identification of Anions: **Carbonate (CO₃²⁻)**: Add dilute acid → CO₂ gas → bubble through **limewater** → turns **cloudy/milky** (white CaCO₃ precipitate).
Identification of Cations – NaOH Test: Add **few drops aq. NaOH** → observe precipitate colour; then **excess NaOH** → note solubility.
Identification of Cations – Ammonia Test: Add **few drops aq. NH₃** → observe precipitate; then **excess NH₃** → note solubility.
Flame Tests for Metal Cations: Clean **nichrome or platinum wire** by dipping in conc. HCl and heating until no colour.
Identification of Gases: **Ammonia (NH₃)**: damp **red** litmus turns **blue**; sharp choking smell.
Key Tips & Common Mistakes: For carbonate test: describe the test (bubble gas through limewater), not just the result.
Carbonate (CO₃²⁻): **Carbonate (CO₃²⁻)**: Add dilute acid → CO₂ gas → bubble through **limewater** → turns **cloudy/milky** (white CaCO₃ precipitate).
limewater: **Carbon dioxide (CO₂)**: bubble through **limewater** → turns **cloudy/milky**.
cloudy/milky: **Carbon dioxide (CO₂)**: bubble through **limewater** → turns **cloudy/milky**.
Halide (Cl⁻, Br⁻, I⁻): **Halide (Cl⁻, Br⁻, I⁻)**: Acidify with **dilute HNO₃**, add **AgNO₃(aq)** → coloured precipitate: **Cl⁻ = white** (AgCl), **Br⁻ = cream** (AgBr), **I⁻ = yellow** (AgI).
dilute HNO₃: **Sulfate (SO₄²⁻)**: Acidify with **dilute HNO₃**, add **BaCl₂(aq)** or Ba(NO₃)₂ → **white precipitate** (BaSO₄).

Thẻ ghi nhớ

What is the test for carbonate ions?

Add dilute acid and bubble the gas through limewater; limewater turns cloudy. Carbonate ions react with dilute acid to produce CO2, which turns limewater cloudy due to formation of calcium carbonate.

Which gas is produced when ammonium ions are warmed with sodium hydroxide solution?

Ammonia Ammonium ions react with hydroxide ions to produce ammonia gas, which turns damp red litmus blue.

What is the colour of the precipitate formed when chloride ions are tested with silver nitrate solution?

White Chloride ions give a white precipitate of silver chloride.

A solution gives a white precipitate with barium nitrate solution after adding dilute nitric acid. Which ion is present?

Sulfate Sulfate ions form a white precipitate of barium sulfate with barium ions. Nitric acid is added to remove carbonates that would also give a precipitate.

A green precipitate forms when sodium hydroxide is added to a solution. The precipitate dissolves in excess sodium hydroxide. Which cation is present?

Chromium(III) Chromium(III) gives a green precipitate with NaOH that dissolves in excess. Iron(II) gives green precipitate insoluble in excess. Copper(II) gives blue precipitate. Aluminium gives white precipitate.

Which gas relights a glowing splint?

Oxygen Oxygen supports combustion and relights a glowing splint. Hydrogen gives a squeaky pop with a burning splint.

A student adds dilute hydrochloric acid to a solid and bubbles the gas through limewater. The limewater turns cloudy. What can be concluded?

The solid contains carbonate or hydrogencarbonate ions. Both carbonate and hydrogencarbonate produce CO2 with acid, turning limewater cloudy. The test does not distinguish between them without further tests.

What is the colour of the flame produced by potassium ions in a flame test?

Lilac Potassium ions give a lilac flame. Sodium gives yellow, lithium red, and barium light green.

Which test is used to identify hydrogen gas?

A burning splint gives a squeaky pop. Hydrogen burns with a squeaky pop when a burning splint is held at the mouth of a test tube.

A solution gives a white precipitate with a few drops of sodium hydroxide, which dissolves in excess. The same solution gives a white precipitate with ammonia that does NOT dissolve in excess. Which cation is present?

Aluminium Aluminium gives a white precipitate with NaOH that dissolves in excess, and with ammonia the white precipitate is insoluble in excess. Zinc dissolves in excess ammonia, calcium gives no precipitate with ammonia.

A gas turns damp blue litmus red and then bleaches it white. Which gas is it?

Chlorine Chlorine gas turns damp blue litmus red then bleaches it white. Sulfur dioxide also bleaches but typically turns damp blue litmus red only (not white). Ammonia turns red litmus blue. CO2 turns blue litmus red but does not bleach.

A student carries out a flame test on a solid and observes a lilac flame. Which cation is present?

potassium Potassium ions produce a lilac flame in a flame test. Sodium gives yellow, lithium red, and calcium orange-red.

Which gas turns damp red litmus paper blue?

ammonia Ammonia is the only common gas that turns damp red litmus paper blue because it is alkaline. Chlorine bleaches litmus, carbon dioxide turns limewater cloudy but does not change red litmus blue, and sulfur dioxide turns acidified potassium manganate(VII) colourless.

A student adds dilute hydrochloric acid to a solid. The gas produced turns limewater cloudy. What is the solid?

a carbonate Carbonates react with dilute acid to produce carbon dioxide, which turns limewater cloudy (milky) due to formation of calcium carbonate. Sulfates, chlorides, and nitrates do not produce CO2 with dilute acid.

A student adds excess aqueous sodium hydroxide to a solution and obtains a green precipitate that does not dissolve. Which cation is present?

iron(II) Iron(II) ions form a green precipitate of Fe(OH)2 with NaOH, which is insoluble in excess. Iron(III) gives a red-brown precipitate. Chromium(III) gives a green precipitate that is soluble in excess NaOH. Copper(II) gives a light blue precipitate insoluble in excess.

A student bubbles a gas through acidified potassium manganate(VII) solution. The solution changes from purple to colourless. Which gas is present?

sulfur dioxide Sulfur dioxide reduces purple potassium manganate(VII) to colourless manganese(II) ions. Carbon dioxide has no effect on potassium manganate(VII). Chlorine would bleach litmus but not necessarily decolourise potassium manganate(VII) in this way. Ammonia would turn red litmus blue but does not decolourise potassium manganate(VII).

How would you design the inquiry for chemical tests for ions and gases?

Compare teacher-demonstrated tests on labelled reference solutions and an unknown solution. Compare the solution tested; record the colour or precipitate observed with a specified reagent; use equal sample volumes and the same reagent amounts.

What limitation matters when applying chemical tests for ions and gases?

A single test can be ambiguous; contamination and mixtures can affect results, so use reference samples and confirming tests.

Unlock all 48 questions, flashcards & more

Tạo tài khoản miễn phí để xem mọi câu hỏi, slide, thẻ ghi nhớ và ghi chú ôn tập cho chủ đề này.

ĐĂNG KÝ — MIỄN PHÍ ĐĂNG NHẬP

Đề thi cũ

Luyện đề thi cũ cho chủ đề này sắp ra mắt.

Sắp ra mắt