Chapter 20 Worksheet Redox - Free Printable
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Step-by-step solution for: Chapter 20 Worksheet Redox
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Step-by-step solution for: Chapter 20 Worksheet Redox
Let's solve each part of Chapter 20 Worksheet: Redox step by step. We'll identify what is oxidized and reduced, determine oxidation numbers, and identify oxidizing and reducing agents.
---
We use the concept of oxidation states (oxidation numbers) to determine:
- Oxidized: loses electrons → oxidation number increases
- Reduced: gains electrons → oxidation number decreases
- Oxidizing agent: gets reduced (causes oxidation)
- Reducing agent: gets oxidized (causes reduction)
---
#### 1. 2Sr + O₂ → 2SrO
- Sr: 0 → +2 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Sr
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Sr
---
#### 2. 2Li + S → Li₂S
- Li: 0 → +1 (oxidized)
- S: 0 → -2 (reduced)
- Oxidized: Li
- Reduced: S
- Oxidizing agent: S
- Reducing agent: Li
---
#### 3. 2Cs + Br₂ → 2CsBr
- Cs: 0 → +1 (oxidized)
- Br: 0 → -1 (reduced)
- Oxidized: Cs
- Reduced: Br₂
- Oxidizing agent: Br₂
- Reducing agent: Cs
---
#### 4. 3Mg + N₂ → Mg₃N₂
- Mg: 0 → +2 (oxidized)
- N: 0 → -3 (reduced)
- Oxidized: Mg
- Reduced: N₂
- Oxidizing agent: N₂
- Reducing agent: Mg
---
#### 5. 4Fe + 3O₂ → 2Fe₂O₃
- Fe: 0 → +3 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Fe
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Fe
---
#### 6. Cl₂ + 2NaBr → 2NaCl + Br₂
- Cl: 0 → -1 (reduced)
- Br: -1 → 0 (oxidized)
- Oxidized: Br⁻ (in NaBr)
- Reduced: Cl₂
- Oxidizing agent: Cl₂
- Reducing agent: NaBr (or Br⁻)
---
#### 7. Si + 2F₂ → SiF₄
- Si: 0 → +4 (oxidized)
- F: 0 → -1 (reduced)
- Oxidized: Si
- Reduced: F₂
- Oxidizing agent: F₂
- Reducing agent: Si
---
#### 8. 2Ca + O₂ → 2CaO
- Ca: 0 → +2 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Ca
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Ca
---
#### 9. Mg + 2HCl → MgCl₂ + H₂
- Mg: 0 → +2 (oxidized)
- H: +1 → 0 (reduced)
- Oxidized: Mg
- Reduced: H⁺ (from HCl)
- Oxidizing agent: HCl
- Reducing agent: Mg
---
#### 10. 2Na + 2H₂O → 2NaOH + H₂
- Na: 0 → +1 (oxidized)
- H: +1 → 0 (in H₂) (reduced)
- Oxidized: Na
- Reduced: H⁺ (in water)
- Oxidizing agent: H₂O
- Reducing agent: Na
---
Recall rules:
- Elements: 0
- Ions: charge
- Oxygen: usually -2 (except peroxides)
- Hydrogen: +1 (except metal hydrides)
- Group 1: +1, Group 2: +2
- Fluorine: -1
- Sum of oxidation numbers = total charge
---
a. sulfate (SO₄²⁻)
- O: -2 × 4 = -8
- Total charge: -2
- So, S: x + (-8) = -2 → x = +6
→ S: +6
b. Sn (elemental)
→ 0
c. S²⁻
→ -2
d. Fe²⁺
→ +2
e. Sn⁴⁺
→ +4
f. nitrate (NO₃⁻)
- O: -2 × 3 = -6
- Total charge: -1
- N: x + (-6) = -1 → x = +5
→ N: +5
g. ammonium (NH₄⁺)
- H: +1 × 4 = +4
- Total charge: +1
- N: x + 4 = +1 → x = -3
→ N: -3
---
---
a. Cr₂O₃
- O: -2 × 3 = -6
- Total neutral → sum = 0
- 2Cr + (-6) = 0 → 2Cr = 6 → Cr = +3
b. Na₂Cr₂O₇
- Na: +1 × 2 = +2
- O: -2 × 7 = -14
- Total: 0
- 2Cr + 2 + (-14) = 0 → 2Cr = 12 → Cr = +6
c. CrSO₄
- SO₄²⁻ has S = +6, O = -2, total -2
- Cr must be +2 to balance → Cr = +2
d. chromate (CrO₄²⁻)
- O: -2 × 4 = -8
- Total charge: -2
- Cr + (-8) = -2 → Cr = +6
e. dichromate (Cr₂O₇²⁻)
- O: -2 × 7 = -14
- Total charge: -2
- 2Cr + (-14) = -2 → 2Cr = 12 → Cr = +6
---
---
#### a. C + H₂SO₄ → CO₂ + SO₂ + H₂O
Assign oxidation numbers:
- C: 0 → +4 (in CO₂) → oxidized
- S in H₂SO₄: +6 (H=+1, O=-2; x + 2(+1) + 4(-2) = 0 → x = +6)
- S in SO₂: +4 (O=-2; x + 2(-2)=0 → x=+4)
- So S: +6 → +4 → reduced
✔ Oxidized: C
✔ Reduced: S
---
#### b. HNO₃ + HI → NO + I₂ + H₂O
- N in HNO₃: +5 (H=+1, O=-2; x +1 +3(-2)=0 → x=+5)
- N in NO: +2 → reduced
- I in HI: -1 → I₂: 0 → oxidized
✔ Oxidized: I⁻ (from HI)
✔ Reduced: N (from HNO₃)
---
#### c. KMnO₄ + HCl → MnCl₂ + Cl₂ + H₂O + KCl
- Mn in KMnO₄: K=+1, O=-2 → x +1 + 4(-2)=0 → x = +7
- Mn in MnCl₂: +2 → reduced
- Cl in HCl: -1 → Cl₂: 0 → oxidized
✔ Oxidized: Cl⁻ (from HCl)
✔ Reduced: Mn (from MnO₄⁻)
---
#### d. Sb + HNO₃ → Sb₂O₃ + NO + H₂O
- Sb: 0 → in Sb₂O₃: O=-2 → 2x + 3(-2)=0 → 2x=6 → x=+3 → oxidized
- N in HNO₃: +5 → in NO: +2 → reduced
✔ Oxidized: Sb
✔ Reduced: N (from HNO₃)
---
Use:
- Oxidizing agent: gets reduced
- Reducing agent: gets oxidized
---
#### a. C + H₂SO₄ → CO₂ + SO₂ + H₂O
- Oxidized: C → reducing agent: C
- Reduced: S (in H₂SO₄) → oxidizing agent: H₂SO₄
✔ Oxidizing agent: H₂SO₄
✔ Reducing agent: C
---
#### b. HNO₃ + HI → NO + I₂ + H₂O
- Oxidized: I⁻ → reducing agent: HI
- Reduced: N → oxidizing agent: HNO₃
✔ Oxidizing agent: HNO₃
✔ Reducing agent: HI
---
#### c. KMnO₄ + HCl → MnCl₂ + Cl₂ + H₂O + KCl
- Oxidized: Cl⁻ → reducing agent: HCl
- Reduced: Mn → oxidizing agent: KMnO₄
✔ Oxidizing agent: KMnO₄
✔ Reducing agent: HCl
---
#### d. Sb + HNO₃ → Sb₂O₃ + NO + H₂O
- Oxidized: Sb → reducing agent: Sb
- Reduced: N → oxidizing agent: HNO₃
✔ Oxidizing agent: HNO₃
✔ Reducing agent: Sb
---
---
#### Problem 1:
| Reaction | Oxidized | Reduced | Oxidizing Agent | Reducing Agent |
|--------|---------|--------|------------------|----------------|
| 1 | Sr | O₂ | O₂ | Sr |
| 2 | Li | S | S | Li |
| 3 | Cs | Br₂ | Br₂ | Cs |
| 4 | Mg | N₂ | N₂ | Mg |
| 5 | Fe | O₂ | O₂ | Fe |
| 6 | Br⁻ | Cl₂ | Cl₂ | NaBr |
| 7 | Si | F₂ | F₂ | Si |
| 8 | Ca | O₂ | O₂ | Ca |
| 9 | Mg | H⁺ | HCl | Mg |
| 10 | Na | H⁺ | H₂O | Na |
---
#### Problem 11: Oxidation Numbers
| Substance | Oxidation Number |
|----------|------------------|
| a. sulfate | S: +6 |
| b. Sn | 0 |
| c. S²⁻ | -2 |
| d. Fe²⁺ | +2 |
| e. Sn⁴⁺ | +4 |
| f. nitrate | N: +5 |
| g. ammonium | N: -3 |
---
#### Problem 12: Chromium Oxidation States
| Compound | Cr Oxidation State |
|---------|-------------------|
| a. Cr₂O₃ | +3 |
| b. Na₂Cr₂O₇ | +6 |
| c. CrSO₄ | +2 |
| d. chromate (CrO₄²⁻) | +6 |
| e. dichromate (Cr₂O₇²⁻) | +6 |
---
#### Problem 13: Oxidized/Reduced Elements
| Reaction | Oxidized | Reduced |
|--------|--------|--------|
| a. C + H₂SO₄ → ... | C | S |
| b. HNO₃ + HI → ... | I⁻ | N |
| c. KMnO₄ + HCl → ... | Cl⁻ | Mn |
| d. Sb + HNO₃ → ... | Sb | N |
---
#### Problem 14: Oxidizing & Reducing Agents
| Reaction | Oxidizing Agent | Reducing Agent |
|--------|------------------|----------------|
| a. | H₂SO₄ | C |
| b. | HNO₃ | HI |
| c. | KMnO₄ | HCl |
| d. | HNO₃ | Sb |
---
Let me know if you'd like this formatted as a printable PDF or need explanations for any specific parts!
---
Problem 1: Determine what is oxidized and what is reduced in each reaction. Identify the oxidizing agent and the reducing agent.
We use the concept of oxidation states (oxidation numbers) to determine:
- Oxidized: loses electrons → oxidation number increases
- Reduced: gains electrons → oxidation number decreases
- Oxidizing agent: gets reduced (causes oxidation)
- Reducing agent: gets oxidized (causes reduction)
---
#### 1. 2Sr + O₂ → 2SrO
- Sr: 0 → +2 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Sr
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Sr
---
#### 2. 2Li + S → Li₂S
- Li: 0 → +1 (oxidized)
- S: 0 → -2 (reduced)
- Oxidized: Li
- Reduced: S
- Oxidizing agent: S
- Reducing agent: Li
---
#### 3. 2Cs + Br₂ → 2CsBr
- Cs: 0 → +1 (oxidized)
- Br: 0 → -1 (reduced)
- Oxidized: Cs
- Reduced: Br₂
- Oxidizing agent: Br₂
- Reducing agent: Cs
---
#### 4. 3Mg + N₂ → Mg₃N₂
- Mg: 0 → +2 (oxidized)
- N: 0 → -3 (reduced)
- Oxidized: Mg
- Reduced: N₂
- Oxidizing agent: N₂
- Reducing agent: Mg
---
#### 5. 4Fe + 3O₂ → 2Fe₂O₃
- Fe: 0 → +3 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Fe
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Fe
---
#### 6. Cl₂ + 2NaBr → 2NaCl + Br₂
- Cl: 0 → -1 (reduced)
- Br: -1 → 0 (oxidized)
- Oxidized: Br⁻ (in NaBr)
- Reduced: Cl₂
- Oxidizing agent: Cl₂
- Reducing agent: NaBr (or Br⁻)
---
#### 7. Si + 2F₂ → SiF₄
- Si: 0 → +4 (oxidized)
- F: 0 → -1 (reduced)
- Oxidized: Si
- Reduced: F₂
- Oxidizing agent: F₂
- Reducing agent: Si
---
#### 8. 2Ca + O₂ → 2CaO
- Ca: 0 → +2 (oxidized)
- O: 0 → -2 (reduced)
- Oxidized: Ca
- Reduced: O₂
- Oxidizing agent: O₂
- Reducing agent: Ca
---
#### 9. Mg + 2HCl → MgCl₂ + H₂
- Mg: 0 → +2 (oxidized)
- H: +1 → 0 (reduced)
- Oxidized: Mg
- Reduced: H⁺ (from HCl)
- Oxidizing agent: HCl
- Reducing agent: Mg
---
#### 10. 2Na + 2H₂O → 2NaOH + H₂
- Na: 0 → +1 (oxidized)
- H: +1 → 0 (in H₂) (reduced)
- Oxidized: Na
- Reduced: H⁺ (in water)
- Oxidizing agent: H₂O
- Reducing agent: Na
---
Problem 11: Give the oxidation number of each kind of atom or ion.
Recall rules:
- Elements: 0
- Ions: charge
- Oxygen: usually -2 (except peroxides)
- Hydrogen: +1 (except metal hydrides)
- Group 1: +1, Group 2: +2
- Fluorine: -1
- Sum of oxidation numbers = total charge
---
a. sulfate (SO₄²⁻)
- O: -2 × 4 = -8
- Total charge: -2
- So, S: x + (-8) = -2 → x = +6
→ S: +6
b. Sn (elemental)
→ 0
c. S²⁻
→ -2
d. Fe²⁺
→ +2
e. Sn⁴⁺
→ +4
f. nitrate (NO₃⁻)
- O: -2 × 3 = -6
- Total charge: -1
- N: x + (-6) = -1 → x = +5
→ N: +5
g. ammonium (NH₄⁺)
- H: +1 × 4 = +4
- Total charge: +1
- N: x + 4 = +1 → x = -3
→ N: -3
---
Problem 12: Calculate the oxidation number of chromium in each.
---
a. Cr₂O₃
- O: -2 × 3 = -6
- Total neutral → sum = 0
- 2Cr + (-6) = 0 → 2Cr = 6 → Cr = +3
b. Na₂Cr₂O₇
- Na: +1 × 2 = +2
- O: -2 × 7 = -14
- Total: 0
- 2Cr + 2 + (-14) = 0 → 2Cr = 12 → Cr = +6
c. CrSO₄
- SO₄²⁻ has S = +6, O = -2, total -2
- Cr must be +2 to balance → Cr = +2
d. chromate (CrO₄²⁻)
- O: -2 × 4 = -8
- Total charge: -2
- Cr + (-8) = -2 → Cr = +6
e. dichromate (Cr₂O₇²⁻)
- O: -2 × 7 = -14
- Total charge: -2
- 2Cr + (-14) = -2 → 2Cr = 12 → Cr = +6
---
Problem 13: Use changes in oxidation numbers to determine which elements are oxidized and reduced.
---
#### a. C + H₂SO₄ → CO₂ + SO₂ + H₂O
Assign oxidation numbers:
- C: 0 → +4 (in CO₂) → oxidized
- S in H₂SO₄: +6 (H=+1, O=-2; x + 2(+1) + 4(-2) = 0 → x = +6)
- S in SO₂: +4 (O=-2; x + 2(-2)=0 → x=+4)
- So S: +6 → +4 → reduced
✔ Oxidized: C
✔ Reduced: S
---
#### b. HNO₃ + HI → NO + I₂ + H₂O
- N in HNO₃: +5 (H=+1, O=-2; x +1 +3(-2)=0 → x=+5)
- N in NO: +2 → reduced
- I in HI: -1 → I₂: 0 → oxidized
✔ Oxidized: I⁻ (from HI)
✔ Reduced: N (from HNO₃)
---
#### c. KMnO₄ + HCl → MnCl₂ + Cl₂ + H₂O + KCl
- Mn in KMnO₄: K=+1, O=-2 → x +1 + 4(-2)=0 → x = +7
- Mn in MnCl₂: +2 → reduced
- Cl in HCl: -1 → Cl₂: 0 → oxidized
✔ Oxidized: Cl⁻ (from HCl)
✔ Reduced: Mn (from MnO₄⁻)
---
#### d. Sb + HNO₃ → Sb₂O₃ + NO + H₂O
- Sb: 0 → in Sb₂O₃: O=-2 → 2x + 3(-2)=0 → 2x=6 → x=+3 → oxidized
- N in HNO₃: +5 → in NO: +2 → reduced
✔ Oxidized: Sb
✔ Reduced: N (from HNO₃)
---
Problem 14: For each reaction in problem 13, identify the oxidizing and reducing agents.
Use:
- Oxidizing agent: gets reduced
- Reducing agent: gets oxidized
---
#### a. C + H₂SO₄ → CO₂ + SO₂ + H₂O
- Oxidized: C → reducing agent: C
- Reduced: S (in H₂SO₄) → oxidizing agent: H₂SO₄
✔ Oxidizing agent: H₂SO₄
✔ Reducing agent: C
---
#### b. HNO₃ + HI → NO + I₂ + H₂O
- Oxidized: I⁻ → reducing agent: HI
- Reduced: N → oxidizing agent: HNO₃
✔ Oxidizing agent: HNO₃
✔ Reducing agent: HI
---
#### c. KMnO₄ + HCl → MnCl₂ + Cl₂ + H₂O + KCl
- Oxidized: Cl⁻ → reducing agent: HCl
- Reduced: Mn → oxidizing agent: KMnO₄
✔ Oxidizing agent: KMnO₄
✔ Reducing agent: HCl
---
#### d. Sb + HNO₃ → Sb₂O₃ + NO + H₂O
- Oxidized: Sb → reducing agent: Sb
- Reduced: N → oxidizing agent: HNO₃
✔ Oxidizing agent: HNO₃
✔ Reducing agent: Sb
---
✔ Final Answers Summary:
---
#### Problem 1:
| Reaction | Oxidized | Reduced | Oxidizing Agent | Reducing Agent |
|--------|---------|--------|------------------|----------------|
| 1 | Sr | O₂ | O₂ | Sr |
| 2 | Li | S | S | Li |
| 3 | Cs | Br₂ | Br₂ | Cs |
| 4 | Mg | N₂ | N₂ | Mg |
| 5 | Fe | O₂ | O₂ | Fe |
| 6 | Br⁻ | Cl₂ | Cl₂ | NaBr |
| 7 | Si | F₂ | F₂ | Si |
| 8 | Ca | O₂ | O₂ | Ca |
| 9 | Mg | H⁺ | HCl | Mg |
| 10 | Na | H⁺ | H₂O | Na |
---
#### Problem 11: Oxidation Numbers
| Substance | Oxidation Number |
|----------|------------------|
| a. sulfate | S: +6 |
| b. Sn | 0 |
| c. S²⁻ | -2 |
| d. Fe²⁺ | +2 |
| e. Sn⁴⁺ | +4 |
| f. nitrate | N: +5 |
| g. ammonium | N: -3 |
---
#### Problem 12: Chromium Oxidation States
| Compound | Cr Oxidation State |
|---------|-------------------|
| a. Cr₂O₃ | +3 |
| b. Na₂Cr₂O₇ | +6 |
| c. CrSO₄ | +2 |
| d. chromate (CrO₄²⁻) | +6 |
| e. dichromate (Cr₂O₇²⁻) | +6 |
---
#### Problem 13: Oxidized/Reduced Elements
| Reaction | Oxidized | Reduced |
|--------|--------|--------|
| a. C + H₂SO₄ → ... | C | S |
| b. HNO₃ + HI → ... | I⁻ | N |
| c. KMnO₄ + HCl → ... | Cl⁻ | Mn |
| d. Sb + HNO₃ → ... | Sb | N |
---
#### Problem 14: Oxidizing & Reducing Agents
| Reaction | Oxidizing Agent | Reducing Agent |
|--------|------------------|----------------|
| a. | H₂SO₄ | C |
| b. | HNO₃ | HI |
| c. | KMnO₄ | HCl |
| d. | HNO₃ | Sb |
---
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Parent Tip: Review the logic above to help your child master the concept of oxidation and reduction worksheet.
