Unit notes and practice questions
Everything here is for unit 4 of the Grade 10 Chemistry textbook: what the chapter covers, the short notes, practice questions with their answers, and the lesson video where one exists.
The cards filed under this chapter on the Grade 10 Chemistry page. Open one at a time.
When you use it
Use when identifying the signs and reactions of anode and cathode in electrochemical cells.
Watch out
Oxidation ALWAYS occurs at the anode and reduction at the cathode in both cells. The anode is negative in a Galvanic cell, but positive in an electrolytic cell.
Drafted from Grade 10 Chemistry, pages 169-200, then checked twice before it went up
| Feature | Galvanic (Voltaic) Cell | Electrolytic Cell |
|---|---|---|
| Energy conversion | Chemical energy to electrical energy | Electrical energy to chemical energy |
| Redox reaction | Spontaneous | Nonspontaneous |
| Anode sign and process | Negative (-), Oxidation | Positive (+), Oxidation |
| Cathode sign and process | Positive (+), Reduction | Negative (-), Reduction |
When you use it
Use when distinguishing between battery operation and electrolysis setups.
Drafted from Grade 10 Chemistry, pages 169-200, then checked twice before it went up
| Property | Metallic Conduction | Electrolytic Conduction |
|---|---|---|
| Charge carriers | Electrons (delocalized) | Ions (cations and anions) |
| Matter transfer | No transfer of matter | Involves transfer of ions |
| Chemical change | No chemical change | Chemical decomposition occurs |
| Effect of temperature | Conductivity decreases as temperature rises | Conductivity increases as temperature rises |
When you use it
Use when comparing conduction in solid metals to molten salts or aqueous solutions.
Drafted from Grade 10 Chemistry, pages 169-200, then checked twice before it went up
When you use it
Use to calculate heat transferred during a temperature change.
Watch out
Temperature change can use Kelvin or degrees Celsius since the temperature difference is numerically identical.
Drafted from Grade 10 Chemistry, pages 169-200, then checked twice before it went up
10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.
Question 1
For an exothermic chemical reaction, what is the sign and value of the enthalpy change (ΔH)?
Answer: B Negative, ΔH < 0
Why
In an exothermic reaction, heat is released to the surroundings, meaning the enthalpy of products is less than the enthalpy of reactants. Therefore, ΔH is negative (ΔH < 0).
Question 2
What are the charge carriers responsible for electrical conductivity in electrolytic solutions?
Answer: C Cations and anions
Why
Electrolytic conduction occurs due to the movement of ions (positively charged cations and negatively charged anions) through the solution or molten salt.
Question 3
In a Daniell voltaic cell, what is the primary role of the salt bridge?
Answer: B To maintain electrical neutrality between the two solutions
Why
The salt bridge allows ions to flow between the two half-cell compartments to maintain electrical neutrality so that the cell can continue to generate electricity.
Question 4
Which of the following is classified as a rechargeable secondary voltaic cell?
Answer: C Lead storage battery
Why
A lead storage battery is a secondary cell because the chemical reactions are reversible and the battery can be recharged by passing a direct electric current through it.
Question 5
What is the SI unit of heat capacity according to the textbook?
Answer: A Joule per Kelvin (J/K)
Why
Heat capacity is defined as the quantity of heat required to change the temperature of an object by 1 K (Heat capacity = q/ΔT), so its unit is Joule per Kelvin (J/K).
Question 6
How does an increase in temperature affect metallic conduction and electrolytic conduction?
Answer: B Metallic conduction decreases, electrolytic conduction increases
Why
In metals, higher temperatures increase the vibration of kernels and create obstacles to electron flow, decreasing conductivity. In electrolytes, higher temperatures increase ion mobility, increasing conductivity.
Question 7
In a zinc-carbon dry cell (Leclanche cell), which component serves as the anode?
Answer: B The outer zinc can
Why
The Leclanche dry cell uses the zinc can as the anode, where zinc is oxidized to Zn2+, and a central graphite rod surrounded by paste as the cathode.
Question 8
A 12 V car battery used in Hawassa contains how many individual lead-storage cells connected in series, and what voltage does each cell deliver?
Answer: B 6 cells, each delivering 2.0 V
Why
Each single lead-storage cell delivers about 2 V. Therefore, six cells connected in series provide a total of 12 V.
Question 9
During the commercial electrolysis of molten sodium chloride (NaCl), what half-reaction occurs at the cathode?
Answer: A Na<sup>+</sup>(l) + e<sup>-</sup> → Na(l)
Why
Reduction always takes place at the cathode. In molten NaCl, positive sodium ions (Na+) gain electrons to form liquid sodium metal: Na+(l) + e- → Na(l).
Question 10
When an automobile lead-storage battery is discharging (in operation), what solid substance is formed at both the anode and the cathode?
Answer: C PbSO<sub>4</sub>(s)
Why
During discharge, the anode reaction converts Pb to PbSO4(s), and the cathode reaction converts PbO2 to PbSO4(s). Thus, lead(II) sulfate is produced at both electrodes.
The app holds 12 questions on this unit, marked as you go. These are the first 10.
Unit 4 runs from page 169 to page 200 of the Ministry of Education edition.
Ministry of Education edition, English, 307 pages
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