Why does an instant cold pack feel cold when ammonium nitrate (NH 4 NO 3 ) dissolves in water?

The dissolution is exothermic and gives off heat to the hand

The dissolution is an ideal solution with no net enthalpy change

Ammonium nitrate reacts chemically with water to freeze the pack

Unit notes and practice questions

Grade 10 Chemistry unit 2: Sollutions

Everything here is for unit 2 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.

4
Cards: 10
Practice questions on unit 2: 51–110
The textbook pages for unit 2

What unit 2 covers

1.Heterogeneous and Homogeneous Mixtures
2.The Solution Process
3.Solubility as an Equilibrium Process
4.Ways of Expressing Concentration of Solution
5.Preparation of Solutions
6.Solution Stoichiometry

Short notes for unit 2

The cards filed under this chapter on the Grade 10 Chemistry page. Open one at a time.

Classification of ColloidsReference tableLiquid · Solid · Gas

Dispersed Phase	Dispersing Medium	Colloid Type	Example
Liquid	Gas	Aerosol	Fog, clouds, mist
Solid	Gas	Aerosol	Smoke, exhaust
Gas	Liquid	Foam	Shaving cream
Liquid	Liquid	Emulsion	Milk, face cream
Solid	Liquid	Sol	Milk of magnesia
Gas	Solid	Foam	Sponge, pumice
Liquid	Solid	Gel	Jelly, cheese, butter
Solid	Solid	Solid sol	Gemstone, milky glass

When you use it

Use this table to identify the colloid type based on the physical states of dispersed phase and dispersing medium.

Watch out

Gas dispersed in gas does not form a colloid, because all gases mix completely to form a true solution.

Drafted from Grade 10 Chemistry, pages 51-110, then checked twice before it went up

Enthalpy of Solution for Ionic SolidsFormula

\Delta H_{\text{soln}} = \Delta H_{\text{lat}} + \Delta H_{\text{hydr}}

\Delta H_{\text{soln}} = \Delta H_{\text{lat}} + \Delta H_{\text{hydr}}

$\Delta H_{\text{soln}}$: molar enthalpy of solution $\text{kJ}\,\text{mol}^{-1}$
$\Delta H_{\text{lat}}$: lattice energy $\text{kJ}\,\text{mol}^{-1}$
$\Delta H_{\text{hydr}}$: enthalpy of hydration $\text{kJ}\,\text{mol}^{-1}$

When you use it

Use this to determine overall heat change when an ionic solid dissolves into water from its lattice and hydration energies.

Watch out

Lattice energy overcomes crystal bonds and is positive (endothermic), while hydration energy is always negative (exothermic).

Drafted from Grade 10 Chemistry, pages 51-110, then checked twice before it went up

Heat of SolutionFormula

q = m C_g \Delta T

q = m C_g \Delta T

$q$: heat released or absorbed $\text{J}$
$m$: mass of the solution $\text{g}$
$C_g$: specific heat capacity of the solution $\text{J}\,\text{g}^{-1}\,{^{\circ}\text{C}}^{-1}$
$\Delta T$: temperature change $^{\circ}\text{C}$

When you use it

Use this formula to find the total heat energy absorbed or released during the dissolution process in a calorimeter.

Watch out

The mass m must be the total mass of the solution (solute mass plus solvent mass), not just the solvent mass.

Drafted from Grade 10 Chemistry, pages 51-110, then checked twice before it went up

Henry's LawFormula

C = k P

C = k P

$C$: concentration of dissolved gas $\text{mol}\,\text{L}^{-1}$
$k$: Henry's law constant $\text{mol}\,\text{L}^{-1}\,\text{atm}^{-1}$
$P$: partial pressure of the gas $\text{atm}$

When you use it

Use this formula to calculate the solubility or concentration of a gas in a liquid at a specific partial pressure.

Watch out

Gases that react chemically with water or form hydrogen bonds such as HCl and NH3 do not obey Henry's law.

Drafted from Grade 10 Chemistry, pages 51-110, then checked twice before it went up

Practice questions on unit 2

10 multiple-choice questions written against this chapter, each with its answer and the reason. Try one before you open the answer.

Question 1

What is the particle size range in a colloidal solution?

A.Less than 0.1 nm
B.Between 1 nm and 100 nm
C.Between 200 nm and 500 nm
D.Greater than 1000 nm

Show the answer and why

Answer: B Between 1 nm and 100 nm

Why

According to the textbook, the size of particles in a colloid is between 1 nm and 100 nm in diameter. This makes them larger than particles in a true solution but smaller than those in a suspension.

Question 2

According to the textbook classification of colloids, milk and face cream are examples of which type?

A.Aerosol
B.Gel
C.Emulsion
D.Sol

Show the answer and why

Answer: C Emulsion

Why

An emulsion is a type of colloid where a liquid is dispersed in another liquid. Milk and face cream are both classified as liquid in liquid emulsions.

Question 3

Which type of mixture has a single uniform phase with no visible boundaries because its components are mixed as individual atoms, ions, or molecules?

A.Homogeneous mixture (solution)
B.Suspension
C.Heterogeneous mixture
D.Coagulated mixture

Show the answer and why

Answer: A Homogeneous mixture (solution)

Why

A homogeneous mixture, also called a solution, has a uniform composition throughout with no visible boundaries because the components are mixed at the atomic, molecular, or ionic level.

Question 4

What happens to the solubility of most gases in liquid solvents when the temperature increases?

A.Solubility increases
B.Solubility decreases
C.Solubility stays completely unchanged
D.Solubility doubles

Show the answer and why

Answer: B Solubility decreases

Why

The solubility of gases in liquids decreases with increasing temperature because added heat breaks the attractive forces between gas molecules and solvent molecules, causing the gas to escape.

Question 5

How are the stearate ions arranged when soap forms an association colloid (micelle) in water?

A.Hydrophilic ends point inward and nonpolar tails face the water
B.Hydrophobic hydrocarbon ends point inward and hydrophilic carboxyl groups face outward toward water
C.Both ends point inward away from the water
D.Both ends face outward toward the water

Show the answer and why

Answer: B Hydrophobic hydrocarbon ends point inward and hydrophilic carboxyl groups face outward toward water

Why

In water, soap forms micelles where the nonpolar (hydrophobic) hydrocarbon tails turn inward to avoid water and trap oil, while the ionic carboxyl groups (hydrophilic) face outward toward the polar water molecules.

Question 6

Based on the solubility rules for ionic solids in the textbook, which of the following compounds is insoluble in water?

A.AgNO3
B.KI
C.BaCO3
D.AlCl3

Show the answer and why

Answer: C BaCO3

Why

Carbonates (CO₃^2-) are insoluble in water, except those of Group 1A elements and ammonium. Since barium (Ba) is in Group 2A, BaCO₃ is insoluble. Nitrates, Group 1A salts (like KI), and most chlorides are soluble.

Question 7

Which step of the solution formation process is exothermic?

A.Separation of solute particles from one another
B.Separation of solvent particles from one another
C.Mixing of solute and solvent particles to form solute-solvent attractions
D.Overcoming the crystal lattice energy of the solid

Show the answer and why

Answer: C Mixing of solute and solvent particles to form solute-solvent attractions

Why

Breaking solute-solute or solvent-solvent attractions requires energy and is endothermic. Forming new attractive solute-solvent interactions releases energy, making step 3 exothermic (ΔH_mix < 0).

Question 8

Why does an instant cold pack feel cold when ammonium nitrate (NH₄NO₃) dissolves in water?

A.The dissolution is exothermic and gives off heat to the hand
B.The dissolution is endothermic and absorbs heat from the surroundings
C.The dissolution is an ideal solution with no net enthalpy change
D.Ammonium nitrate reacts chemically with water to freeze the pack

Show the answer and why

Answer: B The dissolution is endothermic and absorbs heat from the surroundings

Why

Dissolving ammonium nitrate in water is an endothermic process. It absorbs heat from the surroundings, causing the temperature of the pack to drop significantly.

Question 9

In a bottled soft drink in Hawassa, the concentration of dissolved CO₂ is 0.032 M at a partial pressure of 3.0 atm. What is the concentration of dissolved CO₂ if the pressure is increased to 6.0 atm at constant temperature?

A.0.016 M
B.0.048 M
C.0.064 M
D.0.096 M

Show the answer and why

Answer: C 0.064 M

Why

Using Henry's law equation, C₁ / P₁ = C₂ / P₂. Substituting values gives: C₂ = (0.032 M × 6.0 atm) / 3.0 atm = 0.064 M.

Question 10

A student in Bahir Dar dissolves 15 g of table salt (NaCl) in 85 g of pure water. What is the percent by mass of salt in this solution?

A.15%
B.17.6%
C.85%
D.12.5%

Show the answer and why

Answer: A 15%

Why

Percent by mass = (mass of solute / total mass of solution) × 100%. Here, total mass = 15 g + 85 g = 100 g. Therefore, (15 g / 100 g) × 100% = 15%.

The app holds 12 questions on this unit, marked as you go. These are the first 10.

The textbook pages for unit 2

Unit 2 runs from page 51 to page 110 of the Ministry of Education edition.

Ministry of Education edition, English, 307 pages

Download the PDF

All Grade 10 Chemistry short notes

Practise this unit in the app

Temari turns this chapter into timed practice and marks it as you go, with an AI tutor to explain anything that did not land.

Start free

Temari.et is also an Android app, free on Google Play.

About the Temari app