Unit notes and practice questions

Grade 10 Chemistry unit 3: Important inorganic compounds

Everything here is for unit 3 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.

8
Cards: 10
Practice questions on unit 3: 111–168
The textbook pages for unit 3

What unit 3 covers

1.Oxides
2.Acids
3.Salts

Short notes for unit 3

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

Acid Base IndicatorsReference tableLitmus · Phenolphthalein · Methyl orange · +1

Indicator	Colour in Acid	Colour in Base
Litmus	Red	Blue
Phenolphthalein	Colourless	Pink
Methyl orange	Red	Yellow
Universal Indicator	Red	Blue

When you use it

Use this reference table to determine whether a solution is acidic or basic based on the observed colour of added indicators.

Watch out

Phenolphthalein remains completely colourless in acidic solutions, it only turns pink in basic solutions.

Drafted from Grade 10 Chemistry, pages 111-168, then checked twice before it went up

Classification of OxidesReference tableAcidic · Basic · Amphoteric · +2

Oxide Type	Chemical Behavior	Examples
Acidic	Forms acid with water, neutralizes bases	$\mathrm{CO_2}$ , $\mathrm{SO_2}$ , $\mathrm{N_2O_5}$
Basic	Forms base with water, neutralizes acids	$\mathrm{Na_2O}$ , $\mathrm{CaO}$ , $\mathrm{CuO}$
Amphoteric	Reacts with both strong acids and strong bases	$\mathrm{Al_2O_3}$ , $\mathrm{ZnO}$ , $\mathrm{PbO}$
Neutral	Reacts neither with acids nor with bases	$\mathrm{CO}$ , $\mathrm{NO}$ , $\mathrm{N_2O}$ , $\mathrm{H_2O}$
Peroxide	Contains $-O-O-$ link with oxygen in $-1$ state	$\mathrm{H_2O_2}$ , $\mathrm{Na_2O_2}$ , $\mathrm{CaO_2}$

When you use it

Use this table to classify binary oxygen compounds and predict their reaction products with water, acids, or bases.

Watch out

Neutral oxides like CO, NO, and N2O are non-metal oxides that do not form salts.

Drafted from Grade 10 Chemistry, pages 111-168, then checked twice before it went up

Diluting Concentrated AcidCommon mistake

When you use it

Apply when answering questions about laboratory safety rules and procedures for acid dilution.

Watch out

Never add water directly into concentrated acid. Always pour the concentrated acid slowly into water to prevent violent exothermic splattering.

Drafted from Grade 10 Chemistry, pages 111-168, then checked twice before it went up

pH and pOH RelationshipFormula

\mathrm{pH} + \mathrm{pOH} = 14

\mathrm{pH} + \mathrm{pOH} = 14

$\mathrm{pH}$: pH value $1$
$\mathrm{pOH}$: pOH value $1$

When you use it

Use this equation at 25 °C to convert between pH and pOH, especially when finding the pH of a basic solution from hydroxide ion concentration.

Watch out

This relationship is valid strictly at 25 °C where the ionic product of water equals 1.0 x 10^-14.

Drafted from Grade 10 Chemistry, pages 111-168, then checked twice before it went up

pH CalculationFormula

\mathrm{pH} = -\log[\mathrm{H}^+]

\mathrm{pH} = -\log[\mathrm{H}^+]

$\mathrm{pH}$: pH value $1$
$[\mathrm{H}^+]$: Hydrogen ion concentration $\mathrm{mol\,L^{-1}}$

When you use it

Use this formula to calculate the pH of an acidic solution from the molar concentration of hydrogen ions, or to find hydrogen ion concentration from a known pH.

Watch out

For diprotic strong acids like H2SO4, the hydrogen ion concentration is twice the molar concentration of the acid.

Drafted from Grade 10 Chemistry, pages 111-168, then checked twice before it went up

Acids, bases and salts: definitions and neutralizationRuleArrhenius acid · Arrhenius base · Bronsted-Lowry · +4

Term	What it means	Examples
Arrhenius acid	Releases hydrogen ions in water, carried in the solution as the hydronium ion $\mathrm{H_3O^+}$	$\mathrm{HCl}$ , $\mathrm{H_2SO_4}$ , $\mathrm{HNO_3}$ , $\mathrm{CH_3COOH}$
Arrhenius base	Releases hydroxide ions in water. A base that dissolves is called an alkali, and an insoluble base such as $\mathrm{CuO}$ moves no indicator until it reacts with an acid	$\mathrm{NaOH}$ , $\mathrm{KOH}$ , $\mathrm{Ca(OH)_2}$
Bronsted-Lowry	The wider definition: an acid donates a proton and a base accepts one. Ammonia belongs here, since it takes a proton from water and leaves hydroxide behind without carrying an $\mathrm{OH}$ group of its own	$\mathrm{NH_3}$
Salt	The hydrogen of an acid replaced by a metal ion or by the ammonium ion $\mathrm{NH_4^+}$	$\mathrm{NaCl}$ , $\mathrm{KNO_3}$ , $\mathrm{CuSO_4}$ , $\mathrm{NH_4Cl}$
Neutralization	Acid plus base gives salt and water. Between the ions it is $\mathrm{H^+ + OH^- \rightarrow H_2O}$ , and the metal ion with the acid's other ion is left as the salt	$\mathrm{HCl + NaOH \rightarrow NaCl + H_2O}$
Acid on a carbonate	A related but different reaction, giving salt, water and carbon dioxide	$\mathrm{2HCl + CaCO_3 \rightarrow CaCl_2 + H_2O + CO_2}$
The pH scale	A continuous scale, written 0 to 14 for school work at about 25 degrees Celsius. Below 7 is acidic, exactly 7 is neutral, above 7 is basic	pH 6.5 is acidic; pH 7.4 is basic

When you use it

Use when a question asks you to classify a substance as an acid, a base or a salt, or to complete a neutralization equation. Name the definition you are working from, because Arrhenius describes what a substance releases in water while Bronsted-Lowry describes a proton given and taken.

Watch out

Students copy the one to one pattern of HCl with NaOH onto an acid that has two hydrogens, and write H2SO4 plus NaOH giving NaSO4 and H2O. Both hydrogens have to be replaced, so the salt is Na2SO4, two sodium ions against one sulphate ion, and the equation needs two NaOH and two H2O. Build the salt from the charges first, then balance. The same slip produces CaCl instead of CaCl2 with calcium hydroxide.

Common names of chemical compoundsReference tableQuicklime · Slaked lime · Limestone, marble, chalk · +19

Common name	Chemical name	Formula
Quicklime	Calcium oxide	$\mathrm{CaO}$
Slaked lime	Calcium hydroxide	$\mathrm{Ca(OH)_2}$
Limestone, marble, chalk	Calcium carbonate	$\mathrm{CaCO_3}$
Baking soda	Sodium hydrogen carbonate	$\mathrm{NaHCO_3}$
Washing soda	Sodium carbonate decahydrate	$\mathrm{Na_2CO_3} \cdot 10\mathrm{H_2O}$
Soda ash	Sodium carbonate	$\mathrm{Na_2CO_3}$
Caustic soda	Sodium hydroxide	$\mathrm{NaOH}$
Blue vitriol	Copper(II) sulphate pentahydrate	$\mathrm{CuSO_4} \cdot 5\mathrm{H_2O}$
White vitriol	Zinc sulphate heptahydrate	$\mathrm{ZnSO_4} \cdot 7\mathrm{H_2O}$
Oil of vitriol	Sulphuric acid	$\mathrm{H_2SO_4}$
Muriatic acid	Hydrochloric acid	$\mathrm{HCl}$
Plaster of Paris	Calcium sulphate hemihydrate	$\mathrm{2CaSO_4} \cdot \mathrm{H_2O}$
Chloroform	Trichloromethane	$\mathrm{CHCl_3}$
Glacial acetic acid	Ethanoic acid	$\mathrm{CH_3COOH}$
Spirit	Ethanol	$\mathrm{C_2H_5OH}$
Marsh gas	Methane	$\mathrm{CH_4}$
Laughing gas	Dinitrogen monoxide	$\mathrm{N_2O}$
Dry ice	Solid carbon dioxide	$\mathrm{CO_2(s)}$
Potash, pearl ash	Potassium carbonate	$\mathrm{K_2CO_3}$
Table sugar	Sucrose	$\mathrm{C_{12}H_{22}O_{11}}$
Silica	Silicon dioxide	$\mathrm{SiO_2}$
Bleaching powder	Calcium chloride hypochlorite	$\mathrm{Ca(OCl)Cl}$

When you use it

Reach for this when a question, a label or a shop name uses the traditional name and the answer needs the chemical one, or the other way round. Copy the formula column carefully, because several of these names belong to hydrated crystals rather than to the dry salt.

Watch out

Students mix up the three limes, because all three names carry the word. Limestone is the rock you start with, CaCO3. Heat it and it loses carbon dioxide to give quicklime, CaO. Add water to that and it becomes slaked lime, Ca(OH)2, and slaked means water has been added, so it is the only one of the three with OH in it. The vitriols and washing soda hold a second trap: those names belong to the crystals, which carry water. Blue vitriol is copper sulphate pentahydrate and is blue because of that water, so drive the water off and you get white anhydrous CuSO4, which nobody calls blue vitriol.

The five reactions of acidsReference tableMetal hydroxide · Metal above hydrogen · Metal carbonate · +2

Acid reacts with	What you get	Example
Metal hydroxide	A salt and water. This is neutralization.	$\mathrm{HCl(aq) + NaOH(aq) \rightarrow NaCl(aq) + H_{2}O(l)}$
Metal above hydrogen	A salt and hydrogen gas, and only with a dilute non-oxidizing acid such as dilute HCl or dilute H2SO4. Copper, silver and gold sit below hydrogen in the reactivity series and give no reaction with dilute HCl.	$\mathrm{Zn(s) + 2HCl(aq) \rightarrow ZnCl_{2}(aq) + H_{2}(g)}$
Metal carbonate	A salt, water and carbon dioxide. A metal hydrogencarbonate gives the same three products.	$\mathrm{CaCO_{3}(s) + 2HCl(aq) \rightarrow CaCl_{2}(aq) + H_{2}O(l) + CO_{2}(g)}$
Metal oxide	A salt and water. A metal oxide is a basic oxide, so this is neutralization as well.	$\mathrm{CuO(s) + 2HCl(aq) \rightarrow CuCl_{2}(aq) + H_{2}O(l)}$
Ammonia	An ammonium salt and no water. Ammonia is the base here, but it carries no hydroxide and no oxide, so there is nothing to build water from. The NH4Cl forms as a white solid.	$\mathrm{NH_{3}(g) + HCl(g) \rightarrow NH_{4}Cl(s)}$

When you use it

Use when you have to predict the products of an acid reaction or write the balanced equation for one. A salt forms whenever the hydrogen of an acid is replaced by a metal or by the ammonium ion, and every one of these five rows produces one.

Watch out

Students write the salt before checking the metal's valency, so they get Zn + HCl giving ZnCl + H2 and never find the 2 that belongs in front of HCl. Build the salt from the ion charges first, since Zn2+ with Cl- gives ZnCl2, then balance the acid to match it. The same habit of copying a pattern without checking produces the other favourite mistake, Cu + 2HCl giving CuCl2 + H2. Copper sits below hydrogen in the reactivity series, so nothing happens, and that is exactly why copper reaches row four as CuO instead.

Practice questions on unit 3

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

Question 1

According to the textbook, what is an oxide?

A.A binary compound containing oxygen and any other element
B.A ternary compound containing hydrogen, oxygen, and a metal
C.Any compound containing carbon and oxygen
D.A substance that produces hydroxide ions in water

Show the answer and why

Answer: A A binary compound containing oxygen and any other element

Why

Oxides are binary compounds consisting of oxygen and any other element (metal, non-metal, or metalloid).

Question 2

What colour does phenolphthalein develop in an aqueous solution of a basic oxide or base?

A.Colourless
B.Pink (red)
C.Yellow
D.Orange

Show the answer and why

Answer: B Pink (red)

Why

Phenolphthalein is colourless in acidic solutions and turns pink (red) in basic solutions.

Question 3

According to the Arrhenius definition, what is an acid?

A.A substance that releases hydroxide ions (OH-) in water
B.A substance that releases hydrogen ions (H+) or hydronium ions (H3O+) in aqueous solution
C.A compound that turns litmus paper blue
D.A substance that accepts protons from water

Show the answer and why

Answer: B A substance that releases hydrogen ions (H+) or hydronium ions (H3O+) in aqueous solution

Why

Arrhenius defined an acid as a substance that releases hydrogen ions (H⁺) or hydronium ions (H₃O⁺) in aqueous solution.

Question 4

Which of the following acids is classified as a diprotic acid?

A.HCl
B.HNO3
C.H2SO4
D.H3PO4

Show the answer and why

Answer: C H2SO4

Why

Sulfuric acid (H₂SO₄) contains two ionizable hydrogen atoms per molecule, making it a diprotic acid.

Question 5

Which of the following oxides shows both acidic and basic behavior and is classified as an amphoteric oxide?

A.Na2O
B.SO2
C.Al2O3
D.CaO

Show the answer and why

Answer: C Al2O3

Why

Aluminium oxide (Al₂O₃) reacts with both strong acids and strong bases to form salt and water, which makes it an amphoteric oxide.

Question 6

Which pair consists only of neutral oxides?

A.CO and N2O
B.SO2 and CO2
C.Na2O and CaO
D.Al2O3 and ZnO

Show the answer and why

Answer: A CO and N2O

Why

Carbon monoxide (CO) and dinitrogen monoxide (N₂O) do not react with acids or bases, so they are neutral oxides.

Question 7

When dilute hydrochloric acid reacts with calcium carbonate (CaCO₃), which gas is evolved?

A.Hydrogen gas (H2)
B.Carbon dioxide (CO2)
C.Sulphur dioxide (SO2)
D.Oxygen gas (O2)

Show the answer and why

Answer: B Carbon dioxide (CO2)

Why

Acids react with carbonates to produce a salt, water, and carbon dioxide gas (CO₂).

Question 8

When preparing a dilute solution of concentrated sulfuric acid in a chemistry laboratory in Hawassa, what is the safe procedure?

A.Pour water quickly into the concentrated acid
B.Pour the concentrated acid slowly into water
C.Boil the concentrated acid before mixing with water
D.Add solid sodium carbonate directly into the pure acid

Show the answer and why

Answer: B Pour the concentrated acid slowly into water

Why

To dilute concentrated acids safely, always pour the concentrated acid into water, never water into the acid.

Question 9

A solution of hydrochloric acid has a concentration of 0.01 M. What is its pH value?

A.1
B.2
C.7
D.12

Show the answer and why

Answer: B 2

Why

Because HCl is a strong acid, [H⁺] = 0.01 M = 1.0 × 10^-2 M. Therefore, pH = -log(1.0 × 10^-2) = 2.

Question 10

What is the oxidation state of oxygen in peroxides such as Na₂O₂ and CaO₂?

A.-2
B.-1
C.+1
D.+2

Show the answer and why

Answer: B -1

Why

Peroxides are compounds in which oxygen has an oxidation number of -1 and contains the -O-O- link.

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

The textbook pages for unit 3

Unit 3 runs from page 111 to page 168 of the Ministry of Education edition.

Ministry of Education edition, English, 307 pages

Download the PDF

All Grade 10 Chemistry short notes

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