The Characteristic Properties Of Acids And Bases

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Properties of Acids

Acids have pH < 7, sour taste (if edible), and are corrosive.
Acids neutralise bases to form a salt and water.
In water, acids release hydrogen ions (H⁺); e.g., HCl → H⁺ + Cl⁻.
Acids react with metals (above H in reactivity series) to give salt + H₂.
Acids react with metal oxides/hydroxides (bases) to give salt + water (neutralisation).
Acids react with metal carbonates to give salt + CO₂ + H₂O.

Properties of Bases & Alkalis

Bases have pH > 7; a water‑soluble base is an alkali.
Bases neutralise acids to form a salt and water.
In water, alkalis release hydroxide ions (OH⁻); e.g., NaOH → Na⁺ + OH⁻.
Bases are usually metal oxides or hydroxides.
Alkalis react with ammonium salts (e.g., NH₄Cl) to give salt + water + NH₃ (test: damp red litmus turns blue).

Indicators

Litmus: red in acid, blue in alkali (not sharp for titrations).
Methyl orange: red in acid, yellow in alkali.
Thymolphthalein: colourless in acid, blue in alkali.
Universal indicator: mixture of dyes giving a colour range for pH 1–14.

Universal indicator colours across the pH scale

Neutralisation & Ions

Neutralisation: H⁺ + OH⁻ → H₂O (net ionic equation).
Acids are sources of H⁺; alkalis are sources of OH⁻.
Not all acid reactions are neutralisations (e.g., acid + metal produces no water).
The pH scale is logarithmic: a change of 1 pH unit = ×10 change in [H⁺].

The pH scale

pH Scale & Hydrogen Ion Concentration

pH 0–2: strong acid; pH 3–6: weak acid; pH 7: neutral.
pH 8–11: weak alkali; pH 12–14: strong alkali.
Lower pH = higher [H⁺]; higher pH = higher [OH⁻].
Universal indicator gives approximate pH by matching colour to a chart.

H+ ion concentration relative to pH

Classifying Oxides

Acidic oxides (non‑metal + O): react with bases to form salt + water; produce acidic solutions (e.g., CO₂, SO₂).
Basic oxides (metal + O): react with acids to form salt + water; produce alkaline solutions (e.g., CuO, CaO).
Amphoteric oxides (e.g., ZnO, Al₂O₃): react with both acids and bases to give salt + water.
Neutral oxides (e.g., N₂O, NO, CO): do not react with acids or bases.

Metals form basic oxides, non-metals form acidic oxides

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Câu hỏi luyện tập

Xem trước miễn phí — 8 trên 52 câu hỏi. Đăng ký để xem tất cả.

1.All bases are soluble in water and are called alkalis.
Easy
True or false?
2.Which of the following is the correct net ionic equation for the neutralisation of an acid by a base?
Easy
- AH⁺(aq) + OH⁻(aq) → H₂O(l)
- BH⁺(aq) + OH⁻(aq) → H₂O₂(l)
- CH⁺(aq) + O²⁻(aq) → H₂O(l)
- DH₂O(l) → H⁺(aq) + OH⁻(aq)
3.State the colour of litmus in an alkali.
Easy
4.Complete the sentence about the reaction of acids with metals.
Easy
When an acid reacts with a metal, the products are a ____ and hydrogen gas.
5.A solution has a pH of 3. How many times greater is the hydrogen ion concentration compared to a solution of pH 5?
Medium
- A100
- B120
- C90
- D110
6.Match each oxide to its classification.
Medium
- CO₂
- MgO
- Al₂O₃
- Acidic oxide
- Basic oxide
- Amphoteric oxide
7.Name the gas produced when an acid reacts with a metal carbonate.
Easy
8.Which indicator is NOT suitable for determining the endpoint in an acid-alkali titration?
Medium
- ALitmus
- BMethyl orange
- CThymolphthalein
- DUniversal indicator

Thêm câu hỏi

9.Arrange the following oxides in order of increasing pH when dissolved in water (lowest pH first).
Medium
- SO₂
- CO
- CaO
10.Amphoteric oxides react with both acids and bases to form a salt and water only.
Medium
True or false?
11.Write the chemical formula of the salt formed when aluminium oxide reacts with sodium hydroxide.
Medium
12.Complete the word equation for the reaction of ammonium chloride with sodium hydroxide.
Easy
Ammonium chloride + sodium hydroxide → sodium chloride + water + ____
13.Which of the following is the colour of litmus in an alkali?
Easy
- ARed
- BBlue
- CGreen
- DPurple
14.Which of the following are acidic oxides? (Select all that apply)
Medium
- ACO2
- BMgO
- CSO2
- DNa2O
- ENO2
15.Match each indicator to its colour in an alkali.
Easy
- Litmus
- Methyl orange
- Thymolphthalein
- blue
- yellow
- blue
16.Arrange the following steps in the correct order to test for ammonia gas from an ammonium salt.
Medium
- Warm the mixture gently
- Add alkali to the substance
- Test gas with damp red litmus paper
- Observe colour change of litmus paper
17.In an experiment, 30 cm³ of dilute hydrochloric acid is placed in a polystyrene cup and 1 g of solid C is added. The temperature increases by 4°C. When the experiment is repeated with 2 g of solid C, the temperature increase is 8°C. Assuming the reaction goes to completion and no heat loss, what temperature increase would be expected with 3 g of solid C?
Hard
- A12°C
- B10°C
- C6°C
- D16°C
18.A student adds 50 cm³ of 1.0 mol/dm³ sodium hydroxide to a polystyrene cup and measures the temperature. Then 5.0 cm³ portions of 1.0 mol/dm³ acid A are added, and the temperature is recorded after each addition. The temperature rises until a total of 25 cm³ of acid is added, then begins to fall. Which statement explains the temperature fall?
Hard
- AThe neutralisation reaction is exothermic and further addition of acid dilutes the mixture, cooling it.
- BAfter neutralisation, excess acid reacts with the sodium hydroxide endothermically.
- CThe thermometer is not sensitive enough to measure further changes.
- DThe reaction becomes endothermic after all alkali is neutralised.
19.When an acid reacts with a metal, the products are salt and water.
Easy
True or false?
20.In a titration, 25.0 cm³ of 0.10 mol/dm³ hydrochloric acid neutralises 20.0 cm³ of sodium hydroxide solution. What is the concentration of the sodium hydroxide?
Medium
- A0.125 mol/dm³
- B0.080 mol/dm³
- C0.10 mol/dm³
- D0.20 mol/dm³
21.In an experiment to investigate the reaction between an acid and a solid, a student measures the temperature change. Which apparatus is most suitable for measuring the volume of acid accurately?
Easy
- Ameasuring cylinder
- Bburette
- Cbeaker
- Dvolumetric flask
22.When an acid reacts with a metal, water is always produced.
Easy
True or false?
23.A student adds 5.0 cm³ portions of acid to 50 cm³ of sodium hydroxide and records the temperature after each addition. The temperature rises until a maximum and then decreases. What does the maximum temperature indicate?
Medium
- AThe acid is in excess
- BThe alkali is in excess
- CThe neutralisation point has been reached
- DThe reaction is complete and no more heat is produced
24.All bases are soluble in water.
Easy
True or false?
25.Which of the following is the colour of methyl orange in an alkali?
Easy
- ARed
- BYellow
- CBlue
- DColourless
26.Which of the following oxides is classified as acidic?
Easy
- AMgO
- BCO2
- CAl2O3
- DCaO
27.The reaction between a metal and an acid is a neutralisation reaction.
Easy
True or false?
28.Which of the following are properties of acids? (Select all that apply)
Medium
- ApH less than 7
- BSour taste
- CTurn litmus blue
- DReact with bases to form salt and water
29.Which of the following are properties of alkalis? (Select all that apply)
Medium
- AThey have a pH greater than 7
- BThey turn red litmus paper blue
- CThey react with acids to produce salt and water
- DThey are all soluble in water
- EThey produce hydroxide ions in water
30.Which of the following is the colour of thymolphthalein in an alkali?
Easy
- ARed
- BBlue
- CColourless
- DYellow
31.The reaction between a metal carbonate and an acid produces a salt, carbon dioxide and water.
Easy
True or false?
32.Which of the following are reasons why a polystyrene cup is used as a container in acid-base temperature change experiments? (Select all that apply)
Medium
- AIt is a good conductor of heat.
- BIt is a poor conductor of heat.
- CIt minimises heat loss to the surroundings.
- DIt is transparent so the reaction can be observed.
- EIt is inexpensive and disposable.
33.In an experiment, 25.0 cm³ of 0.10 mol/dm³ hydrochloric acid neutralises 20.0 cm³ of sodium hydroxide solution. What is the concentration of the sodium hydroxide?
Hard
- A0.125 mol/dm³
- B0.080 mol/dm³
- C0.100 mol/dm³
- D0.200 mol/dm³
34.In an experiment to measure the temperature change when an acid reacts with a solid, a student uses a polystyrene cup. Why is a polystyrene cup preferred over a glass beaker?
Easy
- AIt is cheaper and easier to stir
- BIt is a better thermal insulator, reducing heat loss to the surroundings
- CIt is transparent, allowing observation of the reaction
- DIt is more durable and can be reused many times
35.Which of the following is the colour of thymolphthalein in an acid?
Easy
- Acolourless
- Bblue
- Cred
- Dyellow
36.Acids have a pH value above 7.
Easy
True or false?
37.Which of the following is a basic oxide?
Easy
- ACO2
- BSO2
- CMgO
- DAl2O3
38.A student investigates the temperature change when different masses of solid C are added to 30 cm³ of dilute hydrochloric acid. The results are plotted on a graph. From the graph, the temperature change for 6 g of solid C is 12 °C. What is the temperature of the solution when 6 g of solid C is added, if the initial temperature of the acid is 20 °C?
Medium
- A20 °C
- B32 °C
- C12 °C
- D8 °C
39.The reaction between a metal carbonate and an acid is an exothermic reaction.
Easy
True or false?
40.A student investigates the reaction between dilute hydrochloric acid and solid calcium carbonate. Which of the following are valid reasons why a polystyrene cup is used as the container in this experiment? (Select all that apply)
Medium
- AIt is a good conductor of heat.
- BIt minimises heat loss to the surroundings.
- CIt is cheap and disposable.
- DIt reacts with hydrochloric acid.
- EIt is a good insulator.
41.Complete the sentence: Acids react with metal carbonates to produce salt, carbon dioxide and ____.
Easy
Acids react with metal carbonates to produce salt, carbon dioxide and ____.
42.What is the pH of a neutral solution?
Easy
43.Complete the sentence.
Medium
When ammonium chloride is warmed with sodium hydroxide, the products formed are ammonia, water and ____.
44.A solution has a pH of 2. How many times more concentrated in hydrogen ions is it than a solution of pH 5?
Medium
45.State the colour of methyl orange in an alkali.
Easy
46.A solution has a pH of 4. How many times greater is the hydrogen ion concentration compared to a solution of pH 6?
Medium
47.Explain why litmus is not suitable for use in titrations.
Medium
48.Explain why the reaction between a metal and an acid is not classified as a neutralisation reaction.
Medium
49.In an experiment, a student adds 1.0 g of solid calcium oxide to 50 cm³ of dilute hydrochloric acid. The temperature increases by 15 °C. The student repeats the experiment using 1.0 g of powdered calcium carbonate instead. The temperature increase is only 5 °C. Explain why the temperature changes are different.
Hard
50.What is the pH of a neutral solution?
Easy
- A9
- B6
- C8
- D7
51.A solution has a pH of 2. How many times more concentrated in hydrogen ions is it than a solution of pH 5?
Medium
- A1000
- B1200
- C1100
- D900
52.A solution has a pH of 4. How many times greater is the hydrogen ion concentration compared to a solution of pH 6?
Medium
- A110
- B100
- C90
- D120

Thẻ ghi nhớ

What is the pH range of acids?

Acids have pH values below 7.

What ions do acids produce when added to water?

Acids produce hydrogen ions (H+).

What is the general equation for the reaction of an acid with a metal?

acid + metal → salt + hydrogen

What is the general equation for the reaction of an acid with a base?

acid + base → salt + water

What are the products when an acid reacts with a metal carbonate?

salt + carbon dioxide + water

What is the colour of litmus in acid and in alkali?

Litmus is red in acid and blue in alkali.

What is the colour of methyl orange in acid and in alkali?

Methyl orange is red in acid and yellow in alkali.

What is the colour of thymolphthalein in acid and in alkali?

Thymolphthalein is colourless in acid and blue in alkali.

What is the pH range of bases?

Bases have pH values above 7.

What ions do alkalis produce when added to water?

Alkalis produce hydroxide ions (OH-).

What is the net ionic equation for neutralisation?

H+(aq) + OH-(aq) → H2O(l)

What is the pH of a neutral solution?

pH 7

How many times more concentrated in H+ is a pH 3 acid compared to a pH 4 acid?

10 times more concentrated.

What is universal indicator used for?

To measure the pH of a solution by matching the colour to a pH colour chart.

What type of oxide is formed when a non-metal combines with oxygen?

Acidic oxide

What type of oxide is formed when a metal combines with oxygen?

Basic oxide

Give an example of an acidic oxide.

Carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen dioxide (NO2), or silicon dioxide (SiO2).

Give an example of a basic oxide.

Copper(II) oxide (CuO) or calcium oxide (CaO).

What are amphoteric oxides?

Oxides that can behave as both acidic and basic, reacting with both acids and bases to form salt and water.

Give two examples of amphoteric oxides.

Zinc oxide (ZnO) and aluminium oxide (Al2O3).

What are neutral oxides?

Oxides that do not react with either acids or bases, e.g., N2O, NO, and CO.

What happens when an alkali is warmed with an ammonium salt?

A salt, water, and ammonia gas are produced; ammonia turns damp red litmus paper blue.

Why is litmus not suitable for titrations?

Because its colour change is not sharp and it goes through a purple transition colour in neutral solutions, making it difficult to determine the endpoint.

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