Acids and Bases Flashcards
Define acid
Acid is a substance that dissociates/ionises in water to form hydrogen ions, H+
What is the role of water in acids?
Acids only display their properties when they are dissolved in water. This is because acids produce hydrogen ions (H+) only in water. It is the hydrogen ions which give acids their acidic properties.
State the physical properties of acids.
- Acids have a sour taste.
- Good electrical conductors due to its mobile ions and electrons/ Acids dissolve in water to form solutions that can conduct electricity due to its mobile ions that carry charges.
- Acid turns blue litmus paper red.
- Turn universal indicator to orange/red
Why can acids conduct electricity?
As acid molecules dissociate in water to form mobile ions and electrons, an acid solution is a good conductor of electricity. (Acids can conduct electricity due to its mobile positive and negatively-charged ions and not just due to mobile H+ ions)
Describe qualitatively the difference between strong and weak acids in terms of the extent of ionisation.
Strong acids dissociate completely in water to form hydrogen ions. Weak acids dissociate partially in water to form hydrogen ions. For the same concentration and volume of acids used, a stronger acid produces a higher concentration of hydrogen ions.
What are the factors that determine pH?
- Strength of an acid (Strong acids will have a lower pH than weak acids)
- Basicity of an acid (The higher the basicity of an acid, the lower the pH)
- Concentration of an acid (mol/ππ^3, number of particles per unit volume; The higher the concentration of an acid, the lower the pH)
Define basicity of an acid.
The number of hydrogen ions produced by one molecule of acid during dissociation in water.
Explain the difference between strength and concentration.
Strength - extent to which an acid is dissociated into its respective ions (how easily an acid/alkali dissociates when dissolved in water)
Concentration - number of solute particles per unit volume in solvent. (mol/dm^3; dilute vs concentrated; how much of an acid is dissolved in the solution)
Give examples of a monobasic, dibasic and tribasic acid respectively.
HCl is a (strong) monobasic acid. Monobasic acids give one H+ ion for each acid molecule that dissolves in water.
H2SO4 is a (strong) dibasic acid. Dibasic acids produces two H+ ions for each acid molecule that dissolves in water.
H3PO4 is a (weak) tribasic acid. Tribasic acids produces three H+ ions for each acid molecule that dissolves in water.
Why do strong acids undergo faster rate of reaction than weak acids?
Due to the higher concentration of hydrogen ions in strong acid.
What are the exceptions to metals that cannot be used in the reactions of acids?
Unreactive metals
- Wonβt react
- Copper (Cu), Silver (Ag), Gold (Au)
Too reactive
- Will explode upon reaction
- All Group 1 metals
State the three reactions of acids.
- Acid + reactive metal β salt + hydrogen
- Acid + metal carbonate β salt + water + carbon dioxide
- Acid + base (metal oxide/ metal hydroxide) β salt + water
How can we test for hydrogen gas?
Place a lighted splint at the mouth of the test tube. Hydrogen gas extinguishes the lighted splint with a βpopβ sound.
How can we test for carbon dioxide gas?
Bubble the gas through limewater. Carbon dioxide forms a white precipitate with limewater.
Define base.
A base is any metal oxide or hydroxide that reacts with an acid to produce salt and water only.
Define alkali.
An alkali is a substance that produces hydroxide ions, OH-, in aqueous solution. (bases that are soluble in water are called alkalis)
Name the alkalis/ bases that are soluble in water.
- Group I oxides/ hydroxides: NaOH, Na2O, KOH
- Ba(OH)2
- Ca(OH)2
- Aqueous ammonia, NH3
All are in (aq).
What are the physical properties of alkalis?
- Alkalis have a bitter taste and feel soapy.
- Aklalis turn red litmus paper blue.
- Alkalis react with acids to form a salt and water only.
- Alkalis produce hydroxide ions (OHβ) when dissolved in water
DOESNβT APPLY TO INSOLUBLE BASES (solid).
State the 3 chemical reactions of alkalis.
- [NEUTRALISATION] Alkali/ Base + Acid β Salt + Water
- Alkali + Ammonium Salt β Salt + Water + Ammonia gas
- [CATION TEST] Alkali + Metal Salt β Salt + Metal Hydroxide
Ammonium salts: anything that starts with ammonium
Metal salts: cations
State the default ionic equation for any neutralisation reaction between an acid and an alkali.
H+ (aq) + OH- (aq) β H2O (l)
State the uses of alkalis/ bases.
Soaps, detergents - Dissolve dirt and grease
Toothpaste - neutralise acids from decaying food particles
Indigestion tablets - neutralise excess acids in stomach
Calcium hydroxide (slaked lime) and calcium oxide (quick lime) - treat acidic soil
Calcium oxide - neutralise SO2 and prevent pollution from industries
State the pH of acids.
- Acidic solutions: pH < 7
- The smaller the pH β the more acidic the solution β the higher the concentration of H+ ions
State the pH of alkalis/ bases.
- Alkaline solutions : pH > 7
- The bigger the pH β the more alkaline the solution β the lower the concentration of H+ ions and the higher the concentration of OHβ ions
What are the four types of oxides?
Acidic, basic, amphoteric and neutral
Define acidic oxides.
Most oxides of non-metals are acidic oxides. Most acidic oxides dissolve in water to give acidic solutions, pH < 7. Acidic oxides do not react with acids. However, they react with alkalis to form a salt and water.
(SO2, SO3, CO2, NO2, P4O10)
Define basic oxides.
The oxides of most metals are basic oxides. If it dissolves in water (because most are insoluble in water), it will give an alkaline solution with pH > 7. They react with acid to form a salt and water.
(MgO, Na2O, CaO, CuO)
Define amphoteric oxides.
Amphoteric oxides are metallic oxides that react with both acids and bases to form salts and water. (aka exception to some metal oxides) Amphoteric oxides can behave either as an acidic or basic oxide.
(ZAP)
Define neutral oxides.
Oxides of non-metals that show neither acidic or basic properties are known as neutral oxides. They are insoluble in water.
(H2O, CO, NO)
What are the observations made when alkali reacts with ammonium salt?
Effervescence observed. Pungent gas turns moist red litmus paper blue.
What are the observations made when alkali/ base reacts with acid?
Solution feels warm, temperature increases.
