Flashcards in this deck (79)

• What is an acid?

  • Definition: Substance with replaceable hydrogen that gives \(H^{+}\) or \(H_3O^{+}\) in aqueous solution
  • Key ion: \(H^{+}\)
  acid definitions chemistry
• How does hydrochloric acid ionise?

  • \(HCl \rightarrow H^{+} + Cl^{-}\)
  acid examples
• How does sulfuric acid ionise?

  • \(H_2SO_4 \rightarrow 2H^{+} + SO_4^{2-}\)
  acid examples
• Name three common properties of acids.

  • Turns blue litmus red
  • Sour taste
  • pH < 7
  acid properties indicators
• What is a base?

  • Definition: Substance containing hydroxyl groups that gives \(OH^{-}\) in aqueous solution
  • Key ion: \(OH^{-}\)
  base definitions chemistry
• How does sodium hydroxide dissociate?

  • \(NaOH \rightarrow Na^{+} + OH^{-}\)
  base examples
• How does calcium hydroxide dissociate?

  • \(Ca(OH)_2 \rightarrow Ca^{2+} + 2OH^{-}\)
  base examples
• Name three common properties of bases.

  • Soapy feel
  • Turns red litmus blue
  • pH > 7
  base properties indicators
• What is an alkali?

  • Definition: A soluble base that dissolves in water to give \(OH^{-}\)
  • Examples: NaOH, KOH, NH_4OH
  alkali definitions
• What is a salt?

  • Definition: Compound formed by full or partial replacement of acid hydrogen by a metal or ammonium ion
  salt definitions
• Give an example of a normal salt.

  • Normal salt: NaCl
  salt examples
• Give an example of an acid salt.

  • Acid salt: NaHSO_4
  salt examples
• Give an example of a basic salt.

  • Basic salt: Mg(OH)Cl
  salt examples
• What is the pH scale?

  • Definition: Scale measuring \([H^{+}]\) concentration in solution
  • Range: 0–14
  ph definitions
• How is pH calculated?

  • \(pH = -\log[H^{+}]\)
  ph formula
• What pH values indicate acidic, neutral, and alkaline?

  • Acidic: pH < 7
  • Neutral: pH = 7
  • Alkaline: pH > 7
  ph classification
• Give pH examples for a strong acid and a strong base.

  • HCl (strong acid): pH ≈ 1
  • NaOH (strong base): pH ≈ 13
  ph examples
• What is ionisation?

  • Definition: Formation of ions from neutral molecules in solution (often for molecular acids)
  • Example: \(HCl \rightarrow H^{+} + Cl^{-}\)
  ionisation definitions
• What is dissociation?

  • Definition: Separation of ionic compounds into ions when dissolved
  • Example: \(NaCl \rightarrow Na^{+} + Cl^{-}\)
  dissociation definitions
• How do ionisation and dissociation differ?

  • Ionisation: neutral molecules form ions
  • Dissociation: ionic compounds separate into existing ions
  ionisation dissociation compare
• What is a hydronium ion?

  • Hydronium: \(H_3O^{+}\) formed when \(H^{+}\) associates with water
  • Represents hydrated proton in aqueous acid solutions
  hydronium acid
• What is a neutralisation reaction?

  • Definition: Acid + Base → Salt + Water
  • Example: \(HCl + NaOH \rightarrow NaCl + H_2O\)
  neutralization reactions
• What ions do acids and bases produce in water?

  • Acids: produce \(H^{+}\) or \(H_3O^{+}\)
  • Bases: produce \(OH^{-}\)
  ions acid base
• What distinguishes a strong from a weak acid or base?

  • Strong: nearly complete ionisation/dissociation (e.g., HCl, NaOH)
  • Weak: partial ionisation (e.g., CH_3COOH, NH_4OH)
  acids bases strength
• Why is pure water neutral at pH 7?

  • Water autoionises so \([H^{+}] = [OH^{-}] = 10^{-7}\) mol·L^{-1}$, giving \(pH = 7\)
  water ph neutral
• What is 'dissociation' in ionic compounds?

  • Separation of pre-existing ions
  • Example: \(\mathrm{NaCl} \rightarrow \mathrm{Na^{+}} + \mathrm{Cl^{-}}\)
  chemistry ionic
• Give an example of acid dissociation.

  • Example: \(\mathrm{HCl} \rightarrow \mathrm{H^{+}} + \mathrm{Cl^{-}}\)
  acids dissociation
• What is a 'normal salt'?

  • All replaceable H+ replaced by metal
  • Nature: Neutral
  • Examples:
  • NaCl
  • K2SO4
  salts classification
• What is an 'acid salt'?

  • Partial replacement of H+ in acid
  • Nature: Acidic
  • Examples:
  • NaHSO4
  • NaHCO3
  salts classification
• What is a 'basic salt'?

  • Result of partial neutralisation of a base
  • Nature: Basic
  • Examples:
  • Pb(OH)Cl
  • Mg(OH)NO3
  salts classification
• State the general neutralisation reaction.

  • Acid + Base \(\rightarrow\) Salt + Water
  • Example: \(\mathrm{HCl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{H_{2}O}\)
  reactions neutralisation
• What ionic reaction forms water in neutralisation?

  • \(\mathrm{H^{+}}\) from acid combines with \(\mathrm{OH^{-}}\) from base to form \(\mathrm{H_{2}O}\)
  • Process is exothermic
  ions neutralisation
• What happens when an acid reacts with a metal?

  • Metal + Acid \(\rightarrow\) Salt + Hydrogen gas
  • Example: \(\mathrm{Zn} + 2\mathrm{HCl} \rightarrow \mathrm{ZnCl_{2}} + \mathrm{H_{2}}\uparrow\)
  reactions metals
• Why do metals produce hydrogen with acids?

  • Metals above hydrogen in the reactivity series displace H+ ions
  • Displaced H+ forms \(\mathrm{H_{2}}\) gas
  reactivity metals
• What is the reaction between acid and carbonate?

  • Acid + Carbonate \(\rightarrow\) Salt + Water + Carbon dioxide
  • Example: \(\mathrm{Na_{2}CO_{3}} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{H_{2}O} + \mathrm{CO_{2}}\uparrow\)
  reactions carbonates
• How is CO2 tested in the lab?

  • Bubble gas through lime water (calcium hydroxide)
  • Positive test: lime water turns milky due to formation of calcium carbonate
  tests carbon_dioxide
• What is the reaction of acid with bicarbonate?

  • Acid + Bicarbonate \(\rightarrow\) Salt + Water + Carbon dioxide
  • Example: \(\mathrm{NaHCO_{3}} + \mathrm{HCl} \rightarrow \mathrm{NaCl} + \mathrm{H_{2}O} + \mathrm{CO_{2}}\uparrow\)
  reactions bicarbonates
• What is the reaction of acid with sulphite?

  • Acid + Sulphite \(\rightarrow\) Salt + Water + Sulfur dioxide
  • Example: \(\mathrm{Na_{2}SO_{3}} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{H_{2}O} + \mathrm{SO_{2}}\uparrow\)
  reactions sulphites
• How is SO2 detected qualitatively?

  • SO2 reduces acidified potassium dichromate from orange to green
  • Indicates SO2 presence
  tests sulfur_dioxide
• What is the reaction of acid with sulphide?

  • Acid + Sulphide \(\rightarrow\) Salt + Hydrogen sulfide
  • Example: \(\mathrm{FeS} + 2\mathrm{HCl} \rightarrow \mathrm{FeCl_{2}} + \mathrm{H_{2}S}\uparrow\)
  reactions sulphides
• How is H2S tested qualitatively?

  • H2S has a rotten egg smell
  • It blackens lead acetate paper (forms lead sulfide)
  tests hydrogen_sulfide
• What happens when a base reacts with an ammonium salt on heating?

  • Ammonium salt + Base (heat) \(\rightarrow\) Salt + Ammonia + Water
  • Example: \(\mathrm{NH_{4}Cl} + \mathrm{NaOH} \rightarrow \mathrm{NaCl} + \mathrm{NH_{3}}\uparrow + \mathrm{H_{2}O}\)
  reactions ammonium
• How is ammonia (NH3) tested qualitatively?

  • NH3 turns red litmus blue
  • NH3 gives white fumes with hydrogen chloride (NH4Cl)
  tests ammonia
• What is the ionic equation for neutralisation?

  • Net ionic: \(\mathrm{H^{+}} + \mathrm{OH^{-}} \rightarrow \mathrm{H_{2}O}\)
  ions neutralisation
• Give an example of a salt formed by acid and metal.

  • Example: \(\mathrm{Zn} + 2\mathrm{HCl} \rightarrow \mathrm{ZnCl_{2}} + \mathrm{H_{2}}\uparrow\)
  • Product: zinc chloride (salt) and hydrogen
  reactions metals
• Give an example of acid reacting with carbonate and the observable gas.

  • Example: \(\mathrm{Na_{2}CO_{3}} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{H_{2}O} + \mathrm{CO_{2}}\uparrow\)
  • Gas: CO2 effervescence
  reactions carbonates
• Give an example of acid reacting with sulphite and the gas produced.

  • Example: \(\mathrm{Na_{2}SO_{3}} + 2\mathrm{HCl} \rightarrow 2\mathrm{NaCl} + \mathrm{H_{2}O} + \mathrm{SO_{2}}\uparrow\)
  • Gas: SO2 which is a reducing gas
  reactions sulphites
• List the observable tests for gases from acid reactions.

  • CO2: turns lime water milky
  • SO2: turns acidified K2Cr2O7 orange to green
  • H2S: rotten egg smell; blackens lead acetate
  • NH3: turns red litmus blue; white fumes with HCl
  tests gases
• How do you classify the 'nature' of salts?

  • Neutral salt: neither acidic nor basic
  • Acid salt: acidic in nature
  • Basic salt: basic in nature
  salts properties
• What gas is evolved when a carbonate reacts with dilute HCl?

  Carbon dioxide (\(CO_2\)); test: lime water turns milky
  carbonates gases tests
• Write the reaction of sodium carbonate with HCl

  \(\text{Na}_2\text{CO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + CO_2 + H_2O\)
  equations carbonates
• What gas is evolved when a bicarbonate reacts with dilute HCl?

  Carbon dioxide (\(CO_2\)); observation: effervescence, lime water milky
  bicarbonates gases tests
• Write the reaction of sodium bicarbonate with HCl

  \(\text{NaHCO}_3 + \text{HCl} \rightarrow \text{NaCl} + CO_2 + H_2O\)
  equations bicarbonates
• What gas is evolved when a sulphite reacts with dilute HCl?

  Sulfur dioxide (\(SO_2\)); test: \(K_2Cr_2O_7\) orange → green
  sulphites gases tests
• Write the reaction of sodium sulphite with HCl

  \(\text{Na}_2\text{SO}_3 + 2\text{HCl} \rightarrow 2\text{NaCl} + SO_2 + H_2O\)
  equations sulphites
• What gas is evolved when a sulphide reacts with dilute HCl?

  Hydrogen sulphide (\(H_2S\)); observation: rotten egg smell (and blackens lead acetate)
  sulphides gases tests
• Write the reaction of sodium sulphide with HCl

  \(\text{Na}_2\text{S} + 2\text{HCl} \rightarrow 2\text{NaCl} + H_2S\)
  equations sulphides
• General products when an acid reacts with a carbonate

  Salt + \(H_2O\) + \(CO_2\); key test: lime water milky
  reactions carbonates
• General products when an acid reacts with a bicarbonate

  Salt + \(H_2O\) + \(CO_2\); key observation: CO_2 effervescence
  reactions bicarbonates
• General products when an acid reacts with a sulphite

  Salt + \(H_2O\) + \(SO_2\); observation: pungent choking gas
  reactions sulphites
• General products when an acid reacts with a sulphide

  Salt + \(H_2S\); observation: rotten egg smell
  reactions sulphides
• What happens when an acid reacts with a metal?

  Salt + \(H_2\) gas; observation: effervescence (bubbling) Example: \(2\text{HCl} + \text{Mg} \rightarrow \text{MgCl}_2 + H_2\)
  reactions metals
• What are the products of acid + base (neutralisation)?

  Salt + \(H_2O\); observation: heat evolved (exothermic) Example: \(\text{HCl} + \text{NaOH} \rightarrow \text{NaCl} + H_2O\)
  neutralisation reactions
• What occurs when a base reacts with an ammonium salt?

  Salt + \(NH_3\) + \(H_2O\); observation: ammonia gas evolved Example: \(\text{NH}_4\text{Cl} + \text{NaOH} \rightarrow \text{NaCl} + NH_3 + H_2O\)
  ammonia reactions
• Why is NH4Cl acidic in solution?

  Because \(NH_4^+\) hydrolyses to give \(H^+\): \(NH_4^+ + H_2O \rightarrow NH_3 + H_3O^+\)
  hydrolysis salts
• Why is CH3COONa basic in solution?

  Because \(CH_3COO^-\) hydrolyses to produce \(OH^-\): \(CH_3COO^- + H_2O \rightarrow CH_3COOH + OH^-\)
  hydrolysis salts
• Why is NaCl neutral in solution?

  Formed from a strong acid and a strong base; neither ion hydrolyses significantly
  salts ph
• Why doesn't dry HCl gas turn blue litmus red?

  Dry HCl is not ionised; it needs water to produce \(H^+\) (acidic solution) to turn litmus red
  acids tests
• How does CO2 make lime water milky?

  CO_2 reacts with \(Ca(OH)_2\) to form insoluble \(CaCO_3\) precipitate, causing milky appearance
  co2 tests
• How is SO2 detected with potassium dichromate?

  SO_2 reduces \(K_2Cr_2O_7\) from orange \(Cr_2O_7^{2-}\) to green \(Cr^{3+}\); colour change orange → green
  so2 tests
• How is H2S commonly detected?

  By its rotten egg smell and by turning lead acetate paper black due to \(PbS\) formation
  h2s tests
• What visible observation indicates H2 evolution in acid-metal reactions?

  Effervescence (bubbling) and sometimes a 'pop' test on ignition
  hydrogen observations
• Why do salts containing oxygen or sulfur anions release gases like CO2, SO2, H2S with acid?

  Acid protonates the anion or converts oxyanions to gaseous oxides, releasing corresponding gas
  reasoning anions
• Give the ionic equation for carbonate reacting with acid

  \(CO_3^{2-} + 2H^+ \rightarrow CO_2 + H_2O\)
  ionic carbonates
• Give the ionic equation for sulphite reacting with acid

  \(SO_3^{2-} + 2H^+ \rightarrow SO_2 + H_2O\)
  ionic sulphites
• Give the ionic equation for sulphide reacting with acid

  \(S^{2-} + 2H^+ \rightarrow H_2S\)
  ionic sulphides
• What quick tests should you memorise for exam questions on this topic?

  Gas tests: CO_2 → lime water milky; SO_2 → \(K_2Cr_2O_7\) orange→green; H_2S → rotten egg / blackens lead acetate; NH_3 → turns moist red litmus blue
  exam tips
• Exam tip: common structure of ICSE questions from this chapter

  Expect 3 marks reasoning + 2 marks reaction equation + 1 mark product identification; practise gas tests and pH reasoning
  exam strategy
• What observation indicates ammonia evolution from base + ammonium salt?

  Pungent smell, turns moist red litmus blue, white smoke with HCl fumes (forming \(NH_4Cl\))
  ammonia tests