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Pure chemistry 🧫⚗️💉 > Chapter 8 part 2: Bases > Flashcards

Chapter 8 part 2: Bases Flashcards

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1
Q

What is a base?

A
  • A base is a metal oxide/a metal hydroxide.
  • Most bases are insoluble in water.
  • E.g. Magnesium oxide, magnesium hydroxide, copper (II) oxide, and copper (II) hydroxide do not dissolve in water.
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2
Q

What is an alkali?

A
  • An alkali is a soluble base that produces hydroxide ions (OH-) when dissolved in water.
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3
Q

What are the names and chemical formula(s) of some common alkalis?

A
  1. Sodium hydroxide:
    Chemical formula: NaOH
  2. Potassium hydroxide
    Chemical formula: KOH
  3. Calcium hydroxide
    Chemical formula: Ca (OH)2
  4. Aqueous ammonia
    Chemical formula: NH3
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4
Q

Do all alkalis produce hydroxide ions (OH-) in aqueous solutions?

A
  • Yes, all alkalis produce hydroxide ions (OH-) in an aqueous solution.
  • E.g. KOH (aq) –> K+ (aq) + OH- (aq)
  • E.g. NaOH (aq) –> Na+ (aq) + OH- (aq)
  • E.g. Ca (OH)2 (aq) –> Ca2+ (aq) + 20H- (aq)
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5
Q

Does ammonia contain any metals like other alkalis?

A
  • No, ammonia does not contain any metals like other alkalis
  • NH3 (g) + H2O (l) –>/<– OH- (aq) + NH4+ (aq)
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6
Q

What are some properties of alkalis?

A

Alkalis:
- Have a bitter taste.
- Feel soapy.
- Conduct electricity due to the mobile ions produced when they dissolve in water.
- Turn red litmus paper blue.

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7
Q

What is a Alkali + acids
–> salts + water reaction?

A
  • Alkalis react with acids to form salts and water.
    Alkali + acid –> salt + water
  • E.g. Sodium hydroxide + nitric acid –> sodium nitrate + water
    NaOH (aq) + HNO3 (aq) –> NaNO3 (aq) + H2O (l)
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8
Q

What is the reaction between an acid and an alkali?

A
  • The reaction between an acid and an alkali is known as a neturalisation reaction.
  • The hydrogen ions from the acid react with the hydroxide ions from the alkali to form water.
  • The ionic equation for a neutralisation reaction:
    H+ (aq) + OH- (aq) –> H2O (l)
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9
Q

What is the reaction between an alkali and ammonia salts?

A
  • Alkalis react with ammonium salts on heating to form salts, water and ammonia gas.
    Alkali + ammonium salt –> salt + water + ammonia
  • E.g. Sodium hydroxide + ammonia chloride –> sodium chloride + water + ammonia
    NaOH (aq) + NH4 Cl (aq) –> NaCl (aq) + H2O (l) + NH3 (g)
  • E.g. Potassium hydroxide + ammonia sulfate –> potassium sulfate + water + ammonia
    2KOH (aq) + (NH4)2 SO4 (aq) –> K2SO4 (aq) + 2H(square 2)O (l) + 2NH3 (g)
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10
Q

How can the ammonia gas produced during the reaction of an alali with an ammonium salt be identified?

A
  • The ammonia gas produced during the reaction of an alkali with an ammonium salt can be identified using damp (moist) red litmus paper.
  • Ammonia gas turns damp red litmus paper blue.
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11
Q

What is the factor that affects acidity?

A
  • Acidity depends on the concentration of hydrogen ions (H+) relative to that of hydroxide ions (OH-) in a solution.
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12
Q

How can we tell if the solution is acidic?

A
  • If the concentration of hydrogen ions in a solution is higher than the concentration of hydroxide ions, the solution is acidic.
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13
Q

What is the factor that affects alkalinity?

A
  • Alkalinity depends on the concentration of hydroxide ions (OH-) relative to that of hydrogen ions (H+) in a solution.
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14
Q

How can we tell if the solution is alkaline?

A
  • If the concentration of hydroxide ions in a solution is higher than the concentration of hydrogen ions, the solution is alkaline.
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15
Q

Is a neutral solution acidic/alkaline?

A
  • In a neutral solution, the concentrations of hydrogen ions and hydroxide ions are the SAME.
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16
Q

What are the functions of a pH scale?

A
  • The pH scale is used to indicate the acidity and alkalinity of solutions.
  • The lower the pH value, the higher the concentration of hydrogen ions compared to that of hydroxide ions in the solution, and higher the acidity.
  • The higher the pH value, the higher the concentration of hydroxide ions compared to that of hydroxide ions in the solution, and the higher the alkalinity.
  • pH value: < 7
    Nature of solution: Acidic
  • pH value: (=) 7
    Nature of solution: Neutral
  • pH value: > 7
    Nature of solution: Alkaline
17
Q

What is a universal indicator?

A
  • A universal indicator is an indicator that shows a variety of colours at different pH values.
18
Q

What are the colours of the universal indicator at pH 1-14?

A
  • pH: 1
    Colour: Red
  • pH: 2
    Colour: Red-orange
  • pH: 3
    Colour: Orange
  • pH: 4
    Colour: Beige
  • pH: 5
    Colour: Yellow
  • pH: 6
    Colour: Lime-green
  • pH: 7
    Colour: Green
  • pH: 8
    Colour: Dark green
  • pH: 9
    Colour: Turquoise
  • pH: 10
    Colour: Pale blue
  • pH: 13
    Colour: Violet
  • pH: 14
    Colour: Purple
19
Q

What are the different indicators and their colour changes in acidic and alkaline solutions?

A
  1. Methyl orange:
    Colour in acidic solution:
    - Red
    pH range at which indicators changes colour:
    - 3-5
    Colour in alkaline solution:
    - Yellow
  2. Screened methyl orange:
    Colour in acidic solution:
    - Violet
    pH range at which indicators changes colour:
    - 3-5
    Colour in alkaline solution:
    - Green
  3. Bromothymol blue:
    Colour in acidic solution:
    - Yellow
    pH range at which indicators changes colour:
    - 6-8
    Colour in alkaline solution:
    - Blue
20
Q

What are the functions of soil?

A
  • Soil of appropriate pH provides sufficient amount of the required nutrients to plants.
  • Different plants thrive on soil of different pH values, and in general, plants grow better in soil with pH range of 5-7.
21
Q

Can soil be more acidic over time (gradually)?

A
  • Yes, soil tends to become more acidic overtime due to different environmental conditions such as acid rain.
22
Q

What is liming (process)?

A
  • Liming is the process of adding slaked lime to soil, and bases such as calcium hydroxide (slaked lime) can be added to soil that is too acidic.

** Slaked lime: Calcium hydroxide**

23
Q

What happens during liming?

A
  • During liming, the base reacts with the acids present in the soil to raise the pH of the soil.
  • To ensure that the right amount of the base is added, the pH of the soil should be measured before, and during the process (of liming).

Pure chemistry 🧫⚗️💉 (12 decks)

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