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O level combined chem > acids and bases > Flashcards

acids and bases Flashcards

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1
Q

what are acids?

A
  • substances that produces hydrogen ions (H+) when dissolved in water
  • acids can conduct electricity in water due to mobile ions
  • will turn damp blue litmus paper red
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2
Q

what is a base?

A
  • a metal oxide or metal hydroxide which react with acid to give salt and water only
  • most bases are insoluble in water
  • turns damp red litmus paper blue
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2
Q

what are alkalis?

A

alkalis are soluble bases that dissolve in water to produce hydroxide (OH-) ions

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2
Q

what does the pH of a solution relate to?

A

it relates to the concentration of hydrogen ions (H+) in the solution
H+ > OH- (acidic solution)
H+ = OH- (neutral solution)
H+< OH- (alkaline solution)

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2
Q

why does the chemical formula NH4OH for aqueous ammonia not exist?

A

it gets broken down immediately into NH4+ and OH-

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2
Q

what are the 3 reactions of acids?

A

acid + metal –> salt + hydrogen gas (MASH)
acid + base (metal oxide/ metal hydroxide) –>salt + water (neutralisation) (ABSW)
acid + carbonate –> salt + water + carbon dioxide (CASWC)

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2
Q

between amphoteric, basic, neutral and acidic, which ones are metal oxides and which ones are non-metal oxides?

A

amphoteric and basic are metal oxides while neutral and acidic are non-metal oxides

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2
Q

how to identify amphoteric metal oxides?

A
  • react with both acids and alkalis
  • ZnO, Al2O3, PbO only (ZAP)
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2
Q

how to identify basic metal oxides?

A
  • react with acids only
  • other metal oxides other than zinc oxide, aluminium oxide, lead (II) oxide
  • most basic oxides are insoluble in water
  • basic oxides such as sodium oxide and potassium oxide dissolve in water to form alkaline solutions
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3
Q

how to identify neutral non-metal oxides?

A
  • do not react with acids or alkalis
  • NO, CO, H2O only (monoxides)
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4
Q

how to identify acidic non-metal oxides?

A
  • react with alkalis only
  • other non-metal oxides that are not NO CO H2O
  • most acidic oxides dissolve in water to form a acid
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5
Q

What are the 2 reactions of alkalis?

A

alkali + acid = salt + water (neutralisation)
alkali + ammonium salt = salt + water + ammonia (displacement of ammonia)

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6
Q

What is the ionic equation for:
sodium hydroxide;
potassium hydroxide;
aqueous ammonia

A

NaOH (aq) –> Na+ (aq) + OH- (aq)
KOH (aq) –> K+ (aq) + OH- (aq)
NH3 (g) + H2O (l) <–> NH4+ (aq) + OH- (aq)

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6
Q

What are salts?

A

Salts are ionic compounds. The metal will displace the hydrogen ions in the acid.

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6
Q

What is the ionic equation for:
hydrochloric acid;
nitric acid;
sulfuric acid

A

HCL (aq) –> H+ (aq) + CL- (aq)
HNO3 (aq) –> H+ (aq) + NO3- (aq)
H2SO4 (aq) –> 2 H+ (aq) + SO4^2- (aq)

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7
Q

What are weak acids and alkalis?

A

Weak acids and weak alkalis (ammonia) ionise partially in water to produce a low concentration of H+ ions and OH- ions respectively.

8
Q

What are strong acids and alkali?

A

Strong acids (HCL, HNO3, H2SO4) and strong alkali (NaOH, KOH) ionise completely in water to produce a high concentration of H+ ions and OH- ions respectively.

9
Q

What chemical substances have different colours in acidic and alkaline solutions?

A

methyl orange and phenolphthalein indicators

9
Q

If a few drops of methyl orange indicator are added into a solution and it turns yellow, what does it suggests?

A

It suggests that the pH of the solution is greater than 5

9
Q

What do farmers often add to their soil to allow their plants to grow better and how?

A

They often add calcium hydroxide Ca(OH)2 to neutralise the excess acid in the soil. This increases the pH of the soil and allows the plants to grow better.

10
Q

If a few drops of phenolphthalein indicator are added into a solution and it turns colourless, what does it suggest?

A

It suggests that the pH of the solution is lesser than 8

10
Q

If the pH of the solution is greater than 10 and a few drops of phenolphthalein indicator was added, what colour would the solution be?

A

The solution would turn pink

11
Q

If the pH of the solution is less than 3 and a few drops of methyl orange indicator was added, what colour would the solution be?

A

The solution would turn red

O level combined chem (21 decks)

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