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OCR A-level Chemistry > Chapter 4 - Acids and bases > Flashcards

Chapter 4 - Acids and bases Flashcards

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1
Q

What is an acid?

A

An acid releases hydrogen ions (H+) into the solution, in water

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2
Q

What is a strong acid?

A

A strong acid releases all of its hydrogen atoms into solution as H+ ions and completely dissociates.

e.g. Hcl(aq) -> H+(aq) + Cl-(aq)

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3
Q

What is a weak acid?

A

A weak acid only releases a small proportion of its hydrogen atoms into solution as H+ ions and partially dissociates in aqueous solution.

e.g. CH3COOH(aq) H+(aq) + CH3COO- (aq)

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4
Q

What is a base?

A

A base is a compound that neutralises an acid by accepting a hydrogen ion to form a salt.

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5
Q

What kind of compounds are bases?

A

Metal oxides (CuO, MgO, Na2O), metal hydroxides, metal carbonates, and ammonia (NH3) are classified as bases.

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6
Q

What is an alkali?

A

An alkali is a base that dissociates in water (soluble) forming hydroxide ions (OH-).

e.g. NaOH(s) + aq -> Na+(aq) + OH-(aq)

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7
Q

What is a salt?

A

Product of a reaction in which the H+ ions from the acid are replaced by the metal or ammonium ions.

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8
Q

Give the definition of neutralisation.

A

H+(ions) react with a base to form a salt and neutral water. H+ ions replaced by metal or ammonium ions from the base, in the acid.

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9
Q

Write ionic equation for neutralisation.

A

H+(aq) + OH-(aq) -> H2O(l)

Acid + alkali -> salt + water

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10
Q

What are the products of neutralisation of an acid with carbonates?

A

Salt, water and CO2

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11
Q

What is titration used for?

A

Used to accurately measure the volume of one solution that reacts exactly with another solution.

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12
Q

Other than finding the concentration of a solution, what can titrations be used for?

A
  • Identification of unknown chemicals

- Finding purity of a substance

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13
Q

What piece of equipment is used to make standard solution?

A

Volumetric flask

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14
Q

How do you prepare a standard solution?

A
  1. ) Dissolve weighed solid in beaker using distilled water
  2. ) Transfer solution into volumetric flask and fill to graduation line by adding distilled water.
  3. ) Invert volumetric flask to mix solution
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15
Q

Describe acid-base titration procedure.

A
  1. ) Add measured volume of one solution to conical flask using a pipette.
  2. ) Add other solution to a burette, and record initial burette reading.
  3. ) Add indicator to solution in conical flask
  4. ) Run solution in burette into conical flask and swirl to make sure solutions mix. When the indicator changes colour this marks end of titration.
  5. ) Record final burette reading - volume added by burette called titre.
  6. ) Run trial titration
  7. ) Repeat until two concordant results occur (within 0.10cm^3)
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16
Q

What is the titre?

A

Volume added from the burette in a titration.

17
Q

How do you determine unknown concentration of a solution from a titration?

results: pipette: 25.00cm^3of 0.100moldm^-3 KOH
titre: 25.70cm^3 of H2SO4

A 
- find amount of standard solution:
n = c x v            v = 0.025dm^3
n = 0.1 x 0.0025 
n = 0.0025 mol
-  find molar ratio from equation:
2KOH + H2SO4
- find moles of unknown, then concentration
n = 0.00125mol
c = 0.00125/0.02457 = 0.0486moldm^-3
18
Q

What is oxidation number?

A

Measure of the number of electrons involved in bonding to a different element

19
Q

What is the oxidation number for elements?

A

oxidation number is always 0.

20
Q

Why is oxidation number 0 for pure elements?

A

Any bonding is to atoms of the same element.

21
Q

What does the sum of the oxidation numbers equal?

A

Overall charge

22
Q

What is the oxidation state/number of Iron (III)?

A

+3

23
Q

What is reduction in terms of electrons?

A

Reduction is the gain of electrons

24
Q

What is oxidation in terms of electrons?

A

oxidation is the loss of electrons

OILRIG

25
Q

What is oxidised and reduced in:

2Fe + 3Cl2 -> 2FeCl3

A

Fe -> Fe3+ 3e-
Iron loses electrons, so is oxidised
Cl2 +2e- -> 2Cl-
Chlorine gains electrons, so is reduced

26
Q

What is reduction in terms of oxidation number?

A

Reduction is a decrease in oxidation number.

27
Q

What is oxidation in terms of oxidation number?

A

Oxidation is an increase in oxidation number

28
Q

What is oxidised and reduced in: Cu + 2AgNO3 -> 2Ag + Cu(NO3)2

A

oxidation state:
Cu: 0 -> +2
Ag: +1 -> 0

Cu oxidation number increases by 2, so is oxidised

Ag oxidation number decreases by 1, so is reduced

OCR A-level Chemistry (30 decks)

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