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OCR Chemistry > Module 2: Acids and redox > Flashcards

Module 2: Acids and redox Flashcards

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1
Q

Why are acids proton donors?

A

Release H+ ions in solution.

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2
Q

Give examples of acids.

A

H2SO4, HCL (aq), HNO3, CH3COOH.

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3
Q

Define strong acid and give examples.

A

Fully dissociates in aqueous solutions e.g. HCL (aq), HNO3, H2SO4.

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4
Q

What is a base?

A

Accepts H+ ions from another substance ie proton acceptors. Bases neutralises an acid to form a salt.

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5
Q

Examples of strong bases?
Example of weak base?

A

NaOH, KOH.
NH3.

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6
Q

Define weak acid with examples.

A

Partially dissociates in aqueous solutions e.g. CH3COOH.

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7
Q

Bases can include …

A

Metal oxides/hydroxides/carbonates and ammonia.

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8
Q

What about copper oxide CuO?

A

Base ONLY as it’s insoluble in water.

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9
Q

Group 1 metal hydroxides are …

A

Soluble in water.

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10
Q

A salt is formed when …

A

Hydrogen ions in an acid are replaced by metal ions or ammonium ions.

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11
Q

What is an alkali?

A

Soluble base that releases OH- ions in aqueous solutions.

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12
Q

What is neutralisation?

A

Where H+ ions in an acid react with a base to form salt and water only

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13
Q

Ethanoic acid would make …

A

Metal ethanoate salt.

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14
Q

Metal + acid =
Metal oxide + acid =
Acid + alkali =
Metal carbonate + acid =
Metal + water =

A

Salt + hydrogen.
Salt + water.
Salt + water.
Salt + water + CO2.

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15
Q

Titration accurately measures …

A

Volume of one solution needed to react with another solution.

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16
Q

What is standard solution?

A

Solution of known conc. This is reacted with a solution of unknown conc to work out this concentration.

17
Q

Steps to prepare a standard solution?

A
  1. Weigh mass of solid on 2dp mass balance
  2. Transfer solid to beaker, and use distilled water to wash out any bit of solid from the weighing boat into the beaker.
  3. Add water to beaker to completely dissolve solid, stirring with a glass rod.
  4. Once dissolved, transfer solution to volumetric flask using a funnel. Rinse beaker and glass rod with distilled water and transfer this to the volumetric flask.
  5. Pour more water into volumetric flask up until the graduation line, so the bottom of the meniscus touches it. Use a pipette to add the final few drops.
  6. Put lid on flask and invert several times to thoroughly mix the solution.
18
Q

What happens if too much water is added to the volumetric flask?

A

The solution will be too dilute, the titre would be less. It must be prepared again.

19
Q

Problems with preparing a standard solution?

A

Systematic errors on balance, loss of substance during transfer, overfilling the volumetric flask.

20
Q

PAG: Explain how to carry out titration.

A
  1. Fill burette with standard solution of known concentration, and ensure jet space is filled with no air bubbles.
  2. Use a pipette to transfer 25cm3 of unknown conc to conical flask. add 2-3 drops of phenolphthalein to it.
  3. Record initial burette reading and start adding contents from burette drop by drop until indicator undergoes a definite colour change.
  4. Record final burette reading and calculate titre volume.
  5. Do a rough titration first to get an idea where the end point is. Then repeat until at least 2 concordant results are obtained (within 0.1cm3 of each other.
21
Q

How to reduce uncertainties in titration?

A

Increase volume of substance in conical flask so you have a higher titre. Also, uncertainties in titration must be combined to find overall uncertainty.

22
Q

Experiment to find relative molecular mass?

A
  1. Add sample of volatile liquid to a small syringe via a needle, then weigh the small syringe.
  2. Inject sample into gas syringe and reweigh small syringe to find mass of volatile liquid added to the gas syringe.
  3. Place syringe in boiling water. The liquid vaporises, producing a gas and the pressure is recorded.
23
Q

How can you find the RMM from this?

A

You can use the ideal gas equation to first find the moles of liquid, then do mass in g/moles to find RMM.

24
Q

Define redox.

A

1 element is oxidised and another reduced.

25
Q

Oxidation number tells us …

A

How many electrons atoms have lost or gained.

26
Q

When is the oxidation number 0?

A

For pure elements e.g. Ar, or elements bonded to identical elements like O2, H2, S8. Monatomic ion like Na+ is just their charge.

27
Q

Make sure the sign …

A

Is written before the number.

28
Q

All oxidation numbers of the atoms in a compound must add up to the …

A

Total charge of the compound. Overall charge on a molecule is 0!

29
Q

Oxygen is more electronegative than …

A

Chlorine.

30
Q

Oxidation is …

A

Losing electrons and INCREASE in oxidation number.

31
Q

Reduction is …

A

Gaining electrons and DECREASE in oxidation number.

32
Q

Define oxidising agent.

A

Causes an element to be oxidised and accepts electrons.

33
Q

Define reducing agent.

A

Causes an element to be reduced and donates electrons.

34
Q

Removal of hydrogen is called …

A

Oxidation, and vice versa.

35
Q

What is a disproportionation reaction?

A

The same species is both oxidised and reduced. Shown by an increase and decrease in oxidation number for that species.

OCR Chemistry (16 decks)

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