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A level practicals - Chemistry > Practical 4 - Back Titration > Flashcards

Practical 4 - Back Titration Flashcards

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1
Q

What’s the aim of this back titration?

A

To determine the % of calcium carbonate in limestone

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2
Q

Whats the volume of the volumetric pipette used?

A

25cm^3

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3
Q

What’s the volume of the conical flask used?

A

250cm^3

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4
Q

What’s the volume of the burette used?

A

50cm^3

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5
Q

What type of tablets do we use?

A

Antacid tablets or limestone chips

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6
Q

Concentration of the sodium carbonate

A

0.2moldm^-3

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7
Q

Concentration of the hydrochloric acid

A

0.5moldm^-3

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8
Q

Which indicator do we use?

A

Phenolphthalein

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9
Q

What’s the risk involved with NaOH and HCl?

A

Irritants

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10
Q

What are the irritants in this practical?

A

NaOH and HCl

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11
Q

What’s the risk involved with phenolphthalein?

A

Flammable

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12
Q

What is flammable in this practical?

A

Phenolphthalein indicator

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13
Q

What’s the first step of this practical?

A

Grind the tablet into a fine powder using a pestle and mortar

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14
Q

How much of the antacid powder do we weigh and what in?

A

0.5g on a 3 decimal place digital balance, in a conical flask

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15
Q

What do we do after weighing the powder?

A

Add 25cm^3 HCl solution using a pipette

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16
Q

How much HCl solution do we use?

A

25cm^3 (in excess)

17
Q

What do we do once we’ve got our HCl solution with our ground up tablet?

A

Stir the mixture vigorously with a stirring rod and heat gently with regular stirring

18
Q

How hot should we heat the HCl and tablet solution? Why?

A

Not too hot - will lose acid ions

19
Q

What happens if we heat the HCl and tablet solution too hot?

A

We will lose ions

20
Q

How could we lose acid ions in this practical?

A

Heating it too hot over the Bunsen burner

21
Q

What do we heat up during this practical and how?

A

HCl and powder solution, with a Bunsen burner

22
Q

How long do we heat the HCl and powder solution for?

A

Until the powder has dissolved

23
Q

What do we do after the antacid tablet has fully dissolved?

A

Cool it to room temperature

24
Q

What do we do after the tablet and HCl solution has cooled to room temperature?

A

Add a few drops of phenolphthalein indicator and titration against the standardised NaOH solution - will turn from clear to pink

25
Q

What do we titration the HCl and antacid tablet solution against?

A

Standardised NaOH solution

26
Q

What will the colour change of the indicator be when the reaction has ended?

A

From clear to pink

27
Q

What’s the final step of this practical?

A

Record the volume of NaOH solution needed to neutralise the excess HCl solution and use to calculate the % CaCO3 in the tablet (instructions are in the official deck)

28
Q

What value do we need from the titration in order to calculate the % of CaCO3 in the tablet?

A

The volume of NaOH solution needed to neutralise the excess HCl solution

29
Q

What would using more acid/less chalk do to our practical?

A

Give us larger titres for smaller % error

30
Q

How would we get larger titres and what would this lead to?

A

Use more acid/less chalk
Smaller % error

31
Q

How would we get a smaller % error in this practical?

A

Use more acid/less chalk
(Gives larger titres)

32
Q

Which methods used within this practical help speed up the reaction?

A
  • crushing the tablet into a powder
  • heating the solution
    -stirring the solution
33
Q

What does crushing the tablet, heating the solution and stirring the solution all do to the reaction?

A

Speed it up

34
Q

Why is the flask heated in the practical?

A

To ensure all of the tablet has dissolved

35
Q

Why do we crush the tablet?

A

To increase the surface area for a faster reaction

36
Q

Why must we use a slightly large beaker?

A

To avoid loss of ions

37
Q

What could lead to loss of ions in this practical?

A

Using a beaker that’s too small

38
Q

How do we speed up the rate of reaction in this titration?

A

-Crush up the chalk (larger surface area)
-Heat up the chalk in the acid

A level practicals - Chemistry (18 decks)

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