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Flashcards in Experiments Deck (296)
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1

Prep of a solution

-rinse pipette, burette, w/ d.i water, and with solutions/chemicals

(if using powder/crystals )-weigh out solute on weighed clock glass, subtract mass of clock glass
-put into (clean) beaker, rinsing clock glass w/ d.i. beaker to ensure all solute goes into it (rinsings)
-stir, dissolve
-use funnel, pour into volumetric flask, rinsing again as you do so using d.i. water
/
(If using a solution)-fill pipette with pipette filler up to mark with the bottom of meniscus on the mark
-transfer into volumetric flask using a funnel, then rinse funnel to ensure all of the solution goes into it

-fill up close to the mark with d.i. water, add final amount using dropper until bottom of meniscus on mark. Read at eye level.
-stopper, invert several times to ensure solute uniform through solution

2

Iron tablet experiment - procedure for making up solution

-crush tablets with mortar and pestle
-washed into beaker
-stirred to dissolve
-transferred into flask using funnel
-rinsings added to flask
-add using dropper
-top up carefully until bottom of meniscus level with mark
-stopper, invert multiple times

3

iron tablet - why use dilute sulfuric acid in making up solution

to prevent air oxidation of Fe²⁺ in solution to Fe³⁺

4

iron tablet - why was more dilute sulfuric acid added before titration commenced?

to prevent formation of manganese(IV) (Mn⁺⁴) (brown precipitate) in solution

5

iron tablet - how was end-point detected?

colourles to pink

6

iron tablet - why nitric acid could not be used to provide acidic conditions for this reaction

nitric acid could not be used as it is a strong oxidising agent

7

measuring the heat of neutralisation (of ethanoic acid by sodium hydroxide) in the school laboratory

-suitable container (polystyrene cup / calorimeter / glass vessel such as beaker) of known head capacity
-known vols & concs of acid and base
-measure initial temp, mix and note new (highest) temp
-calculate heat produced using mcdeltatheta
-calc for 1 mole H+ / calc heat of neutralisation

8

why ethanoic acid and sulfuric acid would have diff heats of neutralisation

sulfuric acid: strong acid - dissociated, present as ions, energy not needed to dissociate)

ethanoic acid: weak acid (undissociated, slightly dissociated, present as molecules, energy needed to dissociate)

9

water of crystallisation experiment - primary standard reagent which could have been used to standardise the HCL solution

anhydrous sodium carbonate

10

water of crystallisation experiment - suitable indicator, colour change,

methyl orange

yellow to red

11

water of crystallisation experiment - why not more than 1-2 drops of indicator should be used

methyl orange is a weak acid

12

describe the correct procedure for rinsing the burette before filling it with the solution to deliver + describe filling it

rinse with deionised water
rinse with solution

-use funnel, pour in at top, take meniscus into account
-remove funnel
-ensure area below tap is filled

13

why is it important to fill the part below the tap of the burette?

air will be displaced by solution

14

describe procedure for weighing + making up solution from hydrated sodium carbonate crystals (for powders/crystals)

-weigh on clock glass using electronic balance
-transfer solution to beaker + rinse clock glass with d.i water using wash bottle to ensure all is transferred
-dissolve in d.i water
-transfer to volumetric flask using funnel + rinse with d.i water to ensure all is transferred
-add d.i water to up to near mark on flask
-add final amount using dropper, taking meniscus into account
-stopper, invert several times

15

describe procedure for washing the pipette and using it to measure the solution

-rinse with d.i water, followed by solution

-fill up to mark with pipette filler taking meniscus into account
-transfer to flask with tip against side of flask to avoid splashing

16

three precautions with burette that should be taken in order to ensure an accurate measurement

-vertical/read at eye level
-add dropwise using dropper near end-point
-rough titration first

17

sodium carbonate crystals, is not a primary standard but anhydrous sodium carbonate (Na₂CO₃) may be used as a primary standard. Why is this the case?

-Na₂CO₃ is pure, stable, anhydrous (not hydrated), no water loss
-solution of exact concentration can be made, no need to standardise by titration, any opposite point for sodium carbonate crystals

18

proceedure to measure out water from a beaker to a conical flask

-rinse pipette with d.i water and then the water sample
-use 25cm² pipette twice
-read mark at eye level, bottom of meniscus on mark
-touch tip against inside wall of conical flask, empty it out, do not blow out last drop from pipette

19

describe how the melting point of the crude product/recystallised product of benzoic acid could have been measured

-know diagram

-sample on heating block
-thermometer in melting block
-block heated
-note temp range over which sample melts

20

melting point benzoic acid experiment - two ways how you could conclude from melting points that the recrystallised product was purer than crude product

-higher melting point
-melting point closer closer to correct (in tables) value
-sharper (narrower range)

21

one important use of benzoic acid or its salts

-food preservative
-disinfectant (antiseptic, fungicide)
-calibration

22

describe the flame test

-dip platinum wire in HCl to clean, clean if it does not change flame colour
-dip in HCl
-dip in sample of salt, sticks to wire
-place salt in/over Bunsen flame
-note colour of flame observed
-if question specifies a salt, write the colour the flame should turn into

23

flame test - the metals and their colours

Barium nitrate: yellow-green

Copper sulfate: blue-green

Lithium carbonate: deep red

Potassium sulfate: lilac

Sodium sulfate: yellow

Strontium nitrate: red

24

flame test - why do metals give off a characteristic colour in a flame?

energy differences between energy levels in metal atoms vary from metal to metal. Using energy from flame, electrons move to higher energy levels then return to lower e levels, emitting light whos energies are equal to energy diff between higher e levels and lower e levels.

25

flame test - what procedure is used to avoid cross contamination?

Platinum wire: cleaned with concentrated HCL after each test

Wooden splint: diff splint used for each test

26

redox reactions of halogens - What is observed when chlorine gas is bubbled into an aqueous solution of sodium bromide? Explain your answer in terms of oxidation and reduction.

-solution turns red-brown

-bromide ions oxidised to bromide
Br⁻ --> Br₂

-chlorine reduced to chloride ions
Cl₂ --> Cl⁻

27

How do halogens react? + order of oxidising power

As oxidising agents, as they often react by taking an electron from another element.

F > Cl > Br > I > At

28

Why some halogens cant be used for the redox reaction

-Fluorine extremely poisonous
-Astatine unstable + radioactive

29

Ethanoic acid in vinegar - measuring sample of vinegar and diluting it with d.i water

-use pipette previously rinsed with deionised water and then rinsed with the vinegar solution it will contain
- pipette: read at eye-level, bottom of meniscus on mark, don't shake out/blow out last drop

-transfer to volumetric flask previously rinsed with deionised water, fill with d.i water until bottom of meniscus on mark (dropper at end), stopper + invert number of times

30

Ethanoic acid in vinegar - indicator

phenolphtalein