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chemistry > C2 > Flashcards

C2 Flashcards

1
Q

how can time be measured?

A

digital stop watch

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2
Q

how is temperature measured

A

mercury-in-glass thermometer or a thermocouple

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3
Q

how is mass measured?

A

balance

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4
Q

what is a beaker used for

A

to estimate liquid volume

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5
Q

what is a measuring cylinder used for

A

more accurate way to measure liquid volume

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6
Q

what is a pipette used for

A

measures fixed volumes of liquid accurately so that they can be transferred from one container to another

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7
Q

what is a burette used for

A

measures variable volumes of liquids accurately

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8
Q

what are impure substances

A

substances that contain more than one type of particle
they disrupt the original arrangement of particles
they alter melting and boiling point of the substance

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9
Q

what is chromatography used for

A

a method used to identify and separate substances within an impure solution

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10
Q

what happens during chromatography

A

the solutes (unknown substances) are carried up the filter paper by a solvent

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11
Q

when will the chromatography paper show up in the same way

A

when two substances are the same

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12
Q

what will happen when a substance is a mixture in chromatography

A

it will separate on the paper to show all the different components on separate spots

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13
Q

how can one identify impure and pure substances on chromatography

A
  • impure substances show up with more than one spot

- pure substances only show up with one spot

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14
Q

how can you measure solubility in chromatography

A

the further up the spot is, the more soluble it is

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15
Q

which solvents can be used for chromatography

A

propanone or water

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16
Q

formula for Rf value

A

distance moved by substance (origin line to pigment color ink) / distance moved by solvent (origin line to solvent front)

17
Q

what are fixed points

A

the defined melting/boiling points of a pure substance - has only one melting/boiling point

18
Q

what are solvents

A

liquid in which substance, called a solute, dissolves in

19
Q

in chromatography, why should the origin line be drawn in pencil?

A

the ink of a pen might dissolve in the solvent and affect the results

20
Q

in chromatography, why must the solvent level in the beaker be below the baseline?

A

to prevent the solute (spots) from dissolving away

21
Q

what is filtration

A
  • it is used to separate an insoluble solid from a liquid

- it is used to remove unwanted substances, leaving a pure filtrate or to obtain particular solid from solution

22
Q

what is crystallization used for

A

used to obtain pure crystals of a particular solid from a solution as it cools
separates two soluble solids from a solution

23
Q

how does crystallization work

A

As temperature of solution decreases (cooling) , less space is available within the liquid for solid particles.
particles are pushed out and gradually grow as crystals

24
Q

explain the four steps in purifying impure solids

A
  1. add solvent that the solid is soluble in and dissolve it
  2. filter the mixture to remove the insoluble impurity
  3. heat the solution to remove some solvent, leave it to crystallize
  4. filter off the crystals, wash with cold solvent and dry them
25
Q

what are the two methods to purify impure solids

A

simple distillation

fractional distillation

26
Q

what is simple distillation used for

A

it is used to separate pure liquid from mixture of liquids
it works when liquids have different boiling points (the different in these two boiling points must be at least 50 degrees celsius)

27
Q

explain the process of simple distillation

A
  1. solution is heated within the round bottomed flask
  2. one of the liquid which has lower boiling point boils and changes state to gas
  3. vapor passes along the condenser (cold water runs through the condenser to absorb heat energy from gas)
  4. This cools the gas until it is turned back into liquid. liquid is collected in the beaker
  5. the other liquid which has higher boiling point is left behind in the round bottomed flask
28
Q

what is fractional distillation used for

A

used to separate a mixture of different liquids
it works only when liquids have different boiling points (the difference in the boiling points of these two liquids must be at least 25 degrees celsius)

29
Q

explain the process of fractional distillation

A
  1. mixture is boiled and the liquid with the lowest boiling point turns to vapor first
  2. this vapor rises up the fractionating column and is condensed back to liquid in the condenser
  3. the next lowest boiling point liquid comes off and continues until all the liquids have been separated
30
Q

how can you check the purity of solids and liquids

A

use heat to find the temperature at which they melt or boil

  • impure solid has lower melting point than pure solids
  • liquid containing dissolved solid has higher boiling point than pure solvent

chemistry (2 decks)

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