Chapter 12 - Chemical analysis Flashcards by Georgina Jolliffe

what is a pure substance?

something made from just one substance

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what can a pure substance be?

an element or a compound

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what are the fixed points of an element or compound?

its melting and boiling points

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test for water

turns white, anhydrous copper sulfate blue

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test for PURE water

its melting point is exactly 0 degrees and its boiling point is exactly 100

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how can the fixed points of a substance be used to identify it?

pure substances have specific temperatures at which they boil/melt and these can then be checked in a data base

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what will impurities do to the melting point of a substance?

it will lower it

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what will impurities do to the melting range of a substance?

it will increase it

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what will impurities do to the boiling point of a substance?

it will increase it

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how to test a substance’s purity

measure its melting and boiling points

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what is a formulation?

a mixture with a specific purpose

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examples of formulations 4

paint
tablets
cosmetics
fertilisers

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main components of a tablet 4

active drug
smooth coatings
colourants
sweeteners

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why is the formulation of a tablet so important?

it must have a long enough shelf life, be consumable and deliver the drug to the right part of the body

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main components and functions of these in paint

pigment (for colour)
solvent (alters viscocity for easy painting)
binder (forms a protective film when paint dries)

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what is chromatography?

an analytical method used to separate substances in a mixture

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what are the two phases in chromatography?

mobile phase

stationary phase

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what is the mobile phase?

where the molecules can move. It is a liquid and is what carries molecules up the stationary phase

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what is the stationary phase?

where the molecules can’t move and are carried by solvent

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what is the Rf value?

a ratio of the distance travelled by the solute and the solvent

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how to calculate Rf value?

distance travelled by substance / distance travelled by solvent

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why is the Rf value useful?

if two Rf values match, the substance may be present It is an easy means of comparison

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what does a single spot on a chromatogram show?

a pure substance

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what does the amount of time molecules spend in each phase depend on?

how soluble they are in the solvent

how attracted they are to the paper

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what happens to molecules with a higher solubility and lower attraction to paper?

they will travel further

how are components of a substance separated?

they have different forces of attractions to the paper

what is formed between the mobile and stationary phases during chromatography?

an equilibrium

which reaction to do to test for hydrogen?

react zinc and sulfuric acid to form zinc sulfate and hydrogen

test for hydrogen

hold a lit splint in hydrogen | if hydrogen is present, it will make a squeaky pop

test for oxygen

a glowing splint relights

test for carbon dioxide

limewater (calcium hydroxide) turns cloudy

test for chlorine

damp litmus paper is bleached white

what is a cation?

a metal ion

process of a flame test

a nichrome wire is dipped in hydrochloric acid then heated to clean it redip wire in acid then into unknown substance hold loop in blue flame record colour of flame

what colour flame does a lithium ion have?

crimson

what colour flame does a sodium ion have

yellow

what colour flame does a potassium ion have

lilac

what colour flame does a calcium ion have

orange-red

what colour flame does a copper ion have

green

problem of flame tests

doesn't work with mixtures - some flame colours may hide others

advantages of modern instrumental methods 3

more sensitive (only a small amount of sample needed) faster very accurate

disadvantages of modern instrumental methods 3

expensive special training needed results can only be interpreted by comparing with known substances

what is flame emission spectroscopy used for?

analyse samples for metal ions

process of flame emission spectroscopy

sample placed in a flame ions heat up electrons become excited and jump into higher shells when they drop back, they emit energy as light light passes through a spectroscope

what happens when light emitted passes through a spectroscope?

different wavelengths of light are detected to produce a line spectrum

what is a substance's line spectrum?

the characteristic pattern of radiation absorbed and emitted

why are no two ions' line spectrums the same?

it depends on the ion's charge and electron arrangement so different ions emit different wavelengths of light, leading to different line spectrums

what does the intensity of a spectrum indicate?

the concentration of that ion in solution

how can flame emission spectroscopy be used to identify different ions in mixtures?

the spectras for the different ions are created and then compared to a database

how can the machine used for FES indicate the concentration of an unknown?

the spectrometer measures the intensity of light with a specific wavelength that is known to be a characteristic of an ion the machine is calibrated using solutions of the metal ion of known concentrations it can then give a value for the unknown concentration

how to test if a substance is a carbonate?

it will fizz and produce carbon dioxide

equation and ionic equation for carbonate + acid

carbonate + acid -> carbon dioxide + water | CO3 (^2-) + 2H(^+) -> CO2 + H2O

which two acids do you have to add to test for sulfate?

barium chloride and hydrochloric acid

what will form if sulfate ions are present when HCL and Barium chloride are added?

a white precipitate (barium sulfate)

why must you add HCl before barium chloride when testing for sulfates?

the hydrochloric acid gets rid of any carbonate ions, which would also form a precipitate with the barium chloride and confuse results

ionic equation for testing for sulfates

Ba (^2+) + SO4 (^2-) -> BaSO4

what are the three halides we will be testing for?

chlorine (Cl-) bromine (Br-) Iodine (I-)

process/test for halides

add a few drops of dilute nitric acid to the unknown then add a few drops of silver nitrate solution if a precipitate forms, halide ions are present

why is nitric acid added when testing for halides?

it dissolves compound and removes any carbonate ions as they would also form a precipitate and confuse results

what colour precipitate will a chloride ion form and what is it?

white (silver chloride)

what colour precipitate will a bromide ion form and what is it?

cream (silver bromide)

what colour precipitate will a iodide ion form and what is it?

yellow (silver iodide)

ionic equation for testing for chloride ions

Ag+ + Cl- -> AgCl

ionic equation for testing for iodide ions

Ag+ + I- -> AgI

ionic equation for testing for bromide ions

Ag+ + Br- -> AgBr

general ionic equation when testing for halides

Ag+ + X- -> AgX

which ions form white precipitates with sodium hydroxide solution?

aluminium, calcium and magnesium

how to distinguish between calcium, magnesium ad aluminium ions?

use a sodium hydroxide test (aluminium precipitate will dissolve eventually) Use flame test

what colour precipitate do calcium ions form in sodium hydroxide solution?

white

what colour precipitate do copper ions form in sodium hydroxide solution?

blue

what colour precipitate do iron (II) ions form in sodium hydroxide solution?

green

what colour precipitate do iron (III) ions form in sodium hydroxide solution?

brown

what colour precipitate do aluminium ions form in sodium hydroxide solution?

white but will eventually dissolve

what colour precipitate do magnesium ions form in sodium hydroxide solution?

white

ionic equation for calcium ion + sodium hydroxide solution

Ca2+ + 2OH- -> Ca(OH)2

ionic equation for copper (II) ion + sodium hydroxide solution

Cu2+ +2OH- ->Cu(OH)2

ionic equation for iron (II) ion + sodium hydroxide solution

Fe2+ + 2OH- -> Fe(OH)2

ionic equation for iron (III) ion + sodium hydroxide solution

Fe3+ +3OH- -> Fe(OH)3

ionic equation for aluminium ion + sodium hydroxide solution

Al3+ +3OH- -> Al(OH)3

ionic equation for magnesium ion + sodium hydroxide solution

Mg2+ +2OH- -> Mg(OH)2

why is a precipitate formed?

it is insoluble