C8- Chemical Analysis Flashcards
Can boiling or melting a substance tell you how pure a substance is
Yes
Define formulations
Mixtures with exact amounts of components
How to test for chlorine
Chlorine bleaches damp litmus paper, turning it white. (It may turn red for a moment first though- that’s because a solution of chlorine in acidic)
How to test for oxygen
If you put a glowing splint inside a test tube containing oxygen, the oxygen will relight the glowing splint
How to test for carbon dioxide
Bubbling carbon dioxide through (or shaking carbon dioxide with) an aqueous solution of calcium hydroxide (known as lime water) causes the solution to turn cloudy
How to test for hydrogen
If you hold a lit splint at the open end of a test tube containing hydrogen, you’ll get a “squeaky pop”. ( The noise comes from the hydrogen burning quickly with the oxygen in the air to form H2O).
what do tests for anions often give
Precipitation
Na2C)3(aq) + 2HCL(aq) →
CO2(g) +2NaCl(aq) + H2O(l)
Ba^2 (aq) + SO4^2- (aq) →
BaSO4(s)
What is a formulation
a term used in various senses in various applications, both the material and the abstract or formal
What are the two phases called in chromatography
Stationary phase and a mobile phase
in paper chromatography how ,many spots will a pure substance from on the paper
One
What colour does litmus paper turn in the presence of chlorine
Red and then to white
Describe a test you could use to test for the presence of carbonate ions
An acid , such as dilute hydrochloric acid, is added to the test compound. Carbon dioxide gas bubbles if carbonate ions are present. Limewater is used to confirm that the gas is carbon dioxide.
How do you conduct a flame test
- Dip a clean wire loop into a solid sample of the compound being tested
- Put the loop into the edge of the blue flame from a Bunsen burner
- Observe and record the flame colour produced
What colour precipitation do iron (III) compounds form with sodium hydroxide
Aluminium, Al3+ White Calcium, Ca2+ White Magnesium, Mg2+ White Copper(II), Cu2+ Blue Iron(II), Fe2+ Green Iron(III), Fe3+ Brown
What occurs an addition of excess sodium hydroxide to a solution containing containing AL^3+ ions
Colourless
Describe how flame emission spectroscopy work
Lundegårdh sprayed a solution of the sample material into a condensing chamber and then into an air-acetylene flame, where excitation occurred.
What does the intensity of a flame emission spectrum of a solution relate to
It indicates the concentration of that ion in a solution
Give three advantages of using machines to conduct chemical analysis
- Very sensitive- they can detect even the tiniest amounts of substances
- Very fast and tests can be automated
- Very accurate
What is a pure substance?
A pure substance is a single element or compound, not mixed with any other
substance
What is a formulation and how is it made? Give examples
- A formulation is a mixture of compounds in measured quantities that has been
designed as a useful product. - Formulations include fuels, cleaning agents, paints, medicines, alloys,
fertilisers and foods. - E.g. alloys are mixtures of metals; they are harder than pure metals, so have
a particular purpose.
Describe paper chromatography.
a) A start line is drawn near the bottom of the paper. The mixture is spotted on the line.
b) A beaker is filled with small amount of solvent (it cannot touch or go above the start line
when paper is placed in a beaker)
c) Paper is hung on a rod and placed in a beaker.
d) Solvent travels up the paper, thus separating the components.
e) Before solvent level reaches the end, the paper is taken out and the finish line is
marked. The paper is dried.
f) The procedure works when different compounds have different affinities for the
solvent/paper. Stronger attraction for the paper - travels slowly with the solvent etc.
g) Paper is called the stationary phase - it doesn’t move. Solvent is the mobile phase.
How is Rf calculated?
Distance moved by the spot / distance moved by solvent
In a paper chromatography experiment, a
compound A was found to have an Rf
value of
0.85 - what does it tell you about the compound?
It has a higher affinity for the solvent than for the paper.
Describe the tests for hydrogen, oxygen, carbon dioxide and
chlorine
Hydrogen – pop with burning splint over gas
Oxygen – glowing splint relights
Carbon dioxide – turns limewater (Ca(OH)2) milky
Chlorine – bleaches damp litmus paper and makes it white
Describe the test for carbonate anions
Add dilute acid, e.g. HCl
Fizzing observed, as CO2
is released.
E.g. Na2CO3 + 2 HCl → 2 NaCl + H2O + CO2
Describe sulfate tests and give an equation
Add a solution containing Ba2+ cations, e.g. a solution of BaCl2 White precipitate of BaSO4 forms E.g. K2SO4 \+ BaCl2 → 2 KCl + BaSO4 (!!!) can also be thought of a test for barium (II); add sulfates - white precipitate forms.
Describe silver nitrate tests and give equations
Add a solution of AgNO3 (acidified with HNO3
)
Chlorides - white precipitate, silver chloride; Ag+ + Cl−
→ AgCl
Bromides - cream precipitate, silver bromide; Ag+ + Br−
→ AgBr
Iodides - yellow precipitate, silver iodide; Ag+ + I−
→ AgI
What are instrumental methods?
They are accurate, sensitive and rapid methods which are useful when the amount
of sample is very small
Describe the flame emission spectroscopy
a) instrumental method used for identifying metal ions in solution or measuring
their concentration
b) Spectroscope measures the exact wavelength of the light emitted by a metal
ion
c) That allows for definite identification - sometimes colours are difficult to
distinguish.
d) Concentrations are found by measuring the intensity of light emitted. The
more intense light, the greater the concentration of the metal ion in a solution.
e) From the intensity vs concentration graph, you can read off a relevant
concentration value at a given intensity.
What are cations and anions?
Cations are the positive ions; anions are the negative ions.
