Topic 8

Question 1

What is a pure substance?
How can you tell if a substance is pure?

Answer 1

something that contains one compound or element throughout.
A chemically pure substance will boil and melt at a specific temperature.
The closer you are to the melting and boiling point the purer the substance is

Question 2

what will impurities in your sample do a melting point ?
Boiling point ?

Answer 2

Lower melting point increasing
increase boiling point

Question 3

What are formulations ?
How are they made ?
Give an example of a formulation.
What does this consist of ?

Answer 3

useful mixtures with the precise purpose made by following a formula .
Paint -Pigment
solvent -dissolve components and alter the viscosity
Additives -added to change physical and chemical properties
Binder-forms a film that holds pigments in place after paint has been painted on

Question 4

What anions are there tests for

Answer 4

carbonates,sulfates and halides

Question 4

What can help us detect for carbonates ?
What is the word equation when you add carbonates and acids?
How do you work out if carbonates is present ?

Answer 4

carbonate+acids _salt +carbon dioxide +water
dilute acid can help detect for carbonates
add dilute hcl to test solution ,take gas produced and run it through lime water ,if it turns cloudy carbonates are present

Question 5

How do you test for sulfate?
How do we know if barium is present?

Answer 5

reacts with barium to create chloride creating barium sulfate (white precipitate)
before adding barium we put dilute hydrochloric acid to make sure there are no carbonates or sulfites (could react with our barium ions )
If white precipitate forms its a positive result

Question 6

Test for halide ions
What are the halide ions
what will you get ?

Answer 6

Add silver nitrate to test for halides
add dilute nitric acid no impurities
Chloride -silver chloride
Bromide silver chloride
iodide- silver e chloride
cib

Question 7

What test do you do to identify cations?
What do you do to the nichrome wire to ensure it is clean?
Lithium
sodium
potassium
calcium
copper
When will it only work ?

Answer 7

to identify cations (positive ions ) you would do the flame test
put nichrome wire in concentrated HCL in a roaring bunsen burner and repeat until no color is produced emphasizing that it is clean .
Lithium iron-crimson
Sodium ion-orange
potassium -purple
calcium-orange red
copper-green
If its not a mixture has to be pure “’/;

Question 8

metal hydroxide precipitates
How do you work out the presence of certain metal
ions
MAC?
Copper?
Cu 2
CU3

Answer 8

use sodium hydroxide to work out certain metal ions
magnesium ,aluminium and calcium (Mac )all white
however if you add in excess it will redissolve it and becomes colourless .
copper -blue
iron -green 2
iron-brown 3

Question 9

What do metal ions emit when they are heated?
What is specific to the metal ion 2 ?
Why is the flame test not so good?
what does light pass through?
How can you see the concentration of a metal ion?

Answer 9

when metal ions are heated they emit light
wavelength is specific to particular metal ion and has unique line spectrum
similar to flame test however complication if colours are similar ,and if sample contains multiple metals
light passes through a spectroscope
intensity of lines shows concentration of metal iom

Question 10

What is the main advantage of flame emission spectroscapy ?
What happens if the substance contains multiple metal ions ?
How do we identify the unknown iones ?
What are the three main benefits of this instrumental method ?

Answer 10

If the substance contains multiple metal ions the spectrum will show the lines for all of them
compare unknown spectrum to known to identify the ions and calculate the concentration of each ion (how intense the lines are?
accurate ,fast(can be automated ) ,sensitive (detect even the smallest amount )