9) Separate Chemistry 2 Flashcards
What colour does lithium burn?
Crimson
What colour does copper burn?
Blue-green
What colour does calcium burn?
Orange-red
What colour does potassium burn?
Lilac
What colour does sodium burn?
Yellow
What is the process of the flame test practical?
1) Submerge nichrome wire loop in dilute hydrochloric acid to clean
2) Place nichrome wire loop onto sample to be tested
3) Hold nichrome wire loop in Bunsen burner’s blue flame
4) Observe any change in colour to flame
What do flame tests identify?
Metal ions in an ionic compound
What reactants produce precipitates?
The reaction of metal ions and sodium hydroxide
How can metal ions precipitate out of solution?
React with sodium hydroxide
What is the formula for sodium hydroxide?
NaOH
Can precipitates be dissolved in water?
No, they are insoluble solids
What precipitate does magnesium form?
White magnesium hydroxide
What is the formula for producing the white precipitate magnesium hydroxide?
Mg2+(aq) + 2OH-(aq) –> Mg(OH)2(s)
What state are precipitates?
Solid
What precipitate does aluminium form?
White aluminium hydroxide
What is the formula for producing the white precipitate aluminium hydroxide?
Al3+(aq) + 3OH-(aq) –> Al(OH)3(s)
How can aluminium hydroxide be distinguished from other hydroxides?
Is dissolved in excess sodium hydroxide producing a colourless solution
What precipitate does calcium form?
White calcium hydroxide
What is the formula for producing the white precipitate calcium hydroxide?
Ca2+(aq) + 2OH-(aq) –> Ca(OH)2(s)
How can magnesium hydroxide and calcium hydroxide be distinguished?
Flame test
What precipitate does copper form?
Blue copper(II) hydroxide
What is the formula for producing blue copper(II) hydroxide?
Cu2+(aq) + 2OH-(aq) –> Cu(OH)2(s)
What precipitates do iron form?
Green iron(II) hydroxide Brown iron(III) hydroxide
What precipitate does ammonia form?
Water and ammonia
Ammonia gas evolves out of solutions
What is the formula for producing water and ammonia?
NH4+(aq) + OH-(aq) –> NH3(g) + H2O(l)
What is the chemical test for ammonia?
Placing damp litmus paper at mouth of test tube
Blue litmus paper if ammonia present
What colour does damp litmus paper turn if ammonia is present?
Blue
What ion characteristic do all carbonates have?
CO32- ions
What does the reaction of a carbonate and dilute acid give?
Salt
Carbon dioxide
Water
What is the test for carbonates?
(carbon dioxide test)
Bubble hydrochloric acid and carbonate gas through limewater
If solution turns cloudy carbon dioxide is present
What is the test for sulfates?
1) Add dilute hydrochloric acid to solution to remove carbonate ions which could disrupt results
2) Add barium chloride and a white precipitate barium sulfate will form
What ions do sulfates contain?
SO4 2-
What type of ions are halide?
Anions
Negatively charged
What is the test for halides?
1) Add dilute nitric acid to remove carbonates
2) Add silver nitrate, halides will form a precipitate with the silver ions
What colours can the precipitate silver halide be?
White (silver chloride)
Cream (silver bromide)
Pale yellow (silver iodide)
What is the order of testing for cations?
1) Flame test
2) Coloured precipitate with sodium hydroxide
3) Test evolving gas for ammonium
What is the order of tests for anions?
Carbonates- test for carbon dioxide gas
Sulfates- presence of white barium sulfate
Halides- colour of silver halide corresponds to halide anion in a positive result
What are the 3 anion types?
Carbonates
Sulfates
Halide ions
Why does the test for an anion have to be carried out in a logical order?
If any HCl or BaCl2 is added to the test for a carbonate or sulfate, there will be chloride ions in the solution
These will be tested and there will be a false positive result for chloride ions
What are advantages of instrumental methods? (3)
Greater sensitivity and accuracy
Quicker at producing results
Able to analyse tiny samples
What are disadvantages of instrumental methods? (3)
Instruments are often expensive
Special training needed for use
Results are often only useful when compared to data from known substances
What is the use of flame emission spectroscopy?
Working out the identity and concentration of the metal ions present in a solution
What is the process of flame emission spectroscopy? (2)
1) Place sample of metal solution into a flame, light will be given off
2) Light given off is captured by a spectroscope which generates a line spectrum by distinguishing between light with different wavelengths
How is the concentration of an ion shown on a line spectra?
The intensity of line spectra
