C8

Question 1

What is a pure substance?

Answer 1

A single element or compound, not mixed with any other substance

Question 2

How do you tell the difference between pure substances and mixtures?

Answer 2

By measuring their melting and boiling points.

Question 3

What will impurities do to the melting and boiling point?

Answer 3

Impurities will lower the melting point and increase the boiling point.

Question 4

What is a formulation?

Answer 4

A Formulations is a mixture that has been designed as a useful product ( each chemical has a particular purpose).

Question 5

How are formulations made?

Answer 5

Formulations are made by mixing the components in carefully measured quantities to ensure the products has the required properties.

Question 6

Examples of formulations in everyday life?

Answer 6

Fuels, cleaning agents, paints, medicines, alloys, fertilisers and food.

Question 7

What does chromotography do?

Answer 7

Chromotography can be used to seperate mixtures of soluable substance and can help to identify substances.

Question 8

Steps for how paper chromotaography can be used to seperate and distinguish between coloured substances ( RPA)

Answer 8

1) Using A ruler,measure 1cm from the bottom of the chromatography paper and mark with a dot using a pencil. Rule a line along the bottom of the chromotography paper with a pencil, through the dot you have just made.
2)Using a pipette, drop small spots of each of the inks onto the pencil line. Leave a sufficent gap between each ink so they dont merge.
3) Get a beaker and pour a suitable solvent. The solvent shouldnt touch the chromotography paper or go over the ink spots (cause the inks to run into each other)
4) Put the paper into the the beaker and let the solvent move up the paper.
5)Just before the solvent line reaches the top of the paper, remove the chromotogram from the paper and allow it to dry.
6) Once the chromatogram has dried, measure the distance travelled by the solvent.
7) Measure the distance travelled by each ink spot.
8) Calculate the Rf value- compare the Rf value of each of the spots.

Question 9

What are the two stages of chromotgraphy and what are they?

Answer 9

Mobile Phase- solvent (moves through the paper carrying the subsatnces with it)
Stationary phase- chromotography paper

Question 10

What is the difference between pure and impure subsatnces in chromotography?

Answer 10

Pure substances have 1 spot on a chromatagram -made from 1 substance.
Impure substances have 2 or more spots - contain multiple substances.

Question 11

How do you calculate the Rf value?

Answer 11

Distance travelled by substance (basdline to the centre of the spot) divide by distance travelled by solvent (solvent front)

Question 12

What is the test for oxygen?

Answer 12

If you put a glowing splint inside a test tube with oxygen, the oxygen will relight the glowing splint.

Question 13

What is the test for carbon dioxide?

Answer 13

Bubbling carbon dioxide through an aqueous solution of calcium hydroxide (limewater) causes the solution to turn milky (cloudy).

Question 14

What is the test for chlorine?

Answer 14

Chlorine bleaches damp litmus paper, turning it white.

Question 15

What is the test for hydrogen?

Answer 15

If you hold a burning splint at the open end of a test tube containing hydrogen youll get a squeaky pop.

Question 16

How do u use flame tests to identify the ions in unknown single ionic compounds RPA

Answer 16

1) Dip a wire loop into a sample of the ionic compound being tested
2) Place the loop into the flame of the bunsen burner (roaring flame)
3)Observe the colour of the flame produced and record it.

Question 17

What can flame tests be used for?

Answer 17

To identify some metal ions (cations)

Question 18

What are the flame tests? (mneomonic)

Answer 18

Lithium compounds (Li+) - crimson flame (LiCk)
Sodium compounds (Na+) -yellow flame (NaY)
Potassium compounds (K+)-lilac flame (kiL)
Calcium compounds (Ca2+)-orange/red flame (CaOR)
Copper compounds (Cu2+)-green flame (CuG)

Question 19

How do you identify metal ions that form coloured precicipiates?

Answer 19

Add sodium hydroxide.

Question 20

Which solutions form white precipitates when sodium hydroxide is added?

Answer 20

Solutions of calcium, magneisum and aluminium all form white precipiates but only aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution.

Question 21

Which metal ions form coloured precipiates?

Answer 21

Copper (II), iron (II) and iron (II) all form coloured precipitates when sodium hydroxide is added.
Copper (II)- blue
Iron (II)-green
Iron (III)-brown

Question 22

Ionic equations for precipiate formation

Answer 22

Ca2+ (aq) + 2OH- (aq) —> Ca(OH)2 (s)
Cu2+ (aq) + 2OH-(aq) —-> Cu(OH)2 (s)
Fe2+ (aq) + 2OH-(aq) —-> Fe(OH)2 (s)
Fe3+ (aq) +3OH- (aq) —-> Fe(OH)3 (s)
Al3+ (aq) +3OH- (aq) —-> Al(OH)3 (s)
Mg2+ (aq) +2OH- (aq)—–> Mg(OH)2 (s)

Question 23

How do you test for carbonates (CO3 2-) ?

Answer 23

-Add a small sample of the carbonate and and a few drops of hydrochloric acid using a pipette.
-Connect the test tube to a test tube of limewater.
-If carbonate ions are present bubble of carbon dioixde will be produced turning the limewater cloudy.

Question 24

How do you test for sulfate ions (SO4 2-)?

Answer 24

Using a pipette add a few drops of barium chloride to the sample and then add a few drops of hydrochloric acid. If sulfate ions are present, a white precipitate will form.

Question 25

How do you test for halide ions?

Answer 25

Using a pipette add a few drops of nitiric acid to the sample, and then a few drops of silver nitrate solution.

Question 26

What coloured precipiates do each halide ion produce?

Answer 26

Chloride- white precipitate
Bromide ions- cream precipitate
Iodide ions- yellow precipitate

Question 27

What is flame emission spectroscopy?

Answer 27

An instrumental method used to analyse metal ions in solutions.

Question 28

Advantages of instrumental methods compared to chemical tests?

Answer 28

• Can identify different ions in mixtures howevere flame tests only work for substances that contain 1 metal ion.
  -Very sensitive
  -Very fast
  -Very accurate

Question 29

How does flame emission spectroscopy work?

Answer 29

1) The sample is put into a flame and the light given out is passed through a spectroscope.
2) The output is a line spectrum that can be analysed to identify the metal ions in the solutions and measure their concentrations.