Scientific Knowledge I.e. The things I Should Know But Forgot

Question 1

How do the flame tests work? Also: list the colours

Answer 1

Sterilise a clear wire loop in sodium hydroxide then distilled water. Place some of the substance onto the loop, then put the loop into the blue part of the fire
Lithium ➯ crimson flame
Sodium ➯ yellow flame
Potassium ➯ lilac flame
Calcium ➯ red flame
Magnesium ➯ white
Barium ➯ green

Question 2

How do you test for ammonium?

Answer 2

Gently heat sodium hydroxide with the substance . Ammonia should be given off. Then test that.

Question 3

How do you test for metal ions?

Answer 3

Add a few drops of sodium hydroxide to the substance, then look at the precipitate.
Copper ➯ blue
Iron 2 ➯ green
Iron 3 ➯ brown
Aluminium ➯ white then dissolved to be colourless
Calcium ➯ white
Magnesium ➯ white

Question 4

How do you test for chloride, bromide or iodide ions?

Answer 4

Add dilute nitric acid and silver nitrate to the substance.
Chlorine ➯ white precipitate
Bromide ➯ cream precipitate
Iodide ➯ yellow precipitate

Question 5

How do you test for sulphate?

Answer 5

Add dilute hydrochloric acid, then barium chloride solution. A white precipitate(barium sulfate) means it is a sulfate.

Question 6

How do you test for a carbonate?

Answer 6

Add hydrogen chloride solution. It should fizz and produce CO2. Test this with limewater.

Question 7

What is the test for hydrogen?

Answer 7

Placing a lighted splint in a tube of hydrogen produces a ‘squeaky pop’

Question 8

What is the test for oxygen?

Answer 8

Check if it relights a glowing splint

Question 9

What is the test for CO2? What are its properties?

Answer 9

It should turn limewater milky.

CO₂ is denser than air, and soluble in water at a high pressure

Question 10

What is the test for ammonia(NH3)?

Answer 10

When warmed it should produce a distinct smell and turn red litmus blue.

Question 11

What is the test for chlorine?

Answer 11

It bleaches damp litmus paper to white

Question 12

What is the test for pure water?

Answer 12

It turns anhydrous copper sulfate blue. Boils at exactly 100°C

Question 13

How does filtration work?

Answer 13

• separate an insoluble solid from a liquid, e.g. Sand and water
• use a funnel and filter paper

Question 14

How does simple distillation work?

Answer 14

• to separate a solvent from a solution, e.g. Water from salt
• this is when the one you want has a lower boiling point that the one you don’t want
• When the solution is heated, the water evaporates. It is then cooled and condensed in a separate container. The salt does not evaporate and so it stays behind.

Question 15

How does fractional distillation work?

Answer 15

• separating a liquid from a mixture of two or more liquids
• This method works because the liquids in the mixture have different boiling points. When the mixture is heated, one liquid evaporates before the other.

Question 16

How does paper chromatography work?

Answer 16

• to separate two dissolved substances
• often used when the dissolved substances are coloured, such as inks, food colourings and plant dyes.
• It works because some of the coloured substances dissolve in the solvent used better than others, so they travel at different speeds, further up the paper.
• to work out the comp of an unknown substance compare the chromatogram to know substance, and see where they match. This will be where they have the same compound

Question 17

What are the relative masses and charges of the sub atomic particles?

Answer 17

Charge: proton = +1, electron = -1, neutron = 1
Mass: proton = 1, electron = negligible, neutron = 1

Question 18

What is the atomic number?

Answer 18

The number of protons/electrons (the smaller number)

Question 19

What is the atomic mass?

Answer 19

The number of protons and neutrons. (The larger number)

Question 20

How is the periodic table organised?

Answer 20

It is an arrangement of elements in order of atomic number.
The group shows the number of electrons in the outer shell.
The period shows the number of shells.

Question 21

What are the conditions needed for rusting?

Answer 21

When iron comes into contact with oxygen and water

Question 22

How can one prevent rusting?

Answer 22

Some prevent oxygen:
• oiling, e.g. Bicycle chain
• greasing, e.g. Nuts and bolts
• painting, e.g. Car body
Galvanising:
• the iron or steel object is coated in a thin layer of zinc.
• This stops oxygen and water reaching the metal underneath - but the zinc also acts as a sacrificial metal.
• Zinc is more reactive than iron, so it oxidises in preference to the iron object.

Question 23

What are oxidation and reduction?

Answer 23

OIL RIG: oxidation is loss of electrons, reduction is gain of electrons
Oxidation is gain of oxygen, reduction is lost of oxygen

Question 24

Wha is an isomer?

Answer 24

Two substances with the same molecular formula but a different structure

Question 25

What is an isotope?

Answer 25

An atoms of the same element with different masses, as protons the same but different number of neutrons

Question 26

How do reactions w water or dilute acids allow you to work out the reactivity series?

Answer 26

K, Na, Li, and Ca all react with both water and acids
Mg, Zn, and Fe react with acids and v slowly w water
Cu doesn’t react with either.
The more things a substance reacts with, and the more vigorous the reaction, the more reactive it is.

Question 27

How do displacement reactions w metal oxides or salts in water allow you to work out the reactivity series?

Answer 27

• introduce a more reactive metal and displacement will take place
• introduce a less reactive metal and no displacement will take place

Question 28

What conditions are needed for iron to rust?

Answer 28

• water
• oxygen
• becomes hydrated iron oxide

Question 29

What is the combustion of hydrogen?

Answer 29

(With oxygen:)
2H₂ + O₂ ⇒ 2H₂O
Water and energy produced

Question 30

How do you work out the percentage of oxygen in air using copper?

Answer 30

Some copper is set up in a tube, with a gas syringe with a known amount of air in it on either side. A known amount of air, e.g. 100cm3 is passed over heated copper. As Copper Oxide is formed in reaction with the air’s oxygen, the air in the gas syringes will decrease in vol. at tend, only roughly 80% of air remaining, ∴ O2 make up roughly 20% of air.

Question 31

What are the percentage of the gases in air?

Answer 31

nitrogen 78 per cent
oxygen 21 per cent
argon and CO₂ 1 per cent

Question 32

How do Mg, C, and S burn in air?

Answer 32

• C and S burn, giving out heat and light to bond w O2, becoming non metal oxides, i.e. Acids
• Mg burns to form a metal oxide ∴ basic

Question 33

What happens during the thermal decomposition of metal carbonates?

Answer 33

• make carbon dioxide and a metal oxide

E.g. CuCO3 ⇒ CuO + CO₂

Question 34

What are the uses of CO₂?

Answer 34

• dissolved into drinks at high pressure ∴ makes CO2 bubbles in fizzy drinks
• some fire extinguisher guises have CO2 as denser than air ∴travels over it creating a barrier btw air and fire ∴ fire can’t burn as needs O2

Question 35

What is the arrangement and movement of particles in a solid?

Answer 35

Close together in a regular pattern. They vibrate on the spot

Question 36

What is the arrangement and movement of particles in a liquid?

Answer 36

Close together, random arrangement. Move around each other

Question 37

What is the arrangement and movement of particles in a gas?

Answer 37

Far apart, random arrangement. Move quickly in all directions

Question 38

How do you find out the size of particles using diffusion?

Answer 38

• get a double ended test tube and put ammonium solutions and HCl acid at each end, and bung it.
• when the gases meet they forma white ring
• the ring is nearer to the HCl ∴ ammonia solution travelled further than the HCl in the same amount of time
• ∴ ammonia solution must be the lighter gas w smaller particles, as it travelled faster

Question 39

What is dilution? How does heat affect it?

Answer 39

• Put a coloured substance in a solvent, e.g. Food colouring in water. Over time the colour spreads through you and becomes weaker.
• more heat ∴ more KE ∴ particles move to the different areas quicker ∴ time take for it to be fully diluted decreases

Question 40

How do you find out the small size of particles using dilution?

Answer 40

• place a spatula of any strongly coloured substance, e.g. Potassium permanganate in the bottom of a glass full of water, using a straw
• purple most conc at bottom and least at top
• diffusion eventually happens, but v slow in liquids as the coloured particles don’t have much space to move between the water particles.
• in gases quicker, ad particles are v far apart