EOY exam Flashcards
What are the colours of the metal ions flame test?
Lithium, Li+ - Red Sodium, Na+ - Yellow Potassium, K+ - Lilac Calcium, Ca2+ - Orange-red Barium, Ba2+ - Green Copper, Cu2+ - Blue-green
Why do we clean the wire loop in the flame test?
To sterilise it to ensure that the results are accurate
To ensure an adequate amount of powder sticks to it
Why do we dip the wooden stilts in hydrochloric acid?
To make it burn longer
To make the powder stick to it
To sterilise it and ensure results are accurate
What was the composition of Earth’s early atmosphere and why?
lots of CO2 and water vapour , steam, methane and ammonia because volcanoes were erupting releasing gases from inside the Earth
No oxygen because there was no metal oxides in layers of rock
What is the composition of the atmosphere now and what changed to cause this?
The magma cooled forming a thin layer of crust. The water vapour therefore condensed and fell as rain creating oceans.
Photosynthetic organisms evolved taking in O2 and releasing CO2 and some CO2 got locked up in fossil fuels and rocks
O2 increase
CO2 decrease
78% nitrogen
21% CO2
0.04% CO2
the rest is others
build of oxygen lead to the ozone layer blocking harmful rays from the sun and allowing more complex organisms to evolve
What is the test for oxygen?
If the gas will relight a glowing splint
What is the difference between the greenhouse gas effect, global warming and climate change?
Green house gas- We release greenhouse gases such as methane into the air by farming and CO2 by combustion. These get trapped in the atmosphere and when light rays try to bounce back to the atmosphere they are reflected back to Earth
Global warming - Is the gradual warming of our planet due to the reflection of light rays
Climate change - ice caps melting/ increase in average temperature / out of control weather
Discuss group 2?
As you go down the group they get more reactive because more shells mean there is bigger gap between the positive nucleus and negative electrons means there is a weaker electrostatic force so they react with other elements electrons more easily and lose their outer electron easier.
Discuss group 7?
The atoms at the top are more reactive because it has less shells so there isn’t as much shielding and the positive nucleus is closer to the electrons it wants to attract.
What is the calculation for percentage yield?
Percentage yield = actual yield / theoretical yield x100
How do you work our percentage yield if there is a reaction of 2Fe203 + 3C -> 4Fe + 3CO2
with 50kg or iron oxide and 18.9kg of iron
work out the relative formula mass for iron oxide and the relative atomic mass of iron Mr (Fe2O3) = (2x56) + (3x16) = 160 Ar (Fe) = 56 Work out number of moles of iron oxide (50 x 1000) divided by 160 = 312.5 moles
The equation tells you that 2 moles of iron oxide makes 4 moles of iron so 312.5 moles of iron oxide produces (312.5 / 2) x 4 = 625 moles of iron
Then work out the theoretical yield of your desired product (iron)
mass = moles x ar
625x56=35000g = 35kg
use equation and the actual yield of 18.9kg from question
18.9/35 x100 = 54%
Why do you never get 100% yield?
incomplete reactions
practical losses like transferring between containers
unwanted reactions
human error
What is the equation for atom economy?
atom economy = total Mr of desired products / total ?Mr of all products x 100
What does a high atom economy mean?
the higher the atom economy, the more reactants have been turned into desired and useful products
the higher the atom economy, the greener the process
Hydrogen gas can be made by…
Calculate the atom economy of the reaction:
CH4 + H20 -> CO + 3H2
identify the desired product (hydrogen gas H2)
calculate the Mr of all the prodcuts
Mr (CO) 12+16 = 28
Mr (3H2) 3x (1x2) = 6
28+6=34
Then work out the Mr of just the desired products
3 x Mr (H2) = 3 x (2x1) = 6
Use the formula to calculate atom economy
6/34 x100 = 18%
Why is a high atom economy better?
It doesn’t use up the products as quickly
Doesn’t maje waste materials that need to be disposed of
More profitable
What are some properties of transition metals?
Hard Strong Shiny Malleable Good conductors of electricity and heat High melting points High densities
Make good catalyst
Iron is the catalyst used in the haber process
What is an alloy?
Different size atoms so by mixing two different elements together it creates an irregular shape giving it strength
Describe alloys of iron (steels)?
Steel is made by adding small amounts of carbon to pure iron
Steel is harder than iron and stronger
Doesn’t corrode or rust
Bronze= copper+tine is harder tan copper and used for medals and statues
Brass = copper +zinc brass more maleable
Good alloys for jewellery because malleable and shiny
Aluminium alloys for aircrafts
What is rusting of iron ?
A redox reaction
Metals can corrode in the presence of oxygen and water to form their metal oxides
Corrosion of metals is caused by redox reactions where the metal loses electrons so its oxidised
