May Revision - Wrong Answers Flashcards
State one difference between Mendeleev’s periodic table and the modern periodic table
Mendeleev’s periodic table had gaps for undiscovered elements, but the modern periodic table no longer has gaps because the elements have now been discovered
Hydrogen burns in air at a temperature well above 100C to form water … use this information to add the missing state symbols to the equation for the reaction taking place as the hydrogen burns
2H2 - (g)
2H2O - (g)
Which way should water flow in a condenser?
Cold water in at the bottom (right) and out at the top (left)
The flask was heated with a Bunsen burner. Give the name of an alternative piece of apparatus that could be used to heat the flask
Electric heater
The changes shown are physical changes. Explain why these changes are called physical changes rather than chemical changes
- doesn’t result in formation of a new substance
- can be easily reversed
State time when the gas first started to form a liquid (from a graph)
At start of state change (when line goes flat) - 2 minutes
Give a reason why the bulb of the thermometer should be level with the side arm (obtaining pure water from ink)
This is so it records the temperature of the vapours. If its too low it will be too close to the boiling liquid and will read higher than true vapour temperature
Explain why ’T’ contains the greatest number of coloured substances
Has greatest number of ink spots - has separated into the most colours
Nickel is a metal. Explain how the structure of a nickel atom, Ni, changes when it forms a nickel ion
- loses 2
- negatively charged electrons
Explain, in terms of their structure and bonding, why metals have high melting points
- very strong metallic bonds between delocalised electrons and metal ions
- which require a lot of energy to break
Describe what is meant by a covalent bond
- a shared pair of electrons
- attracted to positive nuclei
Explain why chlorine is a gas, rather than a liquid, at room temperature
- chlorine has low boiling point
- because it has weak intermolecular forces between chlorine molecules
- which don’t require a lot of energy to break
A solid ionic compound is dissolved in water to form a solution. Describe a simple experiment to show that charged particles are present in this solution
- insert electrodes into aqueous solution
- connect to electrical supply
- ammeter shows current
Explain how the water in sea water separates to produce the pure water in this apparatus
- water + salt have different boiling points
- water evaporates at 100˚C and evaporate into tube and condense separately from the salt
The boiling point of nickel tetracarbonyl is 43˚C.
The boiling point of iron pentacarbonyl is 103˚C.
These two liquids mix together completely.
Describe the process to separate these two liquids.
- (fractional) distillation could be used as the liquids have different boiling points
- heat mixture to around 50˚C
- as nickel tetracarbonyl has lower boiling point it will evaporate, and condense separately from the iron pentacarbonyl
Describe how a sample of pure, dry sodium chloride crystals can be obtained from the filtrate
- crystallisation
- filtrate put in evaporating basin and heated gently with Bunsen burner until half solution has evaporated
- allow remaining water to evaporate
- then dry with paper towel
State what could be changed in the chromatography experiment to make the Rf value more accurate
Use longer paper