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
In this experiment, ink sample Y did not move from the start line. Explain a change to the experiment that would be needed to separate the dyes in ink sample Y.
- different solvent
- dyes in sample Y are not soluble in the current solvent
Describe how a sample of pure, dry nickel sulfate crystals can be obtained from the mixture of nickel sulfate solution and excess solid nickel carbonate in the beaker
- filter mixture through filter paper to remove excess solid nickel carbonate (filtration)
- crystallisation - put filtrate in evaporating basin, then heated gently with Bunsen burner
- allow to cool, then dry crystals
The hydrogen ion concentration in a solution is decreased by a factor of 10
State how the pH of this solution changes
Increases by 1
X = pH 3.40
Y = pH 4.40
What is the concentration of hydrogen ions in solution X compared with that in solution Y?
D - ten times higher
During experiment the pH changes from 2 to 10. If phenolphalein indicator is added, state the colour change that occurs
Colourless —> pink
Explain, in terms of the particles present, why the pH increases during the experiment
- the concentration of H+ ions decreases as they react
- concentration of OH- ions increases as bases contain OH- ions
- pH increases as it becomes less acidic
Explain why dilute hydrochloric acid is described as a strong acid
- low pH
- easily dissociates to give H+ ions
1cm3 of hydrochloric acid of pH 2 is made up to a volume of 10cm3 with distilled water.
State the pH of the new solution
3
How do you do complicated ionic equations?
- write soluble ionic substances as their ions
- then cancel out ones that appear both sides
- balance
State and explain how the pH changes as the magnesium hydroxide is added to the dilute hydrochloric acid
- neutralisation reaction - pH increases towards neutral (pH 7)
- hydrochloric acid contains H+ ions - concentration decreases as they react
- less H+ ions to dissociate fully - so pH increases
- bases contain OH- ions so concentration of OH- ions increases
What are the products when molten zinc chloride is electrolysed?
Chlorine + zinc
Describe what you would see if damp, blue litmus paper is placed into chlorine gas
- turn red
- then bleach white
When the gas hydrogen chloride is dissolved in water, a solution forms. Blue litmus paper dipped in this solution turns red. State why the litmus paper turns red
It forms an acidic solution which turns litmus paper red
Explain, in terms of electronic configurations, the increase in reactivity from lithium to sodium to potassium
- atoms have more shells as you go down group 1, meaning OUTER electron is further away from nucleus
- less attraction between outer electron and positive nucleus, so they require very little energy to lose outer electron
- so more reactive
Describe what is seen when chlorine water is added to potassium bromide solution and the mixture shaken
- solution turn from colourless (potassium bromide) to brown (bromine precipitate)when it is displaced by chlorine
In this reaction, chlorine has been reduced.
Explain, using the equation, how you know that chlorine has been reduced
- reduction is the gain of electrons
- chlorine gains 2 electrons
- to form a chloride ion
What is the formula for aluminium chloride?
AlCl3
Describe what you would see when a small piece of rubidium is dropped on to water
- flame produced as it burns
- react vigorously (more so than potassium)
- melt very quickly
- disappear almost instantly with explosion
- form colourless solution + hydrogen gas
Describe the test to show that a gas is chlorine
Damp blue litmus paper will turn red, then bleach white if chlorine is present
State the name of the solution formed when hydrogen bromide dissolves in water
Hydrobromic acid
Predict the colour and state of astatine at room temperature
- black (/grey)
- solid
Name the solids:
Flame test - red-orange flame
Add dilute nitric, followed by silver nitrate solution - white precipitate forms
Cation: calcium
Anion: chloride
Give reason why adding a few drops of sodium hydroxide solution to a solution of a solid and obtaining a white precipitate does not identify
(a) the cation
(b) the anion
(a) More than one cation produces a white precipitate - calcium + aluminium
(b) Sodium hydroxide not used to test for anions
Give a reason why instrumental analysis may be better than other methods of analysis
Improve sensitivity
The green iron(II) hydroxide precipitate gradually turns brown when exposed to air. Explain this observation
- iron(II) hydroxide oxidised by air
- goes brown due to formation of iron(III) hydroxide
Describe how you could show that both potassium and sodium ions are present in a sample
- flame photometer (can detect multiple ions in a mixture)
- uses a spectroscope which detects individual wavelengths emitted unique to each
