Common Mistakes Flashcards
What is meant by molar mass
Mass of one mole of a compound
Number of protons, neutrons and electrons in 18, 8 O2-
8 p
10 n
10 e
State the difference, if any, between the chemical properties of the isotopes 6Li and 7Li, giving a reason for your answer.
There would be no difference as there is the same number of electrons in the outer shell
Why is the Ostwald process carried out at a temperature of around 900 degrees celcius
It is a compromise temperature between high yield and high rate
A temperature too low - slow reaction
A temperature too high - too low yield
Explain why there has been much research to find a better catalysts
As less temperature is needed
Increased yield
Faster equilibrium is reached
State one example of an industrially or environmentally important heterogenous catalyst. Identify the reaction catalysed and name the catalyst
Iron in the Haber Process for the production of ammonia
Ionic equation between silver and chlorine
Ag+ + Cl- —> AgCl
Potassium is ignited and put in a jar with oxygen to form potassium oxide
State what can be seen as the reaction proceeds
- lilac flame
- potassium melts
- white solid forms
State whether you would expect rubidium to be more reactive or less reactive than potassium.
Give a reason for your answer
More reactive
Group 1 elements become more reactive down the group due to the electron being more easily lost as there is decreasing ionisation energy
A student added 2.0 g of calcium to some water and collected the hydrogen gas formed.
The student repeated the reaction using the same mass of barium.
He noticed that the volume of gas, still at the same temperature and pressure, was less. Why?
Less moles of barium used as barium has a higher atomic mass
Why are halogens oxidising agents?
They gain one electron to complete the outer shell
They take the electron from another species
State, giving a reason, which halogen is the strongest oxidising agent
Fluorine
Greatest electron affinity
Least electron shielding
Greatest effective nuclear charge
Give the physical states of chlorine and iodine at room temperature
Chlorine is gas
Iodine is solid
State what is observed (if anything) when chlorine and iodine are added separately to potassium bromide solution.
Write an equation for any reaction.
Chlorine - solution turns from colourless to orange/brown
Cl2 + 2Br- —> 2Cl- + Br
Iodine - no change no reaction
Marged adds a strip of magnesium to dilute hydrochloric acid
State what she would observe as this reaction proceeds
Stream of bubbles or effervescence as hydrogen is produced
Magnesium disappears
Heat is given off
Marged separately adds a strip of magnesium and beryllium to dilute hydrochloric acid.
State whether you would expect beryllium to be more or less reactive than magnesium. Explain your answer clearly
Less reactive
G2 reactivity decreases up the group
Harder to lose the 2 electrons as there is a greater effective nuclear charge
State observations made during the reaction between calcium to hydrochloric acid
- becomes warm
- gas bubbles or effervescence of the hydrogen form
- calcium dissolves
Give the ionic equation between calcium bromide and aqueous silver nitrate
Ag+ + Br- —> AgBr
State the observation for the reaction between barium sulfate and water
Gas bubbles
Colourless solution as barium hydroxide is soluble in water
A smaller volume of hydrogen was obtained than expected when potassium methanoate was heated to produce potassium oxalate and hydrogen.
Suggest why?
- not all potassium methanoate had reacted
- wasn’t pure
- inadequate heating
How to know if enough solution has been added to react with all the reactants present when forming a precipitate
Allow to settle then test the filtrate by adding some of the solution again and if cloudiness forms not enough was added
Explain briefly the origin of atomic absorption spectra in terms of electron transitions
Electrons absorb energy from radiation
Excited
Low to high energy level
Black lines on coloured background
What is meant by atom economy
Amount of percentage by mass of all the reactants that ends up in the desired products
Give an example of a species containing a coordinate bond
Al2Cl6NH4+
Density equation
Mass/ volume
Explain why ice and water have different densities at 0•c
Ice has a more open structure due to the hydrogen bonds holding it so
Although they’re in water aswell the hydrogen bonds extend throughout the whole ice structure
Why incorrect titres may have been obtained when carrying out titrations
- funnel still in burette- more acid in burette smaller titre
- air bubble in burette - bigger titre as acid used to fill jet
- burette not rinsed - bigger titre as acid is more dilute
