C3 Part B Flashcards
What is the numerical form of a “mole”? Give it in standard form
6.023 x 1023
How many atoms of carbon-12 weigh exactly 12g?
6.023 x 1023
(A mole)
Fill in the gaps:
A mole of ………. of any element or compound weighs the same number of ………… as the ……………… (Ar) of the element or compound.
A mole of atoms/molecules of any element or compound weighs the same number of grams as the relative atomic mass (Ar) of the element or compound.
Give two possible units that concentration of a substance can be measured in
moles per dm3
grams per dm3
1 litre = 1000 cm3 = 1 dm3
Fill in the gaps:
The …….. solute you dissolve in a given volume, the more crowded the solute ……. are and the …… ……….. the solution.
The more solute you dissolve in a given volume, the more crowded the solute molecules are and the more concentrated the solution.
What kind of experiment is used to measure how much acid is needed to neutralise an alkali?
Titration
Describe the process of a titration
- Put an alkali in a flask, along with indicator (phenolphthalein or methly orange)
- Add the acid to the alkali a little bit at a time using a burette, giving the flask a regular swirl
- When the indicator changes colour, it means all the alkali has ben neutralised
- Record the amount of acid needed to neutralise the alkali
What are the two main titration equations? Draw the equation pyramid if it helps
- Number of moles = Concentration (moles/dm3) x Volume (dm3)
- Mass in grams = Number of moles x Relative formula mass
Fill in the gaps
An exothermic reaction is one that gives out …….. to the surroundings, usually in the form of ……. and shown by a ……… in temperature.
An ………… reaction in one which takes in energy from the ……….., usually in the form of heat and shown by a …… in temperature.
An exothermic reaction is one that gives out energy to the surroundings, usually in the form of heat and shown by a rise in temperature.
An endothermic reaction in one which takes in energy from the surroundings, usually in the form of heat and shown by a fall in temperature.
Energy must be supplied to break existing bonds, so bond breaking is what kind of reaction?
Endothermic
Energy is released when new bonds are formed, making it what kind of reaction?
Exothermic
Fill in the gaps:
In an endothermic reaction, the energy required to break old bonds is ……… than the energy ……….. when new …….. are formed.
In an ………. reaction, the energy released in bond ……….. is greater than the energy used in ……… old bonds.
In an endothermic reaction, the energy required to break old bonds is greater than the energy released when new bonds are formed.
In an exothermic reaction, the energy released in bond formation is greater than the energy used in breaking old bonds.
How can energy transfer be measured in endothermic/exothermic reactions?
By measuring temperature change.
What are the issues with the fuels we currently use and have relied on for decades to provide energy?
- Burning fuels releases CO2 and contributes to the greenhouse effect, causing a rise in global temperature and thermal expansion of the seas to occur
- Developing alternative, renewable sources of energy costs losts of money
- Crude oil is a finite resource
- The transportation of oil, which can only be found in certain places on earth, costs money and causes harmful emissions to be released.
By what process is fuel energy calculated?
Calorimetry
Outline the process of calorimetry
- Put a defined amount of water in a copper can and record its temperature
- Weigh the spirit burner and the lid that is being used
- Put the spirit burner underneath the can and light the wick. Heat the water, stirring constantly until the temperature reaches about 50°C.
- Put out the flame, using the burner lid and measure the dinal temperature of the water.
- Weigh the spirit burner and the lid again.
(almost exactly the same process can be used to calculate the amount of energy produced by food)
What is the equation for working out energy transfer in calorimetry?
Q = mcΔT
Energy transferred (joules) = Mass of water (grams) x Specific heat capacity of water (4.2) x Temperature change (in °C)
What is the main difference between the energy level diagrams of endothermic and exothermic reactions?
In exothermic reactions, the products are at a lower energy than the reactions, whereas in endothermic reactions the products are at a higher energy than the reactants.
Draw and annotate sketches of energy level diagrams for endothermic and exothermic reactions
What is the activation energy of a reaction?
The minimum energy required for reeacting particles to break their bonds
How can the activation energy of a reaction be lowered and how is this represented on an energy level diagram?
A catalyst can be addes so that the reaction occurs more easily and more quickly. This will be evident on an energy level diagram by a lower curve.
Note: The overall energy change for the reaction remains the same
What are the bond energies applied to:
H-H
Cl-Cl
H-Cl
H-H = 436 kj/mol
Cl-Cl= 242 kj/mol
H-Cl = 431 kj/mol
How much energy is required to break one mole of H-H and one mole of Cl-Cl bonds?
(H-H = 436 kj/mol
Cl-Cl= 242 kj/mol)
436 + 242 = 678 kj
How much energy does forming two moles of H-Cl release?
2 x 431 = 862 kj
Prove that overall more energy is released than is used to form products using the example of hydrogen and chlorine bonds used to make two moles of HCl
H-H = 436 kj/mol
Cl-Cl= 242 kj/mol
H-Cl = 431 kj/mol
Breaking the bonds:
436 + 242 = 678 kj required
Forming two moles of HCl:
2 x 431 = 862 kj
Energy released:
862 - 678 = 184 kj/mol
The reaction between hydrogen and oxygen is exothermic, how is this useful?
Hydrogen and oxygen react to produce water, which isn’t a pollutant. Because the reaction is exothermic, energy from the reaction can be harnessed - either in a combustion engine or a fuel cell.
Hydrogen gas can be burnt to power vehicles, what are the pros and cons of this?
Pros: It’s clean energy
Cons: A special, expensive engine is needed. Hydrogen is hard to store safely. Energy is required to make hydrogen from water.
What is a fuel cell? When were they developed and why?
A fuel cell is an electrical cell that’s supplied with fuel and oxygen and uses energy from the reaction between them to generate electricity.
Fuel cells were developed in the 1960s as part od a space programme, because they’re more practical than solar cells and safer than nuclear power. (They’re still used on Space Shuttle missions) Fuel cells don’t run down or need recharging, they’ll produce energy as long as fuel is supplied.
The car industry is developing fuel cells to replace conventional petrol/diesel engines. What are the two main advantages of fuel cells in cars?
- They don’t produce any conventional pollutants (no greenhouse gases, no nitrogen, no suldur dioxide, no carbon monoxide - only water and heat)
- They could help countries become less dependent on crude oil.
Why are fuel cells unlikely to mean the end of our dependence on fossil fuels?
- Hydogen is a gas so takes up a lot of space to store
- Hydrogen is very explosive
- Hydrogen fuel is often made from hydrocarbons (from fossil fuels) or by the electrolysis of water (which uses electricity - fossil fuels)
Flame tests can be used to identify metal ions. What colour flame do each of these metals create and what are their ionic symbols?
Lithium
Sodium
Potassium
Calcium
Barium
Lithium (Li+) - crimson flame
Sodium (Na+) - yellow flame
Potassium (K+) - lilac flame
Calcium (Ca2+) - red flame
Barium (Ba2+) - green flame
Outline how you might carry out a flame test in a lab
Distill a wire loop by dipping it into hydrochloric acid and rinsing it with distilled waster. Dip the clean wire loop into a sample of the compound you are testing and place it in the clear blue part of a bunsen flame, wait to see what colour the flame turns.
Other than using a flame test, how else might you test for metal ions?
Some metal ions form a coloured precipitate with NaOH, so you can add a few drops of sodium hydroxide to the substance you wish to test. If you get a coloured insoluble hydroxide, you can tell which metal was in the compound.
When reacted with NaOH, what colour precipitate do each of these metals form and what is the ionic reaction involved?
Calcium
Copper(II)
Iron(II)
Calcium - White:
Ca2+(aq) + 2OH-(aq) ⇒ Ca(OH)2(s)
Copper (II) - Blue:
Cu2+(aq) + 2OH-(aq) ⇒ Cu(OH)2(s)
Iron(II) - Green:
Fe2+(aq)) + 2OH-(aq) ⇒ Fe(OH)2(s)
When reacted with NaOH, what colour precipitate do each of these metals form and what is the ionic reaction involved?
Iron (III)
Aluminium
Magnesium
Iron(III) - Brown:
Fe3+(aq) + 3OH-(aq) ⇒ Fe(OH)3(s)
Aluminium - White at first, but then redissolves in excess NaOH to make a colourless solution:
Al3+(aq) + 3OH-(aq) ⇒ Al(OH)3(s)
Magnesium - White:
Mg2+(aq) + 2OH-(aq) ⇒ Mg(OH)2(s)
To test for carbonates in a substance you have to detect CO2, what is the method used for this?
- You must react your substance with a dilute acid, as carbonates will react to produce CO2.
acid + carbonate ⇒ salt + water + carbon dioxide
- You can test to see if the gas produced is carbon dioxide by bubbing it through limewater, if it is CO2 then the limewater will go cloudy.
How might you test for halide ions in a substance?
To test for chloride, bromide or iodide ions, add dilute nitric acid (HNO3), followed by silver nitrate (AgNO3).
Chloride gives a white precipitate of silver chloride.
Bromide gives a cream precipitate of silver chloride.
Iodide gives a yellow precipitate of silver chloride.
How would you test for sulfate ions (SO42-) in a substance? (2 main steps)
- Add dilute hydrochloric acid (HCl) , followed by barium chloride solution (BaCl2)
- If a white precipitate of barium sulfate is formed, it means the original compound was a sulfate.
