Triple & Further Science: Chemistry (III) Flashcards
What was the early periodic table based on?
Their physical / chemical properties and their atomic mass
What did Newland set out for his periodic table?
Newland’s law of octaves – every 8th element had similar properties
What did Mendeleev do with his periodic table?
Mendeleev left gaps and predicted new elements – he put known ones in order of atomic mass
Why were the gaps so important in Mendeleev’s periodic table?
The gaps predicted the properties of undiscovered elements
What is the modern periodic table based on?
Electron structure – this can predict the element’s chemical properties (group number is equal to the number of electrons in the outer shell)
What are the alkali metals and what properties do they have?
Alkali metals are group 1 elements – they become more reactive down the group (outer e- further from nucleus) and have lower melting and boiling points
They also have a low density (Li, Na and K less dense than water)
How many electrons in the outer shell are present in group 1 elements (alkali metals)?
1 electron – making them very reactive and forming ionic compounds with non-metals (which produce white compounds that dissolve in water forming colourless solutions)
How do the alkali metals react when placed in water?
They react vigorously producing hydrogen gas and form hydroxides that dissolve producing alkaline solutions
2Na (s) + 2H2O (l) → 2NaOH (aq) + H2 (g)
2K (s) + 2H2O (l) → 2KOH (aq) + H2 (g)
What are the group 7 elements known as and what are their properties?
Halogens – they are non-metals with 7 outer electrons and become less reactive (as it is harder to gain an e- as the outer shell is further from the nucleus) and have higher melting and boiling points
What colour vapours do the halogens fluorine, chlorine, bromine and iodine form?
Fluorine = yellow gas; chlorine = green gas; bromine = red-brown liquid; iodine = dark grey solid / purple vapour
What do the halogens form with metals?
Ionic bonds with metals (1- ions) called halides
What will more reactive halogens do too less reactive ones?
A more reactive halogen will displace a less reactive halogen from an aqueous solution of its salt
Cl2 (g) + 2Kl (aq) → I2 (aq) + 2KCl (aq)
Cl2 (g) + 2KBr (aq) → Br2 (aq) + 2KCl (aq)
What are the transition elements?
Transition elements are positioned between group 2 and 3 and are good conductors of heat and electricity; dense, strong, and shiny
What are the properties of the transition metals?
Transition metals often have more than one ion (e.g. Fe+2, Fe+3), form colourful compounds and make good catalysts
What is hard water and what does it make?
Hard water makes scum and scale (instead of lather with soap) due to calcium and magnesium ions dissolved in the water (scale is mostly calcium carbonate which is a thermal insulator and making heating elements less efficient)
*But calcium ions are good for teeth / bones and it is suggested minerals in hard water reduce heart disease
What ions cause hardness in water?
Calcium ions (Ca+2) and Magnesium ions (Mg+2)
How is hard water made soft?
The calcium and magnesium ions are removed
What is temporary / permanent hardness caused by and how is this removed?
Temporary hardness is caused by HCO3- and can be removed by boiling (HCO3- decomposes to insoluble CO3)
Permanent hardness can only be softened using washing soda (Na2CO3) where the carbonate ions react with the Ca+2 and Mg+2 ions
How can the hardness of water be compared?
Titrations – soap solution can be added to the water until a lasting lather was created
How can water quality be improved?
Filtration (removal of materials) and chemicals added to kill microbes
Why are chlorine / fluoride added to water and what problems may these cause?
Fluoride is added to drinking water to help reduce tooth decay and chlorine is added to prevent disease
Some studies have linked fluoride and chlorine to increased cancer
What is a reversible reaction?
A reversible reaction is one where the products of the reaction can themselves react to produce the original reactants
What happens if a reversible reaction takes place in a closed system?
Equilibrium is reached – the amounts of reactants and products will reach a balance
How can the position of the equilibrium in a reversible reaction be changed?
The temperature and pressure can be changed
How does temperature affect and exothermic and endothermic reaction?
All reactions are exothermic reaction in one direction and endothermic in the other
- Temp. raise causes endothermic reaction to increase (use up the extra heat)
- Temp. fall causes exothermic reaction to increase (give out more heat)
How does pressure affect an exothermic and endothermic reaction?
Many reactions have a greater volume on one side (either reactants or products)
- Pressure raise encourages the reaction will produces less volume
- Pressure fall encourages the reaction will produces more volume
What does a catalyst do to the equilibrium position?
Catalysts do not change the equilibrium position – they speed up both the forward and reverse reactions by the same amount
What is the Haber process?
Ammonia production
Nitrogen + Hydrogen Ammonia
N2 (g) + 3H2 (g) 2NH3 (g)
What conditions are needed for the Haber process?
Nitrogen from air and hydrogen from natural gas at 200 atmosphere pressure and 450oC with an iron catalyst
How does the Haber process recycle its ‘waste’?
What is the functional group of an alcohol and what is the general formula of them?
-OH functional group
General formula: -
CnH2n+1OH
Draw the structure of methanol, ethanol and propanol
Methanol – CH3OH
Ethanol – C2H5OH
Propanol – C3H7OH
What are the properties of alcohols and how are they used?
Alcohols are flammable, burn to produce CO2 and H2O, are used as solvents / fuels and ethanol is used for alcoholic drinks
What are carboxylic acids?
Carboxylic acids have a functional –COOH group and their names end in –anoic acid
What are carboxylic acids used for?
Soap and ester production
Draw the structure of methanoic acid, ethanoic acid and propanoic acid
Methanoic acid – HCOOH
Ethanoic acid – CH3COOH
Propanoic acid – C2H5COOH
What is the functional group of esters and how are they formed?
Esters have the functional group -COO- named -oate
They are formed from an alcohol and carboxylic acid
Alcohol + carboxylic acid → ester + water
How would the ester ethyl ethanoate be produced?
A reaction between ethanoic acid and ethanol
What properties do esters have?
Esters are volatile, smell nice but do not mix well with water
What are esters used for?
Esters smell nice so are used as perfumes / flavourings / aromas
What is a mole?
A mole is 6.023 x 1023
602,300,000,000,000,000,000,000
This precise number of atoms of carbon-12 weighs exactly 12g
How can concentration be measured?
Concentration is a measure of how many things there are in a given space, measured in moles per dm3
1 litre = 1000cm3 = 1dm3
How can concentrations be measured?
Titrations – how much acid /alkali is needed to measure a quantity of alkali / acid
How can concentration be calculated in moles per dm3?
Concentration = number of moles ÷ volume
*Volume in dm3
How can energy transfer be measured?
Measure the temperature of the reagents and mix in a polystyrene cup (though energy is still lost to the surroundings) and record the highest temperature produced
How can concentration be calculated in grams per dm3?
Mass = number of moles x relative formula mass
What is an exothermic reaction?
Exothermic reactions give out energy to the surroundings (usually in the form of heat and show a rise in temperature)
What is an endothermic reaction?
Endothermic reactions take in energy from the surroundings (usually in the form of heat and show a fall in temperature)
What type of reaction is bond breaking?
Endothermic
What type of reaction is bond forming?
Exothermic
What is calorimetry?
Calorimetry measures the energy in a fuel – using Q = mcΔT
Energy transferred (J) = mass of water (g) x specific heat capacity (c) x temperature change (oC)
Draw an exothermic reaction energy level diagram (ΔH (energy change) is negative))
Draw an endothermic reaction energy level diagram (ΔH (energy change) is positive))
What do catalysts do to the activation energy?
They lower it
When hydrogen and oxygen react what is released?
Hydrogen and oxygen react to form water and release energy (e.g. fuel cells to generate electricity)
What are the flame tests for the following positive ions: -
- Lithium (Li+)
- Sodium (Na+)
- Potassium (K+)
- Calcium (Ca+2)
- Barium (Ba+2)
Lithium (Li+) – crimson flame
Sodium (Na+) – yellow flame
Potassium (K+) – lilac flame
Calcium (Ca+2) – red flame
Barium (Ba+2) – green flame
What colour precipitate do the following metal ions form with NaOH:
- Calcium
- Copper (II)
- Iron (II)
- Iron (III)
- Aluminium
- Magnesium
Calcium – white
Copper (II) – blue
Iron (II) – green
Iron (III) – brown
Aluminium – white (but then re-dissolves in NaOH)
Magnesium - white
How can you test for carbonates?
CO2 release (turns limewater cloudy)
How can you test for halides?
Halide ions form a precipitate in HNO3 followed by AgNO3
- Chloride gives white precipitate of silver chloride
- Bromide gives a cream precipitate of silver bromide
- Iodide gives a yellow precipitate of silver iodide
How can you test for sulfates?
HCl is added followed barium chloride solution – a white precipitate forming means sulfate presence
