Chemistry Flashcards
What are the alkali metals
The elements in group 1
What are the properties of alkali metals
Metals with low density (Li, Na and K are less dense than water)
React with water, releasing hydrogen
Form hydroxides that dissolve in water to give alkaline solution
React with non-metals to form ionic compounds (+1).The compounds are white solids that dissolve in water to form colourless solution
In Group 1, the further down the element is …
The more reactive the element
The lower its melting and boiling point
Compared to the alkali metals, transition elements:
Have higher melting points (except Mercury) Have higher densities Are stronger and harder Less reactive Do not act vigorously with water
What are halogens
Elements in group 7
What happens when halogens react with metals
The halide ion carries a charge of -1
In Group 7, the further down the group an element is:
The less reactive it is
The higher the melting point and boiling point
A more reactive halogen can displace a …
… less reactive halogen from an aqueous solution of its salt
Why can the trends in reactivity within groups in the periodic table be explained
The higher the energy level of the outer electrons, the more easily electrons are lost and the less easily electrons are gained
What is formed when soap reacts with soft water
Lather
What does hard water react with soap to form
Scum so more soap is needed to form a lather
What is a benefit of soap-less detergents
They do not form scum
What does hard water contain
Dissolved compounds, usually of calcium and magnesium. The compound dissolve when the water comes in contact with rock
What are the two types of hard water
Temporary hard water - softened by boiling
Permanent hard water - remains hard when boiled
What does temporary hard water contain
Hydrogencarbonate ions (HCO3)
What happen to Hydrogencarbonate ions when they decompose thermally
The produce carbonate ions which react with calcium and magnesium ions to form precipitate
Negative of permanent hard water
Increased costs because more soap is need to create a lather
Negative of temporarily hard water
When it is heated up, it can create lime scale which reduces the efficiency of heating systems and kettles
Benefit of hard water
Calcium compounds are good for the development and maintenance of good bones and teeth as well as helping reduce heart disease
How can permanently hard water be made soft
Removing the dissolved calcium and magnesium ions
How can permanently hard water be made soft by adding sodium carbonate
It reacts with the calcium and magnesium ions to form a precipitate of calcium carbonate and magnesium carbonate
How can permanently hard water be made soft by using commercial water softeners
Ion exchange columns contain hydrogen ions or sodium ions, which replace the calcium and magnesium ions when water passes through the column
What is water of the correct quality essential for
Life
What should drinking water for humans have
Sufficiently low levels of dissolved salts and microbes
What can water filters containing carbon, silver and ion exchange resins do
Remove some dissolved substances from tap water to improve the taste and quality
Why might chlorine be added to drinking water
To reduce microbes
Why might fluoride be added to drinking water
To improve dental health
How can pure water be obtained
Distillation which requires a large amount of energy and thus is very expensive
How is water of the correct quality produced
Choosing an appropriate source
Passing the water through filter beds to remove any solids
Sterilising with chlorine
What information is given from calorimetry
Relative amount of energy released when substances burn
Used to compare the energy released by foods and fuels
What is energy released in
Joules (J)
How can the energy released or absorbed by a chemical reaction in solution be calculated
The measured temperature change of the solution when the reagents are mixed in an insulated container
(Used for neutralisation reaction and reactions of solids and water)
During a chemical reaction:
Energy must be supplied to break bonds
Energy is released when bonds are formed
What happens in an exothermic reaction
The energy from forming new bonds is greater than the energy needed to break existing bonds
What happens in an endothermic reaction
The energy to break existing bonds is greater than the energy released from forming new bonds
What do catalysts provide
A different pathway for a chemical reaction that has a lower activation energy
What can hydrogen be burned as
A fuel in combustion engines but they’re expensive
Hydrogen + oxygen -> water
Where can hydrogen be used
In fuel cells that produce electricity to power vehicles
What can the flame test be used to do
Identify metal ions
What colour does lithium result in during the flame test
Crimson
What colour does sodium compounds result in during the flame test
Yellow
What colour does potassium result in during the flame test
Lilac
What colour does calcium result in during the flame test
Red
What colour does barium result in during the flame test
Green
How do you test for aluminium, calcium and magnesium ions
They form white precipitates with sodium hydroxide but the aluminium hydroxide precipitate dissolves in excess sodium hydroxide solution
How do you test for copper (II), iron (II) and iron (III)
Coloured precipitates with sodium hydroxide solution.
What colour precipitate does copper (II) form with sodium hydroxide solution
Blue
What colour precipitate does iron (II) form with sodium hydroxide solution
Green
What colour precipitate does iron (III) form with sodium hydroxide solution
Brown
What do carbonates react with dilute acids to form
Carbon dioxide
How does carbon dioxide react with limewater
It forms a white precipitate. This turns lime water cloudy
In the presence of dilute nitric acid, how do halide ions in solution react with silver nitrate solution
Precipitates are produced
In the presence of dilute nitric acid, silver chloride reacts to silver nitrate solution to give what colour precipitate
White
In the presence of dilute nitric acid, silver bromide reacts to silver nitrate solution to give what colour precipitate
Cream
In the presence of dilute nitric acid, silver iodide reacts to silver nitrate solution to give what colour precipitate
Yellow
In dilute hydrochloric acid, sulfate ions in solution reacts with barium chloride solution, to give what
A white precipitate
What can you measure using titration
The volumes of acid and alkali solution that react with each other.
If you know the concentration of one of the reactants, what can you figure out
The concentration of the other reactant using the results of the titration
What are the raw materials in the Haber process
Nitrogen - from the air
Hydrogen - natural gas or other source
How is the Haber process carried out
The purified gases are passed over a catalyst (iron)
At 450 degrees and a pressure of 200 atmospheres
Some hydrogen and nitrogen reacts to form ammonia
Some ammonia breaks down back into hydrogen and nitrogen
The ammonia liquefies when cooled and is removed
The unused reactants are recycled
When is equilibrium reached, when a reversible reaction occurs in a closed system
When the reactions occur at exactly the same rate on each direction
What depends on the conditions of the reaction
The relative amounts of all the reacting substances at equilibrium
If the temperature is raised in a reversible reaction …
… The yield from the endothermic reaction increased and the yield from the exothermic reaction decreases
If the temperature is lowered in a reversible equation…
… The yield from the endothermic reaction decreases and the yield from the exothermic reaction increases
What happens when the pressure is increased in a gaseous reaction
The reaction that produces the least amount of molecules will be favoured (as shown by the equation)
Which functional group do alcohols contain
-OH
What are the first three members of a homologous series of alcohols
Methanol
Ethanol
Propanol
Properties of methanol, ethanol and propanol
Dissolve in water to form a neutral solution
React with sodium to produce hydrogen
Burn in air
Are used as fuels and solvents
(Ethanol is the main alcohol in alcoholic drinks)
How can ethanol be oxidised to ethanoic acid
Chemical oxidising agents
Microbial action
Ethanoic acid is the main acid in which aqueous solution …
… Vinegar
What is ethanoic acid a member of
Carboxylic acids
Which functional group does carboxylic acids have
-COOH
Properties of carboxylic acids
Dissolve in water to make acidic solutions
React with carbonates to produce carbon dioxide
React with the alcohols in the presence of an acid catalyst to produce esters
Do not ionise completely when dissolved in water and so are weak acids
Aqueous solution of weak acids have a higher pH value than aqueous solutions of a strong acid with the same concentration
What is ethyl ethanoate
An ester produced by ethanoic acid and ethanol
What is the functional group of esters
-COO
Properties of esters
Volatile compounds with distinctive smells and are used as flavouring and perfumes
What happens in water treatment works
Water passes through a mesh screen to remove large pieces
Chemicals added to make solids and microbes stick together and fall to the bottom
Water filtered through gravel beds to remove solids
Water is chlorinated to kill off any harmful microbes
Equation for titration experiments
Number of moles = concentration * volume
CV of the alkali = CV of the acid
Method of calorimetry
Put 50g of water in the copper can record its temperature
Weight the spirit burner and lid
Put the spirit burner underneath the can and light the wick. Heat the water, stirring constantly, until the temperature reaches approx. 50 degrees
Put out the flame using the burner lid, and measure the final temperature of the water
Weigh the spirit burner and lid again
Fuel cells
An electrical cell that’s supplied with a fuel and oxygen and uses energy from the reaction between them to generate electricity
Pros of fuel cells in the car industry
Doesn’t produce any conventional pollutants
Only by-product is water (helpful in cities with air pollution)
Could eventually help countries to become less dependent on crude oil
Cons of fuel cells in the car industry
Hydrogen is a gas and takes a lot of storage space as opposed to liquids (petrol)
Hydrogen is very explosive and so hard to store safely
The hydrogen fuel is often made from hydrocarbons (fossil fuel) or by electrolysis of water (uses electricity)
How to do titrations
Use pipette to put alkali in conical flask
Add indicator (phenolphthalein or methyl orange)
Pour acid in the burette until the meniscus is at 0
Do a rough titration to find an idea of acid needed
Record results of titration until you have 3 titres within 0.1 cm3 of each other
