C5 Chemical Changes Flashcards
Acid
When dissolved in water, its solution has a PH value less than 7. Acids are proton(H+ ion) donors, forms H+ ions in water. They ionise in aqueous solution.
Alkali
A base which dissolves in
water to form a solution with a Ph greater than 7. Alkalis form OH- ions in water. They are soluble hydroxides
Base
A base is a substance with a PH greater than 7.
Displacement reaction
A reaction in which a more reactive element takes the place of a less reactive element in one of its compounds or in solution. For example, when adding copper metal to a colourless silver nitrate solution. The more reactive metal will form ions(e.g. copper ions ) and the less reactive metal will end up being a regular solid(e.g. silver will be shown as grey crystals).
Equilibrium
The point in a reversible reaction at which the forward and backward rates of reaction are the same. This is because, as the reactants react, their concentrations fall, so the forward reaction will slow down. But as more products are made and the concentrations rise, the backward reaction speeds up. After a while the forward reaction goes at exactly the same rate as the backward one, but there’s no oferall effect. The amount of substances present in the reacting mixture remain constant as well as the concentrations of reactants and productd not changing.
Neutral
A solution with a PH value of 7 that is neither acid nor alkaline/something that carries no electrical charge
Neutralisation
The chemical reaction of an acid with a base in which a salt and water are formed.
Ore
Rock which contains enough material to make it economically worthwhile to extract the metal
Oxidation
A reaction where oxygen is added to a substance/electrons are lost from a substance,
Reduction
A reaction in which oxygen is removed from a metal oxide or electrons are gained.
e.g. 2CuO + C: 2Cu + CO2
Strong acids
These acids completely ionise in an aqueous
solution. The concentration of H+ ions is higher than in weak acids, so the rate of reaction will be faster and strong acids will be more reactive than weak acids of the same concentration.
Salt
A compound formed when some/all of the hydrogen in an acid is replaced by metal or ammonium ions
Weak acids
Acids that do not ionise completely in aqueous solutions. The ionisation of a weak acid is a reversible reaction. As the molecules of the weak acid split up to form H+ ions and negative ions, the ions recombine to form the original molecules again. A position of equilibrium is reached where both whole molecules(the majority) and their ions(the minority) are present.
Examples of acids(name 3)
Stomach acid
Vinegar
Lemon juice
Acid rain
Examples of neutral substancws
Pure water
Examples of alkalis
Washing-up liquid
Soap powder
Bleach
Caustic soda(drain cleaner)
What is an indicator?
An indicator is a dye that changes colour depending on whether it’s above or below a certain PH.
Wide range indicators contain a mixture of dyes that means they gradually change colour over the broad range of PH, useful for estimating the PH of a solution.
What is a Ph probe?
A pH probe attached to a pH meter is used to measure pH electronically. The probe’s placed in the solution you’re measuring and the Ph is given on a digital display as a numerical value, so is more accurate than an indicator
Neutralisation reaction(between acids and bases)
Acid + base: salt + water
Examples of strong acids
Sulfuric acid, hydrochloric acid and nitric acid
Examples of weak acids
Ethanoic, citric and carbonic acids
When only can equilibrium be reached
If the reversible reaction occurs in a closed system
What factors affect the position of equilibrium
The temperature - heating a reaction moves the equilibrium to the right(concentration of products greater than concentration of reactants) and cooling it moves it to the left(the concentration of the reactants is greater than the concentration of the products)
The pressure(only in equilibrium involving gases).
The concentration of the reactants and products
How does the PH of an acid or alkali relate to the concentration of H+ ions in the solution
For every decrease of 1 on the PH scale, the concentration of H+ ions increases by a factor of 10.
Factor H+ ion concentration changes by = 10-x
Concentration
How much acid there is in a certain volume of liquid. A dilute solution is not very concentrated
Acid strength
The proportion of the acid molecules that ionises in water
Why does acid concentration affect PH?
PH decreases with increasing acid concentration
Neutralisation reaction(acid + metal oxide)
Acid + metal oxide: salt + water
Neutralisation reaction(acid + metal hydroxide)
Acid + metal hydroxide: salt + water
Acid and metal carbonate reaction
Acid + metal carbonate: Salt + water + carbon dioxide
Practical(making soluble salts using an insoluble base)
1)Use an acid and insoluble base.
2)Gently warm the dilute acid using a Bunsen burner, then turn it off.
3) Add the insoluble base to the acid a bit at a time until no more reacts. You know when the acid has been neutralised, because, after stiring, the excess solid will sink to the bottom of the flask.
4)Filter out the excess solid to get the salt solution.
5)To get pure, solid crystals of the salt, gently heat the saturated solution using a water bath or electric heater to evaporate some water(to make it more concentrated), then stop heating and leave the solution to cool. Leave the solution at room temperature.Crystals of the salt should form which can be filtered out of the solution and dried(crystallisation).
Reactivity series of metals(with water + acid)
From most reactive to least reactive:
Very reactive metals:
Potassium
Sodium
Lithium
Calcium
Fairly reactive metals:
Magnesium
Aluminium
Carbon
Zinc
Iron
Tin
Lead
Not very reactive metals:
Hydrogen
Copper
Silver
Gold(so unreactive it’s in the Earth as a metal itself)
Metals’ reactions with water
Potassium, sodium, lithium, calcium: they fizz, giving off hydrogen gas, leaving behind
an alkaline solution of metal hydroxide
Magnesium, aluminium, zinc and iron: React slowly with water
Tin + lead: slight reaction with steam
Copper, silver + gold: no reaction
Metals’ reactions with dilute acid
Potassium, sodium, lithium, calcium: they explode with dilute acid
Magnesium, aluminium, zinc and iron: They fizz, giving off hydrogen gas and forming a salt
Tin + lead: React slowly with warm acid
Copper, silver + gold: no reaction
Metals’ reaction with acid(equation)
Acid + metal: salt + hydrogen