C3 Flashcards
What is the conservation of mass theory?
During a chemical reaction, no atoms are destroyed and no atoms are created.
Why might the mass increase in an experiment?
One of the reactants is a gas that’s found in the air (eg. oxygen), and the products are solids/liquids/aqueous.
Before the reaction, the gas is floating around in the air. It’s not accounted for the mass of the reactants in the container.
When the reaction happens, the gas outside of the container forms part of the product.
Therefore, the mass inside increases.
Why might the mass decrease in an experiment?
One of the products is a gas.
If the container isn’t closed, the gas can escape from the container when it is formed. It’s no longer contained and can’t be accounted for the mass of the product.
Therefore, the mass of the stuff inside the container decreases.
What ion does Lithium form?
Li⁺
What ion does Sodium form?
Na⁺
What ion does Potassium form?
K⁺
What ion does Magnesium form?
Mg²⁺
What ion does Calcium form?
Ca²⁺
What ion does Carbonate form?
CO₃²⁻
What ion does Sulfate form?
SO₄²⁻
What ion does Oxide form?
O²⁻
What ion does Sulfide form?
S²⁻
What ion does Hydroxide form?
OH⁻
What ion does Nitrate form?
NO₃⁻
What ion does Fluoride form?
Fl⁻
What ion does Bromide form?
Br⁻
What ion does Chloride form?
Cl⁻
What ion does Iodide form?
I⁻
What is the overall charge of an ionic compound?
Zero. Therefore, all the negative charges must balance all the positive charges.
What does “diatomic” mean?
A molecule made up of 2 atoms
What are the reactants?
The chemicals on the left side of a chemical equation
What are the products?
The chemical on the right side of a chemical equation
What does (s), (l), (g), and (aq) mean?
(s) - Solid
(l) - Liquid
(g) - Gas
(aq) - Aqueous
What does aqueous mean?
Dissolved in water
How do you write an ionic equation?
You have to rewrite the equation showing all of the ions separately, and then cancel out any ions which remain the same on both sides of the equation.
What do half equations show?
How electrons are transferred in a reaction.
What does e- stand for in a half equation?
One equation
What is the size of a mole?
6.022 x 10²³
What is Avogadro’s constant?
6.022 x 10²³
What is one mole of an atom or molecule equal to?
One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance.
How do you find the number of atoms in a certain number of moles?
You multiply the number of moles by Avogadro’s constant (6.022 x 10²³). If it were a molecule like Oxygen, you’d have to multiply the result by 2 as there are 2 atoms of oxygen in each molecule of oxygen gas.
How do you find the mass of an atom of a certain element?
Relative atomic mass ÷ Avogadro’s constant
How do you calculate the number of moles in something using the mass and MR?
Number of moles = Mass in g ÷ Relative formula mass
What is the limiting reactant in a reaction?
It’s the reactant which prevents the reaction from continuing as it has been used up.
How are the limiting reactant and product formed linked in a reaction?
The amount of product formed is directly proportional to the amount of limiting reactant. This is because if you add more limiting reactant, more product is made.
How can you use a balanced equation to work out the mass of product formed from a given mass of limiting reactant?
Use the moles to find the mass.
How can you find the balanced symbol equation for a reaction with the masses of reactants/products?
Divide the number of moles of each substance by the smallest number of moles in the reaction.
What is an exothermic reaction?
A reaction which gives out energy to the surroundings.
What form is the energy given out in an exothermic reaction, and how is it shown?
In the form of heat, and it is shown by a rise in temperature in the surroundings
What is an endothermic reaction?
A reaction which takes in energy from the surroundings
What type of energy is taken in in an endothermic reaction, and how is it shown?
In the form of heat, and it is shown by a fall in temperature in the surroundings
What do reaction profiles show?
The energy levels of the reactants and products in a reaction.
What does the difference in height between the reactants and products shown in an exothermic reaction profile?
The energy given out.
What does the difference in height between the reactants and products shown in an endthermic reaction profile?
The energy taken in.
What is the activation energy in a reaction?
The minimum amount of energy needed for bonds to break and a reaction to start
How is activation energy shown on a reaction profile?
The energy difference between the reactants and the highest point on the curve.
Is bond breaking exothermic or endothermic?
Endothermic - energy must be supplied to break existing bonds
Is bond forming exothermic or endothermic?
Exothermic - energy is released when new bonds are formed
In endothermic reactions, what is the difference between the energy used to break bonds and the energy released by forming them?
In an endothermic reaction, the energy used to break bonds is greater than the energy released by forming them.
In exothermic reactions, what is the difference between the energy used to break bonds and the energy released by forming them?
In an exothermic reaction, the energy used to break bonds is less than the energy released by forming them.
How can you find the overall energy change for a reaction using the bond energies?
Overall Energy Change = Energy required to break bonds - Energy released by forming bonds
If an energy change in a reaction is positive, is it endothermic or exothermic?
Endothermic
If an energy change in a reaction is negative, is it endothermic or exothermic?
Exothermic
What is the pH scale?
It goes from 0 to 14 and is a measure of how acidic or alkaline a solution is.
What is an acid?
A substance with a pH less than 7.
What do acids form in water?
H⁺ ions
What is a base?
A substance with a pH greater than 7
What is an alkali?
A base that dissolves in water.
What do alkalis form in water?
OH⁻ ions
What is the relationship between the pH and the concentration of hydrogen ions in a solution?
The pH is inversely proportional to the concentration of hydrogen ions. As the concentration of hydrogen ions increases, the pH decreases.
What is an indicator?
A dye that changes colour depending on whether it is above or below a certain pH. eg. Universal indicator
What is a pH probe?
A pH probe attached to a pH meter can be used to measure pH electronically. The probe is placed in the solution and the pH is given on a digital display as a numerical value. It is more accurate than an indicator.
What must you do inbetween different reading with a pH probe?
You have to calibrate it correctly (by settings it to read pH 7 in a sample of pure water) and rinse it with deonised water between uses.
What is the reaction called between acids and bases, and what does it produce?
Neutralisation - it produces a salt and water.
What are titrations used for?
They show how much of an acid is used to neutralise a base of unknown concentration, or vice versa.
What are titration curves?
Titration curves are used to show where neutralisation happens during titration. There’s a vertical point in the curve which is where the solution is neutral.
How do strong acids behave in water?
They ionise almost completely in water. A large proportion of acid molecules dissociate to release H⁺ ions.
How do weak acids behave in water?
They do not fully ionise in solution. Only a small proportion of acid molecules dissociate to release ions.
What is special about the ionisation of a weak acid?
It is a reversible reaction.
What is acid strength?
The proportion of the acid molecules which ionise in water.
What is acid concentration?
How much acid there is a litre (1 dm³) of water.
What happens if you increase the concentration of H⁺ ions by a factor of 10?
The pH decreases by 1. eg. if you increase concentration by 10² (100), the pH decreases by 2.
What happens if you decrease the H⁻ ions by a factor of 10?
The pH increases by 1
What product do you get when the reactants are an acid and a metal?
Acid + Metal → Salt + Hydrogen
What product do you get when the reactants are an acid and a metal carbonate?
Acid + Metal Carbonate → Salt + Water + Carbon Dioxide
What product do you get when the reactants are an acid and an alkali?
Acid + Alkali → Salt + Water
How can you find the precise amount of alkali needed to neutralise an acid and create a pure soluble salt?
Titration
What happens when you react an acid with an insoluble base?
You can make a soluble salt.
How do you know when an acid and insoluble base have formed a salt?
After adding the base to the acid, you will know when the acid has been neutralised because the excess solid will just sink to the bottom of the flask.
How do you make an insoluble salt?
You can use a precipitation reaction. You need to pick the right two soluble salts, and when they react they form an insoluble salt.
Name an example of forming an insoluble salt.
When lead nitrate and sodium chloride and mixed together, lead chloride is produced as a result of precipitation.
What is oxidation?
The reaction with or addition of oxygen.
What is reduction?
The removal of oxygen.
What is oxidation in terms of electrons?
A loss of electrons
What is reduction in terms of electrons?
A gain of electrons
What is a redox reaction?
REDuction and OXidation happen at the same time, and so it is called a redox reaction.
What does an oxidising agent do?
It accepts electrons and gets reduced.
What does a reducing agent do?
It donates electrons and gets oxidised.
What is electrolysis?
The breaking down of a substance using electricity.
What is electrolyte?
A molten or dissolved ionic compound.
What happens when an electric current passes through electrolyte?
It decomposes. The cations in the electrolyte move towards the cathode and gain electrons. The anions in the electrolyte move towards the anode and lose electrons.
What happens as ions gain or lose electrons in electrolysis?
The uncharged substances are formed and are discharged from the solution.
What is an electrochemical cell?
A circuit made up of an anode, a cathode, electrolyte, a power source and the wires connecting the electrodes.
Why is a molten ionic compound used in electrolyte and not a solid one?
Solid ionic compounds are in fixed positions and don’t conduct electricity, whereas molten ionic compounds can move freely and conduct.
What happens at the cathode in electrolysis?
Positive metal ions gain electrons, and are reduced to atoms.
What happens at the anode in electrolysis?
Negative ions lose electrons, and are oxidised to atoms.
In the electrolysis of aqueous solutions, what is present alongside the ions from the ionic compound?
Hydrogen ions (H⁺) and hydroxide ions OH⁻, from the water.
In the electrolysis of aqueous solutions, what happens if H⁺ ions and metal ions are present?
Hyrdogen gas will be produced if the metal is more reactive than hydrogen. If the metal is less reaction than hydrogen, then a solid layer of the pure metal is produced instead.
In the electrolysis of aqueous solutions, what happens if halide ions are present at the anode?
If halide ions are present (Cl⁻, Br⁻, I⁻), molecules of chlorine, bromide or iodine will be formed.
In the electrolysis of aqueous solutions, what happens if halide ions aren’t present at the anode?
If halide ions aren’t present, oxygen is formed from the hydroxide ions.
How do you set up an electrochemical cell?
Connect the electrodes to a power supply.
What happens to non-inert electrodes during electroylsis?
They can decompose into the electrolyte. For example, you could use copper electrodes in a solution of copper sulfate.
What happens to the mass of the copper electrodes in non-inert electrolysis?
The mass of the anode will decrease and the mass of the cathode will increase. This is because the copper is transferred from the anode to the cathode.
