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82 Cards in this Set
- Front
- Back
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What is the mass of 1 mole of a substance called? |
It's molar mass. |
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What is molar mass? |
Relative formula mass in grams. |
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What is the formula of metal carbonate thermally decomposing? |
Metal carbonate > metal oxide +carbon dioxide |
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How can mole calculations be used? |
To work out masses of elements or compound |
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How do you calculate number of moles? |
Number of moles = mass of chemical / molar mass |
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What is the empirical formula? |
The simplest whole number ratio of each type of atom of an compound |
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How do you calculate empirical formula? (5 steps) |
-Write down mass of each element -Look up relative atomic mass of each element -Work out how many moles there are of each element -Choose the amount present the least -Divide all amount by the one present least |
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How do you find the percentage of an element in a compound? |
% mass of element = total mass of the element in the compound / relative formula mass of compound x 100 |
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How do you calculate empirical formulae from percentage composition by mass? (5 stages, 3 typos remember???!!?!?!) |
-Mass of each element in 100g of acid -Relative atomic mass of each element -Convert to moles of each element (stage 1 divided by stage two) -Identify the element present least -Divide all by smallest |
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What happens as concentration increases? |
The solute particles become more crowded |
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What happens if a solution is diluted three times? |
It will take up three times more volume |
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How do you convert cm3 to dm3? |
Divide by 1000 |
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What is the relationship between the amount of moles, concentration in mol/dm3 and volume in dm3? |
Amount in moles = concentration x volume |
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What does the traffic light system for foods show? |
The types of foods such as sugar, salt and fat and their quantities, it also shows the GDA. |
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Why are sodium ions essential in our diets? |
For water balance and nerve responses. |
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What can too much sodium cause? |
High blood pressure and heart disease. |
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What is the main source of sodium ions? |
Salt |
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Why do food labels need to be read with care? |
Some list the amount of sodium, some list the amount of salt. |
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What happens in titration? |
An acid and an alkali neutralise. |
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What is the formula for titration? |
acid + alkali = salt + water |
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What is the end point of a titration graph? |
Where all the acid reacts with the alkali. |
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What happens at the end point? |
The pH changes very suddenly. |
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What do you need to know to get the perfect titration curve? (4) |
-the starting pH -the end pH -the end point volume (most vertical section of the curve) -the pH range over which the change takes place |
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Why are indicators chosen? |
They give sharp colour changes at certain pH |
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What colour does litmus paper go in an acid and alkali? |
Blue in alkali, red in acid |
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What colour does phenolphthalein go in alkali and acid? |
Pink in alkali, colourless in acid. |
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What colour does screened methyl orange go in acid and alkali? |
Green in alkali, pink in acid |
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Why does a single indicator need to be used to show the end point? |
Mixed indicators like universal indicator give continuous colour changes which are harder to see. |
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Why are titrations repeated? |
So an average reading can be calculated to make the technique reliable. |
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How do you measure gas with an upturned burette? |
It must be filled with water before it is turned upside down, the volume is read off the scale on the side. |
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How do you measure gas with a scale? |
A loose plug of cotton wool in the neck of the flask prevents a spray. |
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At room temperature and pressure, how much volume does 1 mole take up? |
24dm3 |
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How do you work out the number of moles of gas if its volume is unknown? |
Number of moles = volume of gas in dm3 / 24 |
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What is the limiting reactant? |
The reactant that is used up first |
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What happens when the limiting reactant is all used up? |
There are no more particles of that substance to collide with the other reactant, so the amount of product formed is directly proportional to the amount of limiting reactant. |
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When is a reaction at equilibrium? |
When a balance of amounts of reactants and products is reached. |
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What us equilibrium? |
The rate of the forward reaction equals the rate of the backwards reaction. The concentrations of reactants and products do not change. |
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When are the concentrations of reactants and products never equal? |
When the forward and backward rates balance. |
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When is the equilibrium position left? |
If the concentration of reactants is greater than that of the products |
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When is the equilibrium position right? |
If the concentration of reactants is less than that of the products |
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When does equilibrium not work? |
If it is not a closed system and the chemicals 'get out' |
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How is equilibrium reached? |
Initially, the forward reaction rate is fast, but then it slows as the reactants are used up. At the same time, the backward reaction rate increases as more is available to react. Eventually the backward reaction is as fast as the forward reaction. |
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What can alter the position of the equilibrium? |
Changing temperature pressure or concentration. |
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What does LeChateliers principle state? |
If a change is made in a closed system, the equilibrium will shift in a way to reduce the effect of the change. |
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What happens in the contact process? |
The reaction between sulfur dioxide and oxygen is reversible. |
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What is the word equation for the contact process? |
Sulfur dioxide + oxygen >< Sulfur trioxide |
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What is the symbol equation for the contact process? |
2SO2(g) + O2(g) >< 2SO3(g) |
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How do you obtain the most economic yield in the contact process? |
The reaction is carried out at 450 degrees at atmospheric pressure using a catalyst of vanadium pentoxide (V2O5) |
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How does the temperature of the contact process help it achieve the most economic yield? |
The forward reaction is exothermic so high temperatures drive the equilibrium to the left, but if the temperature is too low the rate of reaction is too slow. High temperatures increase the rate of reaction, the temperature is a compromise. |
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How does the pressure of the contact process help it achieve the most economic process? |
There are three gas molecules on the left of the equation and two on the right so high pressure increases the yield - it forces the equilibrium further to the right. The equilibrium already lies on the right anyway so high pressures are not needed. |
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How does the catalyst of the contact process help it achieve the most economic process? |
Catalysts do not affect the position of the equilibrium, they make the reaction go faster. |
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What happens to acid molecules in water? |
They ionise |
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What is the formula for strong acids completely ionising in water? |
Strong acid -> hydrogen ions + other ions |
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What is the formula for weak acids ionising in water? |
Weak acids >< hydrogen ions + other ions |
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What are acid reactions caused by? |
Hydrogen ions, H+ |
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What is used to show the concentration of H+ ions? |
The pH scale. |
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What does a high concentration of H+ show? |
Low pH number |
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What doe a low concentration of H+ show? |
High pH number |
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What does HCl turn into when it completely ionises in water? |
HCl -> H+ + Cl- |
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What is the equation for the reversible reaction of ethanoic acid? |
CH3COOH >< H+ + CH3COO- |
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What is rate? |
A measure of the number of collisions every second, this is the collision frequency. |
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When is the collision frequency higher? |
In strong acids when the concentration of H+ ions is higher |
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When is the collision frequency lower? |
In weak acids when the concentration of H+ ions is lower |
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Why do weak acids not conduct as well as strong acids in electrolysis? |
They have fewer H+ ions to move through the liquid. |
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Why will the same amount of gas be made if the same number of reactants are used in electrolysis? |
A weak acid will use some of its H+ ions to react and be used up first, so more molecules of acid will ionise producing more H+ ions. |
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What will the amount of reactant determine in electrolysis? |
The amount of product formed as strong or weak acids will produce just as many ions in the end. |
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What is produced at the cathode? |
Hydrogen because H+ ions are positive and so migrate to the cathode. |
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Why is ethanoic acid less conductive than hydrochloric acid? |
There is a lower concentration of H+ ions to carry the charge. |
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What does the concentration of an acid tell us? |
How many moles of acid there are in 1dm3 of solution |
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What does the strength of an acid tell us? |
How much an acid ionises, the degree if ionisation |
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What does a concentrated solution of weak acid still have? |
A low concentration of H+ ions. |
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What do ionic substances form? |
Ionic lattices. The ions are fixed in position within the solid lattice. |
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What does the lattice of an ionic substance do in water? |
Breaks apart and the separated ions can move. |
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What happens in precipitation reactions? |
The reactant ions can move in solution but must collide to react. |
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What happens in a precipitation reaction involving mixing two different ionic solutions? |
There is an extremely high collision frequency between the ions of the two solutions, so the reaction is extremely fast. The insoluble precipitate is formed so fast it appears to be instant. |
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What can precipitation reactions be summarised as? |
AB + CD -> AD + CB |
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What is used as a test for sulfate ions? |
Precipitation reactions of barium chloride with sulphate ions |
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What is used as a test for iodide and chlorine ions? |
Precipitation reactions of lead nitrate with halide ions |
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How do you prepare a clean and dry sample of an insoluble salt? (4 stages) |
- Mix the two solutions to make barium sulfate and sodium chloride -Filter the precipitate of barium sulfate, which stays in the filter paper -Wash with distilled water to remove traces of the sodium chloride solution -Dry by leaving the precipitate in a warm place for the water to evaporate |
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What happens when lead nitrate and sodium iodide react? |
Only lead ions react with iodide ions as these are precipitated out of the solution. The other ions do not directly take part in the reaction. |
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What are spectator ions? |
Ions that do not directly take part in the reaction. |
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What happens in an ionic equation? |
Only the reaction ions are shown. Spectator ions are left out. |
