# C5- How Much?

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• Created by: Janviixo
• Created on: 13-02-16 14:42
Define ' molar mass'
the mass of one mole
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What is molar mass measured in?
grams per mole (g/mol)
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What is the formula to find the number of moles?
no. of moles = mass / molar mass
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Define relative atomic mass
it is the average mass of an atom compared to the mass of 1/12th of an atom of carbon-12
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What is the percentage composition?
It is the amount of mass of an element in a compound
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How can you calculate the percentage composition by mass?
= (atomic mass x no. of atoms) / molar mass (x 100%)
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What is an empirical formula?
it gives the smallest number whole number ratio of atoms in a compund
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What information do you need to calculate the empirical formula?
the mass of each element or the composition percentage by mass
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Find the empirical formula of iron oxide produced when 44.8g of iron reacts with 19.2g of oxygen
Fe= 44.8g O= 19.2g -------> 2:3
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Define concentration?
it is a measure of how crowded things are
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What is concentration measured in?
moles per dm
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What is the formula for concentration?
concentration = no. of moles / volume
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Why might something be diluted?
to make a weaker solution
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What does GDA of food packaging stand for?
Guideline Daily Amounts- amount of nutrients average adult should eat
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What can you use to estimate the mass of salt?
the sodium content
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What is a titration used for?
allows you to find out exactly how much acid is needed to neutralize an alkali
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Name the 7 things needed for a titration experiment?
Pipette, pipette filler, burette, conical flask, acid, alkali, indicator
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What is a pipette and pipette filler used for?
To fill a solution (25cm ) and emptying it into a conical flask.
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What is the end-point?
It is when the colour of the solution changes as it has all become neutralised
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Name the 2 types of indicators that can be used for titration?
Litmus and Phenolphthalein
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What is the error margin when you repeat the titraion?
0.2cm
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Why is universal indicator not used in the titration experiment?
It can turn a variety of colours which gradually changes, we need a sudden colour change
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Name the colour change when using the different indicators?
Litmus: red to blue Phenolphthalein: clear to pink
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What do pH curves show?
shows the pH against the volume of the acid/ alkali added
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What standard apparatus is used when collecting gases?
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What can you used a gas syringe to collect?
Collect pretty much any gas. Give volume accurate to nearest cm
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What can be a problem when using a gas syringe?
If the reaction is vigorous, it can blow of the plunger out of the syringe
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Name and describe another collection method of gases?
upturned measuring cylinder or burette - delivery tube bubbles gas into cylinder/ gas jar filled with water
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Name a gas which wouldn't be suitable for using an upturned cylinder?
Ammonia/ hydrogen chloride- dissolves in water
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Why would a burette be more accurate than a cylinder?
can measure to the nearest 0.1cm
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What experiment can you use to measure the mass of gas?
mass balance
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Explain how you would use mass balance?
A gas is released, the mass disappearing is measured on the balance. Most accurate but releases gas into air
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What volume is 1 mole of gas occupied in?
One mole always occupies 24dm at room temperature (25 C) and pressure (1 atm)
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What formula can use you use to find no. of moles in a gas?
no. of moles = volume of gas / 24
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Why might there be some reactant left if the reaction has stopped?
When the reaction stops, one of the reactants is used up and the others are just excess
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What is the limiting reactant?
It is the reactant used up in the reaction
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Explain why when you halve the amount of limiting reactant, the gas produced also halves
The amount of product formed is directly proportional to the amount of limiting reactant.
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How can you tell a reaction was fast on a graph?
Faster rates of reaction are shown by steeper curves
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What is a reversible reaction?
It is when the products of the reaction can react themselves to produce the original reactants
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Define the term 'equilibrium' in a reaction
It is when the forward reaction is going at exactly the same rate as the backwards reaction
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Why is there no overall effect during the reaction?
At equilibrium, both reactions are still happening. This means the concentrations have reached a balance .:. won't change
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What is a closed system?
When none of the products or reactants can escape
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Name 3 things that can change the position of the equilibrium
Temperature, Concentration and Pressure (gases only)
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Explain why adding a catalyst doesn't change the position of equilibrium?
Catalyst speeds up forward and backward reaction by same amount .:. reaches equilibrium quicker
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What happens to the equilibrium when you decrease the temperature?
It will try to move in the exothermic direction to produce more heat
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What happens to the equilibrium when you increase the pressure?
Equilibrium moves to the side where there are less moles of gas to reduce pressure
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What happens to the equilibrium when you increase the concentration of the reactants?
The equilibrium tries to decrease it by shifting to the right.
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What conditions are needed to give you the most ammonia?
High pressure and low temperature
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What process is used to make sulfuric acid?
Contact process
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What is made when sulfur dioxide is oxidised?
Sulfur trioxide is made
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What temperature is used to make sulfur trioxide?
compromise temperature of 450 C - to get quite high yield quite quickly
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Why is increasing the pressure unnecessary?
It is really expensive and equilibrium is already on the right
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What catalyst is used to increase the rate of reaction?
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What type of ions do acids produce?
Hydrogen ions, H+
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What type of acids ionise completely in water? Give an example
Strong acids- nitric, hydrochloric, sulfuric
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Why don't weak acids fully ionise?
only small numbers of H+ ions are released
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What kind of reaction is the ionisation of a weak acid?
reversible reactions- sets up equilibrium mixture
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What does the strength (strong/weak) of an acid tell you?
tells you what proportion of the acid molecules ionise in water
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What does the concentration of an acid show you?
it measures how many moles of acid there are in a litre of water.
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Why are strong acids better at conducting electricity?
Ions carry the charge so the more ions there are the better it conducts electricity
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Why is the rate of reaction slower with a weak acid?
Weak acid releases only a few ions when in water. When magnesium is added, there's a low collision frequency.
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What is a precipitation reaction?
when two solutions react together to make an insoluble substance, solution usually turns cloudy
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What is the insoluble substance called?
a precipitate
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Why does the reaction have to be in solution or molten?
Most reactions involve ions. For ions to react they need to move, they can't move in solids
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What is a spectator ion?
Ions that were dissolved in the solution before and after reaction- don't change during
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How can you test for sulfate ions?
add dilute HCl and barium chloride, white precipitate = sulfate compound
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How can you test for chloride, bromide or iodide?
Add dilute nitric acid and lead nitrate, white = chloride, cream = bromide, yellow = iodide
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What type of reaction is used to make insoluble salts?
precipitation reactions
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What ions do you need to make an insoluble salt of lead iodide?
lead ions and iodide ions
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Why does the ions need to be in a solution?
so they can move around
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Why is the reaction not finished when you've mixed the ingredients together?
the salt will be wet and mixed in with other stuff
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Describe stage 1 of the precipitate, filter and dry method
Add 1 spatula of compound 1 to test tube and fill with distilled water. Mix until it has dissolved and repeat for compound 2. Tip tubes into beaker and mix till salt precipitates out
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## Other cards in this set

### Card 2

#### Front

What is molar mass measured in?

#### Back

grams per mole (g/mol)

### Card 3

#### Front

What is the formula to find the number of moles?

### Card 4

#### Front

Define relative atomic mass

### Card 5

#### Front

What is the percentage composition?

#### Back

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