C5 - Monitoring and Controlling Chemical Reactions Flashcards
What is concentration?
A measure of how much solute you dissolve in s given volume
What units is concentration measured in?
1) g/dm³
2) mol/dm³
State the formula used to find the concentration from the mass of solute.
mass of solute (g) = concentration (g/dm³) x volume of solution (dm³)
How do you convert from g/dm3 to mol/dm3?
Divide the concentration in g/dm³ by the relative formula mass of the solute
What is a standard solution?
Any solution that you know the concentration of
Why are titrations used?
To find out exactly how much acid is needed to neutralise a given quantity of alkali
How do you carry out a titration?
1) Using a pipette, measure out a set volume of the alkali into a flask. Add a few drops of an indicator - usually phenolphthalein or methyl orange
2) Fill a burette with a standard solution of acid
3) Use the burette to add the acid to the alkali a bit at a time. Swirl the flask regularly. Go slowly ( a drop at a time) when the alkali’s almost netralised
4) The indicator changes colour when all the alkali has been neutralised (this is called the end point)
5) Record the volume of acid used to neutralise the alkali (called the titre)
6) Repeat this process a few times, making sure you gt very similar results each time. You can then take the mean of your results
What colour is phenolphthalein in alkakis and acids?
1) pink in alkalis
2) colourless in acids
What colour is methyl orange in alkalis and acids?
1) yellow in alkalis
2) red in acids
State the formula used to find concentration in mol/dm3.
number of moles (n) = concentration (mol/dm³) x volume of solution (dm³)
What is molar volume?
The volume occupied by one mole of a gas
What units is molar volume measured in?
dm³/mol
State the formula used to calculate molar volume.
number of moles (n) = gas volume (dm³) / molar volume (dm³/mol)
What volume does one mole of any as always occupy at room temperature and pressure (RTP)?
24dm³
What is RTP?
1) 20°C
2) 1 atmosphere
What is yield?
The amount of product you get from a reaction
State the formula used to calculate percentage yield.
percentage yield = (actual yield/theoretical yield) x 100
What is theoretical yield?
The mass of product you would make if all the reactants were converted to products
Why is it important to use reactions with the highest yield possible?
1) to reduce waste
2) to keep costs as low as possible
What is atom economy?
What percentage of the mass of the reactants has been converted into your desired product
State the formula used to calculate atom economy.
atom economy = (total Mr of desired products/total Mr of desired products) x 100
What factors need to be considered in industry?
1) the percentage yield of the reaction
2) the rate of reaction
3) whether the reaction is reversible
What is the rat of a reaction?
How quickly a reaction happens
State the formula used to calculate the rate of reaction.
rate of reaction = amount of reactant used or amount of product formed / time
List some ways that the rate of a reaction can be measured?
1) precipitation
2) change in mass
3) the volume of gas given off
How would you measure the rate of a reaction by recording precipitation?
1) mix the two reactant solutions and put the flask on a piece of paper that has a mark on it
3) observe the mark through the mixture and measure how long it takes for the mark to be obscured. The faster it disappears, the faster the reaction
How would you measure the rate of a reaction by recording change in mass?
1) measure the rate of a reaction that produces a gas using a mass balance
2) the quicker the reading on the balance drops, the faster the reaction
3) you can use your results to plot a graph of change in mass against
How would you measure the rate of a reaction by recording the volume of gas given off?
1) use a gas syringe to measure the volume of gas given off
2) the more gas given off during a set time interval, the faster the reaction
3) you can use your results to plot a graph of gas volume against time elapsed
How does surface area affect reaction rate?
The greater the surface area of the solid reactants, the faster the reaction
How does concentration affect reaction rate?
The higher the concentration, the faster the reaction
