(3.1.2) PC - Amount of Substance

The average mass of an atom of an element relative to 1/12th the mass of one atom of Carbon-12.

The average mass of an atom of an isotope of an element relative to 1/12th the mass of one atom of Carbon-12.

It is the number of particles in a mole, 6.022×10²³

Number of particles = Number of moles x Avogadro constant

Moles = Mass of substance / Mr

Moles = Concentration x Volume

1. The volume of a given mass is not fixed.

2. It changes with temperature and pressure.

Pressure x volume = constant

pV = nRT

Pressure (Pa) x Volume (m³) = Number of moles x Gas Constant (8.31 J K^-1 mol^-1) x Temperature (K)

K = Temperature + 273

A solvent with a solute dissolved in it.

The amount of solute in a solvent in mol dm^-3

All are soluble (aq).

1. They are mostly soluble (aq).

2. Silver and lead chlorides are insoluble (s).

1. They are mostly soluble (aq).

2. Barium and lead sulfates are insoluble (s).

3. Calcium sulfates are both.

1. Potassium carbonates are soluble (aq).

2. Mostly insoluble (s).

3. Sodium carbonates are both.

1. Mostly soluble (aq).

2. Transition metal and aluminium hydroxides and insoluble (s).

1. Write the full balanced equation.

2. Split any dissolved ionic species into ions.

3. Remove any ions that appear on both sides.

It gives the smallest whole number ratio of atoms of each element in a compound.

1. Find the masses of each of the elements in the compound.

2. Work out the number of moles of atoms in each element.

3. Convert the number of moles into a whole number ratio.

It is the actual number of atoms of each element in a compound.

It is the mass of the product that should be formed in a chemical reaction, assuming no chemicals are ‘lost’ in the process.

It is the actual mass of product.

Percentage Yield = (Actual Yield/Theoretical Yield) x 100

It is the amount of reactants that end up as useful in a chemical reaction.

(Mr of desired product/Total Mr of all products/reactants) x 100

1. Makes more efficient use of the raw materials.

2. Its a waste of money if large quantities of the raw materials produce relatively small amounts of the desired product and lots of by-products.

3. Less waste is produced, so the company will have less waste to deal with.

1. Many raw materials are in limited supply, so they should be used as efficiently as possible, so they last longer.

2. Producing less waste is better for the environment as waste chemicals are harmful to the environment.

3. It can be difficult to dispose of waste in a way that minimises their harmful environmental effects.

It is called a neutralisation reaction and produces salt and water.

1. Titrations allow you to find out exactly how much acid is needed to neutralise a measured quantity of alkali (or the other way round).

2. You can use this data to work out the concentration of the alkali.

A standard solution is any solution that you know the exact concentration of.

1. Work out the moles and mass of the solid you are going to dissolve into the water.

2. Pour it into the weighing boat and place it onto the balance and then weigh the required mass of the solid, then tip it into a beaker.

3. Weigh the weighing boat, which may still contain traces of the solid, and subtract the mass of the boat from the mass of the boat and the solid together to find the precise mass of solid you have weighed out.

4. Add distilled water to the beaker and stir until all the solid has dissolved.

5. Tip the solution into a 250cm³ volumetric flask through a funnel.

6. Rinse the beaker, stirring rod and funnel with distilled water and add that to the flask too, to make sure there’s no solute clinging to the beaker or rod.

7. Now top the flask up to the correct volume with more distilled water, making sure the bottom of the meniscus is on the line.

8. Stopper the flask and turn it upside down a few times to make sure it’s mixed well, then calculate the exact concentration of the standard solution.

1. Use a pipette to measure out a set volume of the solution that you want to know the concentration of.

2. Put it in a flask.

3. Add a few drops of an appropriate indicator to the flask.

4. Then fill a burette with a standard solution of the acid and use a funnel to carefully pour the acid into the burette.

5. First do a rough titration by taking an initial reading of how much acid is in the burette, then gradually adding the acid to the alkali, giving the flask a regular swirl and when the colour changes, take a final reading.

6. Then do an accurate titration, by taking an initial reading, then run the acid in to within 2 cm³ of the end point.

7. When you get to this stage, add it dropwise, and wait for a colour change.

8. Find the amount of acid used to neutralise the alkali by subtracting the final reading from the initial reading - the titre.

9. Repeat the titration a few times, until you have at least three results that are concordant.

10. Use the results from each repeat to calculate the mean volume of acid used.

To get an idea where the end point (the point where the alkali is neutralised and the indicator changes colour) is.

1. Pipettes measure a set volume of solution, e.g. 25 cm³.

2. Burettes measure different volumes and let you add a solution drop by drop.

1. Safety goggles.

2. Wear safety gloves.

3. Glassware - be careful so that it doesn’t drop and break.

4. Pour the liquid at eyelevel, so that it doesn’t fall into your eyes.

1. Phenolphthalein

2. Methyl Orange

It makes it easy to see the colour change.

Water could dilute or change the concentration of the substance in the burette.

They are titres that are within 0.1 cm³ of each other.

Some of the reactants may not be mixed in and may be on the side of the flask, so this mixes them in.

1. Increasing the mass.

2. This is because it will require a larger titre, so there will be less uncertainty.

It means that all reagents are able to react.

An air bubble can form.