Amount of substance

What is the value of Avogadro’s number (L)?

6.022 × 10²³

Give an equation for calculating the number of particles of a substance using Avogadro’s number and moles.

Number of particles = Avogadro’s number x number of moles

Give an equation for calculating the number of moles using mass and Mr.

Number of moles = mass (g) / Mr

Give an equation that works out the number of moles in a solution when you know it’s volume and concentration.

Number of moles = concentration (mol dm^-3) x volume (dm³)

How do you convert from cm³ to dm³ and vice versa?

Divide by 1000 to get from cm³ to dm³, multiply by 1000 to get from dm³ to cm³.

What is relative atomic mass (Ar)?

The weighted average mass of an atom of an element taking into account it’s naturally occurring isotopes, relative to 1/12 the mass of a carbon-12 atom.

What is relative molecular mass (Mr)?

The weighted average mass of a molecule of a compound taking into account it’s naturally occurring isotopes, relative to 1/12 the mass of a carbon-12 atom.

What equation do you use to work out the number of moles in a specific volume of gas?

The ideal gas equation.

Give the ideal gas equation and all the units involved in it.

pV = nRT

(pressure x volume) = (number of moles x gas constant x temperature)

p = Pa

V = m³

n = mol

R = JK^-1 mol^-1

T = K

What are the standard conditions for temperature and pressure?

298K, 100kPa

How do you convert from m to dm and then from dm to cm?

m to dm = x10

dm to cm = x10

(m to cm = x100)

How many dm are in 1m?

10dm.

How many cm are in 1dm?

10cm.

How do you convert from m² to dm² and then from dm² to cm²?

m² to dm² = x100

dm² to cm² = x100

(m² to cm² = x10,000)

How do you convert from m³ to dm³ then from dm³ to cm³?

m³ to dm³ = x1000

dm³ to cm³ = x1000

(m³ to cm³ = x1,000,000)

True or false? Balanced symbol equations can be used to work out theoretical masses.

True.

What is the general idea of a titration?

Working out the concentration of a solution of which you only know the volume with another solution of which you know both the concentration and the volume.

What is the empirical formula?

The simplest whole number ratio of atoms of each element in a compound.

Talk me through how to work out the empirical formula of a compound using the percentages of each element in the compound.

1) Write out all the elements involved in the compound.

2) Write out the percentages of each element in the compound as a mass in grams.

3) Divide these masses by the relative atomic mass of each element to get the number of moles of each element in the compound, n = m / Ar

4) Divide all the numbers of moles by the smallest number of moles, this will give you the simplest whole number ratio (the empirical formula of the compound).

What is the molecular formula?

A formula that shows the actual number of atoms of each element in a compound.

Talk me through how to work out the molecular formula of a compound when you know it’s empirical formula.

1) Divide the molecular mass of each element by the relative mass of the empirical formula of the compound, this gives you the number of atoms of each element in the compound.

2) Assemble these values to get the molecular formula.

Talk me through how to work out the empirical formula of a product when you know the masses of the reactants.

1) Divide the masses of the reactants by their relative molecular masses to get the number of moles of each reactant, n = m / Mr

2) Know that the reactant contains however many moles (indicated by small number) of an element in it and therefore the product must contain the new number of moles of that element in it (do this for both reactants).

3) Divide these mole values by the smallest mole value obtained to get the simplest ratio of the elements in the product.

4) Assemble these values to get the empirical formula of the compound.

Give an equation for calculating % yield with actual yield and theoretical yield.

% yield = (actual yield / theoretical yield) x 100

What does the theoretical yield of a product assume?

That all of the reactants completely react.

True or false? Yield of a product is never 100%.

True.

What does the atom economy of a reaction tell us?

How efficient a reaction is.

Give the equation for calculating % atom economy.

% atom economy = (molecular mass of desired product / sum of molecular masses of all reactants) x 100

Why are reactions with high atom economy values more sustainable?

The raw materials are used more efficiently.

Why are reactions with high atom economy values better for the environment?

Less waste is produced.

Why are reactions with a higher atom economy value economically better?

Less by-products are produced meaning less time and energy has to be spent separating the desired products from the by-products.

Give the equation for percentage atom economy.

Give an equation for calculating % purity.