Quantitative Chemistry

Limiting Reagent

Concentration

Conservation of Mass

Relative Formula Mass

Mass is never lost or gained in chemical reactions.

Mass is conserved, the total of the reactants would equal the

In practice, some product may be lost when it is removed from the reaction mixture

some of the reactants may react in an unexpected way.

The limiting reagent that still remains would be in a smaller amount as a lot of reacted with the initial reagent

Once a reaction stops, and one of the reactants is completely used up, then it is the limiting reagent

Uncertainties

Take an average of results

Afterwards, to the uncertainty divide the range by half

Examples:

24 + 24.5 + 23.5 + 25 + 23

Divide the result by 5

uncertainty = (25 - 23)/2

24 cm^3 +/- 1 cm^3

Used to calculate moles, adding the relative atomic mass of all the elements in an equation

i.e H20 = 1 + 1 + 16 = 18

The symbol is Mr

Concentration is the amount of substance (usually in grams) that is present in a given area (usually in liters)

This means that the unit of measure would be g/l or in other cases mol/liter

The formula for this would be moles divided by volume

Moles

Moles is the unit given to measure the quantity of a substance or element in an equation (i.e one mole of magnesium)

Moles can be used to find out and can be used with many things such as mass (g, kg), volume of gas (dm^3) and representative particles

To find the representative particles you must divide avogadro's number by the number of moles

i.e 6.02*10^23 divided by 2.00 mol

To find the mass you must divide the Mr by the number of moles

To find the volume of gas (STP) you must divide 22.4 L by the number of moles

Reacting mass calculations

Write a balance chemical equation

Work out the relative formula mass (Mr) of each substance you're trying to find the mass of

Multiply the Mr for each substance you want to find the mass of by the number of moles.

Work out the ratio of reactant to product

Multiply and substitute the ratio by the substances which have known mass

By doing this, you should have found the mass of the substance you want.

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