# C3 Topic 2

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• Created by: Hannah
• Created on: 30-04-13 18:47

A mole is precisely that the number of particles of any element or compund then it will weigh exactly the same number of grams as the relative formula mass. The relative formula mass is always equal to the mass of 1 mole of that element or compound. This number is called Avogadro's number.

Number of moles= mass/relative formula mass

Number of moles of a porduct from a given equation

For a chemical reaction, elements or compounds on the left side of the equation are called reactants and these on the rights are called product.

Steps: 1. Find out how many moles are in that substance.

2.Write out the balanced equation

3. Find the ratio.

4. Work out the mass.

How much is dissolved by evaporating water?

1. Weigh a clean dry evaporating basin. Weigh out the required amount of the solution.

2. Gently heat the basin to evaporate the water.

3. When the water has evaporated, weigh the dry evaporating basin and the solid. Reheat and reweigh the evaporating basin and content until their is not further change in mass.

Solute: A solid that can be dissolved in a particular solvent.

Solvent: The liquid where the solute can be dissolved in e.g. water.

Solution: A dissolved solute withing the solvent.

Concentration can be expressed as the number of moles in a particular volume or the number of grams in a volume.

Number of moles= concentration times by volume divided by 1000.

Concentration: mol/dm3

Volume: cm3

Mole concentration (mol/dm3): mass concentration times by the relative formula mass

Mass concentration (g/dm3): mole concentration times by the relative formula mass.

Titration

A titration is a procedure used to identify the concentration of a solution by reacting it with a solution of a known concentration and measuring the volume required for a complete reaction. It is a neutralisation reaction where hydrogen ions from the acid react with the OH ions in the soluble base (alkali).

Methods:

1. Set up the burette in a clamp stand and use a filter funnel to place the unknown concentration of the hydrochloric or any acid into the burette. Once done, remove the filter funnel.

2. Using a pipette and a pipette filler, measure out 25 cm3 of soduim carbonate and then transfer it to a 250cm3 conical flask.

3. Add a few drops of phenolphthalein (used for a weak acid and a strong alkali). Other indicators can be used e,g. Methyl Orange (strong acid and a weak alkali), but if both the acid and the alkali is strong then any acid base indicator can be used. The phenolphthalein turns the…