# Chemistry

Chemistry revision cards for topic 3

## Tests for Acids and Alkalis

An Indicator is a dye that changes colour

Litmus: Blue litmus paper turns red if lots of H+(aq) ions are present (acids).

Red Litmus paper turns blue if lots of OH-(aq) ions are present

Phenolphthalein: Is pink in alkalis but colourless in acids

Methyl orange: Is yellow in alkalis but  red in acids

Add metal to the substance: If it is an acid then Hydrogen atoms will be given off (squeeky pop test)

Heat the Substance with an Ammonium salt: Hydroxides give off ammonia gas when heated gently with an Ammonium compound (Bad smell test)

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## Measuring Amounts - Moles

One mole is The exact number of atoms or molecules of any element or compound that make the mass in grams weigh the exact same number as the relative atomic mass.

Number of moles =     Mass in grams                                                                                                            Relative Formula Mass

This is important so that chemists in industry can calculate exactly how much reactant they need to use to produce the desired amount of product.

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## Calculating Volumes

Avagadro's Law: One mole of any gas occupies exactly 24 dm3 (24,000 cm3) at room temperature and pressure (25oC and 1 atmosphere).

Volume of a gas(in dm3)= Mass of the gas   X24                                                                                                         Mr of the gas

You can use this equation to convert masses into Volumes

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## Quantitative Chemistry and Solutions

Concentration is the amount of any substance dissolved in the solution per unit of volume.

Mass concentration(g per dm3) =   Mass (g)                                                                                                                        Volume (dm3)

Mole concentration(m per dm3) = Number of Moles/Voulme (dm3)

You can also convert them: Mass concentration = Mole concentration X Mr

Evaporating and titrations are the main experiments for determining Concentrations

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## Titrations

Titrations allow you to find out exactly how much acid it takes to neutralise a quantity of Alkali.

1) Using a pipette add an exact quantity of Alkali to a conical flask along with two or three drops of indicator (usually Phenolphthalein)

2) Fill a burette with acid (below eye level for safety)

3) Add the acid to the conical flask a bit at a time swirling the conical flask regularly

4) Record the volume of the acid required. Do one rough and several accurate ones

Calculation: 1) calculate the number of moles of the known substance (the Alkali)

2) Write out and balance the equations and account for this in the number of moles

3) Then use the concentration calculate to calclate the concentration of the acid

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## Water

Drinking water comes from resevoirs, resevoir water flows in from rivers and groundwater.

Water is filtered at water treatment plants. Chemicals are added to remove bacteria and the water is then filtered again.

To monitor quality the water companies take samples of water and test them.

Water dissolves most ionic compounds. Water molecules surround the ions, attracting them more than they attract each other, so the solid structure falls apart.

In agriculature water is needed for irrigation

In industry water is used as a raw material, as a solvent, and for cooling. For example power stations use huge quatities of water for cooling.

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