Chapter 8 Acids and Alkalis

It is a way of measuring the acidity or alkalinity of a solution

A substance that changes color based on the pH9

are acids that have been mixed with a lot of water before putting them out for use. Their bottles are labelled with a hazard symbol

Methyl orange Phenophthalein Litmus

Yellow in alkaline Red in acids

Pink in alkaline Colorless in acidic

Blue alkaline Red Acidic

Hydrochloric acid - HCL Nitric acid - HNO3 Sulfuric acid - H2SO4

Amount Dissolved Concentration=—————————————– Volume of solution

1000

By the concentration of hydrogen ions in the solution.

Strong acids and Weak acids

their molecules dissociate (break up) completely into ions when dissolved in water and produce a high concentration of hydrogen ions

its concentration - concentrated/dilute If its weak or strong

Bases are substances that neutralize acids to form a salt and water ONLY.

Solid (s) Liquid (l) Gas (g) Aqueous (aq)

Safety filler pipette Flask Beaker Burrette Stand Tap

Fill the burette with acid.  Record the initial volume of acid in the burette.  Measure alkali into a conical flask using a pipette and pipette filler.  Add a few drops of indicator in the conical flask.  Add acid from the burette by opening the tap.  Continue to add acid until colour change occurs (end-point reached)  Record the final volume of acid in the burette.  Calculate the titre (by subtracting final-initial volume)  Repeat the titration until concordant titres are obtained (values that agree within ± 0.20 cm3 ).  Calculate the average volume(titre) of acid needed to neutralise the alkali.  Use the burette to add the average volume of acid without the indicator.  Add salt solution to an evaporating basin  Heat to evaporate some of the water and allow the solution to cool down so that crystals form.  Filter excess liquid  Leave the crystals to dry in a warm place/warm oven

• Add the solution from the burette drop by drop near the end-point- Stop the titration when the indicator changes colour permanently- Repeat the titration until we get two concordant results, two titres that agree within 0.20 cm3 and find an average titre value

To test for hydrogen, place a lighted splint in the tube of gas. If a squeaky pop is heard, the gas is hydrogen.

Bubble the Gas through limewater, if the limewater turns from colorless to milky/cloudy

When a reaction causes a insoluble precipitate to form

• Mix the solutions in a beaker to form a precipitate • Filter the mixture • Rinse the beaker with a little distilled water and pour this through the funnel. • Pour a little distilled water over the precipitate in the funnel. • Carefully remove the filter paper containing the precipitate and dry it in a warm oven/leave it to dry in the air/dry on filter paper or tissue

• write down the full equation for the reaction and balance it • for dissolved ionic substances (aq), write the ions separately, keeping the state symbol next to each ion. • for all liquids, gases and solids (whether ionic or not), rewrite the full formula. • cross out all the ‘spectator’ ions (the ions that do not take part in a reaction) • Write the ‘net’ ionic equation