chem - chemical changes (3)

• Acids produce H+ ions in aqueous solutions.
• Alkalis produce OH- ions in aqueous solutions.
• In an electrochemical experiment, the Cu2+ ions deposited as Cu at the cathode from the solution are replaced by Cu2+ ions from the anode, meaning the concentration of Cu2+ ions in the solution remains constant.
• The PH scale measures the acidity/alkalinity of a solution and can be measured using universal indicator.
• pH 7 is neutral.
• pH 7 is acidic.
• pH 7 is alkaline.
• Phenolphthalein changes colour from Alkaline to pink in acidic conditions and from colourless to pink in alkaline conditions.
• Methyl orange changes colour from Alkaline to yellow in acidic conditions and from red to yellow in alkaline conditions.
• Litmus solution changes colour from Alkaline to blue in acidic conditions and from red to blue in alkaline conditions.
• Blue litmus paper changes colour from blue in acidic conditions and stays blue in alkaline conditions.
• Red litmus paper changes colour from red in alkaline conditions and stays red in acidic conditions.
• The higher the concentration of hydrogen ions in an acidic solution, the lower the pH.
• The higher the concentration of hydroxide ions in an alkaline solution, the higher the pH.
• As hydrogen ion concentration in a solution increases by a factor of 10, the pH decreases by 1.
• Core Practical: Investigate the change in pH on adding powdered calcium hydroxide or calcium oxide to a fixed volume of dilute hydrochloric acid.
• Concentrated means a larger amount of substance in a given volume of a solution.
• Dilute means a lesser amount of substance in a given volume of a solution.
• Strong acid fully dissociates in aqueous solution, releasing a large number of H+ ions, resulting in a low pH.
• Examples of strong acids include hydrochloric, nitric and sulfuric acids.
• Weak acid partially dissociates in aqueous solution, releasing a smaller number of H+ ions, resulting in a higher pH.
• Examples of weak acids include ethanoic, citric and carbonic acids.
• The stronger an acid, the greater the dissociation, the more H+ ions released, the lower the pH.
• Examples of alkalis are soluble metal hydroxides.
• Neutralisation reaction is a reaction between an acid and a base.
• Soluble salts are prepared from an acid and a soluble reactant, requiring the use of titration to measure the exact amount of volumes that react.
• At the cathode (-), the ions in water (OH- and H+) are discharged.
• The titre, or the volume of alkali, is the difference between the first and second readings on the burette.
• The exact amount of acid has been added to the soluble reactant, resulting in a leftover solution that is only salt and water, no acid or alkali, as they have been completely neutralised.
• Add acid from the burette to the alkali until the endpoint is reached, as indicated by the indicator.
• The method used to prepare a pure, dry sample of an insoluble salt involves mixing the two solutions needed to form the salt, filtering the mixture using filter paper, washing the salt using distilled water, and leaving the salt to dry on filter paper.
• Electrolysis is the process where electrical energy, from a direct current supply, decomposes electrolytes.
• To prepare a pure, dry salt, you warm the salt solution to evaporate the water, causing crystals to form.
• Any insoluble salts formed will precipitate, as any soluble salts will remain in solution.
• Ions are discharged at the electrodes producing elements.
• During electrolysis, positively charged ions (cations) move to the negative electrode (cathode), and negatively charged ions (anions) move to the positive electrode (anode).
• When you have an ionic solution, it will contain the ions that make up the ionic compound, and the ions in water (OH- and H+).
• Use a 25cm3 pipette to add 25cm3 of alkali into a conical flask, drawing the alkali into the pipette.
• To carry out a titration, first wash the burette using the acid and then water, then fill it to 100cm3 with acid, positioning the base of the meniscus on the 100cm3 line.
• Electrolytes are ionic compounds in the molten state or dissolved in water.