pH Monday, 1 September 2014
Metals with Hydrochloric Acid aluminium copper magnesium + + + hydrochloric acid hydrochloric acid hydrochloric acid calcium + hydrochloric acid magnesium chloride + hydrogen 2 No reaction 2 aluminium chloride + hydrogen 2 2 3 6 calcium chloride + hydrogen 2
Acids and Bases Copy Acid • When acids dissolve in water they release Hydrogen ions, and these make the solution acidic. Base • Bases have the opposite chemical action to acids. They neutralise acids by removing the Hydrogen ion.
Common acids Copy • Stomach acid = hydrochloric acid * • Battery acid = sulfuric acid * • Lemon juice = citric acid • Vinegar = ethanoic acid * Sour pH 1-6 *Commonly used at school
Common neutrals Copy • Most tap water • Salts such as NaCl, FeCl3, KNO3 pH 7
Common basics Copy • Caustic soda = NaOH * • Baking soda = NaHCO3 * • Ammonia = NH3 Bitter Soapy pH 8-14 *Commonly used at school
pH Copy • The pH is a value given to a solution and indicates the acidity of the solution. • pH is a measure of the amount of Hydrogen ions in the solution. • The lower the pH value the more hydrogen ions are in the solution.
pH Values Copy • pH values 1-6 are acidic (lots of acid) • pH values 8-14 are basic (not much acid) • pH value 7 is neutral.
Aim Copy • Assign the colours of Universal Indicator liquid to the different pH values.
Expt • Add 4 drops of the universal indicator to each substance. • Record the substance and the observed colour in a table. • Calculate the pH of each substance.
Questions to answer • Which of the tested substances were acids? • Which of the tested substances were bases? • Which of the tested substances were neutral?
Indicator Summary For NCEA you need to know…. • Red litmus turns blue in base • Blue litmus turns red in acid • Universal indicator is a range of colours… • Red orange and yellow are acids • Green is neutral • Green/Blue blue purple are bases
Indicator Table Copy
Neutralisation Monday, 1 September 2014
Acid + Base Salt + Water Copy all • Neutralisation is a reaction that produces substances with a pH value of 7, neutral.
Expt Copy Aim Aim: Use universal indicator liquid to prove that you have neutralised the acid and base.
Method • Add 1mL HCl to a clean test tube. • Add 1mL NaOH to the same test tube. • Add 4 drops of universal indicator. • Adjust the amounts of HCl or NaOH until you reach the neutral pH of 7. What colour are you aiming for???? Green HINT: Precision and patience
Online expt • http://www.bgfl.org/bgfl/custom/resources_ftp/client_ftp/ks3/science/acids/index.htm • You can access this web site from home. • Good for revision • Great virtual expt
Important…. Copy • A salt is always made during an neutralisation expt. • Not just NaCl (salt on your dinner) but other types of salts too…. • Na2SO4 KCl
How do you make these salts? What substances would you react together to make these salts? NaCl Na2SO4 CuCl2 PbSO4
Answers: NaCl = sodium metal with hydrogen chloride Na2SO4 = sodium metal with hydrogen sulfate CuCl2 = copper metal with hydrogen chloride PbSO4 = lead metal with hydrogen sulfate
Examples of neutralisation • Bee stings are acidic. They can be neutralised using baking powder, which contains sodium hydrogen carbonate. • Farmers use lime (calcium oxide) to neutralise acid soils. • Your stomach contains hydrochloric acid, and too much of this causes indigestion. Antacid tablets contain bases such as magnesium hydroxide and magnesium carbonate to neutralise the extra acid.
Copy Metal oxide + Acid Metal salt + water • This is a type of acid – base reaction.
Copy Metal + Acid Metal salt + waterhydroxide • This is also a type of acid – base reaction. • Metal hydroxides are bases – eg. NaOH
Acid + Metal Metal + Carbon + Water carbonate salt dioxide Copy
Acid + Metal hydrogen Metal + Carbon + Water carbonate salt dioxide Copy
Hokey Pokey When powdered baking soda is stirred into molten sugar, heat causes the soda react, releasing bubbles of carbon dioxide gas.
Expt Aim: Prove that the gas produced by the acid-carbonate reaction is carbon dioxide. Copy aim
delivery tube marble Limewater hydrochloric acid Method: Use this diagram to carry out this method. Copy diagram test tube
delivery tube marble Limewater hydrochloric acid Written requirement • Write a conclusion that explains how you proved that the gas is carbon dioxide. • Write a detailedmethod for this experiment. Here is the picture to remind you. test tube