pH Friday, 18 September 2015

Metals with Hydrochloric Acid 2 hydrogen+magnesium chloride  hydrochloric acid +magnesium Mg+HCl  MgCl 2 +H2H2 No reaction  hydrochloric acid +copper Cu+HCl  -- hydrogen+aluminium chloride  hydrochloric acid +aluminium Al+HCl  AlCl 3 +H2H2 hydrogen + calcium chloride  hydrochloric acid +calcium Ca+HCl  CaCl 2 +H2H2 2 2

Acids and Bases 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. Copy

Common acids Stomach acid = hydrochloric acid * Battery acid = sulfuric acid * Lemon juice = citric acid Vinegar = ethanoic acid * Sour pH 1-6 *Commonly used at school Copy

Common neutrals Most tap water Salts such as NaCl, FeCl 3, KNO 3 pH 7 Copy

Common basics Caustic soda = NaOH * Baking soda = NaHCO 3 * Ammonia = NH 3 Bitter Soapy pH 8-14 *Commonly used at school Copy

pH 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. Copy

pH Values pH values 1-6 are acidic (lots of acid) pH values 8-14 are basic (not much acid) pH value 7 is neutral. Copy

Aim Assign the colours of Universal Indicator liquid to the different pH values. Copy

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. SubstanceColour changepH

Questions to answer 1.Which of the tested substances were acids? 2.Which of the tested substances were bases? 3.Which of the tested substances were neutral?

Video to follow…..sound needed

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 Strong acid Weak acid NeutralWeak base Strong base pH Red litmus No change blue Blue litmus RedredNo change Universal indicator RedOrange- yellow GreenGreeny- blue Blue- purple

Neutralisation Friday, 18 September 2015

Acid + Base Salt + Water Neutralisation is a reaction that produces substances with a pH value of 7, neutral. Copy all

Expt Aim: Use universal indicator liquid to prove that you have neutralised the acid and base. Copy Aim

Method 1.Add 1mL HCl to a clean test tube. 2.Add 1mL NaOH to the same test tube. 3.Add 4 drops of universal indicator. 4.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 ftp/client_ftp/ks3/science/acids/index.htmhttp:// ftp/client_ftp/ks3/science/acids/index.htm You can access this web site from home. Good for revision Great virtual expt

Important…. A salt is always made during an neutralisation expt. Not just NaCl (salt on your dinner) but other types of salts too…. Na 2 SO 4 KCl Copy

How do you make these salts? What substances would you react together to make these salts? NaClNa 2 SO 4 CuCl 2 PbSO 4

Answers: NaCl = sodium metal with hydrogen chloride Na 2 SO 4 = sodium metal with hydrogen sulfate CuCl 2 = copper metal with hydrogen chloride PbSO 4 = 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.

Metal oxide + Acid Metal salt + water Copy This is a type of acid – base reaction.

This is also a type of acid – base reaction. Metal hydroxides are bases – eg. NaOH Metal + Acid Metal salt + water hydroxide Copy

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

Method: Use this diagram to carry out this method. test tube hydrochloric acid delivery tube marble Limewater Copy diagram

Written requirement 1.Write a conclusion that explains how you proved that the gas is carbon dioxide. 2.Write a detailed method for this experiment. Here is the picture to remind you. hydrochloric acid delivery tube marble Limewater test tube