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pHpHWednesday, 19 April 2023
Metals with Hydrochloric Acid
2
hydrogen+magnesium chloride
hydrochloric acid
+magnesium
Mg + HCl MgCl2 + H2
No reactionhydrochloric acid
+copper
Cu + HCl - -
hydrogen+aluminium chloride
hydrochloric acid
+aluminium
Al + HCl AlCl3 + H2
hydrogen+calcium chloride
hydrochloric acid
+calcium
362 2
Ca + HCl CaCl2 + H22
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.
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Common acids
• Stomach acid = hydrochloric acid *• Battery acid = sulfuric acid *• Lemon juice = citric acid• Vinegar = ethanoic acid *
SourpH 1-6 *Commonly used at
school
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Common neutrals
• Most tap water
• Salts such as NaCl, FeCl3, KNO3
pH 7
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Common basics
• Caustic soda = NaOH *
• Baking soda = NaHCO3 *
• Ammonia = NH3
Bitter
Soapy
pH 8-14
*Commonly used at school
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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.
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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.
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Aim
• Assign the colours of Universal Indicator liquid to the different pH values.
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ExptExpt
• 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.
Substance Colour change pH
Questions to answerQuestions 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 TableCopy
Strong acid
Weak acid
Neutral Weak base
Strong base
pH 1-3 4-6 7 8-10 11-14
Red litmus
No change
No change
No change
blue blue
Blue litmus
Red red No change
No change
No change
Universal indicator
Red Orange-yellow
Green Greeny-blue
Blue-purple
NeutralisatioNeutralisationn
Wednesday, 19 April 2023
Acid + Base Salt + WaterAcid + Base Salt + Water
• Neutralisation is a reaction that produces substances with a pH value of 7, neutral.
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ExptExpt
Aim:
Use universal indicator liquid to prove that you have neutralised the acid and base.
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MethodMethod1. 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????
GreenHINT:
Precision and patience
Online exptOnline 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….Important….
• A salt is always made during an neutralisation expt.
• Not just NaCl (salt on your dinner) but other types of salts too….
• Na2SO4 KCl
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How do you make these salts?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 neutralisationExamples 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
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•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 + waterhydroxide
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Acid + Metal Metal + Carbon + Water carbonate salt dioxide
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Acid + Metal hydrogen Metal + Carbon + Water
carbonate salt dioxide
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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
marbleLimewater
Copy diagram
Written requirement1. 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
marbleLimewater
test tube
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