acids and alkalis can you think of some common, household acids and alkalis? acidsalkalis vinegar...
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Acids and Alkalis
Can you think of some common, household acids and alkalis?
Acids AlkalisVinegarFruit Juice
Baking SodaIndigestion PowderOven Cleaner In Toothpaste
USES:
WASP STING IS ALKALINE IT IS NEUTRALISED BY VINEGAR AN ACID
•LIME AN ALAKLI IS ADDED TO ACIDIC SOIL
•VINEGAR IS USED AS A PRESERVATIVE
•AMMONIA IS USED AS A HOUSEHOLD CLEANER
COMMON LAB
ACIDS
ACID
FORMULA
COMMON LAB
ALKALIS
ALKALI
FORMULA
HYDROCHLORIC
(hydrogen chloride)
SODIUM
HYDROXIDE
SULPHURIC
(hydrogen sulphate)
POTASSIUM
HYDROXIDE
ETHANOIC AMMONIUM
HYDROXIDE
NITRIC
(hydrogen nitrate)
LITHIUM
HYDROXIDE
HCl(aq)
H2SO4(aq)
CH3COOH(aq)
HNO3(aq)
NaOH(aq)
KOH(aq)
NH4OH(aq)
LiOH(aq)
Laboratory Acids and Alkalis
Can you work out the FORMULAS from the name?You MUST remember the FORMULAS of these!!!
INDICATORS SUBSTANCES THAT CHANGE COLOUR WITH CHANGING pH
pH scale Used to measure acidity or alkalinity of SOLUTIONS
Scale runs from under 0 to above 14
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14
Neutral 7 only
Anything under 7 is acidic
Anything above 7 is alkaline
Testing for Acids and Alkalis
The pH scale is based on the pH of pure water being =7When we measure the pH of a solution, we are measuring to what degree a solute has changed the pH of waterUniversal indicator to cover the whole range
Red pink orange green blue/green blue purple
Strong acid weak acid neutral weak alkali strong alkali
The pH Scale
1. Prepare a test solution
2. Add universal indicator (or drop onto pH paper)
3. Allow colour to develop
4. Compare with standard colour chart
Rules when testing pH
Testing for pH
Name of Solution pH Acid / Alkali / Acid
Follow the rules for “Testing pH” and test 5 different solutions
Non-metal Oxides
Name of oxide
Appearance of oxide
Universal indicator
Sulphur dioxide
Carbon dioxide
Oxides of nitrogen
Hydrogen oxide
Colourless, pungent gas
Colourless, odourless gas
Colourless or brownPungent gas
Colourless and odourless
RED
RED
RED
GREEN
Non-metal Oxides
Oxides of carbon and sulphur are prepared by burning sulphur and carbon in air.
Oxides of nitrogen are prepared by sparking air
RULE:Oxides of NON-METALS make ACIDIC SOLUTIONS
EXCEPTION:Oxide of HYDROGEN is NEUTRAL (water)
Starter question
Which of the following substances when dissolved in water would produce an acidic solution
1)Magnesium oxide
2)Hydrogen oxide
3)Ammonium hydroxide
4)Phosphorus oxide
Answer 4)
Explanation the rule is soluble non-metal oxides make acidic solutions
Metal Oxides
Experiment 1:1. Add a tiny quantity of CALCIUM OXIDE into a dimple tray2. Add a few drops of WATER3. Test the pH of the solution with UNIVERSAL INDICATOR
Name of OxideAppearance
of Oxide pH of solution
Metal Oxides
When a metal oxide reacts with water, the METAL HYDROXIDE is formed
eg Sodium oxide reacts and forms SODIUM HYDROXIDE
Na2O (s) + H2O (l) 2NaOH (aq)
Making Metal Oxides
Experiment 2:1. Ignite a little of MAGNESIUM RIBBON2. Allow magnesium to burn and form MAGNESIUM OXIDE3. Drop the white ash onto a dimple tray4. Check the pH of the SOLUTION
Write the balanced equation for making MAGNESIUM OXIDE:
RULE:Oxides of METALS make ALKALINE SOLUTIONS
HOWEVER:Like non-metal oxides, they must be SOLUBLE in water for them to change the pH of water
Metal Oxides
Insoluble Oxides and Hydroxides
Experiment:1. Add a small quantity of copper (II) oxide to a test-tube2. Add approx 5ml of water3. Shake the tube and try and dissolve the solid4. Use a dropper to transfer a sample of the clear liquid to the spotting tile5. Check the pH with Universal Indicator
Some metal oxides (such as copper (II) oxide) are INSOLUBLE in water, as these don’t dissolve, they CANNOT alter the pH of water.
Ammonia
NH3(g) is ammonia gas
(covalently bonded compound)
When dissolved in water ammonium hydroxide is formedThe equation for the reaction when ammonia gas dissolves in water to form ammonium hydroxide
NH3(g) + H2O NH4OH(aq)
THIS SOLUBLE HYDROXIDE MUST BE AN ALKALI
Fountain Experiment
Starter Question
Put these four oxides in order of the one which will give the HIGHEST pH to the one that will give the LOWEST pH:
Hydrogen oxideMagnesium oxideCarbon dioxideCopper (II) oxide
(The flow-chart from last day will help you!!)
Acids
Name of acid Formula
Hydrochloric
Sulphuric
Nitric
Ethanoic
HCl (aq)
H2SO4 (aq)
HNO3 (aq)
CH3COOH (aq)
Which element is COMMON to all acids?
AcidsLooking at the formula of the acids – which type of BONDING would you expect?
Think……..Would you expect it to CONDUCT ELECTRICITY??
Experiment:1. Set up the circuit shown2. Use HYDROCHLORIC ACID and determine if it conducts3. Repeat with both SULPHURIC and NITRIC ACIDS
Acids
Acids are:Compounds which dissolve in water to give a pH less than 7
All acids contain the element HYDROGEN
Acid solutions are able to conduct electricity
Electrolysis of Acids
1. Set up apparatus as shown – using DIRECT CURRENT (DC)
2. Upturn a test-tube FULL OF WATER over each electrode
3. Turn on the power supply – set to 6V
4. Collect a tube-full of gas from one electrode.
5. Keep the tube inverted to prevent losing any gas.
6. Test the tube for HYDROGEN GAS.
7. Repeat for other electrode.
Experiment:
Electrolysis of Acids
Draw a labelled diagram of the apparatus used last day
Underneath your diagram copy the note below:Electrolysis is the breaking down of a compound using electricity.
When acids undergo electrolysis, HYDROGEN GAS is formed at the negative electrode.
Why does hydrogen form?
+ve -ve
H+
e-
H+
H+
H+H+
H+
e-e-
e-
HHH
Although acids are made up of non-metalsthey exist as IONS.
The hydrogen ions (H+) pick up electrons from the negative electrode and producehydrogen gas.
AlkalisCan you now put these into a table?Can you get their formula?Can you work out the IONS present?
Name of Alkali Formula Ions
The pH scale - dilutionExperiment:• Measure 10ml of acid into test-tube (A) – test pH
• Take 1ml of A and dilute with 9ml of water (B) – test pH
• Take 1ml of B and dilute with 9ml of water (C) – test pH
• Repeat for test-tubes D, E and F – testing pH of each
Results:Test-tube pH
The pH scale - dilution
Answer these questions in your NOTES jotter.Write in sentences – these will be your notes for this activity!!
• What happens to the ACIDITY as the ACID is diluted?• What is happening to the concentration of H (aq) ions?• What happens to the pH as the ACID is diluted?
+
The pH scale - dilutionExperiment (This is a repeat of yesterday’s using ALKALI):• Measure 10ml of ALKALI into test-tube (A) – test pH
• Take 1ml of A and dilute with 9ml of water (B) – test pH
• Take 1ml of B and dilute with 9ml of water (C) – test pH
• Repeat for test-tubes D, E and F – testing pH of each
Results:Test-tube pH
The pH scale - dilution
Answer these questions in your NOTES jotter.Write in sentences – these will be your notes for this activity!!
• What happens to the ALKALINITY as the ALKALI is diluted?• What happens to the concentration of OH (aq) ions?• What happens to the pH as the ALKALI is diluted?
-
H+(aq) and OH-
(aq) Ions
NEUTRAL solutions contain an EQUAL concentration of H(aq) and OH(aq) ions.
ACIDIC solutions contain a GREATER concentration of H(aq) than OH(aq) ions.
ALKALINE solutions contain a GREATER concentration of OH(aq)
than H(aq) ions.
+
+
+
-
-
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