Presentation on theme: "Acids and Alkalis Can you think of some common, household acids and alkalis? AcidsAlkalis Vinegar Fruit Juice Baking Soda Indigestion Powder Oven Cleaner."— Presentation transcript:
Acids and Alkalis Can you think of some common, household acids and alkalis? AcidsAlkalis Vinegar Fruit Juice Baking Soda Indigestion Powder Oven 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 ETHANOICAMMONIUM HYDROXIDE NITRIC (hydrogen nitrate) LITHIUM HYDROXIDE HCl(aq) H 2 SO 4(aq) CH 3 COOH(aq) HNO 3(aq) NaOH(aq) KOH(aq) NH 4 OH(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 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 =7 When we measure the pH of a solution, we are measuring to what degree a solute has changed the pH of water Universal 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 SolutionpHAcid / 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 brown Pungent gas Colourless and odourless 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 tray 2. Add a few drops of WATER 3. Test the pH of the solution with UNIVERSAL INDICATOR Name of Oxide Appearance 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 Na 2 O (s) + H 2 O (l) 2NaOH (aq)
Making Metal Oxides Experiment 2: 1. Ignite a little of MAGNESIUM RIBBON 2. Allow magnesium to burn and form MAGNESIUM OXIDE 3. Drop the white ash onto a dimple tray 4. 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
Today’s plan: Looking at INSOLUBLE METAL OXIDES AMMONIA GAS and its pH THURSDAY 8th OCTOBER
Insoluble Oxides and Hydroxides Experiment: 1. Add a small quantity of copper (II) oxide to a test-tube 2. Add approx 5ml of water 3. Shake the tube and try and dissolve the solid 4. Use a dropper to transfer a sample of the clear liquid to the spotting tile 5. 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 NH 3(g) is ammonia gas(covalently bonded compound) When dissolved in water ammonium hydroxide is formed The equation for the reaction when ammonia gas dissolves in water to form ammonium hydroxide NH 3 (g) + H 2 O NH 4 OH(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 oxide Magnesium oxide Carbon dioxide Copper (II) oxide (The flow-chart from last day will help you!!)
Acids Name of acidFormula Hydrochloric Sulphuric Nitric Ethanoic HCl (aq) H 2 SO 4 (aq) HNO 3 (aq) CH 3 COOH (aq) Which element is COMMON to all acids?
Acids Looking 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 shown 2. Use HYDROCHLORIC ACID and determine if it conducts 3. 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+H+ e-e- H+H+ H+H+ H+H+ H+H+ H+H+ e-e- e-e- e-e- H H H Although acids are made up of non-metals they exist as IONS. The hydrogen ions (H + ) pick up electrons from the negative electrode and produce hydrogen gas.
Ions in Acids
Alkalis Think!! What common alkalis have you come across before?? How many can you name??
Alkalis Can you now put these into a table? Can you get their formula? Can you work out the IONS present?
The pH scale - dilution Experiment: 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-tubepH
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 - dilution Experiment (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-tubepH
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
Starter Question Have a THINK about the answer to these questions and be ready to answer them……… What are the concentration of hydrogen and hydroxide ions in a 1.NEUTRAL solution? 2.ALKALINE solution? 3.ACID solution?
Water The chemical name for water is HYDROGEN OXIDE The expected bonding is From this bonding COVALENT BONDING WATER SHOULDN’T CONDUCT ELECTRICITY Water DOES conduct electricity For water to conduct, there MUST be charged particles The charged particles present are IONS
Water A beaker of water
Water Water molecules split up into ions: However this process is REVERSIBLE ie at the same time as ions are forming, ions are reforming into water molecules The rate at which the water molecules DISSOCIATE (split up) is equal to the rate at which ions react to form molecules. This means that the CONCENTRATION of molecules and ions is CONSTANT.
Valency Rule Example 1: Write the formula for phosphorous fluoride. Step 1Write the chemical symbols for each element Step 2Identify their valencies from their group number Step 3Cross over the valencies Step 4Cancel any common factor Step 5Omit ‘1’ if present Writing formulae - REVISION
MASS RFMn The relationship between mass, number of moles (n) and relative formula mass (RFM) can be found by using the triangle: Using the triangle: n = MASS RFM MASS = n x RFM RFM = MASS n Moles to Mass - REVISION
Concentration & Making Solutions 1.Calculate the MASS of ONE MOLE of Sodium Chloride 2.Weigh out this quantity accurately 3.Transfer this to a beaker of containing approx 150ml of water 4.Transfer the solution to a 1 litre standard flask 5.Rinse out the beaker and add the washing to the flask 6.Now add water to JUST BELOW the mark on the flask 7.Use a dropper to add water EXACTLY to the mark You have added 1 mole of sodium chloride to 1 litre of water, you have made a 1 mol l -1 (mole per litre) solution!
Concentration & Making Solutions The concentration of an aqueous solution is the amount of SOLUTE dissolved in a certain volume of water. In chemistry, the concentration is expressed as: moles of solute dissolved in 1 litre of water or mol l -1 eg a solution labelled as 1 mol l -1 contains one mole of solute in 1 litre
n V C The relationship between number of moles (n), volume (V) and concentration (C) can be found by using the triangle: Using the triangle: C = n V n = C x V V = n C Moles, Volume & Concentration
Concentration Calculations Example: Calculate the number of moles of NaCl in 500ml of a solution which has a concentration of 0.1 mol l -1 :
Difficult example Example: Calculate the concentration of four grams of sodium hydroxide in 600ml water:
Concentration Calculations In your groups work through Exercise 3.3 in your CLASSWORK jotters
Combining both triangles Example: Calculate the mass of NaCl required to make 500ml of a 0.1 mol l -1 solution:
Past Paper Examples
Conductivity of Concentrated Acids / Alkalis Concentration – a measure of the quantity of solute dissolved in a solution For acids (or ANY ionic solution) – greater concentration means more IONS in solution What was moving when IONIC SUBSTANCES conducted? What will happen to the conductivity when the CONCETRATION INCREASES?
Conductivity of Concentrated Acids / Alkalis Acid ConcentrationConductivity An INCREASE in the CONCENTRATION of an acid (or alkali) solution results in an INCREASE in CONDUCTIVITY as there is an INCREASE in the number of IONS in the solution.
Conductivity of Concentrated Acids / Alkalis CONCENTRATED SOLUTION – greater than 2 mol l -1 DILUTE SOLUTION – less than 2 mol l -1 NOTE!!! A CONCETRATED ACID is NOT the same as a STRONG ACID
Experiment Weak Acid Comparing Strong and Weak Acids Strong Acid pH Conductivity Reaction with Mg
When we looked at water – what did the word DISSOCIATE mean? Strong and Weak Acids A strong acid is one which fully DISSOCIATES ie all the molecules form IONS when dissolved in water
Strong and Weak Acids A weak acid is one which only PARTIALLY DISSOCIATES ie only some of the molecules form IONS when dissolved in water
Strong and Weak Alkalis A strong alkali is one which fully DISSOCIATES ie all the molecules form IONS when dissolved in water
Strong and Weak Alkalis A weak alkali is one which only PARTIALLY DISSOCIATES ie only some of the molecules form IONS when dissolved in water
SUMMARY: Acids & Alkalis ACIDSALKALIS NEUTRALNEUTRAL pH less than 7pH more than 7 Strong Acid Hydrochloric Sulphuric Nitric pH Current Reaction LOW HIGH FAST Weak Acid Methanoic Ethanoic Propanoic HIGH LOW SLOW Weak Alkali Ammonia LOW Strong Alkali NaOH LiOH KOH HIGH