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A-level chemistry

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- 1. Titrations Aim: To understand how to use volumetric analysis to determine the concentration of acids or bases
- 2. Moles in solution No. of moles in solution = M x V ______ 1000
- 3. Moles in solution <ul><li>How many moles of NaCl are there in each of these solutions: </li></ul><ul><li>0.500mol dm -3 . </li></ul><ul><li>0.750mol dm -3 ; 500cm 3 </li></ul><ul><li>0.650mol dm -3 ; 750cm 3 </li></ul><ul><li>1.5mol dm 3 ; 1.5dm -3 </li></ul>
- 4. Calculations – Solution moles <ul><li>Calculate the number of moles of calcium chloride needed to make a 2 Mol dm -3 solution, volume 250cm 3. </li></ul><ul><li>Calculate the mass of Calcium Chloride needed to make up this solution. </li></ul>
- 5. Number 2 <ul><li>Calculate the number of moles of sulphuric acid needed to make a 5 mol dm -3 solution; volume 100cm 3 . </li></ul><ul><li>What mass of sulphuric acid would be needed to make up the solution? </li></ul>
- 6. Solution calculations <ul><li>If 10.3g of sodium bromide was dissolved in 250cm 3 of solution what would its concentration in mol dm -3 be? </li></ul>
- 7. Solution calculation 2 <ul><li>If 8g of copper sulphate was dissolved to make up a solution of volume 500cm 3 , what would be its concentration in mol dm -3 ? </li></ul>
- 8. Using titration to find out the exact concentration of NaOH. <ul><li>Titration involves neutralisation – using an acid of known concentration to find out the concentration of NaOH </li></ul><ul><li>Equation for the reaction: </li></ul><ul><li>HCl + NaOH NaCl + H 2 O </li></ul>
- 9. Titration to find out the concentration of a solution of NaOH. <ul><li>If we know the volume and concentration of HCl needed to neutralise 25cm 3 NaOH we can use this and the mole ratio from balanced equation to work out: </li></ul><ul><li>The number of moles of HCl that have reacted with the NaOH. </li></ul><ul><li>The balanced equation will than tell us the number of moles of NaOH that reacted with the HCl </li></ul><ul><li>Because we know the volume of NaOH and the number of moles we can then calculate the concentration. </li></ul>
- 10. Example <ul><li>In a titration 21.45cm 3 of 0.500mol dm -3 HCl was needed to neutralise 25cm 3 NaOH. What is the concentration of the NaOH? </li></ul><ul><li>Step 1 – Calculate the moles of HCl needed to neutralise the NaOH. </li></ul><ul><li>Number of moles HCl= 21.45 x 0.5/1000 = 0.01072moles </li></ul><ul><li>From the balanced equation work out the mole ratio of NaOH to HCl </li></ul><ul><li>1 mole HCl reacts with 1 mole NaOH </li></ul><ul><li>0.01072 moles react with 0.01072 moles NaOH. </li></ul>
- 11. Part 2 <ul><li>Therefore, in 25cm 3 of solution there are 0.01072moles of NaOH……. What is its concentration? </li></ul><ul><li>No of moles = MV/1000 </li></ul><ul><li>0.01072 = M x 25/1000 </li></ul><ul><li>M = 0.01072 x 1000/25 </li></ul><ul><li>= 0.4288mol dm -3 </li></ul>
- 12. An Experiment to find out the concentration of a solution of Sodium Hydroxide <ul><li>Half fill the 25ml pipette with your solution of sodium hydroxide with a pipette filler. </li></ul><ul><li>Remove the filler and place your thumb or first finger over the round end of the pipette to stop the liquid escaping. </li></ul><ul><li>Invert the pipette a couple of times to rinse the pipette. </li></ul><ul><li>Drain the liquid into an empty beaker – DO NOT BLOW OUT THE LAST DROP OF LIQUID FROM THE PIPETTE. </li></ul><ul><li>Measure out accurately 25ml of the sodium hydroxide solution by using the pipette and filler and in a empty into a small conical flask. Add a few drops of the indicator. </li></ul>
- 13. Experiment continued <ul><li>Fill the burette with the HCl using a funnel with enough acid to rinse the burette out – about 10ml. Place your thumb or first finger over the round end of the burette and invert the burette 2/3 times. </li></ul><ul><li>Drain the burette into a beaker using the tap so that the acid also drains through the jet. </li></ul><ul><li>Fill the burette ensuring that the jet is filled, and note the volume accurately – read to 2 decimal places. </li></ul>
- 14. Experiment (3) <ul><li>Add the solution to the flask slowly and continually swirl the flask. </li></ul><ul><li>As the indicator begins to change colour add the acid drop by drop to the flask. </li></ul><ul><li>When the indicator has turned colourless and the end point has been reached record the volume to decimal places. </li></ul><ul><li>Repeat the titration until 3 CONSISTENT volumes of solution have been obtained – 3 readings within + or – 0.1ml. </li></ul><ul><li>These 3 consistent results should then be averaged to give the mean titre for the experiment. </li></ul>
- 15. Results table Volume delivered in cm 3 Final volume in cm 3 Start volume in cm 3 4 3 2 1 Titre – Volume of solution added from burette
- 16. Calculation <ul><li>Calculate the average volume of HCl that reacted with 25cm 3 of NaOH Show your working. </li></ul><ul><li>Calculate the number of moles of HCl that reacted with the NaOH. </li></ul><ul><li>Using the balanced equation work out the number of moles of NaOH that reacts with this number of moles of HCl. </li></ul><ul><li>Using this number of moles of NaOH and the volume of NaOH used in the experiment calculate its concentration. </li></ul>
- 17. Confirming the concentration of your standard solution of Sodium carbonate <ul><li>Carry out a titration to work out the concentration of your solution of sodium carbonate. </li></ul><ul><li>The acid you are provided with is 0.1M HCl. </li></ul><ul><li>The indicator you will use for this titration is screened methyl orange. The end point is reached when it grey/purple from green </li></ul>
- 18. Experiment write up <ul><li>Diagram and method and explanation for each stage of the practical method. </li></ul><ul><li>A balanced symbol equation for the reaction </li></ul><ul><li>A results table identical to the HCl NaOH practical. </li></ul><ul><li>The calculation to find out: </li></ul><ul><li>The moles of HCl that reacted. </li></ul><ul><li>The moles of Na 2 CO 3 in the solution. </li></ul><ul><li>The concentration of the Na 2 CO 3. </li></ul><ul><li>A comparison of the calculated value v your stated value on the flask. Sources of experimental error? </li></ul>
- 19. Question <ul><li>25.0 cm 3 of a 0.0504 mol dm -3 solution of sulphuric acid was titrated with a solution of sodium hydroxide. The mean titre was 27.8cm 3. </li></ul><ul><li>Write the balanced equation for this reaction. </li></ul><ul><li>Calculate the number of moles of sulphuric acid that reacted with the NaOH. </li></ul><ul><li>Use the balanced equation to calculate the number of moles of NaOH that react with the acid. </li></ul><ul><li>Claculate the concentration of the NaOH. </li></ul>
- 20. Question. <ul><li>Calculate the volume of 0.100 mol dm -3 hydrochloric acid solution required to neutralise 25 cm 3 of 0.0567 mol dm -3 sodium carbonate solution . </li></ul><ul><li>Write the balanced symbol equation for the reaction. </li></ul><ul><li>Calculate the number of moles of sodium carbonate solution. </li></ul><ul><li>Using the balanced equation calculate the number of moles of HCl that reacts with the sodium carbonate. </li></ul><ul><li>Calculate the volume of HCl used in the reaction. </li></ul>

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