Coats and bags to the side / back Drinks and food away please 1

Periodic Table 2

 Recall how to balance equations  Calculate the molar masses of compounds  Convert mass into moles  Convert moles into mass  Carry out a titration and evaluate the accuracy of your approach.  First and foremost what is a mole? 3 NEWS!

Periodic Table 4

 Calculate the molar masses of compounds  What does this tell us?  HCl (aq) + NaOH (aq) → NaCl (aq) + H 2 O (l) REACTANTS Give PRODUCTS  The ratios or stoichiometry of the reaction  It tells us that one amount of hydrochloric acid reacts with one amount of sodium hydroxide to give one amount of sodium chloride and one amount of water.  Na 2 CO 3 + 2HCl  2NaCl + CO 2 + H 2 O  What does this equation tell us about the amounts reacting together?

Periodic Table  Instead of the word AMOUNT chemists use the term MOLE.  A mole is simply an amount of substance  Written as moles or mol for short.  Let’s relate this to actual quantities…..  In terms of quantity:  1 mole of anything contains x particles.  This may be ions or atoms.  You may have seen it quoted as Avagadro’s number. Define the mole

Periodic Table  Look back at this equation  Na 2 CO 3 + 2HCl  2NaCl + CO 2 + H 2 O  We can say how many particles or moles we have of each substance.  1 mole of anything contains x particles.  7

Periodic Table  We know 1 mole of anything has a set number of particles, this is a very large number!  The mole is a relative amount…it relates to something else  Carbon-12.  In the 1900’s it was established that in 12 g of carbon-12 there were x atoms of carbon.  How does this relate to all the other elements? 8

Periodic Table  1 mole of an element is equal to its relative atomic mass  Try some:  1 mole of Ca  1 mole of Mo  1 mole of tungsten  1 mole of arsenic  1 mole of bromine  Answers: Ca (40), Mo (96), W (184), As (75) and Br(80) 9

Periodic Table We can also use this for compounds too… 1 mole of a compound has a mass which is the sum of its component Relative Atomic Masses 1 mole of compound it still contains x formula units (like NaCl) or molecules (like O 2) What is the M r of ……... H 2 KCl HF Cl 2 H 2 O Mg(NO 3 ) 2 Note there are no units….. 10

Periodic Table  So far we have learnt about:  The mole – an amount of substance, quoted in moles  That a mole contains this magical number of x atoms, ions, formula units or molecules.  That 1 mole of anything is equal to its M r  The M r has no units…so how do I weigh out quantities of substances?  We use the formula m = M r X n  Mass = mister mole 11

Periodic Table 12 n = number of moles m n MrMr m = n x M r n = m/M r m = mass in g M r = relative formula mass (relative molar mass)

Periodic Table M r = (a) 2 mol of Cr atoms M r = 16 (b) 10 mol of O atoms M r = 32 (c) 10 mol of O 2 molecules m = 2 x 52= 104 g m = 10 x 16 = 160 g m = 10 x 32 = 320 g

Periodic Table M r = (d) mol of NaOH M r = 63 (e) 1.5 mol of HNO 3 m = x 40 = 1 g m = 1.5 x 63 = 94.5 g

Periodic Table M r = 2 15 (a) 2g of H 2 molecules M r = 12 (b) 24g of C atoms M r = (c) 1.269g of I 2 molecules n = = 2 mol n = = mol n = 2 2 = 1 mol

Periodic Table M r = (d) g of H 2 SO 4 M r = 286 (e) 71.5 g of Na 2 CO 3.10H 2 O n = = 0.25 mol n = = 0.2 mol

Periodic Table 17

Periodic Table  A numerical value  Most common wet technique for analysing how much of a substance is present is by titration.  A titration uses a solution of known concentration and volume to find out the amount and / or concentration of an unknown substance.  The solution that we know the concentration of is called a Standard Solution! 18

Periodic Table  Key points: standard solution in the conical flask, unknown in the burette, just a few drops of indicator.  An indicator is a chemical that has at least two distinct colours, which change after the equivalence point reached to show the end-point of the reaction. 19

Periodic Table  The equivalence point is reached when enough standard solution has been added to the unknown concentration of solution so that the right proportions have reacted together in accordance to the chemical equation.  The term "end point" is where the indicator changes colour, this is what we document and it is slightly after the equivalence point, as the indicator changes colour due to a slight excess of the standard solution being added by the burette. 20

Periodic Table  This is the same solutions as last week  Different indicator is employed  Watch the demonstration!  You are to carry out your titration with your partner and note down your readings.  Work out an average titre value  Once you have finished tidy away and go through an evaluation of the accuracy of your technique, answering the questions on the sheet. 21

Periodic Table Practical Activity Safety First: Wear safety goggles Stand up Tuck your chair & bags under your desk Tie back long hair

23 Periodic Table return