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Avogadro’s Constant What is it and what information does it give us?

Formula Equations and Moles. Avogadro’s Constant What is it and what information does it give us?. Why are moles important?. As scientists we add elements together to make new substances We like to work out the ratios before we do this so that there is no waste

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Avogadro’s Constant What is it and what information does it give us?

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  1. Formula Equations and Moles Avogadro’s Constant What is it and what information does it give us?

  2. Why are moles important? • As scientists we add elements together to make new substances • We like to work out the ratios before we do this so that there is no waste • Example: a food recipe, you don’t’ want too many eggs as it will spoil the cake

  3. What Avogadro did for us • He worked out an exact figure for the quantity of carbon present in 12 grams • This is a measure of the number of atoms present • This allows us to compare atoms in terms of ratios 6.02 x 1023

  4. Avogadro’s number 6.02 x 1023 • What does this number represent? • Which element did it refer to? • How many particles are present in 2 moles of Na? • How many particles are present in 0.5 moles of Fe? • How many moles are there in 4.167 x1014of particles Pb?

  5. Molecular formula • What is meant by molecular formula? • How can it be calculated? • What is the molecular formula for: • water • magnesium chloride • potassium oxide • silicon iodide

  6. Empirical formula • This is the simplest ratio • is the molecular formula for ethene, but its empirical formula is C1 : H2 • What is the empirical formula for: • C2H4 • C6H12O6 • C4H8Cl2 • CH3COOH

  7. Calculating the empirical formula from the percentage massesIf a compound gives the following results when analysed, 87.7% C and 14.3% H • What is the empirical and molecular formula? • 87.7/12 = 7.1 carbon • 14.3/1 = 14.3 hydrogen • What is the lowest ratio between these numbers?

  8. Molecular formula:If a mass of a hydrocarbon equals 42, what is the molecular formula? • Work out the following • the empirical formula equals C1:H2

  9. Concentration and Molarity • What is a solute, solvent and a solution? • What do we mean by the concentration of something? Write a sentence to express when something is more concentrated. Use the following words, volume, solute, solvent • Can you remember the equation that calculates the concentration of a liquid? Moles = Conc x Volume

  10. How do we measure liquid concentrations? • When 1 mole of solute is dissolved in 1 decimetre of solution, its concentration is said to be 1 mol dm-3 • This is called 1 M for short • We measure concentration in molarity 1 dm3 = 1000cm3 = 1 litre

  11. Work out how much compound would be needed to make a 1 molar solution for the following • .KHCO3 • .NaCl • .Li2O

  12. Example How many moles are there dissolved in 200 cm3 of 1 M solution of NaHCO3 200/1000 x 1 = 0.2 moles

  13. Work out the molarity of questions 4-6 4.KHCO3 1 mole is dissolved in 2 litres of water 1/2 5.NaCl 2 moles is dissolved in 500cm3 of water 2/0.5 6.Li2O 0.5 moles dissolved in 1.5 dm3 of water 0.5/1.5

  14. How can we work out the amount of solid dissolved in a liquid? Work out the amount of solid dissolved in each solution Example: Work out the number of moles the times by the mass 200/1000 x 1M = 0.2 moles of LiOH 0.2 x 24 (Li = 7 and OH = 17, 7 + 17 = 24) 1.2 grams of LiOH

  15. Calculate the following: • .KHCO3 1 mole is dissolved in 2 litres of water • .NaCl 2 moles is dissolved in 500cm3 of water • .Li2O 0.5 moles dissolved in 1.5 litres of water

  16. To find the concentration of a unknown solution Comparing the unknown to a known solution Helps us calculate the amount of acid or alkali present When would this be used in the real world? The purpose of a titration

  17. You have created a known molarity for the alkali sodium hydroxide: • Work out the mass of NaOH • Na = 23 O = 16 H = 1 add together = 40 • Molarity = 250/1000 = 0.25 0.25/0.25 = 1.0 molar or 1M • Now you can work out the molarity of the unknown substance: • Measure a known volume of acid and add indicator • Neutralise the acid • What equation would you use?

  18. Results: Vol acid = 25cm cubedVol alkali needed to neutralise = 26.5 cm cubed Conc of alkali = 0.95 molar • Molarity of known substance x Volume = • Molarity of unknown substance x volume • Substitute in what you know • 0.95 x 26.5 = ? x 25 • =1.007

  19. Equations: • Write a balanced equation for the reaction between hydrochloric acid and sodium hydroxide • Follow this with an ionic equation NaOH (aq) + HCl (aq) = NaCl (aq) + H2O (l)

  20. For the following examples balance the equation putting state symbols • .NH3 + O2 = NO2 + H2O • .C2H5OH + O2 = CO2 + H2O • .Al + NaOH= Na3AlO3 + H2 • .CO2 + H2O = C6H12O6 + O2 • .C3H8 + O2 = CO2 + H2O • .4Al + 12H2SO4 = 2Al2(SO4)3 + 6SO2 + 12H2O

  21. You have just done an experiment and made Ammonium Sulphate. You started out with 8.6g of Ammonium hydroxide. • What would you react this with to make a sulphate? What is the new class of substance you have made? What is this type of reaction called? • What is the maximum amount you could make? Hint: Moles = mass/ molecular mass You also need to work out the products and ratios in the reaction first. • Now calculate the actual yield when: • The experimental value of the substance is 10.64g How did I work this out? Hint: you need to compare it to your 100% theoretical

  22. The experiment was done again, the yield went up to 83%, what was the amount made? • What could have been done differently? Why will you always not get less than 100% yield no matter how careful you are?

  23. Example: 2NH4OH + H2SO4 = (NH4)2 SO4 + 2H2O • Look at what changes in the ions, first you will need to write out the ions as they exist • Cancel out the ones that don’t change. • Then construct an equation will the essential ions present only. • Try this one now using the same rules CaCO3 + HCl = CaCl2 + CO2 + H2O Mg+ 2HCl = MgCl2 + H2

  24. What equation do we use to calculate gas quantities? If 1.5 dm cubed of Hydrogen was produced from hydrochloric acid when magnesium dissolved, how much magnesium was there to start with? Hint- start with the equation Working out reacting gas amounts

  25. Equal volumes of all gases at the same pressure and temperature contain the same number of particles (same number of moles)

  26. Work out the moles of potassium nitrate Work out the volume of oxygen produced

  27. .Calculate how many dm3 of hydrogen gas are produced when 19.5g of zinc metal dissolved in excess hydrochloric acid at 30oC and 100 KPa. • .C8H18 + O2 = CO2 + H2O Balance this What volume of oxygen reacts with 10 dm3 of petrol? How many moles of petrol are there? How many moles of oxygen are required? What is the mass of CO2 produced?

  28. Calculate the volume of gas produced when 150g of calcium carbonate decomposes to form calcium oxide and carbon dioxide in dm3 at 100 KPa and 25oC Calculate: • Work out the number of moles present • Work out the molarity • The calcium carbonate was reacted with sulphuric acid, write a balanced symbol equation for this putting in the number of moles of each and the masses Hard water from a town’s water supply was measured and found to be 0.4g in 1m3 (The calcium carbonate was weighed after the water was boiled off).

  29. H2SO4 + CaCO3 = CaSO4 + CO2 + H2O • Write a ionic equation for this reaction • An organic compound is shown to have 40% carbon, 6.7% hydrogen and 53.3% oxygen • Deduce the empirical formula • It is shown to have a mass of 180, deduce the molecular formula

  30. A company that makes vinegar has to print the percentage amount of organic acid on their bottles, a reaction between sodium hydroxide was undertaken. 25 cm3 reacted with 29cm3 of 0.1 M of the alkali. • Work out the concentration • The amount of carbon was found to be 48.7%, hydrogen was 8.1% and oxygen was 43.2, work out the empirical formula • The mass of the acid is 74, work out the formula • Write an equation for the neutralization reaction, what is the name of this acid?

  31. What is the relationship, if any? What is the amount of gases measured in? Explain what the greenhouse effect is What other proof is there available that CO2 has an effect on the atmospheric temperature? Answer: Venus atmosphere is 96% CO2 and the temp is 450oC Greenhouse gases

  32. Which gases cause the most warming of the planet? Which are the most abundant greenhouse gases?

  33. On earth, the most abundant greenhouse gases are, in order of relative abundance: • water vapor • carbon dioxide • methane • nitrous oxide • ozone • CFCs • The most powerful greenhouse gases are • water vapor, which causes about 36–70% of the greenhouse effect on Earth. (Note clouds typically affect climate differently from other forms of atmospheric water.) • carbon dioxide, which causes 9–26% • methane, which causes 4–9% • ozone, which causes 3–7%

  34. Work out the percentages present in the double salt • Ammonium iron (II) Sulphate can be made from iron, ammonia and sulphuric acid. • Write the individual equations for each • If 25cm3 of 1.0 M H2SO4 is used work out the mass of FeSO4 made from 1.12g of Fe • The remainder of the acid reacts with the ammonia, work out the mass of ammonium sulphate made. • The total mass of the dried combined salts is 2.8g, workout the 100% theoretical mass then calculate what the yield is?

  35. Fe + H2SO4 = FeSO4 + H2 • Mass 1.12g 1.96 3.04 ? • Moles 0.2 0.025 0.2 ? • 2NH3 + H2SO4 = (NH4)2SO4 • Mass ? ? ? • Moles ? 0.005 ? • Work out the missing masses and moles

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