1 Quantitative ChemistryChemistry Topic 3 Quantitative Chemistry

2 Conservation of mass balanced equationMass conservation and balancing equations Objectives: Describe what is meant by the conservation of mass Explain why the mass might appear to change in some chemical reactions Write balanced symbol equations to represent chemical reactions. Keywords: Conservation of mass balanced equation

3 + + Conservation of mass:In chemical reactions, no atoms can be made or destroyed. Chemical reactions just change how the atoms are bonded together. Conservation of mass is that the mass of the products you have will be equal to the mass of reactants that you started with. + +

4 Boardworks GCSE Additional Science: Chemistry Chemical ReactionsSymbol equations: A symbol equation uses the formulae of the reactants and products to show what happens in a chemical reaction. A symbol equation must be balanced to give the correct ratio of reactants and products. +  S(S) O2(g) SO2(g) This equation shows that one atom of sulfur (S) reacts with one molecule of oxygen (O2) to make one molecule of sulfur dioxide (SO2). Do you think the S and the SO2 would have different masses? Why? + 

5 Relative atomic mass(RAM) Relative formula mass (RFM)Objectives: Describe what is meant by the relative atomic mass of an element Calculate the relative formula mass of compounds using their relative atomic masses Use relative formula masses to prove the conservation of mass in balanced symbol equations Keywords: Relative atomic mass(RAM) Relative formula mass (RFM)

6 Boardworks GCSE Additional Science: Chemistry Quantitative ChemistryRelative Formula Masses: To find the relative formula mass of a compound, add up the relative atomic masses of all the atoms in its formula. Step 1: Write down the formula of the molecule. Step 2: Find the r.a.m. of each type of atom in the molecule. Step 3: Multiply each r.a.m. by the number of atoms of that element and add these values together. What is the relative formula mass of water? Step 1: formula of water is H2O Step 2: r.a.m. values: hydrogen = 1, oxygen = 16 Step 3: relative formula mass = (2 x 1) + (1 x 16) = 18

7 Practice makes perfectPractice makes perfect! The work sheet has a worked example and some questions on, have a go at these 10 mins

8 Self Assess Relative formula mass 32 71 11. 28 44 12. 106 17 13. 40056 102 74 160 100 132 14. 99 15. 63 17 314

9 Proving conservation of mass:Since no atoms are created or destroyed during a chemical reaction, the mass of the reactants and products is always the same. This can be proved using relative formula masses; where the total RFM of reactants will be the same as the total RFM of products, providing the symbol equation is balanced: 2H2 + O2  2H2O What is the relative mass of each of the reactants? You will need to multiply the by the number of molecules of each you have. Add these to get the total relative mass of reactants that you have. What is the total relative mass of each of the products? Remember to multiply by the number of molecules. Add the relative masses of the products together Compare these both sides of the equation, they should be the same to prove that mass is conserved in a chemical reaction.

10 Solute Solvent Solution Concentration Volume MassConcentration of solutions Objectives: Calculate the mass of a solute in a given volume of solution of known concentration (All students) Explain how the mass of a solute and the volume of a solution is related to the concentration of the solution (Higher tier only) Keywords: Solute Solvent Solution Concentration Volume Mass

11 Concentration: When making a drink of orange squash, sometimes you put too much squash in the glass – sometimes you add too much water. How could you rectify both of these scenarios? A chemist would say that you are adjusting the concentration of the solution. To record, interpret and communicate their results, chemists need to express the concentration of the solutions they use. So they quote the amount of substance (solute) dissolved in a certain volume of liquid (solvent) of the solution. From the above sentence, what units could be used to express concentrations? Do you think the concentration of a solution could be calculated? How might you do this?

12 x 1 2 3 Calculating Concentration: Conc. (g/dm3) Vol. (dm3)Solute mass (g). This is the equation for calculating the concentration of a solution. The units for concentration are g/dm3. If the volume of the solution is quoted as cm3 (mL) this must be converted into dm3 (L). How could this be done? What does “m” mean? Practice: What is the concentration of calcium ions in a sample of water that has (show your working): 0.4g of calcium ions dissolved in 2dm3 of water? 0.25g of calcium ions dissolved in 5dm3 of the water? Stretch: A 500cm3 bottle of mineral water contains 0.2g of magnesium ions dissolved in the water. What is the concentration of magnesium ions in g/dm3. m means milli or thoundths

13 Uncertainty Range Mean Percentage UncertaintyUncertainty and Percentage Uncertainty Objectives: Calculate uncertainty in a measurement using equipment Calculate the uncertainty of measurements about a mean Keywords: Uncertainty Range Mean Percentage Uncertainty

14 Which equipment would you use? Why?10mL Measuring Cylinder 50mL Measuring Cylinder 100mL Measuring Cylinder 500mL Measuring Cylinder Which would you use to measure: 250mL water 2mL hydrochloric acid 75mL sodium hydroxide solution 42mL sulfuric acid Answers: 500mL MS 10mL MS 100mL MS 50mL MS

15 What are Uncertainties?What do you think this is? It is very old! It is GRB B and is thought to be the remnants of one of the first stars born after the Big Bang. It is 13,140,000,000 ± 20,000,000 years old What does this mean?

16 Calculating Uncertainties in MeasurementsReading on meter = 12.6 V Smallest division = 0.2 V Measurement is 12.6 V ± 0.2 V

17 End of topic for FOUNDATION TIER STUDENTS