Measurements Math and the Mole Key

Unit 2 – Measurements, Math, & the Mole Nothing in life is to be feared. It is only to be understood. ~Marie Curie 1. Why are sig figs important to use when measuring? They show how accurate the device is. You record all the units on the device, plus go one more digit that’s an estimate. All those numbers count as significant figures. Study Guide 2. (Your labs, worksheets, and homework should also be used) **You must show all your work for credit!** Record the measurement indicated with the correct number of sig. figs (both are in Cm). 3.5 cm 3.50cm 3. How many significant figures are in the following? Underline them too. a. 1000 m b. 3025000 cm c. 0.00740 ml d. 8740. m 1 4 3 4 e. 5400.0 g 5 4. Write the following in scientific notation: a. 646 002 000 000 000 km b. .000 000 000 0215 mm 5. Write the following in ordinary notation a. 2.036 x 105 atoms 203,600 atoms b. 6.548 x 10-4 molecules 0.0006548 molecules 6.46002 x 10 14 km 2.15 x 10 -11 mm 6. Perform the calculations; report your answers in both regular & sci. notation with sig figs. a. (5400s)(3.5s)= b. 34.95 g = c. (6.1 x 103 g) (2.0 x 105 g)= d. 9 x 106 cm = = 19000 s2 11.169 cm3 = 1,200,000,000 g2 8 x 104 cm 3 9 2 Or = 3.129 g/ cm = 1.2 x 10 g =100 or 1 x 102 1.9 x 104 s2 = 3.129 X 100 cm3 7. You find something that looks like a diamond that has a mass of 1.14 g and a volume of 0.56 mL. Real diamonds have a density of 3.26 g/ml Use Sig Figs. a) Calculate the density of this potential diamond. b) How would you know if this is a real diamond? Compare it to the density of 3.26, D= Mass/ volume it’s not real. D = 1.14 g/ 0.56 mL D= 2.0 g/ mL c) Based on the density a real diamond, will it float or sink in water? Explain. Diamonds would sink because the density of water is 1 g/ ml and diamonds are more dense at 3.26 g/ mL. d) What volume would a real diamond be (see density) if it had a mass of 1.14 grams? D = M/ V 3.26 g/ ml = 1.14/ V V= .350 ml 8. Determine the type of metric measurement in each of the following (volume, length, density, mass, area): Abbreviation mm m2 ml g ÷ L cm cm3 L Unit millimeter Meters Milliliter grams/Liter Centimeter Centimeter Liter squared cubed Quantity length Area Volume Density Length Volume Volume measured 9. Put the following metric terms in order from smallest to largest: Meter, millimeter, kilometer, & centimeter, millimeter, centimeter, meter, kilometer 10. Which metric unit would be best to measure the following? a. the mass of a vitamin b. the volume of a key milligrams (mg) milliliters (mL) c. the width of a dime millimeters (mm) 11. Perform unit conversion calculations using the SI system: a. 4800 g to kg b. 5 m to cm c. 25 L to mL 4800 g 1kg 5m 100 cm 25 L 1 000 ml 1000g 1m = 500 cm = 4.8 Kg d. 5 cm3 to ml 5 cm3 1 ml 1 cm3 1L = 25,000 ml = 5 mL 23 12. One mole of any substance contains ____6.02 x 10 ____ particles (aka_ Avogadro’s_number). One mole of any substance in chemistry also has an associated mass called molar mass which can be found on the periodic table of elements. For example, the molar mass of C is 12.01 g/mol while the molar mass of oxygen is 16.00 g/mol. The molar masses of each substance are different because the size/ mass of each substance is different. 13.Calculate the molar mass of the following: a) Ca = 40.08 g/mol b) Cl2 = 70.90 g/mol How to determine: Use the periodic table 2(35.45 g/mol) c) CO2 = 44.01 g/mol d) Ca(OH)2 = 74.10 g/mol C= 12.01 (O) 2= 32.00 40.08 g/mol + 2(16.00 g/mol) + 2(1.01 g/mol) 14. Write the “mole map” that allows you to go between grams, moles, and atoms. Include the conversion factors. Grams molarmass Moles Avogadro'sNumber 15. Convert the following to moles: Use Sig Figs a) 824g of NH3 b) 43.6g of O2 molar mass NH3 = 17.04 g/mol 824 g NH3 = 48.4 1 mol NH3 17.04 g NH3 mol NH3 molar mass O2 = 32.00 g/mol 43.6 g O2 = 1.36 1 mol O2 32.00 g O2 mol O2 Atoms/Molecules c) 1.2 x 10 24 molecules of CaCl2 1.2 x 1024 molecules = 2.0 mol Cl2 1 mol 6.02 x 1023 molecules 16. Convert the following to grams: Use Sig Figs a) 3.00 moles of CO2 b) 0.76 moles of H2 molar mass CO2 = 44.01 g/mol 3.00 mol CO2 = 132 g CO2 44.01 g CO2 1 mol CO2 molar mass H2 = 2.02 g/mol 0.76 mol H2 = 1.5 g H2 2.02 g H2 1 mol H2 c) 3.01 x 10 12 molecules of H20 molar mass H2O = 18.02 g/mol 3.01 x 1023 molecules H2O = 9.01 g H2O 17. Given 4.50 g of CO2, how many molecules do you have? Use Sig Figs 6.02 x 1023 molecules 4.50 g CO2 1 mol CO2 =6.16 x 10 22 molecules 44.01 g 1 mol CO2 1 mol H2O 6.02 x 1023 molecules H2O 18.02 g H2O 1 mol H2O