ASP Study Prep - Chemistry and Industrial Hygiene.pptx

ASP Study Prep - Chemistry and Industrial Hygiene.pptx

1. ASP Study Prep Chemistry and Industrial Hygiene Calculations

2. Atoms, elements, matter Atoms = protons, neutrons, electrons Atomic weight = number of protons + number of neutrons Number of protons defines the element Isotopes = different numbers of neutrons but same number of protons

3. Chemical reactions, balancing, stoichiometry Reaction standard notation has reactants on the left and products on the right Understand how to balance an equation M 1 V 1 =M 2 V 2 Understand how to interpret number of moles per unit of reactant or product e.g. 2(NH 3 ) -> N 2 + 3(H 2 )

4. Unit conversions, dimensional analysis Practice converting units Good idea to know typical conversions (e.g. 1 inch = 2.54 cm)

5. Concentrations Parts per million ( ppm) mg/m 3 specific gravity molarity (M)

6. pH scale, acids, bases pH scale is a logarithmic scale, specifically, the negative log of the concentration of H + atoms Pure water has a concentration of H+ equal to 10 -7 . The –log[10 -7 ] = 7 Acids have a pH less than 7. Bases have a pH greater than 7

7. Gas Calculations Ideal Gas Law PV = nRT P = pressure ( atm ) V = volume (L) n = number of moles R = 0.0821 L* atm / mol *K (or 8.314 J/ mol *K) T = temperature (K)

8. A few things to remember Temperature is in Kelvin, not Fahrenheit or Celsius Celsius = (Temp(F) - 32) x 5/9 Fahrenheit = (Temp(C) x 9/5) + 32 Kelvin = Temp(C) + 273 Pressure is in atmospheres ( atm ) Pressure at sea level = 1 atm (or 760 mmHg) Volume is in Liters Standard temperature and pressure (STP) 273K (0 ⁰C) 1 atm (760 mmHg)

9. Industrial Hygiene Concepts Airborne concentrations in a room Time-Weighted Averages e.g. Short-Term Exposure Limit (STEL), Immediately Dangerous to Life and Health (IDLH) Lower Explosive Limit (LEL) and Upper Explosive Limit (UEL) The minimum and maximum concentration of a substance in air that will produce a fire or explosion Be able to calculate the LEL or UEL of a mixture

10. What is the atomic mass of a ethanol (C2H6O) if hydrogen has an atomic mass of 1, carbon has an atomic mass of 12, and oxygen has an atomic mass of 16? Solution A tomic mass of ethanol = 6x(1) + 2x(12) + 1x(16) = 46

11. Convert 100 feet per second ( ft /sec) to miles per hour (mi/ hr or mph) Solution 100 Feet/sec x 1 mile/5280ft x 60 sec/min x 60 min/hour = 68.18 mph

12. Convert 100 feet per second ( ft /sec) to kilometers per hour (km/ hr ) Solution 100 Feet/sec x 12 inch/ ft x 2.54cm/inch x 1m/100cm x 1km/1000m x 60 sec/min x 60 min/hour = 109.73 km/h

13. Hazardous material spill of acid: Collect 25 mL sample Test 5 mL with pH paper, indicates a pH of around 1. Prepare 0.100 Molar solution of base to perform a cid/base titration Titrate remaining 20 mL of sample, requires 50 mL of base for neutralization What is the molarity of the acid in the sample? Assume acid is HCl and base is NaOH

14. Solution M 1 V 1 =M 2 V 2 Want to solve for M 2 , so M 2 = M 1 V 1 /V 2 = (0.1M)(50mL)/(20mL) = 0.25M

15. The density of an gas at STP is 5 grams per liter. What is the molecular weight of one mole of this gas in grams?

16. Solution Calculate number of moles PV= nRT -> n/V=P/RT Pressure = 1 atm Volume = 1 Liter Temperature = 273K R=0.0821 n/(1)=(1)/(.0821)(273) = 0.0446 Since 0.0446 moles weighs 5 grams, 1 mole is 5 / 0.0446 = 112 grams

17. The density of an gas at 100 ⁰C and 684 mmHg is 5 grams per liter. What is the molecular weight of one mole of this gas in grams?

18. Solution Calculate number of moles PV= nRT -> n/V=P/RT Pressure = 684 mmHg/760 mmHg = 0.9 atm Volume = 1 Liter Temperature = 100 ⁰C = 273+100 = 373K R=0.0821 n/(1)=(.9)/(.0821)(373) = 0.0294 Since 0.0294 moles weighs 5 grams, 1 mole is 5 / 0.0294 = 170 grams

19. One kilogram of solvent spills in a sealed room with dimensions 10m x 10m x 4m. What is airborne concentration of solvent (in mg/m3) after evaporation?

20. Solution Concentration is mg/m3 Convert 1kg to mg Calculate volume of room 1 kg x 1,000g/kg x 1,000mg/g = 1,000,000 mg Room volume = 10m x 10m x 4m = 400m3 concentration of solvent in air = 1,000,000mg/400m3 = 2500mg/m3

21. Calculate the LEL of the following mixture Chemical LEL (%/Vol) % of Total Benzene 1.2 20 Methanol 6.0 40 MEK 1.4 10 Ethanol 3.3 30

22. Solution (Percent of all components)/ ((Percent1/LEL1)+(Percent2/LEL2)+(Percent3/LEL3)+(Percent4/LEL4) (100)/((20/1.2)+(40/6.0)+(10/1.4)+(30/3.3)) LEL of mixture = 2.53