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Old Aug 22nd 2017, 10:21 PM   #1
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Unhappy HCl dilution to non hazardous - formulas?

Hi there,

I am completely new to Chemistry and have to complete a paper with 10 questions as part of a safety degree but this is well outside my current knowledge as it has been 30 years since high school. I WOULD really appreciate some help in where to start on the questions below. Are there formulas for this? Would appreciate a helping hand please to understand what I need to do here! Thanks in advance!

Question 1:
In a practical sense, the corrosive effects on animal tissues of acids and bases occur at pH values ≤ 2 or pH values ≥ 12.
Hydrochloric acid (HCl) is a strong, monoprotic acid that has a number of industrial applications, and is usually provided as an aqueous solution with a concentration of 320 g/L.
Calculate the minimum dilution required to make the solution pH fall in the “non-hazardous” range.
Assume the molecular weight of HCl is 35.5 g/mole, and that 1 mole of HCl produces 1 mole of H+ in solution.

Question 2:
The clean-up of a spill of 2.5 L of concentrated sulfuric acid, H2SO4), which has a concentration of 18 moles/,L requires neutralisation of the acid using lime Ca(OH)2 .
The chemical equation for this reaction is:
H2SO4 + Ca(OH)2 → CaSO4 + 2 H2O
How much lime is required to completely neutralise the spill?
What would be some of the risks associated with adding too much lime?

The combustion of petrol can be described by the following chemical equation:
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
The Molecular weights of the species involved in this reaction are provided below:

Species Molecular weight / g/mole
C8H18 114
O2 32
CO2 44
H2O 18

Calculate the mass of CO2 and H2O produced by the combustion of 1 kg of petrol.

Question 4:
Aqueous Film Forming Foam (AFFF) is very effective as a fire fighting agent. One compound that was used in AFFF formulations was perfluorooctanoic acid (PFOA).
The current reference values for PFOA are:
a) a total intake of 1.5 g/kg/day, and
b) a drinking water concentration of 5 g/L.

1. How many litres of water with this concentration would a person weighing 75 kg need to drink per day to reach the total intake threshold?
2. By considering all exposure routes, comment on whether the drinking water limit is appropriate.

Question 5:
The expansion ratio of LPG gas is 270.
Assuming the density of LPG is 0.52 kg/m3:
i. calculate the volume of gas that would be produced if a 40 kg cylinder of LPG was vaporised into the atmosphere (i.e. the cylinder was opened and the liquid completely converted to gas).
ii. What are some of the risks associated with this event?

Question 6:
The airborne concentrations of gases, vapours and particulate contaminants are expressed gravimetrically as milligrams of substance per cubic metre of air, (mg/m3). For gases and vapours the concentration is also, with a few exceptions, indicated in parts per million (ppm) by volume. Where both gravimetric and volumetric values are given, the volumetric (ppm) value is exact and should be used as it is not affected by changes in temperature and pressure.
To convert between ppm and mg/m3 we use the following formula
Concentration in mg/m3 = (molecular weight x concentration in ppm)/24.4
The TWA for carbon tetrachloride (CCl4) is 0.63 mg/m3.
What is its TWA expressed in ppm? (Make sure you show all working.)
What is the advantage of using ppm as a unit of concentration over mg/m3?

Question 7:

Question: Gas detectors sampling the breathing space of personnel working on the cast-house floor of an iron making blast furnace indicate that they are exposed to a range of gases, including carbon monoxide (CO), sulfur dioxide (SO2) and hydrogen fluoride (H2S). The average concentration of for each gas measured over an 8-hour shift, together with their Time Weighted Average (TWA) thresholds are shown in the Table below.

Gas Average Exposure (mg/m3) TWA / mg/m3
CO 20 34
SO2 2.2 5.2
H2S 1.7 14
Assuming that the health effects of these gases are additive, calculate the effective TWA for this exposure.
Additive effects can be calculated using the formula below[1]:
X = C1/T1 + C2/T2 + … + Cn/Tn
Where C = atmospheric concentration of the substance and T = threshold limit value (TLV).
So X = C1/T1 + C2/T2 + C3/T3
= 20/34 + 2.2/5.2 + 1.7/14
= .5882352941 + 0.4230769231 + 0.1214285714
= 1.1327407886
“If X <1 the mixture does not exceed TLV; if X >1, the mixture exceeds TLV.”[1, p.19]
In this case because X = 1.33 (2dp) the mixture exceeds the TLV.


Last edited by NEWtoChemistry; Aug 22nd 2017 at 10:34 PM.
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acid, dilution, hcl, ph value

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