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In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively.
The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.
The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will be
  • a)
    400 and 100, respectively.
  • b)
    400 and 300, respectively.
  • c)
    500 and 100, respectively.
  • d)
    800 and 200, respectively.
Correct answer is option 'A'. Can you explain this answer?
Most Upvoted Answer
In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 ...
Given:
Concentration of Ca2+ = 100 mg/L
Concentration of Mg2+ = 36 mg/L
Concentration of HCO3- = 122 mg/L

Atomic Mass:
Ca = 40
Mg = 24
H = 1
C = 12
O = 16

To find:
Total hardness and temporary hardness in the water sample (in mg/L as CaCO3)

Solution:
To calculate the total hardness and temporary hardness, we need to convert the concentrations of Ca2+ and Mg2+ into their respective concentrations as CaCO3.

1. Convert Ca2+ concentration to CaCO3:
The molar mass of Ca2+ = 40 g/mol
So, the concentration of Ca2+ in moles per liter = (100 mg/L) / (40 g/mol) = 2.5 mmol/L

To convert this into CaCO3, we need to multiply it by the ratio of molar masses of CaCO3 and Ca2+.
The molar mass of CaCO3 = (40 + 12 + 3*16) g/mol = 100 g/mol

So, the concentration of CaCO3 in mg/L = (2.5 mmol/L) * (100 g/mol) = 250 mg/L

2. Convert Mg2+ concentration to CaCO3:
The molar mass of Mg2+ = 24 g/mol
So, the concentration of Mg2+ in moles per liter = (36 mg/L) / (24 g/mol) = 1.5 mmol/L

To convert this into CaCO3, we need to multiply it by the ratio of molar masses of CaCO3 and Mg2+.
The molar mass of CaCO3 = (40 + 12 + 3*16) g/mol = 100 g/mol

So, the concentration of CaCO3 in mg/L = (1.5 mmol/L) * (100 g/mol) = 150 mg/L

3. Calculate the total hardness:
Total hardness is the sum of the concentrations of CaCO3 and Mg2+ as CaCO3.
Total hardness = Concentration of CaCO3 + Concentration of Mg2+ as CaCO3
Total hardness = 250 mg/L + 150 mg/L = 400 mg/L

4. Calculate the temporary hardness:
Temporary hardness is the concentration of HCO3- as CaCO3.
The molar mass of HCO3- = (1 + 12 + 3*16) g/mol = 61 g/mol

So, the concentration of HCO3- in moles per liter = (122 mg/L) / (61 g/mol) = 2 mmol/L

To convert this into CaCO3, we need to multiply it by the ratio of molar masses of CaCO3 and HCO3-.
The molar mass of CaCO3 = (40 + 12 + 3*16) g/mol = 100 g/mol

So, the concentration of HCO3- as CaCO3 in mg/L = (2 mmol/L) * (100 g/mol) = 200 mg/L

Therefore, the total
Free Test
Community Answer
In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 ...
Total hardness, 

Total alkalinity,

= 100 mg/l as CaCO3  
Temporary hardness (carbonate hardness)
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In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively.The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will bea)400 and 100, respectively.b)400 and 300, respectively.c)500 and 100, respectively.d)800 and 200, respectively.Correct answer is option 'A'. Can you explain this answer?
Question Description
In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively.The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will bea)400 and 100, respectively.b)400 and 300, respectively.c)500 and 100, respectively.d)800 and 200, respectively.Correct answer is option 'A'. Can you explain this answer? for Civil Engineering (CE) 2024 is part of Civil Engineering (CE) preparation. The Question and answers have been prepared according to the Civil Engineering (CE) exam syllabus. Information about In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively.The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will bea)400 and 100, respectively.b)400 and 300, respectively.c)500 and 100, respectively.d)800 and 200, respectively.Correct answer is option 'A'. Can you explain this answer? covers all topics & solutions for Civil Engineering (CE) 2024 Exam. Find important definitions, questions, meanings, examples, exercises and tests below for In a water sample, the concentrations of Ca2+, Mg2+ and HCO3- are 100 mg/L, 36 mg/L and 122 mg/L, respectively.The atomic masses of various elements are: Ca = 40, Mg = 24, H = 1, C = 12, O = 16.The total hardness and the temporary hardness in the water sample (in mg/L as CaCO3) will bea)400 and 100, respectively.b)400 and 300, respectively.c)500 and 100, respectively.d)800 and 200, respectively.Correct answer is option 'A'. Can you explain this answer?.
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