Amount of Substance help
When driving a car, a legal limit for ethanol (Mr = 46.0) is 80mg per 100cm^3 of blood.
What is the concentration in mol dm^-3?
A.) 1.74x10-1
B.)1.74X10-2
C.)1.74X10-3
D.)1.74X10-4
The answer is B
This question has been asked before, but I don't understand how their answer is x10 larger. My working:
80/1000 = 0.08g
0.08g /46 = 1/575mol
This is where i get stuck converting the 100cm^3, any help would be greatly appreciated, thanks.
What is the concentration in mol dm^-3?
A.) 1.74x10-1
B.)1.74X10-2
C.)1.74X10-3
D.)1.74X10-4
The answer is B
This question has been asked before, but I don't understand how their answer is x10 larger. My working:
80/1000 = 0.08g
0.08g /46 = 1/575mol
This is where i get stuck converting the 100cm^3, any help would be greatly appreciated, thanks.
Reply 1
You need to convert the given value from mg to g:
80 mg = 0.08 g
You need to convert the given volume of 100 cm^3 into litres (L):
100 cm^3 = 0.1 L
You must calculate the concentration in g/L:
0.08 g / 0.1 L = 0.8 g/L
You need to convert the concentration from g/L to mol/L (M):
Molecular weight of ethanol = 46.0 g/mol
Concentration in g/L = 0.8 g/L
You can now calculate the number of moles:
0.8 g / 46.0 g/mol = 0.0174 mol
Molar concentration (M) or molarity = number of moles per litre = mol/L
0.0174 mol : 1 L = 0.0174 M = 0.0174 M = 0.0174 mol/L
You need to convert the concentration from M to mol/dm^3:
1 L = 1 dm^3 (because 1 L = 1,000 cm^3
Concentration in molarity = 0.0174 M = 0.0174 mol/L
Concentration in mol/dm^3 = 0.0174 mol/L × 1 dm^3/L = 0.0174 mol/dm^3 = 1.74 10^-2 mol/dm^3
The correct answer is B.
Greetings from Italy,
Nitrotoluene
80 mg = 0.08 g
You need to convert the given volume of 100 cm^3 into litres (L):
100 cm^3 = 0.1 L
You must calculate the concentration in g/L:
0.08 g / 0.1 L = 0.8 g/L
You need to convert the concentration from g/L to mol/L (M):
Molecular weight of ethanol = 46.0 g/mol
Concentration in g/L = 0.8 g/L
You can now calculate the number of moles:
0.8 g / 46.0 g/mol = 0.0174 mol
Molar concentration (M) or molarity = number of moles per litre = mol/L
0.0174 mol : 1 L = 0.0174 M = 0.0174 M = 0.0174 mol/L
You need to convert the concentration from M to mol/dm^3:
1 L = 1 dm^3 (because 1 L = 1,000 cm^3
Concentration in molarity = 0.0174 M = 0.0174 mol/L
Concentration in mol/dm^3 = 0.0174 mol/L × 1 dm^3/L = 0.0174 mol/dm^3 = 1.74 10^-2 mol/dm^3
The correct answer is B.
Greetings from Italy,
Nitrotoluene
(edited 8 months ago)
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