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# Copy of Homework

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## AbdulJabbar Al-Hamood

on 8 February 2014

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#### Transcript of Copy of Homework

Chemistry Homework
What do you guys think?
Done By :-
Abduljabbar Alhamood / Sultan Aldabal

Sultan Aldabal
Question #24
How do you convert between the mass and the number of moles of a substance?
You apply the formula :-

Number of moles = Mass of a substance
Molar Mass of a substance

Sultan Aldabal
Question #25
How do you convert between the volume of a gas at STP and the number of moles of the gas ?
You apply the formula :-
Volume = (the number of moles X molar volume)
Sultan Aldabal
Question #26
Calculate how many grams are in 5.66 mol of CaCO2?
[(Ca x 1) + (C x 1) + (O x 2)] =
[(40.08) + (12.011) + (15.999 x 2)] = 100.091
100.091 x 5.66 = 566.515 grams
You apply the formula :-

Number of moles = Mass of a substance
Molar Mass of a substance

Sultan Aldabal
Question #27
Find the number of moles in 50g of ethonal (C2H6O)
You apply the formula :-

Number of moles = Mass of a substance
Molar Mass of a substance

[(C x 2) + (H x 6) + (O x 1)] =
[(12.011 x 2 ) + (1.0079 x 6) + (15.999 x 1)] =
46.0684
508 / 46.0684 = 11.0032 moles
Abduljabbar Alhamood
Question #28
What is the volume, in Liters, of 1.5 mol Cl2 at STP ?
You apply the formula :-
Volume = (the number of moles X molar volume)
Cl2 = 35.453
1.5 x (35.453 x 2) =
1.5 x (70.906) =
106.359 Liters

Abduljabbar Alhamood
Question #29
Three balloons filled with three different gaseous compounds each have a volume of 22.4 L at STP. Do these balloons have the same mass or contain the same number of molecules? Explain.
All 3 gases have equal number of molecules because the number of moles is directly proportional to the volume at STP. (22.4L = 1 mole at stp) However, the mass of each gas will be different because molar mass is different depending on which gases you are using.
Abduljabbar Alhamood
Question #30
The density of an elemental gas is 1.7824g/L at STP. What is the molar mass of the element?
You apply the formula :-
Molar Mass = ( Density x Molar Volume)
Molar Mass = 1.7824 x 22.4
Molar Mass = 39.92576
Abduljabbar Alhamood
Question #31
The densities of gases A, B, and C at STP are 1.25 g/L, 2.86 g/L, and 0.714 g/L, respectively. Calculate the molar mass of each substance. Identify each substance as ammonia (NH3), sulfur dioxide (SO2), chlorine (Cl2), nitrogen (N2), or methane (CH4).
work out molar mass of each compound
molar mass SO2 = [(32.06) + (2 x 16)] = 64.06 g/mol
molar mass Cl2 = [(35.45 x 2)] = 70.9 g/mol
molar mass N2 = [(14.01 x 2)] = 28.02 g/mol
molar mass CH4 = [(12.01) + (1.008 x 4)] = 16.042 g/mol
molar mass NH3 = [(14.01) + (1.008 x 3)] = 17.034 g/mol
molar mass A = density of A x volume of 1 mole
= 1.25 g/L x 22.4 L/mol
= 28.0 g/mol

molar mass B = density of B x volume of 1 mole
= 2.86 g/L x 22.4 L/mol
= 64.06 g/mol

molar mass C = density of C x volume of 1 mole
= .714 g/L x 22.4 L/mol
= 15.9936 g/mol
Substance A is N2

Substance B is SO2

Substance C is CH4
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