Chem 100 Pre-Lecture Ch6
How many water molecules are in a block of ice containing 2.50 mol of water (H2O)? Express the number of molecules numerically.
1.51×10^24 molecules of H2O molecules of H2O (2.50 x 6.022*10^23/1)
Suppose you needed to calculate the mass, in grams, of sodium in 1.5 grams of sodium chloride? Which of the following equations allows you to correctly calculate the mass of sodium in 1.5 grams of sodium chloride.
1.5gNaCl x molNaCl/58.44gNaCl x molNa/molNaCl x 22.99gNa/molNa
Suppose you have 2.00×10^18 reams of lead (Pb). How many lead atoms do you have?
2.00*10^18 reams of lead (Pb) x (500/1 ream)= 1.00*10^21 atoms.
How many moles of chlorine, Cl, are there in 8 moles of carbon tetrachloride, CCl4?
32
Calculate the number of moles of Cl atoms in 2.41×10^24 formula units of magnesium chloride, MgCl2. Express your answer numerically in moles.
Calculate the number of moles of MgCl2 in 2.41×10^24 formula units of MgCl2. 2.41×10^24 MgCl2 formula units x (1mole MgCl2/6.02 x10^23 MgCl2 formula units) = 4.00 moles MgCl2 Ratio between Cl and MgCl2: 2 moles Cl/1 mole MgCl2 Now, convert 4.00 moles of MgCl2 to moles of Cl given that there are 2 moles of Cl per mole of MgCl2. 4.00*2/1= 8 so ANSWER is 8.00 moles Cl
Suppose a piece of silver jewelry contains 6.89×10^22 atoms of silver (Ag). How many dozens of silver atoms are in the piece of jewelry? Express your answer numerically in dozens.
5.7×10^21 dozen (divided by 12)
How many grams are in 1.20 mol of sodium chloride (NaCl)? Express your answer numerically in grams.
70.1 grams
What relationships are needed to convert 1.5 grams of carbon to the number of carbon atoms?
molar mass and Avogadro's number
Molar mass is the relationship between ____________.
moles and grams
How many formula units make up 38.4 g of magnesium chloride (MgCl2)? Express the number of formula units numerically.
First the molar mass of MgCl2 is (24.30 + 2 × 35.45) g/mol = 95.20 g/mol so 38.4 g MgCl2 x 1 mol MgCl2/95.20 g MgCl2 = 0.403 mol so input the answer 0.403361344.. from calc to multiply from 6.022x10^23/1 which you'll get 2.43×10^23 formula units of MgCl2
Element and Molar mass (g/mol)
Beryllium (Be) 9.012 Calcium (Ca) 40.08 Copper (Cu) 63.55 Cadmium (Cd) 112.41 Bromine (Br) 79.90
Suppose a piece of silver jewelry contains 6.89×10^22 atoms of silver (Ag). How many moles of silver atoms are in the piece of jewelry? Express your answer numerically in moles.
0.114 mol (6.89*10^22/1 x 1/6.022*10^23)
There are several common counting units:
1 dozen= 12, 1 score= 20, 1 ream= 500, and 1 gross= 144. The mole (mol) is a counting unit used by chemists, much like the dozen is a counting unit used by bakers: 1 mol=6.022×10^23
Calculate the number of molecules in 9.00 moles H2S. Express your answer numerically in molecules.
1 mole of H2S contains = 6.022x10^23 molecules so ANSWER is 9.00 x 6.022x10^23 = 5.42x10^24 H2S molecules
PART 1 Given the atomic mass of select elements, calculate the molar mass of each salt
1. The molar mass of CuBr2 is 223.35 g/mol223.35 g/ mol 2. The molar mass of BeBr2 is 168.81 g/mol168.81 g/ mol 3. The molar mass of CdBr2 is 272.21 g/mol272.21 g/ mol 4. The molar mass of CaBr2 is 199.88 g/mol199.88 g/ mol
PART 2 Calculating the molar mass of a substance involves three simple steps: 1. Obtain the molar mass of each element. 2. Multiply each element's molar mass by the number of moles of that element that are present in one mole of the compound. The subscript immediately following an atomic symbol in a molecular formula indicates how many moles of that element are present in one mole of the compound. 3. Calculate the molar mass by adding the masses of the elements.
BeBr2 (9.012 g/mol)(1 mol) + (79.90 g/mol)(2 mol)= 168.81 g/mol CaBr2 (40.08 g/mol)(1 mol) + (79.90 g/mol)(2 mol) = 199.88 g/mol CuBr2 (63.55 g/mol)(1 mol) + (79.90 g/mol)(2 mol)= 223.35 g/mol CdBr2 (112.41 g/mol)(1 mol) + (79.90 g/mol)(2 mol)= 272.21 g/mol
What is the empirical formula of a compound that has a pseudoformula of C3.5H8?
C7H16
Calculate the number of moles of magnesium, chlorine, and oxygen atoms in 5.90 moles of magnesium perchlorate, Mg(ClO4)2. Express the number of moles of Mg, Cl, and O atoms numerically, separated by commas.
In one mol Mg(ClO4)2 contains 1 mol Mg atoms, 2 mol Cl atoms, and 8 mol O atoms. To determine the number of moles of atoms of each element in 5.90 moles of the compound, multiply the number of moles times 5.90. Mg: 5.90 mol Mg(ClO4)2 x (1 mol Mg atoms/1 mol Mg(ClO4)2) = 5.90 Mg atoms Cl: 5.90 mol Mg(ClO4)2 x (2 mol Cl atoms/1 mol Mg(ClO4)2) = 11.8 Cl atoms O: 5.90 mol Mg(ClO4)2 x (8 mol O atoms/1 mol Mg(ClO4)2) = 47.2 O atoms moles of Mg, Cl, O = 5.90, 11.8, 47.2 moles
Calculate the number of moles of aluminum, sulfur, and oxygen atoms in 3.00 moles of aluminum sulfate, Al2(SO4)3. Express the number of moles of Al, S, and O atoms numerically, separated by commas.
In one mole of aluminum sulfate, Al2(SO4)3, there are 2 moles Al atoms, 3 moles sulfur atoms, and 12 moles O atoms. To determine the number of moles of atoms of each element in 3.00 moles of the compound, multiply the number of moles times 3.00. Al: 3.00 mol Al2(SO4)3 x (2 mol Al atoms/1 mol Al2(SO4)3)= 6 Al atoms S: 3.00 mol Al2(SO4)3 x (3 mol S atoms/1 mol Al2(SO4)3)= 9 S atoms O: 3.00 mol Al2(SO4)3 x (12 mol O atoms/1 mol Al2(SO4)3)= 36 O atoms moles of Al, S, O = 6.00, 9.00, 36.0 moles
A sample of propane, C3H8, contains 11.1 moles of carbon atoms. How many total moles of atoms does the sample contain? Express the total number of moles of carbon and hydrogen numerically.
Ratio of moles of carbon atoms to hydrogen atoms is 3:8 Given: 11.1 moles of carbon Total number of moles of carbon and hydrogen = (11.1 x 8∕3 ) + 11.1 = 40.7 moles of carbon atoms and hydrogen atoms
Which of the following statements correctly describes a relationship between empirical formula and molecular formula?
The empirical formula molar mass is less than or equal to the actual molar mass for all compounds.
Calculate the molar mass for Mn2O3, an oxide of manganese. Express your answer to five significant figures.
The molar mass of Mn2O3 can be calculated by multiplying the molar masses of manganese and oxygen by the number of atoms of each in the formula: Molar mass = 54.94(2) + 16.00(3) Molar mass = 157.88g/mol Manganese, Mn= atomic mass: 54.938049, # of Atoms: 2, Mass percent: 69.597% Oxygen, O= atomic mass: 15.9994, # of Atoms: 3, Mass percent: 30.403%
Calculate the molar mass of adrenaline (C9H13NO3), a hormone responsible for regulating heart rate and other functions of the sympathetic nervous system. Express your answer to five significant figures.
The molar mass of adrenaline can be calculated by multiplying the molar masses of carbon, hydrogen, oxygen, and nitrogen by the number of atoms of each in the formula: Molar mass = 12.01(9) + 1.008(13) + 16.00(3) + 14.01(1) Molar mass = 183.20g/mol Hydrogen, H= atomic mass: 1.00794, # of Atoms: 13, Mass percent: 7.152% Carbon, C= atomic mass: 12.0107, # of Atoms: 9, Mass percent: 59.003% Nitrogen, N= atomic mass: 14.0067, # of Atoms: 1, Mass percent: 7.645% Oxygen, O= atomic mass: 15.9994, # of Atoms: 3, Mass percent: 26.199%
