Chem hw 3
Na₂CO₃ *An empirical formula shows the ratio of each element to one another in the formula unit or molecule. The given moles show that there are twice as many moles of Na as moles of C and that there are three times as many moles of O as moles of C. This yields Na₂CO₃. *Divide all by smallest mass
A compound containing Na, C, and O is found to have 1.06 mol Na, 0.528 mol C, and 1.59 mol O. What is the empirical formula of the compound?
C₅H₁₀O₂ *For every 1 mole of carbon, there are 2 moles of hydrogen. For every 2.5 moles of carbon, there is 1 mole of oxygen. This yields C₅H₁₀O₂ as the empirical formula.
A compound that contains only carbon, hydrogen, and oxygen is 58.8% C and 9.87% H by mass. What is the empirical formula of this substance?
an ion *A neutral atom has an equal number of protons and electrons. If there are more or less of one than the other, the atom is an ion.
An atom has nine protons and ten electrons. This makes it:
FeSO₁₁H₁₄
An iron-containing compound is 20.1% Fe, 11.5% S, 63.3% O, and 5.1% H. What is the empirical formula for this compound?
KCl = ionic (metal and nonmetal) CrCl3 = ionic (metal and nonmetal) Cl2O = covalent (nonmetals)
Classify the following compounds as ionic or covalent: KCl, CrCl₃, Cl₂O.
Al2O3 *Aluminum forms ions that have a +3 charge and oxygen forms ions that have -2 charge. It would take two aluminum ions to balance the charge of three oxygen ions. This is the lowest number of each ion to reach a neutral formula unit.
Determine the correct formula for aluminum oxide
TiCl4 *The (IV) in titanium(IV) chloride indicates that the titanium ion has a 4+ charge. Chloride has a -1 charge. Four chloride ions would be needed to balance the charge of the titanium ion.
Determine the correct formula for titanium(IV) chloride.
119.00 amu *The formula weight is the mass of one molecule or formula unit. This can be calculated by adding the atomic mass of each atom. The atomic mass of potassium is 39.10 amu and the atomic mass of bromine is 79.90 amu. 39.10 amu + 79.90 amu = 119.00 amu
Determine the formula weight of KBr
0.29 g C6H12O6 *1.6 x 10^-3 mol C6H12O6 x (180.18 g C6H12O6/ 1 mol C6H12O6) = 0.29 g C6H12O6
Determine the mass in grams of 1.6x10^-3 mol glucose, C6H1206
32.04 g/mol *The molar mass is the mass of one mole of each atom in a molecule or formula unit. This can be calculated by adding the molar mass of each atom in the molecule or formula unit. The molar mass of carbon is 12.01 g, the molar mass of hydrogen is 1.01 g, and the molar mass of oxygen is 16.00 g. There are four moles of hydrogen, one mole of carbon, and one mole of oxygen in CH₃OH. 12.01 g + (4×1.01 g) + 16.00 g = 32.05 g
Determine the molar mass of CH3OH
345.931 g/mol *The molar mass is the mass of one mole of each atom in a molecule or formula unit. This can be calculated by adding the molar mass of each atom in the molecule or formula unit. The molar mass of chromium is 52.00 g, the molar mass of phosphorus is 30.97 g, and oxygen has a molar mass of 16.00 g. There are three moles of chromium, two moles of phosphorus and eight moles of oxygen per formula unit of chromium phosphate, Cr₃(PO₄)₂. (3×52.00 g) + (2×(30.97 g+(4×16.00 g))) = 345.94 g
Determine the molar mass of Cr₃(PO₄)₂.
148.3 g/mol *The molar mass is the mass of one mole of each atom in a molecule or formula unit. This can be calculated by adding the molar mass of each atom in the molecule or formula unit. For example, the molar masses of each atom are added together to calculate the molar mass of Mg(NO₃)₂. The molar mass of magnesium is 24.31 g, the molar mass of nitrogen is 14.01 g, and oxygen has a molar mass of 16.00 g. There is one mole of magnesium, two moles of nitrogen, and six moles of oxygen in a mole of each formula unit. 24.31 g + (14.01 g×2) + (16.00 g×6) = 148.33 g
Determine the molar mass of Mg(NO₃)₂.
0.4998 mol *Stoichiometry can be used. Since formula units of CaCl₂ was provided, that will be the starting point. Avogadro's number provides the conversion factor. 3.00×10^23 formula units CaCl2 × (1 mol CaCl2/6.022×1023 formula units CaCl2) = 0.498 mol CaCl2
Determine the number of moles in 3.00 × 10²³ formula units of CaCl₂.
0.699 mol CaCL2 *4.21x10^23 molecules CaCL2 x (1 mol CaCL2/6.022x10^23 molecules CaCL2) = 0.699 mol CaCL2
Determine the number of moles in 4.21 × 10²³ molecules of CaCl₂
1.2 x 10^-7 g *2.57x10^15 molecules x (1 mol CO/6.022x10^23 molecules) x (28.01 g/ 1 mol) = 1.2 x 10^-7 g
How many grams are in 2.57 × 10¹⁵ molecules of CO?
3.89 g CO2 *5.32x10^22 molecules CO2 x (1 mol CO2 /6.022x10^23) x (44.01 g CO2/1 mol CO2) = 3.89 g CO2
How many grams are in 5.32x10^22 molecules of CO2?
0.55 mol *Stoichiometry can be used. Since grams of RbF was provided, that will be the starting point. The molar mass provides the conversion factor. Add the atomic numbers for Rb and F to get the total grams = 104.47 g RbF 57.0 g RbF ×1 mol RbF/104.47 g RbF = 0.546 mol RbF
How many moles are in 57.0 grams of RbF?
6.7x10^25 molecules CO2 *4.9 kg CO2 x (1 g CO2/ 0.001 kg CO2) x (1 mol CO2/ 44.01 g CO2) x (6.022x10^23 molecules CO2/1 mol CO2) = 6.7x10^25 molecules CO2
If 4.9 kg of CO₂ are produced during a combustion reaction, how many molecules of CO₂ would be produced?
Cu3P2
Predict the chemical formula for the ionic compound formed by Cu²⁺ and P³⁻
Ag20 *silver yields +1 and oxygen yields -2
Predict the chemical formula for the ionic compound formed by the elements Ag and O
Cs3P *caesium yields +1 and phosphorus yields -3
Predict the chemical formula for the ionic compound formed by the elements Cs and P
Avogadro's number and molar mass *To convert from grams to number of molecules, you must first convert the grams into moles, which requires the molar mass, and then you must convert the moles into number of molecules, which requires Avogadro's number.
To convert from grams to number of molecules you need to use:
silicon;germanium
Transistors are made from Si, but in the past, were made from Ge. What elements do these symbols represent?
silver sulfide (Ag2S)
What is the correct IUPAC name for Ag₂S?
Aluminum nitride
What is the correct IUPAC name for AlN?
Barium idodide
What is the correct IUPAC name for BaI₂?
cesium iodide
What is the correct IUPAC name for CsI?
lithium sulfide
What is the correct IUPAC name for Li₂S?
magnesium phosphide
What is the correct IUPAC name for Mg₃P₂?
strontium chloride
What is the correct IUPAC name for SrCl₂?
strontium nitride
What is the correct IUPAC name for Sr₃N₂?
H₂CO *An empirical formula shows the simplest whole number ratio of each element to one another in the formula unit or molecule. For example, HC₂H₃O₂ contains 4 hydrogen atoms, 2 carbon atoms, and 2 oxygen atoms. This can be reduced to 2 hydrogen atoms, 1 carbon atom, and 1 oxygen atom. *Divide by 2
What is the empirical formula of acetic acid, HC₂H₃O₂?
BaCl₂ *Two ions of chlorine are needed to balance out the positive charge on the barium ion.
What is the formula for an ionic compound containing Ba²⁺ ions and Cl⁻ ions?
Sc₂O₃ *Two scandium (+3) ions are needed to balance the negative (-2) charges on the three oxide ions. This is the lowest number of each ion to reach a neutral formula unit.
What is the formula for an ionic compound containing Sc³⁺ and O²⁻ ions?
Ba₃N₂ *Three barium ions are needed to balance out the negative charge of two nitrogen ions. This is the lowest number of each ion to reach a neutral formula unit.
What is the formula of a compound containing Ba²⁺ and N³⁻ ions?
79.887% *Mass percentage can be calculated by finding the ratio of the molar mass of atoms of an element to the total molar mass of a molecule. For example, the mass percentage of C in CH₃CH₃ is 79.88%. (12.01 g×2)/30.07 g × 100 = 79.88%
What is the mass percentage of C in CH₃CH₃?
C₆H₆ *An empirical formula shows the simplest whole number ratio of each element to one another in the formula unit or molecule. The molar mass of CH is 13.02 g. Divide the molar mass of the unknown compound by the molar mass of the empirical formula to find the total number of CH units in the molecular formula. Multiply the empirical formula by this value to get C₆H₆. 78.1 g/13.02 g = 6
What is the molecular formula of a compound with an empirical formula of CH and a molar mass of 78.1 g/mol?
Mg *Elements in Group 2 tend to form a +2 ion by losing its two valence electrons.
Which of the following is most likely to form a +2 ion?