Quiz 5 Name: _______________________________________ Chemistry 102, Lecture 402 – Fall 2015 DS Section: (1 point) ____________________________ 1. Complete the table with the names or formula. (3 points) Formula Name Formula Name HNO3(aq) nitric acid Al(CN)3 aluminum cyanide NH3 ammonia HF hydrofluoric acid CrSO3 chromium(II) sulfite SO2 sulfur dioxide 2. What is the total sample size (in g) of CH3CH2OH that contains 0.755 mol of hydrogen? (2 points) The molar of ethanol (CH3CH2OH) is 46.08 g∙mol−1. ⎛ 1 mol CH3CH2OH ⎞ ⎛ 46.08 g CH3CH2OH ⎞
⎟ ⎜ mol CH CH OH ⎟ = 5.80 g CH3CH2OH 6 mol H
⎝
⎠⎝
3
2
⎠
( 0.755 mol H) ⎜
3. What is the formula of metal carbonate that has a higher and a lower percent composition by mass of oxygen than CaCO3? (2 point) There are many possible answers. For higher, these would include any metal with a 2+ charge that has a lower molar mass (such as Mg, so MgCO3) or a metal with a higher ionic charge (such as Al, Al2(CO3)3). For lower, these would include any metal with a 2+ charge that has a higher molar mass (such as Sr, so SrCO3) or a metal with a lower ionic charge (such as Ag, Ag2CO3). There is a balance though for some of these categories, such as Li2CO3. This would be a 1+ metal ion, but because lithium is much lighter than calcium, it would have a higher, not lower percent of oxygen. [Li2CO3: ~65% O; CaCO3: ~50% O] 4. What is the molecular and empirical formula of a hydrocarbon (contains only carbon and hydrogen) that is 82.6% carbon by mass? The molar mass is 58.14 g∙mol−1. (4 points) ⎛ mol C ⎞
⎛ mol H ⎞
( 82.6 g C ) ⎜
(100 − 82.6 ) g H) ⎜
(
⎟ = 6.88 mol C
⎟ = 17.2 mol H
⎝ 12.01 g C ⎠
⎝ 1.01 g H ⎠
C 6.88 H17.2 → C2H5
6.88
6.88
molar mass (molecule )
molar mass ( empirical formula)
= multiplier =
58.14 g ⋅ mol−1
=2
29.07 g ⋅ mol−1
Molecular formula → C2 x H5 x so C4H10