http://politics.sgforums.com/forums/2297/topics/322824 en-US 60 <p>Brilliant. Thanks.</p> Sat, 05 Jul 2008 00:19:47 +0800 politics.sgforums.com:2297:322824:8218786 secretliker http://politics.sgforums.com/forums/2297/topics/322824 <p>Whenever the question says "81.1% by mass", let the sample mass of compound be 100g. Then, sample mass of Ba in compound&nbsp;is 81.1g, and sample mass of oxygen in compound is 100 - 81.1 = 18.9g.</p> <p>&nbsp;</p> <p>Next, work out number of moles of each element in the compound, using the formula "No. of moles = Sample mass&nbsp;/ Molar mass". Simplify the mole ratio to simplest ratio (ie. divide all numerical values by the smallest value), and you've got your empirical formula.</p> <p>&nbsp;</p> Wed, 02 Jul 2008 08:37:12 +0800 politics.sgforums.com:2297:322824:8211589 UltimaOnline http://politics.sgforums.com/forums/2297/topics/322824 <p>When barium metal is burned in air, an oxide&nbsp;is formed with 81.1% by mass of barium. Calculate the formula of the compound. [Mr of barium=137, oxygen=16]</p> <p>The answer is simple (BaO2), but I'm looking for a proper working instead of guess &amp; check.</p> <p>I tried doing this but I failed:</p> <p>Let compound be Ba(x)O(y)</p> <p>137x / (137x + 16y) = 0.811</p> <p>...</p> Wed, 02 Jul 2008 00:50:05 +0800 politics.sgforums.com:2297:322824:8211329 secretliker http://politics.sgforums.com/forums/2297/topics/322824