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Writing chemical formulas

Posted: Thu Oct 05, 2017 10:02 pm
by Ryan Neis 2L
For questions when we are given the name of a compound, how can we write a chemical formula for it without the molecular formula of the compound being given?

Re: Writing chemical formulas

Posted: Thu Oct 05, 2017 10:03 pm
by Tess McDaniel 1F
I remember Prof Lavelle saying in class that for this test you won't need to generate a chemical formula given just the name because we haven't learned nomenclature rules yet. He did say that we will need to know that by the next test I think though. Hope that helps!

Re: Writing chemical formulas  [ENDORSED]

Posted: Thu Oct 05, 2017 10:10 pm
by Rachel Formaker 1E
When we are given the name of the compound in a problem and we are supposed to find the chemical formula for an equation with no other information, the compound is usually an ionic compound and we are supposed to be able to figure out the formula using the oxidation numbers of its elements.

For example, calcium chloride would be CaCl2 because Ca is in Group 2 and forms a 2+ ion, and Cl is in Group 7 and forms a 1- ion. Since compounds are electrically neutral, there must be 2 Cl- atoms to cancel out the charge of the Ca2+ atom.

However, we will not need to write chemical formulas this way for the test tomorrow.

Re: Writing chemical formulas

Posted: Thu Oct 05, 2017 10:53 pm
by Yashaswi Dis 1K

Just a quick question...when writing chemical reactions and balancing them, if there is a catalyst involved or heat being utilized for the reaction to occur, do we have to also place the catalyst's name above the arrow and place the triangle (representing heat being involved) above the arrow too? Please let me know when possible. I hope we don't lose points for that as long as the reaction is correctly balanced etc.

Thank you.


Re: Writing chemical formulas

Posted: Sun Oct 08, 2017 11:16 pm
by Chem_Mod
Although the catalyst and heat symbols are very important in giving information about the complete chemical reaction (reaction conditions in general are important, often marked above the arrow if they are essential for the rxn to occur), they are not necessarily pertinent when simply balancing an equation. They may have an effect on the percent yield, but this should not have you loose points on the fundamentals exam.

Re: Writing chemical formulas

Posted: Wed Nov 08, 2017 10:54 pm
by tiffanyteguh1C
What is the best way to write a chemical formula when you are given the molar mass and the reaction of a combustion reaction? (i.e. question 6 from test #1)