Today is 8 July 2009 -- We learned basics of scientific measurements

You used the "Hollow Penny" lab as a model for studying measurement.  You reweighed your penny and subtracted the final weight from the initial weight.  This gave you the amount of zinc that reacted with the HCl to produce hydrogen gas (H2) and ZnCl2.

We used this information in a discussion of density (density = mass divided by volume) and an introduction to the mole concept (moles = mass divided by atomic mass).  I explained that the mole referred to a specific quantity, like a dozen means 12, and a pair means 2.  I put the following words on the board for you to know:  meniscus and stoichiometry.  We also used the words divisor, density, limiting reagent, coefficient.  (PLEASE LEARN THESE WORDS AND THEIR MEANINGS).  You learned a little about the metric system, that 1 ml = 1 cubic centimeter (cc), and the prefixes:  mili = 1/1000, centi = 1/100, and deci = 1/10.  We gave examples like cent in century, or as in 1/100 of a dollar, and centavo, as 1/100 of a peso.  Millennium has the root "mil" and means 1000, as 1000 years.  Deci means "10" and is the basis of the decimal system. 

I showed you how to solve problems using addition (decimal points line up) or subtraction, and multiplication (with a brief introduction to scientific notation).  You learned that to divide numbers, the denominator (bottom number in a fraction) goes into the numerator (top number). 

We modeled dilution of an acid.  In particular, we had 37% hydrochloric acid (that is hydrogen chloride dissolved in water) and we diluted 20 ml of it to 100 ml with pure water.  That is what we used in the penny lab.  You solve it like this:

                    37%   100 ml

                   ----  =  ------

                     x       20 ml

Cross multiply and divide by 100   for x = (37%)(20ml)/(100ml) = 7.4%

You used the information on the weight of Zn that reacted with the acid solution to calculate the number of moles of zinc.  From there, you calculated the number of moles of ZnCl2.  Then you found the atomic weight of ZnCl2, multiplied it by the number of moles present and obtained the mass (in grams) of the ) ZnCl2.