Agraduated cylinder weighs 100.0 g. If you add 20.0 g of water and 10 pennies, the mass is now 149.5 g. What is the average mass of the added pennies?

Explanation:

the mass of water + mass  of cylinder + mass of pennies= 149.5 g

  20 + 100+10 X   = 149.5

10  X = The mass of the pennies = 29.5 g

 mass of one penny = 29.5 / 10

                                  = 2.95 g

"you start with 15.67 g mgco3-xh2o, when heated and all the water is removed, you are left with 7.58 g mgco3 only.

therefore, you had 15.67 - 7.58 = 8.09g h2o  

moles of each :

7.58g mgco3 = ? moles = 7.58g / 83.4g/mole = 0.09moles  

8 09g h2o = ? moles = 8.09g / 18g/mole = 0.44moles  

molar ratio between the two by dividing both numbers by the smallest number :

0.09 / 0.09 = 1  

0.44 / 0.09 = 4.8  

mgco3-5h2o"

b. accuracy of the data matters alot more than its number of digits, organization or amount of detail. quantitative observation is more accepted than the qualitative observation.