SURVEY OF CHEMISTRY LABORATORY I
CHEM 1151L
EMPIRICAL FORMULA OF ZINC CHLORIDE
CAUTION!!!CAUTION!!!BE SURE TO WEAR SAFETY GLASSES AT
ALLTIMES IN THE LABORATORY
NO EXCEPTIONS TO THIS RULE!
Students will determine
- the empirical formula of zinc chloride by
a process known as synthesis
- the empirical formula from their data
- the empirical formula from the class average
It is best to perform several experiments and obtain average values for the result
EMPIRICAL FORMULA OF ZINC CHLORIDE
- The lowest whole number ratio of atoms present in a compound
- the lowest whole number ratio of moles of atoms in a compound
For example
- The molecular formula of glucose is C6H12O6
- The empirical formula is CH2O
EMPIRICAL FORMULA
Can be determined by the following methods
Analysis
- A compound is broken down into its element
- The mount of each element present is accurately determined
Synthesis
- Prepared from accurately measured amounts of each of its
elements
EMPIRICAL FORMULA
- Determine the mass of each element found in the formula
(may be grams or percentage composition by mass)
- Convert each mass to moles using the atomic masses of the appropriate elements
- Divide each mole amount by the smallest number of moles
- Round each mole ratio to the nearest integer
- Write the whole numbers as subscripts in the formula
EMPIRICAL FORMULA
EMPIRICAL FORMULA
mol231.6g/mol12.01
g74.83 mol97.24
g/mol1.01
g25.17
000.1mol 6.231
mol 6.231 007.4
mol 6.231
mol 24.97
Assume 100.0 g sample
% of each element equals grams
C H
1.000 ≈ 1 4.007 ≈ 4
Empirical Formula: CH4
Determine the empirical formula of a compound whose composition is determined to be 74.83% carbon and 25.17% hydrogen
ZINC METAL
- Mass about 1 gram of zinc metal
- Record this mass
EVAPORATING DISH
- Mass a clean, dry evaporating dish
- Record this mass
HYCHLORIC ACID
- Use the automatic dispensing bottle
- Dispense 10 mL of 12 M hydrochloric acid (HCl) directly
into the evaporating dish
HYCHLORIC ACID + ZINC METAL
- Carefully add the zinc to the dish containing the HCl
- Must be done in the hood
- Allow all of the zinc to dissolve
EVAPORATE LIQUID
- Gently warm solution on a hotplate
- Must be done in the hood
- Avoid spattering
- A white powdery substance (zinc chloride) will form
COOL AND MASS PRODUCT
- Avoid melting of zinc chloride
- Take the dish off the hotplate when content is dried enough
- Allow the dish to cool
COOL AND MASS PRODUCT
- Mass the dish and the zinc chloride
- Record the mass
CALCULATIONS
- Complete your calculations on the data sheet
- Report the percent by mass of each element to the instructor before leaving the lab
- The class average is needed to complete the lab report