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2. CAUTION!!! BE SURE TO WEAR SAFETY GLASSES AT ALL
TIMES IN THE LABORATORY
NO EXCEPTIONS TO THIS RULE!
3. 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
4. - 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
5. 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
6. - 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
7.
8. ZINC METAL - Mass about 1 gram of zinc metal
- Record this mass
9. EVAPORATING DISH - Mass a clean, dry evaporating dish
- Record this mass
10. HYCHLORIC ACID - Use the automatic dispensing bottle
- Dispense 10 mL of 12 M hydrochloric acid (HCl) directly into the evaporating dish
11. 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
12. EVAPORATE LIQUID - Gently warm solution on a hotplate
- Must be done in the hood
- Avoid spattering
- A white powdery substance (zinc chloride) will form
13. 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
14. COOL AND MASS PRODUCT - Mass the dish and the zinc chloride
- Record the mass
15. 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