## Quiz of the Week - Chemistry 221 Significant Figures

Master the concepts from this week's material by trying these quiz questions which will NOT affect your grade in any way. All scoring is anonymous and known only to you, the user! If you have any questions, please contact me. Good luck!

__A Quick Review of Significant Figures__

- If a decimal point is present in the number, start at the left with the first nonzero digit and count every digit after it moving from left to right.

*Example:*

**0.001840** has 4 significant digits

**0.00184** has 3 significant digits

**2.68** has 3 significant digits

**2.680** has 4 significant digits

- If a decimal point is absent from the number, start at the right and count every digit as you go from right to left;
**HOWEVER** if there is one or more zeros at the right hand end of the number then the number of significant digits is ambiguous. A decimal at the end means the zeroes are significant. For best results, the number must be written in scientific notation in order to make the number of significant digits clear.

*Example:*

**345** has 3 significant digits

**3045** has 4 significant digits

**3450** is ambiguous, could be 3 or 4 significant digits

**3450.** has 4 significant digits (due to the explicit decimal)

**3.450 x 10**^{3} has 4 significant digits (everything in scientific notation is significant)

**3.45 x 10**^{3} has 3 significant digits (everything in scientific notation is significant)

- When
**adding or subtracting**, your answer should have the same number of *decimal places* as the original number that had the fewest decimal places. (i.e. keep the largest doubtful digit). If first digit to be discarded is 5 or higher, **round** the last significant figure up by one unit.

*Example:*

**2.33 + 1.5** = 3.83, round to 1 decimal place (the tenths position) = **3.8**

**123.1 + 3.55** = 126.65, round up by 1 at the tenths decimal place = **126.7**

- When
**multiplying or dividing**, your answer should have the same number of *significant digits* as the original number that had the fewest significant digits. Remember to *round up* the last significant figure if necessary.

*Example:*

**2.33 x 1.5** = 3.495, round to 2 significant digits = **3.5**

**123.1 x 3.55** = 437.005, round to 3 significant digits = **437**

- In a
**calculation that has multiple operations**, **keep track of how many significant digits you should have after each step, but donâ€™t round off your answer until the very end** of the calculation. It may help to write out each step and underline the extra digits that you keep.

*Example:*

**[2.33 + 1.5]/123.1** = 3.8__3__/123.1 (first step gives an answer with 1 decimal place which would give 2 significant digits in the numerator, remember this but use all of the digits in the next step)

= 0.031__11__ (2 significant digits were divided by 4 significant digits, so round to 2 significant digits)

=** 0.031**

__Chemistry 221 - Nomenclature__

1. The number 0.00430 has how many significant figures?

2. The number 9.8020 x 10^{-5} has how many sigifnicant figures?

3. Express **6.3 x 3.25** in proper scientific notation.

4. Add the following numbers together and express in correct significant figures: **12 + 1.2 + 0.12 + 0.012**

5. Express the following result using the correct number of significant figures: **0.002843 * 12.80184 / 0.00032**

6. Use the correct number of significant figures when calculating the molar mass of sulfuric acid, H_{2}SO_{4}: **4 x 15.9994 + 1 x 32.066 + 2 x 1.0079**

7. How many significant figures will be used in the final answer for this calculation: (10.07 + 7.395) / 2.5

8. Round the number 3456.5 to two significant figures:

9. Report the answer using correct significant figures: (1815-1806) x (9.11 x 7.92)

10. Which number has the most significant zeroes?