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 103 has 4 significant digits (everything in scientific notation is significant)
3.45 x 103 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 don’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 = 3.83/123.1 (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)
= 0.03111 (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, H2SO4: 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?