Chapter 1 - Kristina Mack PDF

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Kristina Mack...

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Measurements Significant digits/figures - Start with the first non zero digit, then we’ll know where the exception is; and keep counting - The number of digits known with certainty plus the last estimated digit Measurements - Volume (picture) 10.0 fl. Oz. - Use .0 or .1 for meniscus (estimated digit) example 10.0 fl. oz ^ graduations on measuring device ^ uncertainty in this last digit; if not a digit scale, then we have to estimate this value Number of significant figures - Count the total number of digits starting with the 1st non-zero digit (*note exception*) - Exception is 0’s in the ones place Practice How many sig. fig. are there in 5090.43? (start with first non digit, continue after decimal) Answer = 6 sig. fig.

How many sig. fig. are there in 4.000? Answer = 4 sig. fig.

How many sig. fig. are there in 400? Answer = 1 or more sig. fig.

How many sig. fig. are there in 4.0? Answer = 2 sig. fig.

(No decimal, ones place is zero) (Answer in text would be 1)

How many sig. fig. are there in 400. ?

(decimal = place holder present)

Answer = 3 sig. Fig.

Rounding Rules - If the rounding digit is 5 or above, round up Practice Round off to two sig.figs. 39.103 50010 0.00499 -

Worksheet notes

answer = 39 (39.103 ; 1 Units becoming larger Three behind micro = nano (n)

Conversion Practice We have 39.1 mcg (micrograms) of a “stat”. How many g? kg? (given) Starting measurement : preferred if you start the problem without the proportion (unless there’s no other option) (find) Ending measurement : look for “prompt words” in story problem like ‘what’, ‘how many’, etc. (extra) Extra info : list extra info given ( write chart on notes) Answer : Given - 39.1 mcg Find - g, and kg Solve - 39.1 mcg = 0.0000391 g and Given:39.1 mcg Find: ?kg (two step conversion)

0.0000000391 kg

Solve : 39.1 mcg /1 * 1g/1*10^6mcg

cross out mcg

1g / 1*10^6 * 1kg/1*10^3

add exponenets

3.91*10^1 / 1*10^9

=3.91*10^-8

Worksheet - conversion factors 1. 38.90 mL ----> L 38.90 mL -----------1

1L * ---------= 0.03890 L 1*10^3 mL

2. 7.61*10^8 mcg 1g ------------------- * ---------------1 1*10^6 mcg

3. 50.02 m 1km ----------- * ------------S 1*10^3 m

4. 75.0 g NaCl 1 mol NaCl ---------------- * ---------------58.44 g NaCl

/ 4 sigfigs

=

= 0.05002 km/s / 4 sigfigs

given : 75.0 g = 1.28 mol NaCl / 3 sigfigs find : mols NaCl ? extra : 58.44 g NaCl = 1 mol NaCl...